I have built a number of structures from PVC pipe and several of them
are still in use today. My PVC hoop shadehouses are now over 15 years
old and still in perfect shape. I went through several permutations
before finding a formula that worked.
First, don't use anything less than 1 1/4 inch Sch 40 PVC. Anything smaller is too easily bent and crushed. Over 1 1/4 is overkill and there is a quantum leap in price. 20 foot lengths of PVC can be bent to form a thirteen to fourteen wide house with just over a six foot ceiling at the middle. Trying to lengthen the pipe to get it taller is pretty much futile and will make it weaker. Also, trying to get more arch than that will make it weaker.
There are any number of ways to anchor into the ground. I use 1 inch EMT stubs hammered into the earth and then held in place with a treated 2x4 and pipe straps. The ends of the PVC are simply slipped over the pipe, no attachment necessary as the pylons and covering will hold it down. Pylons (longitudinal wires or pipe) will keep the correct separation at the top and give it structural strength. For my greenhouse that must take a little snowload, I used 1/2 EMT and used 3 of threm. The shade houses are 96 feet long and pipe is too expensive, so I used high tensile strenth vineyard wire with ground anchors and wire grippers to hold the wire in place. The wire then locks the PVC in position by a self tapping screw and washer. I use 2 wires running the entire length. This system has been in place for almost ten years, but was built from the PVC of the old shade hoop house and most of it is 15 years or older.
Greenhouses require a bit more work. I used pipe pylons as mentioned. I also used pipe diagonals on the corners to keep it upright since there is no wire to do the job as in the hoop houses. I also use double wall plastic covering. This achieves two things: it insulated better since you have a dead airlayer, and it also makes the wall stiffer since it is puffed up with air. This also keeps the wind from flapping against the PVC which greatly weakens it.
The only UV problem I have had is that the greenhouse often gets very hot, especially when not in use and the south side PVC starts to turn brown then black from the UV and heat. This in turn heats the film to an unacceptable temperature and breaks it down where it touches the black PVC. My UV resistant film has still lasted four years, but I could have got another year or two if I had covered the top edge of the south half of the PVC with white felt. This felt is commercially available fro TEKsupply.com, as well as film and everything else greenhouse wise. I will use the felt this spring when replacing the film. Oddly enough, using a double wall involves very little more work than a single wall, but you must install a special inflation fan to keep it inflated. These run about $50 from OVG.com. Creative people can probably figure out how to use a processor cooling fan. These are very small fans that run continuously for years.
End walls and doors can be bult out of 2x4 materail, which makes double walling them easy, cover them inside and out with film. Floors are easiest if you use woven ground cloth to keep out the weeds and collect heat in winter since it is black. Put down a layer of gravel or sand first to keep it from getting muddy and make sure it is above grade.
There are a lot more details of course, but if you are doing this yourself you are probably talented enough to figure out the solutions.
First, don't use anything less than 1 1/4 inch Sch 40 PVC. Anything smaller is too easily bent and crushed. Over 1 1/4 is overkill and there is a quantum leap in price. 20 foot lengths of PVC can be bent to form a thirteen to fourteen wide house with just over a six foot ceiling at the middle. Trying to lengthen the pipe to get it taller is pretty much futile and will make it weaker. Also, trying to get more arch than that will make it weaker.
There are any number of ways to anchor into the ground. I use 1 inch EMT stubs hammered into the earth and then held in place with a treated 2x4 and pipe straps. The ends of the PVC are simply slipped over the pipe, no attachment necessary as the pylons and covering will hold it down. Pylons (longitudinal wires or pipe) will keep the correct separation at the top and give it structural strength. For my greenhouse that must take a little snowload, I used 1/2 EMT and used 3 of threm. The shade houses are 96 feet long and pipe is too expensive, so I used high tensile strenth vineyard wire with ground anchors and wire grippers to hold the wire in place. The wire then locks the PVC in position by a self tapping screw and washer. I use 2 wires running the entire length. This system has been in place for almost ten years, but was built from the PVC of the old shade hoop house and most of it is 15 years or older.
Greenhouses require a bit more work. I used pipe pylons as mentioned. I also used pipe diagonals on the corners to keep it upright since there is no wire to do the job as in the hoop houses. I also use double wall plastic covering. This achieves two things: it insulated better since you have a dead airlayer, and it also makes the wall stiffer since it is puffed up with air. This also keeps the wind from flapping against the PVC which greatly weakens it.
The only UV problem I have had is that the greenhouse often gets very hot, especially when not in use and the south side PVC starts to turn brown then black from the UV and heat. This in turn heats the film to an unacceptable temperature and breaks it down where it touches the black PVC. My UV resistant film has still lasted four years, but I could have got another year or two if I had covered the top edge of the south half of the PVC with white felt. This felt is commercially available fro TEKsupply.com, as well as film and everything else greenhouse wise. I will use the felt this spring when replacing the film. Oddly enough, using a double wall involves very little more work than a single wall, but you must install a special inflation fan to keep it inflated. These run about $50 from OVG.com. Creative people can probably figure out how to use a processor cooling fan. These are very small fans that run continuously for years.
End walls and doors can be bult out of 2x4 materail, which makes double walling them easy, cover them inside and out with film. Floors are easiest if you use woven ground cloth to keep out the weeds and collect heat in winter since it is black. Put down a layer of gravel or sand first to keep it from getting muddy and make sure it is above grade.
There are a lot more details of course, but if you are doing this yourself you are probably talented enough to figure out the solutions.
Brent,
Good article.
I'm considering the construction of a structure to protect my bonsai from the summer elements: wind and direct sunlight. I'm in the Sacramento Valley where summer highs can reach 110 F and we routinely have two to three weeks of temperatures above 100. Occasional north winds and associated very low relative humidities are also tough on foliage although I am sheltered from direct winds.
I already have quite a bit of area that receives indirect sunlight (northern exposure) so what I'm looking for is a structure that provides very bright but probably filtered light.
My question is; Would you use a light shade cloth, clear plastic or tinted plastic? I'm leaning toward a plastic due to the winter protection advantages.
Thanks,
Bob N. from Chico
Posted by: Bob Nottelmann | November 28, 2009 at 08:37 AM
Brent,
I should clarify a bit. My space is limited so a hoop structure with flexible plastic sheeting is not an option for me. I plan to build the framework with lumber and use corrugated plastic sheeting. My question is color: clear, opaque, or colored. The structure will not be air tight but will have a couple of partially open sides.
Bob
Posted by: Bob Nottelmann | November 28, 2009 at 09:21 AM