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Posts & Roof

The greenhouse has a two-pitch post and beam roof which rises from the south knee wall at a 45 degree angle to a height of 11, then gently slopes down at 25 degrees to extend three feet past the foundation. The south-facing 45 degree roof gives us the maximum solar gain.

Posts

We culled several young maple and walnut trees from Pendle Hill's campus to use for posts. We stripped the bark and treated the trunks with linseed oil. The posts are anchored to the ground by rebar set in concrete-and-rubble holes. There is a quarter-inch gap between the posts and the ground to prevent moisture from seeping into the maples and rotting them; we choose this simple solution over pressure-treating and sealing the posts with noxious chemicals. There was an unexpected advantage of using tree trunks for posts. Much to our chagrin, we set the main west post's rebar 5 inches too far to the north (the rebar for the center post in the drawing). To compensate, we merely used the natural bend in one the walnut posts. The structure is just as strong, and has an unanticipated but much appreciated organic look.

Beams

The roof beams are conventionally built from recycled 2x6 lumber treated with linseed oil.

Roof

The roof is a single layer of corrugated PVC screwed to the roof beams. This gives us a two-season greenhouse; we could easily add a second layer in the future that would expand this to a year-ground greenhouse.

There will be a vent in the north roof to prevent the greenhouse from overheating and cooking plants in the summer.