DIY Greenhouse Foundation

Basics

• Make a list of what tools you have at your disposal. Do you have plenty of money, or a backhoe? Or are you going to have to do everything by hand with a shovel? This is important to consider before you end up with a big whole in your backyard that you may or may not have the energy to finish. If you have little resources, and drainage is not an issue, just level out a piece of ground using a shovel and an extra-long level. You should still be quite pleased with the results.

Drainage

• The next step in foundation construction is adding drainage. A rubble trench is an easy, effective way of doing this. To create a rubble trench, dig a trench around the perimeter of the building at least one foot wide and one foot deep. The authors of "The Hand-Sculpted House" suggest laying a four-inch perforated polyethylene pipe at the bottom of the trench. This pipe should have its outlet on the downward slope, to carry the water away from the greenhouse. You can also collect the water from this drain for further use by outleting it to a small cistern or pond. After the pipe is laid, fill the trench with clean, small round stones or gravel, packing it down in layers. Then protect the trench from becoming clogged by laying black landscaping fabric over the gravel. The black fabric over the stone has the additional benefit of being a good heat sink.

Floor

• If you want to finish out the floor of your greenhouse, there are several ways to do it. You want the floor to be decay-resistant because you're going to be combining lots of water and humidity in your greenhouse. Also, you want to add heat sinks wherever you can to keep additional heating costs down. Stone and tile are the best materials for both these needs. Commercial greenhouses usually cover the floor with black landscaping fabric, lay a thick layer of gravel over the top. This works very well, but if you can get a load of recycled bricks, tile or stones for free, you can lay these down on a thick layer of sand and they will work just as well.