Ed_in_Sat
Most residential lots are small, relative to greenhouse size. This means that the greenhouse must be sited where there is room, without a whole lot of latitude. Most residential spouses have a pretty good idea what said residential lot should look like and that, also, determines what goes where. It is far better to answer questions about why a greenhouse is too small than to answer question about why a greenhouse is too large.

Structures within this group will vary far too much in size, cost and embellishment level for us to design a greenhouse that is best for any individual. What we will try to do is to provide a working knowledge of the principles and techniques that convert a highly personalized dream structure into a practical reality.

Having received your marching orders on policy matters, it is well to make a rough draft of the proposed site and the structural footprint of the greenhouse. This product will become known as a Site Plan, and it may be a rough sketch on the back of a sales flyer or a finished architectural drawing.

We prefer a little finesse on Site Plans because they are the first and cheapest opportunity to see how things will fit together. Something like this might serve as a starter: Site Plans may be simplified by employing a modestly priced draw program. Suitable programs are sold for planning patios and add-on bedrooms.

Let me caution here that these draw programs have a rather steep drawing curve and are not always user friendly. It sure is easy to scan a scribble!

We use DesignCAD because it prepares a bill of materials as we develop the design. A scaled down version is called DesignCad Express and it also has capability to prepare a bill of materials. There are many other brands that will give adequate service.

Ahowle
I saw Intellicad in Circuit City a while back for $28.00.

Ed_in_Sat
Don't get exotic with a site plan. Stick to basic information you can use on a product you plan to throw away.

Here, for instance, is a working site plan. When you have something like this, cut a greenhouse template to a fairly accurate scale and move it about until the best siting is determined. You will save time here if you hand the drawing and the template to THE MANAGEMENT. You will immediately determine where the greenhouse is going to go.

janetteh
This was the case with our last gh. James can be a wise man at times. :-)

Ed_in_Sat
At this stage, it is well to consider several design elements. Light and heat are certainly critical to good growing, so prepare a model for each in relation to the plot plan. Your models might look something like these:

You will notice that temperature and light plots resemble each other but they may have marked differences in application to plants. Know your material and balance light/temp curves to the best mix for each. Perhaps these diagrams indicate why we orient greenhouse ridges East and West if at all possible. Winter light and solar heat gain are greater than any other arrangement.

I expect a howl on this. The principles we have long followed say the sun will vary a little over 20 degrees in elevation, December to June. It won't make much difference where a greenhouse faces in June: it will be hot. In December, it is quite another story. You need all the heat and light you can get and they both come from the south.

Janetteh
No howl....I agree.

N_Calif_Kathy
I didn't realize how far the shadow of my home cast in mid-winter, it does affect the GH more than I'd thought.

John_in_Arcadia,_CA
Yes, and trees that you think are far enough away suddenly in winter aren't that far! I got the neighbor to cut the 3 trees next to my GH and what a differnce it made.

Ed_in_Sat
Gee, no howls. I'm getting off light tonight.

Don't get carried away on pick and shovel requirements. If your plot has a high point, it may be possible to make a modest cut into the rise and insert the greenhouse base.

This is called 'benching' or 'berming'. While we have the 'benching' picture up, take a look at that roofline. Do you see the offset toward the slope side? Greenhouse structures are light, so they retain strength even when loads are not quite equal in distribution. This drawing shows a ridge offset of about 20% toward the slope. Why would one want to do it this way? Because if the long side of an offset roof faces south, the area of exposure to winter sun will be proportionally greater - at most, more than 20 degrees of elevation greater. The farther north you live, the more important such an offset becomes. As the sun sinks toward the equator in winter, an offset roof, as shown, continues to have a very large face oriented to gather available light and solar heat. Your plants will notice the difference and so will your heating bill.

How much can a roof be offset? In special circumstances, 100%. Here's when we do it: If today's greenhouse is to be a prelude to an expanded greenhouse later, it is well to fully offset the original roof. In almost every case. If a drainage problem were critical, we could offset in another, or even two directions, but the less complicated approach will prove best.

Here's why: If the picture titled 'Expand 2' represents a first greenhouse on the left and an expansion on the right, it will be easily seen that the second phase, the expansion, will require an entirely new roof line involving replacement of the roof framing and glazing. Loss of material will be significant and costly.

When we prepare for expansion by fully offsetting the original roof, however, one may note that there is virtually no loss of framing and glazing. At far right, a new wall is built and basically duplicate roof trusses are added. When glazed and furnished with a ridge seal, roof integrity is as good as a unit-built structure. picture

N_Calif_Kathy
And, goodness knows, glazing can cost a bundle!!

Ed_in_Sat
We've moved along rapidly to this point. Are we all clear on roof design - especially the offset principle? Much greenhouse design must be done from the top down, so we want the basics in mind. To fully understand top down design, talk to my wife Kathy. I dropped one end of a greenhouse on her years ago. Haven't had a warm meal since.

Ahowle
Wish I had known that about roof before I built mine. Always keep expansion in mind.

Gaile
So far, very good- I'm still with you!

Ed_in_Sat
'Roof Management' is only possible where roof height is proportional to other dimensions. Roundtop or essentially flat roof structures do not have the flexibility to support such innovation. They also do not have the temperature management characteristics to provide optimum growing conditions.

I hope no one thinks I dislike flat roof or round top personal greenhouses. I detest flat roof or round top personal greenhouses.

Steve_in_the_Adirondacks
Well, that clears that up. ;-)

N_Calif_Kathy
'Roundtop'? Like those airplane hangar shaped plastic structures??

Ed_in_Sat
yep

N_Calif_Kathy
Will you be expanding a bit on what you mean by "temperature management characteristics to provide optimum growing conditions"?

Ed_in_Sat
Not in this series. Greenhouse design is one thing, growing techniques another. Glad to do it later, but we need to stay focused.

LESSON TWO A - HEAT AND RE-HEAT
We are now going to enter that fuzzy world of "everyone does it another way". This session is critical to the design and operation of a greenhouse, especially a non-commercial greenhouse. In the consulting area, we arbitrarily consider any single greenhouse with an enclosed area of less than 3,000 sq ft to be a non-commercial house for most purposes. It may be a sales house or a specialty growing area in a commercial setup, but the 'range' house starts at 3,000 sq ft. We are going to refer to smaller houses as 'personal greenhouses' when a distinction must be made. Otherwise, all material in this series will be intended for the personal greenhouse even if it may apply equally well to both types.

The essential difference between a commercial house and a personal one is the tendency for air to stagnate in the smaller house. This is a peculiarity of enclosed volume, rather than any plot against the little guy. It may be prevented by good design; it may be cured at enormous expense.

Again: The essential difference between a commercial house and a personal one is the tendency for air to stagnate in the smaller house. This is a peculiarity of enclosed volume, rather than any plot against the little guy. It may be prevented by good design; it may be cured at enormous expense.

This is important: it will be on the quiz!

Here is a diagram of this situation. Please pay careful attention to this part of the discussion. It contains concepts that are at odds with those you have observed and, in many cases, will not agree with what 'everyone' does. I have reasons I consider valid for what I am going to show you. If you give more credit to another opinion, do yourself a favor and be sure you understand exactly what principles are applied in the method. Mine are simple and they work. If someone else has a better deal for you, have at it and clue me in. These three zones exist in all greenhouses. We like to optimize the center zone and reduce the other two, especially the top or hot one.

All enclosed air tends to stratify whether in a greenhouse or elsewhere. We observe this everyday. Hot air rises because it is less dense than temperate or cool air; cool air sinks because it is more dense than hot or temperate air. ERGO: Each summer, the attic is hot and the cellar is cool. Watch where a long-haired dog sleeps. You'll have well-defined zones.

To a lesser degree, dry air is lighter than moist air and will rise; moist air is heavier than hot air and will sink. And all may now respond, "Of course!" Perhaps, but in personal greenhouses without number, I have found stratification problems

Here's what happens: Builders put greenhouse exhaust fans in mid-wall at one side of the greenhouse and then put wet walls or inlet mechanisms at mid-wall on the other side of the greenhouse. They turn both on full blast and expect them to cool the greenhouse. To an extent they do, but they will never do so efficiently, nor will they do so as effectively as they might. The diagram we just examined will show you why. Let's look at it again.

