Doing some preliminary research on building a greenhouse

[kellyincville]

Hi guys:

I haven't been around for a while. I got married late last year and things have been really busy at work but everything finally getting back to normal.

I've been learning a ton about orchids in the last year- joining my local society, reading lots of books, acquiring some new plants. I'm thinking about building a greenhouse in the future and have started to do some research into the details. This might be a rudimentary question but I haven't been able to find an answer.

According to the source of all unbiased knowledge, Wikipedia, on average full sunlight without obstruction is approximately 10,000 fc. So, my first question is- does anyone know of any information that is available for different zones. I'm presuming that my zone 7's max fc is going to be higher than the max fc in Ontario. And the max in Belize is going to be higher than mine. Correct?

So the second part of my question regards how layers of shading work. Suppose that I use triple walled polycarbonate on my hypothetical greenhouse that allows for 65% light transmission. If I assume that my max fc is 10,000, then the max fc in the greenhouse would be 6,500 which would be ok for vandas but not much else.

Then suppose I bought 60% shade cloth and put it on over the greenhouse. Would then the max fc be 2,600 (10,000 x 0.65 x 0.40)?

Thanks for the help.

Kelly

[Anton]

Way too scientific for me.

I just built mine and covered it with construction grade clear plastic. The type they use to lay down prior to laying concrete as a damp course. It is clear and very tough.

Over that I stretched shade cloth. Inside I have made a false ceiling with bubble wrap. This acts as insulation but also acts as a great light refractor spreading light evenly around the GH.

I have also made bubblewrap curtains which I drop at night and during winter for insulation against the cold. During winter it allows light in and acts as a heating source as well.

To me some people go overboard with measuring the light readings, generally your eyes are accurate enough to judge lighting levels. I pugt the high ligh requirers on the top shelf, Dens, Vandas, then Coelogynes, Oncs, Zygs on the middle shelf and Phals, Paphs and othe rlow light species on the lowershelf.

So far they are all looking quite happy and growing well.

I believe in the KISS Principal.

[exasperatus2002]

While I cant help with that, Im going to watch this as Id like to set one up myself someday.

[jerrymeola]

The peak sunlight levels vary with northern distance (the sky filters the light going thought it) but at the peak in the summer the light gets close to 10,000 foot candles most everywhere, just for much shorter durations up north.

Your method of measuring light is basically correct but shade cloth not only filters the light it breaks up the light waves. Light nearer the top is brighter than en feet lower.

You can not tell light levels with your eyes which adapt to make your vision good. You can watch your plants adjust to being moved and that will teach you the level.

[NancyH]

Hi, My experience with my greenhouse has been not a light problem but a cooling problem. I read that when you are in your greenhouse and you put your hnd out over a plant and it casts a shadow there is to much light. I pretty much go by that. I also have the plants organized like Anton's. During the hot summers I had 3 layers of shading. There was plenty of light and I did it mainly for cooling. Be sure and plan your greenhouse to have auto exhaust fans to vent when the heat gets to high. The tripple wall is great for insulation and heating costs. Roof vents are good also. Anything you can do to automate the greenhouse will be of value to you in the future so you will not become it's slave, especially if you want to take a trip away from home. I will be investing in some Aluminet shade cloth. It will reflect back the heat while still allowing light to penetrate. Good luck with you building project. A greenhouse is the best, so rewarding and fun.
Nancy

[Anton]

Cynthia put me on to this company for auto vents.
test

As Nancy says, cooling is the main issue especially here in Oz.

[Cynthia, Prescott, AZ]

Be careful when you buy shade cloth. It is usually specified as % shade, not % sun. So, 64% shade cloth gives 36% sun, or 3600 fc. I have found that during winter I have to reduce my shade cover, something I never did in Glendale, California, when I had a glass house. I am using plastic sheeting now, which may have something to do with it.

[kellyincville]

Thank you for all your thoughts and opinions guys.

Anton & Nancy- That makes a lot of sense about the cooling. Virginia summers in general are very hot and humid so this will be something that I'll definitely have to keep in mind. I'll make a note that I should look for light colored/reflecting shade cloth.

Jerry- Once the house is built, I'll make sure to pay attention to this. Particularly about placing higher light plants higher up and let the lower light plants be below. Thank you!

