The greenhouse consists of a wooden frame to which are attached the structure of polyvinyl chloride (PVC) pipe which hold up the clear plastic film covering.
The instructions we had said "All lumber for construction should be treated for ground contact with an environmentally safe preservative such as CCA. Avoid wood preserved with chemicals such as pentachlorophenol or creosote. Lumber treated for ground contact has a higher concentration of preservative and therefore will last much longer than untreated or lightly treated wood. Except for the covering, the structure should last 10 to 12 years." I actually used red cedar rather than a treated lumber. This was my personal choice a I tend to be sensitive to many chemicals and just didn't want to take the chance. I have seen no rot so far, but figure I can just replace a board if it does rot. I figure that this is better than getting sick from chemicals.
Unless the site is very flat, you will need to level the foundation boards. This is best done by digging a trench on the high side instead of raising the low side, as the foundation boards should contact the ground at all points to ensure a good seal. To keep rainwater out, however, the top of the foundation board should not be below ground level, particularly around the door. The purpose of the stakes at each corner is to anchor the greenhouse and prevent it from moving in high winds. The Dallas area in Texas frequently has very high winds. In fact, the weather folks say that we have more and higher winds than Chicago, the Windy City. The greenhouse has been up for 3 years now, and the stakes have kept it anchored firmly.
The PVC pipe ribs are attached to the side boards of the foundation by drilling holes in the 4" x 4" base boards, just a tad larger than the PVC pipe, and just sticking the pipes in the holes.
PVC pipe may be purchased in 12- or 20-foot lengths in either schedule 40 or schedule 80 weights. Schedule 80 PVC pipe has a thicker wall and is stronger than schedule 40 pipe. It is therefore recommended for greenhouse construction. We used the 12 foot lengths and cut each rib to 10 ft. Five of the 2 ft pieces were cut to use between the ribs across the top length-wise and the rest of them were cut shorter and used to connect the side ribs at the top. PVC pipe may be easily cut with a hand saw, although a neater cut can be made with a pipe-cutting tool specially designed for that purpose. Care must be taken during assembly because the cement used to fasten PVC is fast-acting and permanent. It should not be used when the temperature is below 50 degree Fahrenheit, and should be used in a well ventilated area. Check the directions on the can.
We assembled each rib individually and put them in before we assembled the top. For the ribs to be 2 feet apart, the mid-rib pipe must be cut into pieces about 22 1/2 inches long . After all joints have been cemented and allowed to harden for a few minutes, position the assembly over the foundation boards, bend the ribs, and put the ends of them into the holes drilled through those foundation boards for this purpose. Assembly is best done by 2 or more people, firstly, to prevent overstressing the cemented joints, but more importantly, to avoid knocking a tooth out or knocking yourself silly if something pops out during the process. My greenhouse ended up with the A shape it has instead of the more traditional simple rounded top shape, because with the 6ft width, there was too much stress on the top joints, and it kept breaking the cemented joints on top. So we had to improvise. I personally like the way it turned out much better because with the taller center, it accommodates taller plants and hanging baskets better than a lower rounded top would have. Ten feet of galvanized EMT slid inside the top rib gives the structure added strength and make it possible to hang baskets from it.
The mid-rib pipe is cut into sections about 22 1/2 inches long and rejoined with PVC crosses to which the ribs are attached. Ten feet of EMT is placed inside the mid-rib for strength.
| BILL OF MATERIALS | ||
| Item | Quantity | Description |
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
12 4 2 12 12 2 2 4 4 4 2 2 2 1 1 1 1 1 Misc. 1 |
3/4" PVC pipe, schedule
80,10 ft lengths 3/4" PVC crosses, schedule 80 3/4" PVC tees, schedule 80 3/4" PVC 450 angles, schedule 80 3/4" galvanized electrical tubing straps 4" x 4" x 10' red cedar boards 4" x 4" x 6' red cedar boards 2" x 4" x ?' red cedar boards 2" x 4" x 6' red cedar boards 1" x 2" x 18" red cedar board stakes (pointed on end) 2" x 4" x 8" red cedar boards 1" x 4" x 10' red cedar boards 1" x 4" x 12' red cedar boards to be cut up for door parts set of door hinges plastic sheeting 6 mil 1 can of PVC cleaner 1 can of PVC cement 1/2" by 10' galvanized electrical metal tubing bolts, nuts, washers, screws or nails, staples door latch and handle |
| Please, carefully measure for lengths of PVC pipes and boards BEFORE you cut them. My lengths are estimates. | ||
Construction Details
An Architect I am not, so please forgive my amateurish construction details drawings. I hope you can figure them out.
After all the PVC ribs have been secured, the end frames and door can be constructed. Although there is a door on only one end, both frames are essentially the same. The two diagonals on each end give strength to the structure and make it easy to secure the cover. We connected the end frames together with 1" x 4" boards attached near the top of each end frame. The PVC pipes are then attached to that board 3/4" galvanized electrical tubing straps.
Select the type of cover material. 6-mil plastic sheeting is what we used. It looks kind-of milky to me, but the box says it is clear. After looking everywhere for something to use, we finally found it in the building materials section a Home Depot.
The cover may be attached with small tacks, but staples are much faster and
are more secure. After a couple of years of just stapling the plastic on and
then having to try to get all the old staples out in the spring, I started
putting a thin strip of cheap wood, about the thickness an width of a yard stick
over the plastic sheeting and stapling through that and the plastic into the
boards. The come spring, all you have to do is pry up the wood strips and
all the staples come with it. The plastic also goes on more quickly using
this method, and you use fewer staples. The cover should extend
several inches past the bottom of the foundation boards. Then cover the extra
material with packed soil to prevent the entrance of moles and rainwater. I put
a couple of inches of gravel on the floor to reduce problems with
mud and weeds.
These plans are actually a variation on some other plans that I found on the internet. If you want a little bit larger greenhouse, you might want to give them a look. Just click HERE and you will be taken directly to them. I personally like our variation better because although it is smaller in square feet, it is taller and I can hang my baskets from the top pole.