See that wide zone in the middle of the diagram - the one labeled "Somewhat Variable Area; Good Air Circulation? That area and the one above it will vary as hot air makes a thicker or thinner stratified layer at the top. The air circulates well because we have those exhaust fans on one mid-wall and the wet pads on the other mid-wall.

Know what? The best air in the greenhouse is rushing out through the exhaust fans; hot air is remaining in stratified glory at the ridge; air under the benches is clammy - and the plants are wondering what the heck is going on. The fix is obvious - once someone describes it for you. Comin' up next time.

That ends session one - except for your questions and comments. Fire away!

Ahowle
I can see where I have made some mistakes and now waiting to see how I can correct them. This was very interesting Ed. Too bad you didn't do this 5 years ago.

Gaile
Ed, in your experience- what is more cost effective- stick building your own personal gh, or buying one of the kits?

Ahowle
I enjoyed building mine but its a little rough. I'm not that great a builder and its hard to make corrugated fiberglass tight so I'm paying for it in high heating cost

Ed_in_Sat
Worms and silicon putty will cure almost anything. Worms are those styrofoam strips made to match corrugations. You can stick them up in the gaps from outside or in if you didn't put them down before the glass. Use putty in fairly thin layers until you build up what you need. If it is terribly cold, ice the walls. Take a garden hose outside and spray the walls, letting the water freeze and seal all cracks. Nasty job but effective.

Ahowle
Yeah, but it looks nasty after a few years and if price of propane keeps going up I may forget the whole thing. I used the wooden strips and put Styrofoam on top of them but they didn't always match my fiberglass. I got fiberglass at salvage yard cheap. I have sealed up most of the cracks with sealant. Also have layer of clear plastic on inside

N_Calif_Kathy
I enjoyed building mine too. I learned a lot by building it, and had some help with the electrical and gas installation, but framing it was easy. IMHO if I was to get a kit I'd put it on a short wall so I'd have more height than the kit gives you. As we saw here the hot air stratifies at the top, and in a short Gh that's often where you have plants hanging (= burning) My GH is 11 ft tall at the ridge. Most kits are 7, 7 1/2.

Ed_in_Sat
The handout shows you and I'll talk about a cheap way to get the ridge up another couple of feet.

Charlotte_in_Calif
So is there a compromise angle of the roof to maximize heat in the winter but minimize it in the summer?

Ed_in_Sat
There usually isn't enough 'give' in a personal greenhouse to do what you would like, Charlotte. Something around 60 degrees would be nice but not very practical. There was an article on that subject in the AOS Bulletin from May 1983. pg 496 - Leon Wiard wrote it. Leon and I were friends. He lived up the road a ways after he retired to this area from Mexico. One of the first good pieces on solar design, though, and worth remembering.

ahowle
I have sealed up most of the cracks with sealant. Also have layer of clear plastic on inside

Ed_in_Sat
You can cover the north wall inside with Styrofoam insulating board - the kind they install under siding. It doesn't cut much light and cuts heat loss a lot. Put the foil side toward the plants to reflect light back to them.

Janetteh
That is what we did with ours. The whole north side has a wood line about 30 feet from it so James tore down some old chicken houses and used the wood on that side of the gh. Then came back with the insulation. The silver side out really makes a difference in the light levels on that side of the gh. I'm wrong. He took the metal roofing off of the chicken houses and used that...instead of wood.

N_Calif_Kathy
I did the same on the short wall. My Gh isn't glass to ground so I insulated the short wall with the Styrofoam board. And silicon sealed it.
Speaking of which, Ed will 'glass-to-ground' vs 'not glass-to-ground' be discussed in the future?

Gaile
Why don't you like round top greenhouses, Ed? Is it a functional matter or an aesthetic one?

Ed_in_Sat
Round tops don't provide any reasonable way to bleed off hot air right at the ridge You have to come so far down to vent, the hot air against the roof starts to radiate back into the growing area.

EDDIE_IN_GA
There is a solution for that Ed. Though it does require a lot of tedious work

Ed_in_Sat
Yeah, chimneys will solve the problem, but like we say, it doesn't take much to avoid problems but it costs like heck to cure them.

EDDIE_IN_GA
Got to do what you have to do...

Ed_in_Sat
Re roundtops and other things: I try never to come out wishy washy about such things. It saves time if folks know where you stand IF you have good reasons why. If, then, others want to do it their way, I assume they have better reasons than mine for doing so. OR - the MANAGEMENT wants it that way.

Guess I better pack it up unless somebody has an urgent topic. I enjoyed the evening. A lot of this program I had never heard before, so it was interesting. May try a couple of those things myself! LOL

-end part 1

Ed_in_Sat
We had just seen air stratification in the greenhouse and I want to talk to that for a moment. This was the diagram we saw earlier: See that wide zone in the middle of the diagram - the one labeled "Somewhat Variable Area; Good Air Circulation? That area and the one above it will vary as hot air makes a thicker or thinner stratified layer at the top. The air circulates well because we have those exhaust fans on one mid-wall and the wet pads on the other mid-wall.

Know what? The best air in the greenhouse is rushing out through the exhaust fans; hot air is remaining in stratified glory at the ridge; air under the benches is clammy - and the plants are wondering what the heck is going on. The fix is obvious - once someone describes it for you. Comin' up

I know you are tired of hearing this, but remember: HOT AIR RISES.

With this concept in mind, consider how most greenhouses are cooled: Fresh, hopefully good air enters the greenhouse through a vent or evaporative cooler and bad air leaves the greenhouse via vents or exhaust fans. Trouble is, both incoming and outgoing air will, in all probability, be routed through sidewalls near or just slightly above bench level. Bench level as in 'plant level'.

If hot air rises, why do we persist in trying to vent it through the midwall? The hottest air in ANY greenhouse is at the ridge. The closer to the ridge we remove that air, the more economical and effective our cooling system will be.

Cooling systems can be large or small and still remain easy to adapt to a variety of applications. The only principle we need consider is this one: determine where the most heat will be and make provisions to let it out as near that point as possible. In winter, of course, exactly the same point will collect heat and we can install a modest fan, set to blow down, recycling that heat to the growing area.

I know we are dwelling on this point, but it is absolutely essential to good greenhouse design and operation.

Summer heat will take just a bit more doing. In a personal greenhouse, a heat exit vent may be as simple as one or several turbine ventilators - those whirly things you see atop residences. If you do it that way, include a small fan right under each turbine. Position the fan to blow straight up and it will keep the turbine section turning constantly. VOILA! Heat can get out, insects and rain cannot get in.

Anyone not clear on turbine ventilators? They can solve a lot of problems for a very economical cost!

janetteh
Makes sense.

AHowle
Do power ventilators work the same as putting fan under manual turbine ventilator?

Ed_in_Sat
About the same if we are talking about power ventilators at or near the ridge. If the power vent is in the sidewall, stratification will win every time.

Ahowle
I'm talking about in the ridge or near the ridge

Ed_in_Sat
There may be an advantage to a power vent, Art, but it is small. The primary thing is to have a way out where the heat is. Compression cooling will push it out, and that is what we will describe.

Ed_in_Sat
Larger vents may cover more area, but the principle remains constant: permit hot air to leave and screen them in some way to prevent insects and other baddies from entering. A Styrofoam or other closure device will seal out winter winds. One may then automate a design so far as imagination will serve. The principles, however, stay the same.

When hot air is exhausted, some sort of make-up air must enter the greenhouse to resolve any pressure differential created. Believe it or not, cooler ambient air will come back in using the same vent as the departing hot air. However, we recommend forcing this process just a bit with an evaporative cooler. Yes, we recommend evaporative coolers in the warm Gulf states and in those places where ambient humidity is unbelievable. In our area, we call them 'swamp coolers' and use them despite summer conditions where temperature and humidity are alarmingly near the same number.

Evaporative coolers may be mounted high or low as may be seen in a couple of
pictures. Yes, that is Mount KB in the background!!!

Ahowle
Is there a rule of vents per sq ft or something?

Ed_in_Sat
Let me defer that just a moment.

Ahowle
I remove several 4 x 8 panels from sides of gh in summer, so are ridge vents going to work?

Ed_in_Sat
Every sidewall panel you remove REDUCES the effectiveness of your cooling, Art. If you are not exhausting enough hot air and replacing it with cool, moist air, you need to look to your vents and/or your input system

Ed_in_Sat
High can be ridiculous, as in this case where the guy forgot you have to service a swamp cooler now and again.

