Need advice for planning a greenhouse

My husband and a friend agreed to build a greenhouse for me. I've followed many links in the "sticky," read many of the threads on this forum, ordered catalogs, visited web sites, and I must say I am saturated with information to the point I'm confused. The main question is whether to build from scratch or order a kit. I think a kit for the size I want would be too expensive. We have an old, uneven concrete slab in a perfect location that is about 16 x 20. I would really like a GH about 12 to 14' wide. We have considered using treated lumber and PVC panels (similar to fiberglass panels but stronger), but by the time I add all the accessories for ventilation, etc., I'm afraid I would have just as much invested as buying a kit. I don't want one just to store plants in. I want room to "hang out," re-pot plants, start seedlings, etc. By the way, in NW Fla. it gets extremely hot during the summer. I just retired, so I have plenty of time for my new hobby. I've taken over the dining room with potting soil, seedlings, etc. DG has been SO helpful to me with all of my other questions, I'm hoping that one of you experienced GH owners can steer me in the right direction. Have I set my goals too high?

Any goal in attainable for a price:-) If you are handy and can build yourself you will save about 50% if you take your time, and do your homework. Otherwise, I think I would look into a kit. In your climate I would be most concerned about ventilation if you plan on using all year. What do you dream of growing in this GH???

At first it seems overwhelming, but in time it will all come together . But if you want our help you will be required to share in your progress:-)

Good luck,

Keith,

Keith, "Dream" is probably the right word in my case, although I think I have a "light green" thumb, so to speak. I have a lot of houseplants, I would love being surrounded by all kinds of beautiful flowers in the yard, I especially love all kinds of ferns and I've always loved growing hot peppers as a hobby. Fresh veggies are readily available here and since our yard is mostly clay and I'm not physically able to do heavy gardening, I don't plan to grow many of them, except tomatoes and peppers. I guess I just have the "greenhouse fever." I really love the challenge of growing things from seeds or cuttings and would like to use the greenhouse for that purpose. IF this project gets off the ground, I will be happy to share my progress. I would like to know what any of you think about the PVC corrugated panels as an option, since they are less expensive. As always, I appreciate any advice I receive from the DG members.

I think I've seen on other threads that the PVC panels don't let in the right amount of light or something along those lines. Even if I'm remembering the reason wrong, there's got to be a reason that all the GH kits you buy have polycarbonate panels instead of PVC...if PVC would work then the GH kit makers would all use that instead and improve their profit margins! But literally every single kit GH I've seen with plastic panels is made with polycarbonate, I've never seen one with PVC.

I'm not sure if you have plans to use the GH during the summer--if you do then you'll need to invest significantly in cooling so everything doesn't fry. Honestly even if you just plan to use it in the winter to start seeds, you're going to need some pretty serious ventilation. If it hits 65-70 during the day, a GH without much ventilation will easily be over 100 degrees and that'll fry any seedlings you have.

Just some thoughts on ways I might build in your climate. First a disclaimer as I've never been to Florida, nor have I live in a humid area. I think PVC would be fine for your roof, But might want some glass on the south side to let in more of light spectrum. A bed of white rock along the South would reflect more light in. Probably the coolest thing I've seen Is single garage doors with the wood panels removed and replaced with glass. In the hot summers you could just keep them open, but would still probably need powered fans. I will see if I can find the link and picture of this GH. You also will have to put some thought into drainage with that slab. Not to big a deal to cut in a drain.

Fourks
I'm in the same boat as Sharkey but in a very cold, and windy climate. I like the price of the Harbor Frt GH, but after reading about everyone's experience with them I don't think that's the way we should go. Do you, or anyone else, have any specific recommendations? I want to use it for seed starting and some gardening year around if possible without having to give up eating to pay to heat it. I'm finding this all very confusing and now I'm not sure I even want one. Your comment to sharkey about it being overwhelming was dead on! Helen

ecrane3, You're right about the kits not including PVC panels. I had noticed that as well. One of my catalogs from Growers Supply sells the PVC, however. It states that the light transmission for clear is 90%, but for white and green is less than 2%. The adjacent page shows the polycarbonate sheets and also lists the light transmission for clear as 90%, but less for other colors. I have no doubt that polycarbonate is much better, but it costs $10 more per sheet. Once I decide on a size, I'll know what I can afford. I've been looking at the ventilation equipment, such as vent windows, louver shutters, exhaust fans, etc. I'm sure cooling in the summer would be a bigger challenge here than warming in the winter. N. Fla. weather is a lot different from S. Fla. We've had days lately that might get to 70 degrees, then drop to freezing at night (25 tonight.) But, that happens intermittently. But Florida orange juice definitely doesn't come from my neighborhood.