Cynthia- I'll make sure to double check the stats for the shade cloth/3-walled poly. I was told (in an email from a vendor) that the poly was 65% light transmitting but I'll email her again for confirmation. Thank you! For your glass house how did you hang the shade cloth? From the inside? Or over the outside of the structure?

I would like to build something that is aesthetically pleasing and balance that with efficiency and practicality. Difficult!

[Laura L.]

Hi Kelly, I am new to orchids, but not so with gardening in general. Note I am in a zone 3, so our climates are quite different! Hubbie built me a greenhouse in the fall, and I will be very interested in what you find out about the shade cloths. I believe he used a 7 ply poly for heat retention in our bitter winter, but even when our day temps have been only 10F or so, still can get as high as 90F inside. The automatic vent system is a godsend. Still, I am thinking I won't be able to use the greenhouse in the summer. I appreciate Nancy & Cynthia's comments. Maybe there's hope. I'd no sooner get the plants outside, then I'd have to bring them back in. We've been known to get below freezing in June, and then again in August.

[Brooke]

Hi kellyincville - We had a g/h built of twin wall poly last spring. Twin wall filters 15% of the suns rays - I know nothing about triple wall poly. We use a 50% aluminet over the top and down the west wall. Inside we have another 50% black shade cloth on the west wall.

I am in Lexington KY so am basically due west of you. On a clear day in the summer, you can have fc's of 12,000 with 10,000 being more typical. Last Saturday without the shade cloth over the g/h, the fc's inside were 7,000 outside 10,000.

What do you intend to grow? I grow high light plants on one side and phals, paphs and a few other lower light plants on the west side. Even then, my phals receive brighter light than is needed for optimal growth.

Yes to vent fans and a cooling system - you will need it, winter and summer. There is a vent wall that opens with water running through a system to provide air conditioning type air, sucked through the g/h by two big vent fans in the wall on the opposite side. The system operates in four stages - #1 the wall opens, #2 one fan comes on, #3 second fan comes on, #4 the water runs through the vent wall. There are also two ceiling fans that operate whenever the wall vent fans are off.

In the winter, we only set the vent wall to partially open and one vent fan when it reaches 90 degrees.

I can grow cool growing plants in the cool end of the g/h. In normal summer weather, the cool end stays about 70 degrees. When it is super hot, 95 and above, and super humid outside, the temps spike in the cool end to about 85 for a short period of time. This is usually only for a couple of hours in late afternoon and then the temps go down again.

I hope this helps.

Brooke

[Cynthia, Prescott, AZ]

Kelly, percent sun, transmission, may be standard for the double and triple walled poly. It is just the shade cloth that I know is percent shade.

Nothing beats an evaporative cooler in summer, in fact, I run mine all year in spite of going down to 10F. I replace the batting and water in spring, and by fall/winter, the water is saturated with minerals, and acts as anti-freeze. When it starts getting cold, I throw a cooler cover over the evaporative cooler, and pull a corner back on mild days. Since I spend a lot of time in my GH, I can 'feel' the need to adjust the cooler cover. I buy a 2 stage thermostat to run the 2 stages of my cooler motor, and hard wire it into the GH.

I recently bought a solar powered vent fan to install in the eve of the GH from Harbor Freight, since I usually baffle the vents in winter, leaving open the possibility of it getting too hot in the GH. Last winter a killed a few plants, operator error, having the cooler off for 2 days in January, or there abouts. Haven't installed it yet.

You never want to put the shade cloth inside the GH, as you will at least double your heat load on what ever system you use to cool your GH. Having said that, I do have extra shade cloth inside the GH where my Phals are to give them the lower light they need. But the outside shade cloth takes out most of the heat. On my old redwood and glass GH, I just had the cloth laying on the structure, with slats of similarly stained wood holding it down. Actually, I stapled the cloth to the underside of the slats, then used some studs in the GH ribbing facing up to slide the strips with appropriate holes over the studs and held them down with wing nuts. But, not much clearance between shade cloth and glass. I viewed it as OK in southern California, but would never be acceptable in Phoenix, where the max 20F drop in temp the cooler is capable of is just not enough when the day temps reach 125F to 130F.