There is no real gain in placing swamp coolers high or low; stratification takes place regardless. If incoming air is cool and moist, it will stay in the growing zone and force hot, dry air out top vents. Think of the greenhouse as a box. Fill it with the good stuff and the bad stuff will have to get out of the way.

The exit vent area should be proportional to the inlet area and volume. Remember, however, that a smaller exit vent keeps a little positive pressure in the house, so outside air is not sucked back in. A smaller exit vent simply raises interior or static pressure.

Hummert International supplied most of the evaporative coolers we installed over the years. They stock greenhouse-grade units with ample use of galvanizing and epoxy. Good stuff, always. You pay a bit more initially, but costs even out over a longer use period. We do admit to local buying, however, where swamp coolers are a regular stock item. Hard to argue with the massive freight saving!

The only viable alternative to compression cooling is draft cooling, and this is not always acceptable to THE MANAGEMENT. We mention it here for your consideration. No principles are involved.

In a larger greenhouse, compression cooling may be accomplished by a fan and wet pad system, though not a conventional one. We recommend placing a large fan very close to a conventional Cel-Dek installation. The whole thing is then shrouded so the fan brings in only that air obtained through the wet pads.

janetteh
You're going to have to explain that one a bit. Is this structure inside the gh?

Ed_in_Sat
Let me go one more step, Janette, then we'll discuss. You need to see the other side of the system.

The shroud is on the inside of the greenhouse. Air is directed by means of a louvered shutter (this one is fiberglass) and a diverter that keeps the direct air stream away from the nearest plants. From the front, the setup looks like this. Under shelter of the diverter, a fog compressor performs very nicely. The fan shown produces about 9,000 cfm of inlet air at a nominal 78 degrees at maximum humidity.

Perhaps this will be a better view of the inlet system. The little silver box at the top is the electrical controls.

Ahowle
Now is that fan pulling in or blowing out Ed ?

Ed_in_Sat
The reverse of the shroud face is outside the greenhouse and consists of a conventional Cel-Dek wet pad installation. This one is 5' X 10'. It might be well to mention that this Cel-Dek is 21 years old this year and none of it has been replaced. Ambient water is very hard - 230 ppm of Calcium carbonate, but all water to the pads is softened with Potassium chloride. Longevity of the pads makes the cost of the water softener.

Now we can go into details, if needed. The shroud 'box' is built on the inside of the greenhouse and houses the high velocity fan. The wet pads (the one shown are 5' X 10' in size) are on the outside of the greenhouse. The shroud forces all feed air for the fan to enter through the wet pads. Input air is 78 deg F max temperature and displaces hot air, which is forced out of the greenhouse at the ridge. This is compression cooling. Do we have questions? We can come back to this area at any time.

Ahowle
How large a gh will this one pad cool?

Janetteh
The fan inside the gh is the only fan being used? The one that pulls the air across the wet pads? Other than HAF fans? My question was (and hopefully this one makes sense)....Is the large fan in front of the shroud the only fan that is used? Most of what you see in this area is the wet pads at one end of the gh and the fan at the other.

Steve_in_the_Adirondacks
We can now see why that doesn't work well.

Ed_in_Sat
The fan in the shroud is the only one used. I know what you see but I also know that most other end fans are throwing away the best air in the greenhouse. Our system fills the greenhouse with cool, moist air which forces hot air out the top vents. If someone has better principles than that for cooling we sure want to give them equal time here.

jim4eq
You use ground water for the cooling pads to maintain the 78F, correct? Or can you recycle the same water?

Ed_in_Sat
We use SOFTENED ground water. Softened as with Potassium chloride, not Sodium chloride. The coolant water does recycle in a stainless steel return trough to which make up water is added through a float valve. We also bleed off about 10% of total flow to keep salt levels down. Bleed only works when the system is on and the pump is running.

jim4eq
Makes sense. I was thinking of heat buildup in the water, but evaporation should cool it even in Miami 1,950% R Humidity

Ed_in_Sat
The return water is always cool - almost cold. In extreme conditions like Miami, the cooling process is absorption, not evaporation. Absorption is not as efficient, but it gets the job done. Remember, too, that when you let that heat out at the ridge, you are back to dealing with ambient temp plus maybe 1 or 2 degrees. You only have to cool it to just under 85 to get optimum growing.

Ahowle
Does Hummert sell these pads Ed ?

Ed_in_Sat
Yes, Hummert (www.hummert.com) is the largest full service supplier of nursery/greenhouse equipment. You can find the pads at most suppliers, however. Ask for Cel-Dek and they'll know what you mean even if their brand is different.

janetteh
Jaderloon sells the pads. They usually have a discount on them in the dead of winter if you go pick them up.

Ed_in_Sat
We cannot close a discussion of heat and light without inserting a maxim: ALWAYS USE GREENOUSE HEATING EQUIPMENT THAT EMPLOYS A STANDING PILOT LIGHT. Yes, even when Propane is the fuel. The reason for this is that condensation occurs any time any relatively cool surface is exposed to high humidity. Greenhouses have high humidity and greenhouse heaters have large metal surfaces. A standing pilot will keep the heater cabinet just a few degrees above ambient temperature. A few degrees, true, but it is enough to keep the heater cabinet from condensing moisture and rusting away. The cost of feeding a standing pilot is negligible compared to the cost of a heater. A big second hand residential heating unit has been puffing away in our greenhouse for 20+ years and is still leak-free. I have no idea how old it was when we got it but it was free.

Janetteh
If you think about it, this system would be cheaper to build, install and operate compared to the conventional systems that are being installed.

Ahowle
That's why I'm interested. Also my gh is not tight enough to pull air through wet wall but blowing air through pad might work for me

Ahowle
Do you have any other pictures, later will be okay, that shows this construction better?

Ed_in_Sat
I probably have other pix. These are some I thought most clear. Send me a note (EWRIGHT8@SATX.RR.COM) re specific needs.

Ahowle
Also how large a fan are we talking about?

Ed_in_Sat
Fan size is best matched to each greeenhouse. The one you see in these pix is a 9,000 CFM unit from W.W. Grainger. All ball bearing, been in use about 10 years.

janetteh
Ed, what size gh are we looking at with this system and how would you adapt it to fit different size ghs?

Ed_in_Sat
Janette, the greenhouse I am using is our prototype house. It is 30X40 with a 17' ridge. In a smaller house, it is much more cost effective to use a swamp cooler. Plenty of models available in the 7,000 - 9000 CFM range.

janetteh
I'm talking bigger gh, Ed. Ours is 48 x 60 feet. With a 14 ft. ridge.

Ed_in_Sat
Again, you need to size your setup to your greenhouse size and your greenhouse load, not to my figures. I'll be glad to help with this on an individual basis, but it is too confusing to do each one here.

Ahowle
Ed yours has more than twice as much sq footage and a lot more cu footage than mine.

Ed_in_Sat
OK, but it is half Janette's. Also the heat load is very much different for each area. There are no generalities here. Each installation is a series of compromises based upon local conditions. I can help each one separately, but not here. Contact me as shown and tell me your specifics. I'll ask for what I need and then give you some suggestions.

Let me close this session with the canned stuff I prepared. After that, we'll chat as long as you like: I know all have become weary of this long discussion of heat and the earlier one of offsets and such to deal with light. My apology, but greenhouse design must deal, primarily, with heat and light. When our principles are sure in this area, we can design any sort of structure to optimize our use of them. In our next sessions, we will begin to put all this principle stuff to productive use. THEN we'll see our personal greenhouse design itself.

janetteh
What do you do in the winter, Ed, when you don't use the pads. Do you just cover the vents in front of the fan with something to keep the cold out? I realize in SAT that is probably only 2 weeks but up here it would be more of an issue.

Ed_in_Sat
We're going to cover a typical hobby house in this area. Our system is pretty tight, so we just put Styrofoam sheet over the fiberglass inlet shutter on the coldest nights and that's all. We do drain the wet pad side around Thanksgiving, but it is always ready to fire up again. Three years ago, we had 100 degrees in Feb, so we stay prepared!

janetteh
All of this makes a lot of sense. Wish we had had this discussion before we built ours. But because of the way it is constructed, we can easily go back and adapt most of your ideas into the existing structure.

