I just finished building a small greenhouse that I plan to use for plant starting in the spring. I think I overbuilt it a bit, but I was concerned about the snow buildup this winter.
I started with a frame of pressure treated 4 x 4s and beveled them on the end because I plan to drag the greenhouse to another location next summer when I’m done with it.
I decided to go with a 12/12 roof pitch to help shed snow and five foot sidewalls to give me just enough headroom in the center. After cutting thirty-six plywood gussets, along with studs and rafters, I laid each set out on my basement floor and nailed them together. Okay, you probably see the screw gun sitting there and are thinking I didn’t really nail them. I screwed the first one, but the rest were nailed. It was faster.
Some time later, the six frames were built and ready to go.
A few days later I got the frames screwed to the base and braced. It’s important to have the diagonal braces if the greenhouse will be free-standing. Without them, the frames can tip over end-wise like a bunch of dominoes.
I messed up in calculating the roof rafters and somehow missed the correct length by 7/16 of an inch. As a result, the sidewall studs are not exactly parallel to each other. Can you tell which way they are off? Leaning in at the top or out at the top?
With a little help, I got the 6 mil greenhouse film placed on the frames and fastened it down. It’s supposed to be good for about four years. See the channels at the bottom with the wire-spring things inside? Well, probably you don’t in this picture, but click on the picture for a big version and you will. I had heard that the wire-spring stuff was called wiggle wire, and when I tried to put it in, I found out why. You have to wiggle the wire, first up, then down, then up, then down as you work each bent section into the channel. It went pretty fast, once I was on to it. Maybe I would skip it next time though, to save some money.
The white material on top of the rafters is some kind of packing material that I had lying around. I thought it might protect the plastic from abrasion against the two by fours, and it was a lot cheaper than the felt tape in the greenhouse supply catalog. I suspect it is going to mildew eventually. Sigh, I wish I would have done a less ugly job of cutting and installing it.
In order to hold the plastic around the door frame and the frame against the house, I used two strips of wood, each 3/4″ by 3/4″. One was nailed to the frame and the second was screwed right next to it with plastic trapped between them and under the second one. I just pulled the plastic tightly across the first strip and pushed the second strip into place and screwed it.
Here’s a closeup of it.
To seal against the house, I cut pieces of foam. It’s called sill seal and I think I paid five bucks for a roll at Home Depot.
I covered the shelves with galvanized metal lath that you can buy at any building center.
I made the door from 1 x 3 stock, fastening the pieces together with pocket screws. The top panel has acrylic plastic, but I cheaped out on the bottom with a piece of styrene fluorescent light cover. Bad idea. It cracks really easily when holes are drilled in it. If it fails, I’ll spring for acrylic, which will no doubt happen in the dead of February.
And now it’s done.
It’s a bit on the homely side, but should do the job, I hope. The materials cost about $280, which seems like a lot, now that I think about it. Really, though, I suppose it’s pretty cheap for a fifty square foot greenhouse.
I will be putting a bunch of black water-filled plastic five gallon buckets inside to act as a heat absorber and radiator to see how that works, solar energy-wise Unfortunately, I have only white buckets and black paint probably won’t stick to the polyethylene very well. Still, I will try.
Update January 9, 2010********************
The greenhouse has been doing well for two years, but I really need more room for plants. I decided to bump out both sides, leaving the base the same size. As it turned out, the rock wall on one side kept me from expanding in that direction, so I settled for a one-sided bump out. I hope the greenhouse doesn’t tip over when I fill up that side with plants.
All I did construction-wise is to extend the rafters with 2 x 4s and run more 2 x 4s under the plant shelf to meet the extended rafters. I didn’t think to take any pictures of the process, but here are a couple of photos to show how it ended up. It now looks like a backward 4.
I’ve now doubled my space, though I’ll be able to keep only short plants on the far side of the new shelf.