Currently I just throw the shade cloth over my temporary GH, and just hold it in place at the corners.

[kellyincville]

Thanks for all the info Brook! Your vent fans and cooling system- how is your system different from a swamp cooler? Or it is the same thing?

You also mentioned that you have a cool side to your gh. How do you maintain the temperature difference? Is it just the side that is closer to the vent wall? Does the amount of shading affect the temperature in each portion of the gh significantly?

Thank you for the info about shading the western side. Once you said it, it seems obvious but I wouldn't have thought automatically that it needs extra cover.

I grow about 70-75% Paphs & Phrags and the remainder are a mix of Brassavolas, Bulbos, Oncidiums, Neos, Phals and a few misc species. I try to stick with warm and intermediate growing orchids.

Thanks Nancy! I'm been taking a lot of notes from your posts. I'll make sure to have sufficient shade cloth on the outside of the structure.

Have any of you trying using outside foliage to cut down on light and heat? Maybe something that grows quickly and is not deciduous like bamboo? Or is that not a feasible option? The most realistic area on my property to put a greenhouse is an open field that has no trees around it. I'm anticipating that it will really cook in the summer unless I plant some shade.

[Cynthia, Prescott, AZ]

Too hard to control. If you want pretty GH's, try
greenhouse kit, greenhouse | Sturdi-built - greenhouse kits
I bought my first GH from them and save money by getting it precut, not prefabed.

[Brooke]

The cooling system is a swamp cooler. Having the swamp cooler permits me to have cool-er growing orchids which around here, would be impossible. I grow lycaste, neos, most onc. types, masdies on the table in front of the cooler. The vent wall there shades the plants as the sun travels from east to west. There can be a 15 degree differential between the vent wall side (south) and the opposite end. Phrags I grow on the cool end of the g/h, just across the aisle from the vent wall.

The shade cloth on the west wall is NOT against the wall but several inches away from it. During the winter when the outside shade cloth is removed, you want the sun to help you heat the g/h.

Yesterday our high temp was 39 but the g/h would have gone over 90. We control the vent wall manually in the winter and open it part way and have the one vent fan come on at 90. Thankfully the vent wall is a very tight fit with no air leakage. The two vent fans we bungee a piece of plastic over it on the outside and on the inside, we use foam board over the opening. We get zero air leakage around the vent fans. If you don't use something on the outside, the louvres will flap in the breeze if the wind is from the wrong direction.

Your open field is the best site for your g/h. You do not want any trees that could be uprooted during a storm to fall on it. Bamboo - not on my property. You could provide shading in the summer with deciduous shrubs.

My other suggestions would be when you run the water lines and electrical to the g/h, make sure you have water available in multiple places and more electrical than you think you need. We did great on the water and never have to drag a hose very far but could use twice the electrical outlets. We have three per long side but could use additional.

Have you decided on size? Longer is better than square and the bigger the g/h the more stable you can keep the temps.

Brooke

[kellyincville]

I can't thank you all enough for all the help you have given me. Tons more than I've learned reading everything that I've gotten my hands on through the net.

I was planning on 16x24. Do you think that would be an appropriate size?

Okay so the main things I've learned so far are (and to recap for anyone else who is appreciating this as much as I am!):
1) Light colored shade cloth on the outside in the summer to reflect heat.
2) Dark colored shade cloth on the inside a couple inches off the wall in the winter to absorb heat.
3) More shade will be needed on the western side of the building.
4) Swamp coolers are the way to go for cooling and humidity.
5) Keep the cooler growing plants by the vent wall and the warmer growing ones on the other side.
6) Lots of vents through the vent wall and the ceiling and make sure they are airtight to prevent air leakage and heat loss in the winter.
7) Use solar powered and automation wherever I can to save my sanity.
8) Hang higher light plants above and lower light ones on the benches.
9) Exterior plantings are not reliable to help with cooling.

What do you all think is the best way to go for flooring? Gravel seems to be really popular for drainage but I'm not crazy about the fact that I could never clean it. Is concrete an option? Or does it have a tendency to get slippery being in a hot/humid environment?

You guys rock!!