Ed_in_Sat
Let's talk individually before any of you make drastic changes. Our system works and we have no reservations about it. Still, you can't just make a change here and one there. It is a totally integrated system. One option I like is to use more than one swamp cooler and control them in series. Also, we like to control the wet pad pump separately, swamp cooler or system built. This allows us to dry out the wet pads every night and pads last much longer that way.

janetteh
Thanks for all of this information, Ed. I am really glad that you took the time to put this program together. Gives me all kinds of ideas for things that James can do. :-) Ed, the way our setup is, the only thing that we lack are the roof vents and the wet pad system. We have been talking for the last couple of years about getting an evaporative cooler but one thing or the other has kept us from doing it. I am glad that we waited. We actually read the transcript from a program that you gave way back at the beginning of OS and used a lot of the ideas that you had in there for building our gh. So your influence has been there for some time and you didn't even know it. :-)

Mauro_Brazil
Ed, in this system you're showing is the temperature in the intermediate zone controlled? I mean, is the measured temperatures automatically turning on/off the fan(s)?

Ed_in_Sat
Mauro, we measure temperature just above plant level at a point convenient to us, then set the thermostat to produce what we want in the growing area. The numbers on a thermostat mean very little. We set for the result and don't care what the numbers say.

Mauro_Brazil
Right

Ed_in_Sat
Good evening, all, and welcome to a continuation of our discussion of greenhouse design and construction. Before we get underway, please allow me to apologize for hurting some feelings about round top ("quonset") greenhouses. I was more abrupt than I needed to be and I do sincerely apologize to those who were offended.

To quickly recap the last session, we learned that an informal site plan can save a lot of effort. I hate to mention it, but we learned that heat rises - perhaps the single greatest concern in greenhouse design. We made a first effort toward applying compression cooling techniques. Along the way, we looked at a few tips to use in design and construction phases. Now, we're going to see if we can fit things together.

The area we are going into next can be difficult to those who haven't done a bit of building construction. PLEASE interrupt at any time if you need clarification.

Greenhouses are relatively light-weight structures. This would recommend a very light foundation except for one principle: greenhouses are large in proportion to weight and, therefore, will blow away if suitably inspired. A foundation, then, must not only support the structure, it must anchor the structure. To do this, we prefer pouring a concrete peripheral beam. This is simply a piece of concrete 10" wide that is set into the ground at least 6" - or to 2" below the frost line.

We make them at least 10" wide, because a standard light aggregate concrete block is 8" wide and we're going to stack some on the beam. The extra inch of width on each side of the block will insure that this short wall has a good 'foot' under every block.

Make the beam as level as the site will permit, but we can take out modest variations in a later step. Put in plenty of rebar. It won't keep the foundation from cracking but it will keep most of it close at hand when it does. Old pieces of scrap metal will serve the same purpose as rebar, so if you have any junk, now is the time to imbed it. Discretion is urged in the case of close relatives.

As you prepare to pour the beam, frame it, both sides, all the way around with 2"X4" lumber set on edge. This process will raise a 'lip' on the beam to keep fill material from washing out. At this point, insure that a grade level opening is formed for the doorway. As the beam is poured, 'strike' the top by smoothing it with a piece of scrap lumber. We're going to lay cement block on top of the beam and now is the time to prepare a good footing to do so.

Double check on that doorway. I can't remember how many greenhouses I've seen with a "raised entryway". You'll cuss it every trip.

While the foundation is curing, invite the neighbors in to view progress on the project. Someone is sure to ask what you are going to do with all that good sod inside the greenhouse. If no one asks, by all means mention deliverance from sod as your next step. Generously offer said sod to any neighbor with just one condition: he must start removal within the week and complete within two weeks.

If YOU need sod, go buy it. Trust me on this. Tell the neighbor he can dig out all the attached soil he likes, just so all the sod is removed. Try not to laugh while the work force expands to six hired hands to complete the job.

When sod is gone, remove the 2X4 form boards, clean them and then clean up the beam. This won't amount to much, just knock off the rough spots and patch any holes or low spots. Every void is a cradle for bugs, so be diligent. In the same way, true up the sodless mess your neighbor left. Pay no attention to the tears and sweat, they will not affect growing to any appreciable degree. The cleaned beams should be neatly stacked for later use in building benches.

Brief pause. Any questions?

John_in_Arcadia
Following along just fine, Ed

Ed_in_Sat
Now go buy a metal sprinkling can, couple of gallons of diesel fuel, a bag of dry cement and enough weed barrier cloth to cover the area inside of the peripheral beam. If you don't have any heavy wire, get a roll of fence top wire while you're at the store.

Finally, order a load of whatever fill material you have in mind for the floor. We rule out concrete from the start as this material impedes drainage and grows slime species yet to be cataloged. Our preference is for washed sand - a sort of chat that is considerably coarser than mortar or play box sand. Pea gravel is an option, but if you use it, prepare to be tired because walking in pea gravel can weary anyone.

Washed sand, on the other hand, packs like moist beach sand and stays put. Walkways and bench supports may be made from 8X16X2 patio stones, and once settled will remain usable for years. Resetting is merely a matter of scooping sand about until the proper level is obtained.

N_Calif_Kathy
I had never considered plain old sand... Never saw it even mentioned in any of the books I've bought. Interesting!

John_in_Arcadia
How about pea gravel sized red lava rock? I had that once and it worked great for me.

EDDIE_IN_GA
SAND FLOORS ARE WONDERFUL

N_Calif_Kathy
I agree that it does sound wonderful...I wonder why no one ever mentioned it before (in books, I mean)

Ed_in_Sat
Not plain old sand. Washed sand is still dirty but it has had the fines sifted out to leave a coarse chat. Red lava rock is much like pea gravel - tiring - and it crushes slowly into a goo that is still hard to walk on as well as a mess when wet.

John_in_Arcadia
Strange. I had no problem with it and had it for a few years until we had to move.

ahowle
I have enough problem with the cats using the gravel as a litter box. hate to see what they would do if floor was sand

CynthiaPrescottAZ
I had a gravel floor for 25 years and swore the next would be cement, maybe with pea-gravel imbedded. The fallout in the GH was horrendous and I want to be able to hose it out.

Paul
I have a cement floor because of the radiant heat and I love it. hose it down and you have a clean floor

Mauro_Brazil
Mine is cement too, but slime is a major problem in summer.

Ed_in_Sat
We covered that on the way in, Mauro. Slime on a slab is inevitable. A 10% Sodium bisulphite spray will help control it. (Note: Sodium hypochlorite is the base for Clorox. It is a nominal 6% solution of the hypochlorite form. We use a 7% solution of Sodium bisulfite because it removes or attenuates permanganate stains that abound when one is dealing with iron-rich water treatment. The hypochlorite is much easier to find and I should have referred to that. -Ed)

Janetteh
What is available here (and cheap) is crushed rock (granite) and we purchased the crusher run. The pieces of granite are big but will settle into a hard walkway that still carries the water off in a hurry.

Ed_in_Sat
I see nothing wrong with crusher run or pit run granite, Janette. I'd be a little cautious about pit run marble. Fertilizer will turn it to mush in the long run.

Ed_in_Sat
With materials at hand, proceed in exactly this sequence. Put some diesel fuel into the metal sprinkling can and wet down the entire area inside the peripheral beam. Don't drown it, just wet it well. Don a pair of good rubber gloves. Put some dry cement in a bucket and cast a heavy, even layer of dry cement over the diesel. Put a very light application of diesel over the cement to hold it in place. Leave open to the sun for two or three days.

At the end of this 'aging' period, apply an inch or so of sand over the cement without displacing the cement powder. Install weed barrier cloth over the newly applied sand. This cloth comes in long rolls, 3 or 4 feet wide. Just lap a seam where necessary

Anchor all seams and a spot or two along the way with landscape hairpins. These can be formed from the top wire you purchased. Cut 14" lengths of wire and form a 'hairpin' with 6" legs and a 2" bridge or top span. Drive these into the ground to anchor the barrier cloth, with special attention to the seam lines. Don't ask me why, but this treatment cuts weed sprouting to a minimum through years of use. Weed barrier alone just doesn't have that staying power

Jade
why the diesel??? Strictly for a week killer???

