Building a PVC Greenhouse

Part 1- Framing

I’ve been needing a new greenhouse for years. The old one on the property was designed for starting seeds, not any long term plants. It was built in the 60s or 70s, and it doesn’t get enough sun. It is wood-framed, down to the soil, so it is slowing rotting away at the bottom, and termites are eating the rest. The door is permanently open. I considered many options for a replacement, but the ready-made or assemble-it-yourself types are expensive, and usually smaller than I’d like. Last summer, I decided that we could probably make one out of PVC, and told my daughter we’d get something built for her to protect some of her succulent in during the winter. We decided to use the raised 8×12 bed that we used to grow vegetables in until it became too weedy. That’s the same bed that a couple of weeks later, I re-worked to get it ready for the roses coming from EuroDesert Roses, still promising my daughter that I’d get them out before winter. You can see that bed with the roses in it in my previous blog here: EuroDesert Roses blog. I did get the roses out, but it still took quite a bit of time building the new greenhouse. First, to stop weed growth in the bed, I covered the ground with the cardboard boxes the roses had arrived in, and covered that with the black plastic bags the roses had been in, and laid some old pipes and boards on them so the wind wouldn’t blow them away. Then I looked online for plans that I could adapt to this location. If I’d found all I needed to know, I wouldn’t be writing this. Most plans I found were for large hoop houses, or small framed ones. Nothing for 8×12. Using what information I did find, I proceeded one step at a time, carefully measuring and planning as I went along.

Step 1 was to put in rebar posts where the bottom row of PVC pipe would go. I bought pre-cut 3′ pieces at Home Depot. For this design I needed 11 of them: one in each corner, one on each side of the door, and at 4′ intervals on the sides. I pushed each as far into the soil as they would go, just inside the wood sides of the raised bed. Orchard Supply Hardware sells 1″ PVC pipe pre-cut in various short lengths, at $1 for 3′ pieces. They had 5 in stock, so I bought them and several 4-way connectors.

Detail showing the rebar against the edge of the raised bed, with the PVC pipe over it and resting on the bed edge.

I put the PVC on the rebar posts and put the 4-way connectors on top of them, and then measured the length I needed the horizontal pieces to be before going back to Home Depot to buy and cut 10′ poles to size.

Detail showing a 4-way connector fitting with 1″ PVC pipes

The man working in that part of the store that day loves cutting PVC pipe, and cut all the pieces for me. (You can also borrow a cutter in the store and do it yourself if they are too busy to help you.) I also got more 4-way fittings and a couple of T- fittings for the doorway. I put 2′ pieces above the 3′ pieces, but with the 4-way fittings, the sides are about 5 1/2′ tall. Not all of the fittings are available at OSH or HD. I needed 4-way corner fittings. Those I ordered from Greenhouse Megastore.

Here’s the corner 4-way connector that had to be ordered online.

This is how it looked after my first trip to Home Depot.

I thought for a long time about how to do the roof. If I just used 1″ PVC and the available 45-degree fittings, the 8′ span would make the greenhouse nearly 10′ high, and use a lot of PVC. I didn’t need that height. I asked at Home Depot about arching the roof, but the woman I talked to said I couldn’t do that much of an arch with that size pipe. I looked into using a different angle, but those fittings are hard to find online, and odd ones like that are expensive when you need 8 of them. I took my husband back to HD with me, and we played with the 10′ PVC pipes. We couldn’t really bend the 1″ at all. The 3/4″ would bend, but not enough for an 8′ span. The 1/2″ worked well, so we bought 4 poles, and 8 of the 45 degree fittings, as well as a few more 10′ x 1″ poles to cut at home for the door end. There  was also some piece-work to do. We had plenty of short scraps of 1″ PVC. To connect the 45-degree fittings to the top of the 4-way fittings, we cut 3″ pieces of scrap and set them between the fittings. Then, to narrow the other opening of the 45-degree fittings for the 1/2″ pipes to go into, we put 6″ long scraps of 1″ PVC into that end.

Here you can see the small piece that connects the 4-way to the 45 degree, and the 1″PVC piece used to reduce the opening for the 1/2″ arched PVC

My husband thought the outward and upward force of the arched pipe would push the walls apart, but it didn’t. Just in case, we tied a rope straight across one of the sections at the base of the 45-degree fitting. We put one end of the 1/2″ pipe in a fitting, and bent it till it was at the correct angle to go into the other end, and marked it. Then we cut off the rest of the pole. I waited to put the roof together till I finished the door end.

The end wall showing how the 1/2″ pole slides through the 4-way corner connector that ties the roof ridge line to the wall framing.