[Cynthia, Prescott, AZ]

#1: Well, aluminet is reflective, but light colored is not my cup of tea. I use black polypropylene, as it lasts for decades. The people in Phoenix use aluminet because they have to optimize every single percent gain they can in heat reduction, but is probably over kill for more mild areas. I had a 20' x 20' shade cloth strung up over my patio and half my GH for 25 years, and the only problem I had is that the sewing gave way after a few years, so that I had to resew it up by hand using threads of the material teased out of the cut end of some shade cloth, and that lasted 15 - 20 years+, as I don't know what it did after we sold the property. And note that we had regular Santa Ana winds that beat the poor thing near to death.

#2 doesn't make any sense. There is know heat reduction if the shade cloth is inside the GH.

#3: I don't make any distinction of how much shade cloth to out on any particular side. If others do, maybe they have a particular problem to solve.

#4: Yes for cooling, but you will probably need more humidity creation methods, as evaporative coolers add some humidity, but move an enormous amount of air thru the GH, so the humidity they add is not enough. I am currently using one of those spinning foggers from Fog America. It is best to have a system that is on a humidistat. But some people I know just have a very fine mist from the peak of their greenhouse on a timer to come on several times a day for a very short time. Heavier spray heads aimed at the floor also work, and with a GH the size you are contemplating, one of the Jaybird units would probably work.

#5: I have a horizontal air flow pattern, so that there is a temperature differential from floor to roof peak. I grow cool things on the floor and warm things hang high. This works well for me, but just in front of the cooler is a very cool location.

#6: I planned to have a vent high on the wall above my cooler, so that the cool air enters the GH on that wall and make a U-shaped pass down the length of the GH and back at a high level to exit above the cooler. Over this U-shaped path the air is constantly being warmed by the sun so that it starts out cool and by the time it exits it is quite warm. As it turned out, I made the vent too small, so had to add others that aren't where I would really like them. You want to make the vent area about 2.5 times larger than the cooler opening. If you look at my pbase site, you will see what I did to prevent warm air loss during winter. I don't want to seal the vents completely, as the cooler comes on in winter, and you have to have a vent to allow the cooler's input to be vented, or the cooler won't work, air in requires air out. So, I baffled the vents, so that warm has to go down hill to escape, and warm air does not go down hill.
Temporary Greenhouse Photo Gallery by Admiral Schnitz at pbase.com

#7,8,9: Yep.

I had a gravel floor for 25 years in a GH, and will never do it again. By the end of that time, I had a bark floor, well mixed with twist ties, dead leaves, and you name. My next one will probably be concrete, with a rough surface. I think I want a spot I can open at the floor to hose the garbage out.

[Brooke]

Cynthia refers to g/h's in temperate climates but even in so called temperate, it is not temperate during the spring/summer/fall inside the g/h. We elected the aluminet because it is basically invisible over the structure and reduces the heat by several degrees on the inside. I forget what the actual numbers were, but it was of significant value.

The one problem you do have is when do you remove your shade cloth in the fall without frying plants and when do you put it up again in the spring.

We were told to run the shade cloth from the gutter area on the east side, over the g/h and down the west side. Morning sun is good for everything and it is the west sun that adds mega degrees in the afternoon. The vent wall, which is most of the south wall, blocks the southern sun. We have no shade cloth over the north wall.

We don't have foggers above our plants but under our tables. I want to control what moisture is added to my plants and when. On super hot days the humidity drops very low and then we run the misters under the benches to soak the gravel. If it is just hot without drippy humidity, the cooler keeps enough humidity without the use of additional misters. It is hot and humid when we have a low humidity problem. Humidity at night is never an issue - there is plenty.

We elected to have a gravel floor with landscape fabric under the gravel. The normal watering of the plants saturates the clay underneath the gravel and releases it back into the air. We strongly considered concrete for the reason Cynthia pointed out but we were going to have to have a drain and drain field put in and didn't want this added expense. Call me cheap :>) It would be wonderful to simply hose off the floor and wash everything down the drain.

The size of your g/h sounds great and I know you will enjoy it. It will also cause you sleepless nights during an ice storm, or the tornado warnings we had the other night, or a miriad of other problems that pop up but I wouldn't trade mine for the world.

Did I mention having a generator on hand? :>)

Brooke