EDDIE_IN_GA.
DIESEL FUEL IS A GREAT WEED ,GRASS ,YOUR ORCHIDS KILLER.. BUT DON'T LET THE EPA CATCH YOU DOING IT

N_Calif_Kathy
Does it repel ants too?

Gaile
I imagine the diesel fuel will discourage almost anything.

Janetteh
I don't think that anything repels ants. If they can't come under, they go over.

N_Calif_Kathy
I was hoping, *G*!!

ahowle
Will it keep bamboo from coming up? I'm having a problem with that

Ed_in_Sat
You have to wait until bamboo is fairly large. Then, cut off several pieces per clump and fill the hollow stem with kerosene. We use mastitis syringes, but anything that will fit will work. It takes about 10 days to kill the clump.

Getting back - - Once the weed barrier material is carefully installed to cover every square inch of surface inside the peripheral beam, place a scrap piece of 2X4 across the grade level door opening and fill the remaining space with sand (or pea gravel if you just must do it the hard way).

With the beam interior well filled, set sprinkler hose to wet down the sand. When first wet, the sand will lose about half its volume. Fill the beam surround again and sprinkle again. Continue doing this until the interior is full of packed sand and no more sand will settle below the beam. It will later, but for now, that's enough sand.

That sand will also be surprisingly hard. We use 8X16x2 patio stones or even pieces of them to 'float' on the sand as bench and other support.

Next, construct a cinder block wall on the peripheral beam. Make it 3 blocks high and cap it with 2X8X16 cement stepping or patio stones. If block construction offends, the exterior surface may be stuccoed, brick veneered, tiled or finished otherwise. We just plant fig vine in a couple of places and stand back.

We're going to use both inside and outside support capability of that wall, so bear with me.

You don't need to copy all this - it is in the handout material as part of an article Bill Tippit and I did for the AOS Bulletin. The important thing is to get that support wall on the outside edge of the cement surround structure.

Using all treated lumber, begin to fabricate walls - flat on the ground. In order to get the ridge up high enough, it is well to construct walls of 2X4 precut studs. These require no additional cutting and produce no waste. They also permit you to cut an 8' 2X4 to appropriate length to level plates as needed. This references our earlier comment about not worrying over much about minor variations at grade. Here's where you take care of the dimples!

A cautionary note: never burn treated lumber waste - anywhere. More and more evidence indicates harmful chemicals may volatize if you do. At this point, insure that the grade level gap formed for the doorway is clear.

A handy trick is to place the sill and plate 2X4's next to each other, facing surfaces parallel, and scribe lines for the placement of wall studs on both at the same time. This will insure plumb walls. The second layer at the top - to double the plate - can be applied after the walls are erected. Just be sure lap joints in each layer are not directly under/over each other.

Each wall should have a single sill at the bottom and a double plate at the top, as noted. Slightly adjust the length of the studs to make the double plate level, even if you have to buy an extra-length board or two to replace a stud. This is the grade correction we mentioned earlier. Your builder will know how to do all this or we can answer off-chat questions about the process.

That last item has a lot of jargon. Are we clear on this?

janetteh
I'm a little fuzzy here as to how you are attaching the walls to the cinder blocks. We always use the U-shaped blocks on top of the wall, pour them full of cement and then put bolts into the cement. Then bolt the bottom plate of the wood wall to the cinder blocks.

Ed_in_Sat
We shoot those sills into the cement wall topping with a Ramset gun. Self-tapping cement bolts can also be used. Idea is to be able to cut out a rotted section and replace it without disturbing the integrity of the wall.

N_Calif_Kathy
So the resulting wall will be 8' Plus the height of 3 cinderblocks (8", right?), mortar and a capstone (2")

Ed_in_Sat
The resulting wall will be about 8 feet above the cement surround, for a approaching 10' from the ground. Wall height can be adjusted, of course, but you can get a lot of wall cheap our way and you get that ridge high enough to isolate heat from your plant level.

N_Calif_Kathy
OK. I found this as a picture for framing terms. button http://www.tpub.com/content/construction/14044/css/14044_29.htm

Ed_in_Sat
No sweat. We aren't making furniture here. 1/2" or even an inch won't make much difference so long as the top board of the double plate is level.

At each corner, allow for the adjoining wall to connect with a double upright for added protection. Tell your builder you want a corner buck (similar to the door buck you will need on each side of the door). As walls are completed, raise them atop the stepping stones on top of the cinder blocks. Brace walls carefully until all are in place and secured to provide mutual support. We shoot wall mountings with a Ramset gun, but one may also use concrete screws. We found imbedded J-bolts cumbersome and have not used them in years.

Since you are going to vent your greenhouse at the ridge, or as nearly so as possible, you will not need any windows or vent openings in the sidewalls. Put them in as you like for aesthetics, but they are expensive, waste a lot of growing room and are not very energy efficient. Remember to provide a door, however. THE MANAGEMENT will frown upon entry via the roof. Trust me.

pH
A link for dimensions on various types of concrete block is: button http://www.fizzano.com/specs2.html

Ed_in_Sat
That's nice, but stick with what goes on sale every other weekend at Home Depot or Lowe's. This is a good stopping place - just before we go into making roof trusses and doing other top work. We'll rest there until next time. Thanks for your interest in one of my favorite subjects.
Any questions?

CynthiaPrescottAZ
Is there such a thing as being able to hose out debris on a sand floor?

Ed_in_Sat
No, a hose stream will groove a sand floor. By the same token, it is almost impossible to hose-sweep an aggregate floor. Sand lends itself to being cleaned with a push broom. Be sure to strain out the sand and retain it. Beats hauling in a new load on a regular basis.

ahowle
Yea I think I have my bark in gravel than I have gravel

N_Calif_Kathy
That's why I went with a brick floor, and I think that's why Cynthia went with a cement floor. So we can sweep up all the debris.

CynthiaPrescottAZ
Yes, that's the answer. A bark floor. That's what I had after 25 years. Too cold in Prescott to repot outdoors here like I did in Cal., so I have to pot inside the GH. Fallout is now measured in cu ft per day.

Ed_in_Sat
We've sort of skipped around, but tonight, I want to start off by talking about building the roof. Foundation and walls are conventional, but the roof needs special care.

Having decided your roof profile early on, you can now build roof trusses. These are simply big letter A's with no legs. We build them to patterns chalked on a shop floor. They can be stored on the walls as they are completed, but brace the walls from bowing out with a cross-rope or two.

Erecting trusses will be much easier if you install a temporary upright called a 'gin pole'. The one shown just to the left of the ridge in the next picture was made from a piece of upset tubing (a rigid, high carbon pipe used in oil field work) and erected slightly inside the structure. A gin pole gives you a stable point to use in pulling all the trusses exactly into line, then holding them while you secure them with purlins or other longitudinal members. Use a level and a big roofing square at every opportuinity and then some! Once three or four trusses are in place, the trusses themselves can be used as a moving gin pole, following construction as it progresses. Here's how a gin pole works:

Sorry that pix is so cluttered. The gin pole is the straight upright that extends well above the ridge. No great stroke to a gin pole, but you can save a world of time if you install one and use it to set your first trusses in perfect alignment. Once started right, they tend to stay right, no matter how many you install.

Janetteh
A git-along helps too.

Jade_in_GR
Git along???

Ed_in_Sat
Yeah, although you won't have to put that much pressure on the trusses due to the great leverage involved. A couple of ropes with someone on each end will guide those first critical alignments.

For city folks, a git along, come along, fence stretcher, calf puller and mother in law remover can all be the same thing. It is a close-coupled arrangement of pulleys and cables that helps you move something that is reluctant to git goin.

One trick we learned the hard way is to skin the end trusses before they are erected. Here's a sample for a greenhouse with a vent step at the ridge.

The skinned truss shown actually goes on the other end of the greenhouse, but we can see how the glazing is pre-applied. If corrugated glazing is used, the wall glazing may be adjusted slightly later to line up with the corrugations. Put the lower glazing on LAST. It is the only way to have flexibility in making corrugations and seams line up exactly.