The door was another issue that took some thought. I considered trying to find a small used aluminum screen door, and my husband considered framing a simple wood door but in the end the framing, given the raised bed edge, would be a problem. I did find plans online for making a door with PVC, and decided to use them with some minor modifications. Here is the link to the plan, which is part of a complete hoop greenhouse plan with door and window. DOOR PLAN. For the hinges I bought 1 1/4″ connectors and glued two pairs of them. One part was screwed to the frame before the poly cover went on the greenhouse.  For the center of the door, I couldn’t find a reducing T that would slide over the vertical poles, and allow a 1″ pipe in the horizontal, so I got 1 1/4″ Ts, and a couple reducing fittings to go into the horizontal part that the 1″ pipe goes into. Since the T slides on the vertical poles, I used some duct tape and plastic to widen the poles where the fitting was to stay. Then I taped the fitting to the pole as well.  The door hinges are the only part I have glued. (My husband sanded a flat surface where the glue was going for a broader glued area.) The PVC sticks into the fittings pretty well, so it stays in place without glue. I like the idea of being able to move it someday if we were to prepare a better location. Another way to secure it is to drill pilot holes through fittings and PVC, then put in screws. I did this wherever a piece came loose,using stainless steel screws, 5/8″ long.

The door on its hinges. The Hinges hadn’t been screwed to to door frame yet when this was taken.

Once the door end was done I could measure what PVC pieces were needed to attach the roof ridge line. Like the sides, it is made of 1″ PVC and 4-way connectors. The 1/2″ PVC arches slide through the 4-way connectors. Other connectors and 1″ PVC connect the ridge line to the end walls. Little pieces of PVC were added to the top of the door frame and are attached to the arch with duct tape.

The upper part of the door framing showing the roof ridge line and connections to the door frame. The door isn’t quite in the center of the end wall, so the 1/2″ pole is a bit higher on one side than the other. The slip connector will be screwed to the door frame.

The complete PVC framing except for some screws.

Part 2- Covering

So once all the framing is put together, it’s ready for the clear polyethylene covering. 6-mil is what’s recommended for greenhouses. This sort of thing used to be available in small amounts at OSH, but I can’t find anything like it there now. Home Depot didn’t have small enough boxes of it, so I looked online. The best deal I found was on Amazon.com: a roll of 6′ wide by 100′ long. That’s more than enough, but not so much I won’t eventually use it all making repairs probably. There may be other hardware stores that also sell that size box.

To hold it on the framing, there are clamps you can get at Greenhouse Megastore for about 50 cents apiece. I bought about 60 of them.

Clamps

By the way, that article on door and window framing recommended using one of those clamps glued to the door frame as a latch. I discovered the clamps fit pretty tight onto the PVC pipe, so I think it would put too much stress on the door and frame to be pushing and pulling on it as much as my daughter and I are likely to be doing. I’m just going to use a velcro strap. Where holes need to be made in the poly cover for the door hinges and latch, duct tape will hold it in place and cover the cut edges of the poly so it doesn’t rip.

To cover the greenhouse, I first made one long piece wrapping all the way around, starting and ending at the door frame. I put 4 clamps on each door frame side and each corner. I temporarily duct taped the top of the poly to PVC. When the roof piece goes on, both can be clamped to the horizontal wall tops.

The arched part of the end walls was cut and fitted, then taped onto the arches. A large rectangle was clamped onto the door frame. Again, duct tape covered each cut piece of the poly to get around the hinges. The roof was made of 2 twelve foot long pieces, overlapped by about 8 inches, and taped for the full length on both edges. I used a step ladder to get up there with the poly and clamped it to the ridge line where the two poly sheets overlap. Then I cut 4 of the clamps in half. Remember those little pieces of 1″ PVC I put the arched pipe into? Perfect for clamping the roof poly onto. Clamps were placed wherever poly overlapped the 1″ PVC, so the structure should be fairly sturdy.

Half-size clamp holding roof poly in place.

Here are a few pictures of the complete greenhouse. Duct tape was used to hold pieces of poly in place where there was nothing to clamp. I’m sure there is a better tape for that purpose. I’d appreciate it if someone would tell me the best tape for holding polyethylene together. By the way, the poly has to be a bit loose for the clamps to go on, so you have to allow for that, and it’s best not to put the clamps close to other fittings, as the poly shouldn’t be stretched.

The back wall, showing duct tape holding poly in place.

The front wall and door.

The finished greenhouse. I reused some black plastic bags, taping them to the PVC inside the north side to absorb a bit more heat.

By the way, if any of you readers try this and have improvements, or know of other products or sources that would be useful, please add a comment. By the way, I recommend a white tarp, UV coated, and a bit bigger than the roof to tie on over the greenhouse during stormy or winter weather. With the lower sun angle, it doesn’t really cut down on light, and will help your plastic cover last longer.

I’ve added a follow-up post here: PVC Greenhouse, Part 2