Fourks, I would love to see a photo of that GH you referred to. Also, I think we could drill a drainage hole in the concrete. The slant might be an advantage also. Do either of you think that it would help to put pea gravel on top of the concrete?

I'm expecting more samples and catalogs to arrive within a few days. Maybe that will help. I thank both of you for your advice and will keep you posted.

I seem to remember reading about discoloration and a reduction in PAR light transmission through PVC over a time period as little as a year. Check on that before you decide to use PVC.

Also, while PVC is used for greenhouses (most notably in other countries), it seems like it is always PVC film, as an alternative to PE film. PVC film has the advantage over untreated PE film in that it has low transmittance of LIR and therefore theoretically it should hold heat a little better at night. Treated PE is widely available, however. I share ecrane's concern that you never see PVC used in kits.

Pea gravel...bad idea. Most who have tried it don't like it, it rolls underfoot. As far as cutting in a drain, I would think that drainage would be dependent on the slope, if any, of the slab. If the slab sloped one direction, it might be a lot easier to put some drains around the low edge of the GH wall.

hissunny,

A greenhouse in a cold climate definitely is another set of problems. I do have some experience with this as I am in the same boat. With wind and snow loads, I think the Harbor Freight greenhouse would not last very long. One of the reasons it took me so long to build my greenhouse is finding the right greenhouse that can withstand the forces of nature up here in the Rockies. I was lucky enough to find a stainless steel prototype greenhouse that a company built, called Authentic Greenhouses. They only built two due to the fact stainless steel prices rose so fast. I will post some updated pictures of this greenhouse soon. As far as the structure, I would go with something that is well built, aluminum framed, find out from the manufacturer wind and snow load, and if you are not planning on putting in a real foundation, then polycrbonate is your best bet. As far as heating through the winter, unless you know how to grow money trees (tell me how if you do), it is expensive. Your best bet is to extend your growing season and creating a different zone in the greenhouse. I just finished installing eight 55 gallon drums, filled with water, and am very impressed the results. It was cloudy up here for two days, never rising above freezing, and my greenhouse remained between 40 and 45 degrees. If you would like to see some pictures of construction of this greenhouse, find thread "dream greenhouse at 8600'".

Sharkey,

90 percent light transmission is better then most polycarbonate. It might yellow faster if it is not treated For UV. Still the cost Is much better then poly. You could just replace if you where losing to much light after a few years. I would think in Florida a little less light beating down would be GOOD THING. I do agree that pea gravel would drive you crazy. If your slab has a slop, you might consider cutting a 3 ft wide planter at the low end. Just a thought.

Thanks fourks. I'm still doing my research and probably won't put one up for at least another year. Up here all the pros use the polycarbonate panels. I'm surprised to hear the water in the drums worked so well. We have access to black pickle barrels (plastic for about $8); maybe we should pick them up while they are still available!

what kind of floor does every one have? I'm thinking cement with a drain only because I know critters and dig through the pea gravel. Helen

If your are worried about diggers. put down ckicken wire/roadbase/weedbarrier/peagravel.

Here are some shots of my thermal storage.

This message was edited Mar 9, 2008 1:12 PM

another one.

Fourks - very nice, thanks for showing us. I don't like sounding stupid but with the black drums under the bench, how do they heat up? Just ambient air? What are those containers you are growing in? Helen

Yes, the combination of ambient and the sun hitting heats them. Do a search on solar greenhouses for more information. I think its called the "latent heat of condensation" The BTU's stored in water is amazing. It's been a few years since science class:-) Those are grow bags (cheap) with clay pellets for hydroponic strawberries. yum!!!

This message was edited Mar 9, 2008 5:20 PM

Thanks, I'll look that up as more research! I didn't mean for this to turn into a science project. Yikes! Helen

Latent heat is heat absorbed or released when a substance undergoes phase change, for example, from solid to liquid or liquid to gas. The barrels are only using the principle of latent heat if the water freezes. In this case, they would release heat, and this heat is known as the "latent heat of fusion." Solar greenhouses which use a lot of stored water have been known to keep a GH right at freezing, protecting the plants from damage, when the temps are much lower outside. Keep in mind that all of the heat released (334J/g) will need to be reaborbed if that same barrel of water is to thaw out.

"Latent heat of vaporization" is the heat absorbed when water in the liquid form evaporates. This is the principle behind evaporative cooling.

The principle behind the use of stored water in the GH Fourks speaks of is known as the specific heat capacity. This is the energy required to raise a given mass of water a certain number of degrees. You can see here: http://en.wikipedia.org/wiki/Specific_heat that water's specific heat capacity is much higher than most other materials. It can hold many BTUs of heat.