Before I am asked, a step-vented greenhouse looks like this:

Those narrow windows across the roof 'step' at the ridge are screened on the inside and equipped with a fiberglass outside 'door' that lets down flat on the low roof. This arrangement provides tremendous heat relief. 'Doors' are operated with Thermofor self-powered vent machines that open and close as temperature changes - even during a power failure. The wet pad and fan system we saw earlier was installed in this greenhouse starting at the near corner and going to the left. This house has 8' sidewalls and a 17' ridge. Construction is 3" aluminum I-beams.

Another way of doing the same thing may be seen in this commercial structure. Note the somewhat different way of providing a roof vent. The important thing is, heat is removed when and where it is. This is an under-construction picture from the Stewart range in Natchez, MS. Natural air circulation through the screened sidewalls is very cost effective.

I'll let you catch up a minute. Any comments or questions?

Jade_in_GR
I am drooling at all that space and light. oooooooooooooooohhhh!!!

Ed_in_Sat
It fills up!!!
While working on sidewalls, those of you in cooler climates might consider installing a closure mechanism to fit over the wet pads. Granted, an automatic louver on the inside is very nice to have. Still, an outside closure system will complete that most economical of insulators - a dead air space. Here is one we contrived to solve problems in a personal greenhouse. While we're visiting this house, note the stand off knit shade cloth. We'll come back to that.

We're back on the smaller house pix. That contraption on the back is a fiberglass panel made to fully secure the Cel-Dek wet pads. It is conventional except for the crank mechanism. I want to talk a bit about this closure mechanism because it is more appropriate for a hobby greenhouse. Here's a closer look at that:

Jade_in_GR
That closure mechinism looks like just the ticket .

Ed_in_Sat
Fabrication makes use of two strips of rack gear (obtainable from commercial greenhouse supply houses and two pinion wheels, available from the same source. Here is what a pinion wheel looks like:

The teeth in the pinions drive the rack gear strips to raise and close the cover as a single unit. The supporting structure and the crank rod are bent from vehicle tail pipe material. I don't know about your area, but we have exhaust system benders who cater to low riders and hot rodders. They will NEVER admit there is a shape or application they cannot bend. Two pinion units, two rack gears, two six packs and 12 tacos will put you on your way to creative design in south Texas. Big tube cranks might not be the easiest to use but they are cheap, durable and more than adequate. Plus, as noted, infinitely variable to suit the application.

The advantage of a tube-operated system is cost. They also work well and are reliable. Those rack gear sections are available in several lengths: 3' and 4' are most common. The curve and the set of the teeth are fairly standard, so racks and pinions may be obtained most anywhere.

No reason one could not line a closure like this with styrofoam panel. Even put styrofoam on the inside. Our problem is that we can have 80's and 90's one day, 40's and freezing the next during Jan, Feb and Mar. Tough going if you have to rebuild a wall for every major change. Two years ago, we hit 100 deg in Feb in San Antonio.

I think we better stop the prepared material here for tonight. It is a bit late to introduce the next major subject. With the den mother's OK, let's go to general discussion and I'll stay around awhile to talk greenhouses as you please.

Jade_in_GR
Where is this greenhouse? Geography?

Ed_in_Sat
Corpus Christi, TX

Jade_in_GR
OK. Some winter but not long and grey. Watching all this is making it so tempting but the reality of my geographic location bites.

Ed_in_Sat
Those of you who live in cold country should remember that you are going to get very little light through the north side wall and the north roof slope. You can insulate those areas with foil faced styrofoam and reflect more southerly light on the plants. Does more good than through-the-wall and helps the heating bill immensely.

Janetteh
On the unit you were just showing......covering is fiberglass? Did you have the frame made or make it yourself?

Ed_in_Sat
Our design. We chalked it out on a shop floor and welded the aluminum there. Re fiberglass. This house was 20 years old last September. Back then, fiberglass was the thing. Today, I would use a single layer acrylic with UV inhibitor on this house.

Gaile
Ed, in an area of mostly mild winters (Atlanta) how significantly would this north wall treatment affect the heating costs? Winter heating $$ is a major concern for me.

janetteh
Gail, we probably average about 5 degrees colder than where you are and we have a solid wall on the north side and the styrofoam on the inside. I don't know how much difference it makes in heating costs, but the reflection from the al+++ into the gh makes a lot of difference. It really lights up that side of the gh and the plants appreciate it.

Gaile
Thanks Janette. Heating bill for the house was outrageous last month, can't imagine adding to that bill enough to heat a gh.

Ed_in_Sat
Mild winters don't matter. The colder it is, the more effective an insulated wall treatment is. On those mild days in winter, it isn't worth the trouble. On the days you have arctic conditions, it will pay for itself many times over. There is no one answer.

Jade_in_GR
If I ever do a gh here it will be attached to S. wall of house. Only place for it but definitely would need shadecloth come summer.

Ed_in_Sat
Why shade cloth? Better to contol temp and use the light. We grew Phals in Albuquerque with no shading at all. Probably 7K footcandles plus light intensity. With 4% humidity, we just dropped the temp and stood back. Fed something like 280PPM N in a constant feed system, as I recall.

Jade_in_GR
Could you control the temps with air venting or would you need ac??

N_Calif_Kathy
Are the vents oriented down wind? Or does the prevailing wind matter? About the roof vent (Stewart's) those face away from the prevailing winds? (So wind doesn't stack up inside the house?)

Jade_in_GR
Kathy, I was wondering about that too but figured that the gear will make the seal tighter? Of course some kind of window lock would work.

Ed_in_Sat
They face away from the prevailing wind because wind going over the curved surface becomes staggered: the wind in contact moves slower than the wind above the surface. Stagger translates to lift, just like an airplane foil, and pulls huge amounts of air off the lip of the break. With open sidewalls, wind won't 'stack up' but it will rush in to equalize the lift vacuum.

janetteh
Another interesting thing about Stewarts gh is that the side curtains are only up when that side of the gh is in the shade. I believe that is right. Ed??

N_Calif_Kathy
Would you absolutely positively need to have a gear assembly? Why not just a hinge? (I'm assuming a small GH either 8 - 12 feet wide so how heavy could something like that be?)

Ed_in_Sat
That's a great question, Kath, and I should have covered it. You need rack and pinion control because of the wind. R&P doesn't flutter and flap. Hinges, ropes, pulleys, etc. are almost impossible to damp. Gearmotors work, of course, but at a huge cost.

Jade_in_GR
Aha, yes, Wind. ED, my question was about controlling the summer cooling without shadecloth. Could it be done only with the roof vents and maybe a side vent or would you have to run ac in the gh???

Ed_in_Sat
Jade, if you move enough air through any greenhouse and exhaust it so that it takes all the stratified air away from the high point, the temperature within that greenhouse can never exceed a 5 deg differential from the ambient outside air. If you can live with THAT temp, you only need to work on humidity and fine points.

N_Calif_Kathy
So if Jade was to build her GH on the south side of her house, you'd recommend she berm it, too? By the Way I typed up the article Ed mentioned about solar GH construction and recklessly and shamelessly put it on the web.

Ed_in_Sat
Yep, that's Leon's article. I have another one from the hobby greenhouse assoc people. If I find it I'll send it to you.

I would not berm a structure attached to a house. You'll have enough trouble sealing off condensation in a conventional approach. Berm it and you'll have REAL trouble.

Heck, at the price of poly, you can puff most of a greenhouse in the fall and take the top layer off in the spring and summer. That should save a third on heating costs. Such a plan is NOT recommended where winters can be mild or even warm.

Jade_in_GR
Yes, I can live with the 5 degrees. We don't have AC in house.
Yes, Ed, I would appreciate reading that other article if you find it, Thank you.

janetteh
How do you puff a gh?

Ed_in_Sat
You put a second layer of poly over whatever you have, secure the edges and blow air between the layer. Gives you a lot of insulation at an Eddie price. LOL Tomato growers are the kings of the puff roof greenhouse. If you have any close, drop by and see how they do it. Pretty simple, really. Looks kinda junky but what the hey. You can have a greenhouse that looks good or you can have a greenhouse that grows good. Rarely will one greenhouse do both. Mine grows good.

janetteh
That was what I thought you meant but wanted to be sure. Thanks.

N_Calif_Kathy
I believe Ken Meier in North Virginia has that sort of GH. Says it works very well for him, Snow load doesn't deflate it.

N_Calif_Kathy
Even here in California I have insulated my walls w/ Styrofoam, use twin wall polycarb siding and triple wall on the roof ($$) still I have issues with heating costs. One of these days we'll get Ed to talk about how to seal these high tech polycarbonates so that they have dead air space to increase insulation.. I've seen it on teh web 2 ways... one builder said not to seal the polycarb, the other said to seal with aluminum tape,, I have built both ways in my GH... can't say as I see a difference... but then I wouldn't (in one structure) would I?

Ed_in_Sat
Ed can talk about multi layer glazing materials now. You pay for 1/4" or even 3/8" dead air insulation and that is what you get. You have to have a mighty harsh situation to make that pay off. Seal it tight and it will fill up with condensation and grow so much algae light can't get thru it. I am not a fan, as you can tell.

Gaile
Does that mean that you don't recommend polycarb?

Ed_in_Sat
No. Polycarb comes in many forms. I just think a person should be mighty sure multi-layer types will do a good job. Most folks don't even consider asking questions and then evaluating the answers.

N_Calif_Kathy
I'm not sure I recommend it! I remember looking around the web, looking for the R-value of these twinwall poly carb sheets and it was really low, like R-2 or R-1.4. That's a heck of a lot of money to be paid for somethng that has essentially the same R-value as a single sheet. So - UNLESS I'm completely wrong - (Which I could be - so do your own homework and google it yourself) - check out your materials very carefully. Google them at least.

Jade_in_GR
That is a problem for me. Neighbors would have building inspector out in a flash if I did anything that wasn't code. My basement growing area is only seen by those I let inside. There my scrounging talents shine.

Kathy, I think up here the triple would be what I would use. Need to check with Randy. He has one attached to house and several puffers for his commercial stuff.

Gaile
I noticed how little the R value was (but didn't compare with single layer) and I really noticed how $$ it is.

N_Calif_Kathy
Definitely check with people in your area, because, like I say I'm not impressed. But! Check it out yourselves before taking what I say as gospel. Maybe its not impressive because my winter's are mild... who knows?

Jade_in_GR
Right, cost benefit ratios would be different but Rvalue doesn't change.

N_Calif_Kathy
Yeah, makes you wonder. I scrounged a few double paned windows and used sliding galss doors from folks who were changing out their windows, and had considered using them as siding. (See Eddie! You ain't alone as a 'recycler'!)

IMHO those inflated GHs (like Ken's) may be the way to go in cooler climes, as long as the electricity to the inflating fan doesn't go out.. Anyway, If I lived there I'd look along those lines... (My opinion only)

Jade_in_GR
First and foremost will check zoning codes. But I agree with you Kathy.

Ed_in_Sat
We're going to start putting the final structure together. Hope the weather lets us get the roof on, at least. We like to put staging (bench frames) into the greenhouse before we put on the skin or glazing. First, it insures that the benches will be strong enough to survive long use in a tough environment. Second, it provides a steady place to stand while completing later operations. In this connection, it is best to make the wood frames but defer covering them with wire until plumbing, wiring, lighting and glazing operations are completed.

Studies initially conducted at the University of Kentucky and then amplified elsewhere show that the classic 'dragon tooth' bench layout is the most efficient.

Here is a typical design

AHowle
What minimum size greenhouse is that design for, Ed?

Ed_in_Sat
It won't really matter, Art. The dragon tooth concept is extremely flexible yet produces a good net ratio however applied. In a 30+' X 90' commercial house, we wouldn't often use it because the net would drop as the center aisle (essential in a commercial house) widened.

'Dragon tooth' design can provide a very positive net use ratio and can also be tailored to limit the longest reach to something like 36" - 40". Many different arrangements of door location and aisle width may be employed, but the basic dragontooth layout should be followed. Bench height will usually be dictated by the height of the exterior wall forming a support for the back of the bench. Ideally, this will give us a height of about 30", with benches 36" wide (the maximum comfortable lean for most folks).

If you are unusually short or tall, get a yard stick, place one narrow end against your leg just above the knee and lean out until the yard stick is parallel to the ground. Let your hand slip down the yardstick if necessary. Where the hand stops when the yardstick if parallel to the ground measures the maximum width you should make your benches. Of course you should remember that welded wire fabric comes in 3' and 4' widths, so it is best to round bench width to the nearest of those two widths.

If needed in your installation, consider this pattern for a handicap accessible layout, with wheelchair access all the way around the bench area. It is a very important consideration. Handicapped persons need greenhouses quite as much as they need medicine and extra care.

A detail you might miss the first time around is proper assembly of the bench frame. Details are in the handout, but lets review them quickly here.

Be sure the end pieces (the 'short' pieces across the end) are installed as shown here, with the lap of the short cross pieces on top of the long side pieces. This will insure that the stress of stretching top wire will bear wood to wood and not wood to nail. Benches will stay tight and last much longer if this procedure is employed.

Back to bench construction, please give extra attention to the end construction as shown in the pix. The cross board must lap the long side boards to the outside if the structure is to have enough strength to stretch a long run of top wire.

Even after installing bench top wire, a sheet of plywood over the bench frame will provide stable footing for installing greenhouse glazing or finish work. What I'm trying not to say is that some lead foot gorilla will sag every section of wire in the place if you're not careful. With a place to stand, we can turn our attention to installing whatever material we have chosen for the greenhouse cover. Hopefully, the builder has installed exterior glazing before mounting any section having limited accessibility. Here is a top outside wall section with all glazing installed before erection to the greenhouse frame.

oops - The one missing picture shows an upper end piece with the glazing installed before the section is raised and mounted.

Glazed sections can then be raised and installed at a convenient point in the construction or glazing process. I know this is duplication but you don't want to make a mistake here! The fix requires a LOT of hard work. Modern greenhouse glazing is virtually all acrylic and minimum quality standards require that all glazing be treated to enhance ultraviolet resistance. This is important for plastic longevity and for discouraging insects such as whitefly and thrips.

No shouts on that last? You guys are slipping! Several recent studies show that changes to ambient ultraviolet light may be offensive to whitefly and thrips. Populations in untreated enclosures change significantly when UV is attenuated.

MarilyninOttawa
That is interesting! I use UV resistant floating row cover in my temporary structure and have no thrips on even susceptible specimens!

Ed_in_Sat
I hope you'll look into it, Marilyn. Consultants always look for a fix and never do the hard work necessary to establish a concept or principle.

Ed_in_Sat
Whether flat, double- or triple- wall or corrugated material is chosen, make certain formed urethane closure strips are available to seal edges. On flat material, seals should be installed for long seams, as well. We prefer to seal long seams on corrugated material with silicon putty.

The biggest problem with glazing is finding small quantities. Commercial greenhouse glazing is shipped in minimum units of 5,000 square feet. Lesser quantities incur significant crating and shipping charges. There may be several alternatives. Local plastic supply houses may be able to secure more modest quantities of greenhouse-rated glazing if the buyer can wait for his shipment to be integrated with other bulk product.

It may also be possible to use 'carport and patio' grade material from a home improvement center such as Lowe's or Home Depot. Such glazing will not last as long as premium greenhouse grade material but lower cost may offset reduced quality. After all, we are interested in top quality at the commercial level because of the labor cost to remove and replace glazing. If you are willing to work a bit more, a lower quality product may do the job very nicely. Just check on long term clarity before you buy.

AHowle
Is there a preference of glazing material on your part Ed

MarilyninOttawa
I wonder if supply problems are regional? I was thinking that stock might vary regionally according to use patterns. Lots of triple glaze here because winter is fierce. You can get it in reasonable quantities also since most gh are for private folks with small setups. We were most concerned about ice/hail damage and found the close equivalent to what you suggest worked just fine.

Ed_in_Sat
For Art and Marilyn. Supply problems are definitely regional. In Ohio, a good supplier may be 50 miles away. In El Paso, the nearest may be 400 miles away on the west coast. Availability would be about 90% of my decision on glazing, Art. Again, know what you are paying for a quarter or 3/8" dead air space - if it is dead air.

Ed_in_Sat
[As to ice] You need to keep the roof pitch fairly steep in any design. In Fort Collins, CO and much of the Great Plains, we use knit shade cloth over a well-pitched roof during hail season. Can't leave it up for ice because it loads. In ice areas, the first line of defense is the most uninsulated roofing you can find and a BIG heater. Keep a melted layer under the ice and it will slide off a well pitched roof.