I have come to believe, from talking to a number of GH folks in Colorado including Fourks, that folks at elevation have a tremendous advantage when it comes to using the specific heat capacity of water and achieving maximal solar gain.

Hi, Sharkey! I live in zone 8b also, not too far above you in South GA. I just had a greenhouse built, & I was very concerned about the chemicals in treated lumber leaching out into the hot, humid air in the greenhouse - I imagined my DH finding me on the floor, expired! So, we used untreated cedar - a bit pricey, but strong, bug resistant & safe, plus - it smells so good in there!! We also used the clear polycarbonate panels (called Suntuf, available @ Home Depot) on walls & roof, and added a few operable windows, so I can open them when I'm working. We installed a thermostat - controlled gable vent fan connected to 2 operable louvers on the opposite end, for ventilaltion. I'm not planning to keep anything in it after about April, as it will get too hot! Am researching some shade cloth or something to cover it to keep it cooler. Hope this helps! Samantha

I don't think you really need to worry about the chemicals in PT lumber getting airborne. They might leach a bit into soil which is why if you're doing a raised bed veggie garden people usually recommend not using it, but for a greenhouse base I don't think it can hurt you any. Also PT wood isn't as dangerous as it used to be, CCA has been replaced by safer chemicals. And while they might be able to leach into soil they aren't volatile so the only way you could breathe them in is if you're sawing the wood and inhale the sawdust.

Pour a bucket of water on your cement slab and see what direction the water runs. We built our greenhouse on an old cement cattle pad. It has a slight slope for drainage, nothing you can notice by just looking at it. My DH drilled some holes in the wood base on the lower end. When I water the plants all the water runs to that end and drains out the holes he made. Sometimes leaves and mud from potting soil plugs up the holes so I have a stick I poke through and it clears the debris and out flows the water! Whatever side the water runs to you will have to build up the GH base to make it level, otherwise your panels may not fit right. Just a inch or so difference will cause you problems.

Look around for some package deals. When I bought my 16' GH the package deal contained 4 automatic windows, 2 wall vents and a shade cloth. It's lean times and vendors are hungry. My GH is a Rion which you can buy or at least check out at Sam's Club. I didn't buy mine from them, but you can at least see what they look like. Some Sam's Clubs have them asembled inside the store.

Diana

Diana
Do you happen to have pictures of your GH? I've heard of Rion but that's about it. Thanks, Helen

All I have is a picture of the inside. It gives you some idea of the shape. You can see the big cement pad we built it on. The picture was taken last spring. All that's in there now are 150 sleeping daylilies.

Diana

Thanks Diana - I'll have to read up on that one; it looks like what I want. Keep us posted on how you do all year.

Diana, I love your greenhouse. How wide is it? Can you post a photo of the outside? When I've done searches on Sam's Club website for greenhouses, I have found nothing at the stores in my area. I will try again.

Samantha, thank you for the information. I would love to see a photo as well. In all of my research on GH's, I have found a company based in Alapaha, GA (close to Albany?), Atlas Greenhouse Systems, Inc., that builds mostly commercial GH's, but sells two hobby kits. That's only a couple of hrs. from home. The one that is really affordable is only 10' wide. I would really like a 12" wide GH. The "Frances" is available in a 12' width, but is pricier. I really like it, though. I would love to get opinions about these two models from some of you that have been so kind in offering advice to me.

I bought mine from Mega Greenhouse. Here's a link. They have lots of different greenhouses for sale, also supplies. I bought my shelving from them also. I will go out there today and take a picture of the outside.
http://www.greenhousemegastore.com/

Diana

ecrane - Thanks - I was truly concerned, but am glad I didn't really need to be! Glad we used cedar, though - it smells so great!
Sharkey - I'll try to post some pics if I have time tomorrow, but my car has been acting up & DH & I are taking it to have the battery tested - hope it's that simple! Samantha

Sharkey, here is a picture of my Rion. The daylilies inside look dead, but they are still dormant. It's still nasty and cold up here. No signs of spring. I don't heat the house.
It's 8.5' x 16.5'

Diana, thank you so much for going to the trouble of taking and sending the photo. I love the greenhouse. It looks wider than 8.5', however. I have bookmarked your link as well and will request info from them. I have quite a collection of catalogs and sample materials I've been collecting as a result of all my research.

I've taken advantage of our upper 70 degree weather lately and spent most of my time outside preparing flower beds, then pampering my seedlings until very late at night. So, my greenhouse research and planning have taken a back seat lately. (The downside to this is that the mosquitos are already huge and swarming.) I'll keep you posted.