MarilyninOttawa
When you hear all that ice hitting the roof...yikes! You really hope that things will hold up. We first tried translucent fiberglass sheeting that had an undulated surface. Fitted together just like you have shown and lasted for years (at least 15 yr). The slope must be acute and also when there is heavy snow.

Ed_in_Sat
If home improvement store product is used, it must be carefully installed.

Here is a diagram of an effective method for any corrugated material.

Screw and washer installation uses a coarse tooth screw such as the 1 ¼ " TEK" screw that comes with a stainless steel washer that has a neoprene seal bonded to one face. Make certain that the screw is specifically for wood or metal, depending upon which is the framing material. Although we put these screws in the crown of the panel at one time, we now find that applying the screw and seal in valleys provides the best seal for the long term. Believe it or not, movement by sun and wind will pull crown screws completely out of the wood. Also, valley installation permits later sealing with a dab of caulk through which the screw can be re-inserted. As corrugated material is applied, construction grade silicon putty should be applied to the long seam seal or flap. Be judicious in the amount of putty applied. A fully hidden seam will last much longer than one where the sealant if partially exposed to the elements. The top lap should be faced in the direction least likely to catch wind from a storm.

We prefer to do sidewall glazing last. This permits installers to position roof glazing and pre-skinned side panels more easily. Corrugation and seam lines can be better managed in the lower sidewalls than on the roof.

Janetteh
Also prevents heat buildup in the gh before the fans are installed.

Ed_in_Sat
This next is a bit after the horse has fled, but I'll go ahead with the discussion: We prefer to do sidewall glazing last. This permits installers to position roof glazing and pre-skinned side panels more easily. Corrugation and seam lines can be better managed in the lower sidewalls than on the roof.

In the interest of safety, please listen: there is no safe way to put anything on the roof with more than 5 knots of wind. Everything from poly to shade cloth will become a sail and give you airborne training in a hurry. Don't argue with the wind!!!

Shade cloth is almost always required over new glazing. We never recommend woven shade cloth and for the last 15 years or so would not let our people install it even if client-procured. Knit is so superior both initially and over the long term that it is the only material we consider. For most installations, 60% black knit material is best. Knit material stretches a bit during installation, so it can be installed very smoothly to make a nice, tailored look. Again: shade cloth holds ice in the worst weather and can seriously over-stress a roof.

One warning must be observed with any shade cloth: ELEVATE SHADE CLOTH OVER ACRYLICS UNLESS THE MANUFACTURER SPECIFICALLY DIRECTS OTHERWISE. There will normally be no problem in having shade cloth in contact with fiberglass. The acrylics, however, will bond to shade cloth in the presence of high heat and bright sun. Through several tests, we have been unable to prove any thermal advantage inside the greenhouse to elevated shade cloth.

Here, again, is the smaller greenhouse we saw earlier in which stand-off shade cloth is mounted very nicely. Re elevated shade cloth: TIP: you can do wonders with conduit. Don't be afraid to go right on up to 1" size to eliminate sag. If you splice long runs, replace the splice keeper screws with a self-tapping sheet metal screw that will go through both splice and conduit for a flush outside head. Do not cement connectors with epoxy, crazy glue, etc. Constant flexing will separate the join and make a mess!

CynthiaPrescottAZ
Ed, can you tell me what the current technology is on shade cloth? Years ago you never bought the colored cloth because it wouldn't last, only black polypropylene. My patio/GH covering was still going strong after 25 years, with sewing replaced. What about material longevity these days?

Ed_in_Sat
We have knit shade cloth that has been "up" for 22 years in South Texas. It looks like new. That white stuff with the silver threads may look cute but it won't take what we have to give it. We have never had to replace or repair a knit shade cloth installation. That's all the technology I can offer. Put up anything else you like, just install it so it is easy to replace. Black is the highest UV resistance. You can get green and brown, but we would never recommend it or be involved in any way.

With these discussions completed, we're ready to finish out. We'll do so next time. It won't be a long session, but there are several things one is well-advised to do when others might consider the task complete. We'll talk about those briefly, then encourage an open discussion of points we need to clarify or expand.

Next time, we're going to finish both the greenhouse and this chat series. Please urge all our group to participate in the next session. Not that I'm so hot as a leader, but we are going to talk about a very neglected essential of greenhouse design and operation: greenhouse safety. I've never seen a greenhouse, hobby or commercial, that did not have at least one major hazard. Let's urge everyone to look at this important area now. It sure beats a lifetime of, "I should've". I promise you it will be a short session unless you want to extend the discussion with questions and comment. That does it for the prepared stuff. I'll be around for awhile if you have questions or discussion. Thanks for your interest and attention.

New_User
I've seen a greenhouse that hung their shadecloth on the inside. Are there any advantages to hanging on the inside as opposed to the outside?

Ed_in_Sat
Yes, you get twice the installation experience when you move it outside. Shade cloth is designed to provide shade. If you install it on the inside, the heat involved is already in and you have to deal with that. Sort of hot shade, I guess.

Mauro_Brazil
Ed, I was so glad that I was starting building a new gh. Now, I am very concerned. I'd better hire experts here to do it for me...

Ed_in_Sat
I like consultants, Mauro - after 37 years in the game. By the same token, everything I've done and all I've said here can be summed up in this: heat rises. So long as you observe the laws and rules of nature, you can't build a bad greenhouse; when you don't observe such laws, you can't build a good one.

Mauro_Brazil
Many grh here in Brazil have shade clothes inside, two meters +-away from the plastic cover. Many commercial growers using this inside cover of shade clothes as a brightness regulator

Ed_in_Sat
Why, Mauro? See, I get "why?" all the time and I try to have a valid reason to give as an answer. If your compadres are hanging the shadecloth indoors, they must have an awfully good reason and I would like to know what it is.

Mauro_Brazil
Besides using it as a light intensity regulator I don't know whether is there any other consistent reason. But, now I am curious and gonna ask around why

Ed_in_Sat
Let me see, Mauro. That shade cloth on the INSIDE is a better light regulator than it would be on the OUTSIDE? Not being difficult, but that is the sort of question I run into frequently. My bet is the answer will be closer to "lots of people do it like that and it is easier than getting up on the roof".

Mauro_Brazil
I have to agree with you, and still many, many grhs here have it inside. Should I believe that anyone here have thought about that?

Ed_in_Sat
My point exactly. Light is spread when it comes through most glazing but the heat content of that light is exactly the same. When we lower the volume of light coming through the glazing, we proportionally lower the heat in the same way. The light reaching the plants is not much changed but the heat entering the greenhouse becomes a factor to be reckoned with.

Steve_in_the_Adirondacks
If I had a greenhouse, I might WANT to capture some heat for a few months of the year.

Jim4eq
But you would also cut down on the light when it's the weakest, sort of a trade-off. In northern climes, do they remove shade cloth in winter for stronger light?

N_Calif_Kathy
And would there be an equal number of times in the year when you wouldn't want a heat build up?

Steve_in_the_Adirondacks
For sure. We get some blazing bright days in the winter too so heat might build up even then. Maybe I'll just move to the Bahamas. Then I only need a frame to hold the shade cloth. ;-)

CynthiaPrescottAZ
Steve, if you have never had a greenhouse, you are probably not aware of how fast the heat can build. It can be snowing outside, but bright, and I can tell from my remote temp sensor that the greenhouse is self-heating.

N_Calif_Kathy
Ed, any comment on 'glass to ground' greenhouses? Kits seem to come either as glass to ground on designed to sit on a wall.

Ed_in_Sat
You know I always have a comment, KB. LOL. Glazing to ground makes sense only until you use your weed eater or lawn more. Then you have lace to ground and you mumble to yourself pretty loud. The nice thing is, you can take most glazing to ground houses and set them up on a cinder block or brick wall and solve the problem. Just remember to start with an enclosed area of 150 sq ft or so minimum. This is because every time you open the door you displace about 50 cu ft of air. You have to enclose enough volume to attenuate that or you will shock your plants. You pay a lot to condition the air in a greenhouse. You MUST think about how each activity affects your purchase.

N_Calif_Kathy
I didn't realize that about the volume of air.

CynthiaPrescottAZ
Ed, I have a question about insulation, but I suspect you may have covered insulation on a day I missed, so I will read up on what I missed and ask my question next time.