A customer came to me today with a curious idea. I quote:
"I have an idea for a passive solar retrofit to my house here in the Italian Market. Â I hope you can help me with it. Â I refer to the concept as a "trombe roof". Â It would be like a rooftop greenhouse, but covering the whole roof, and just a few inches high, not a space to walk around in or grow plants - just glazing over a small airspace above the roof. Â The number of btu's from sunlight falling on the roof is twice what we purchase in natural gas. Â I'm hoping this will capture a bunch of those."
"Trombe roof" doesn't fit because there is no significant thermal mass like in a trombe wall. This is more like a storm window, trapping a layer of air as insulation. His idea is to build a frame, cover it somehow (like a greenhouse), trapping air which would heat up in the winter and slow heat loss through the roof. In the summer he wants to take off the cover, exposing the frame, on which he will grow annual vines to shade the roof. It is a flat roof on a rowhouse in Philadelphia. Seems like a lot of work for questionable gain and obvious issues with snow, rain, etc. To me the solution to his problem (heat loss through roof) can be solved with extra insulation and a white roof, but it was interesting thinking about his idea in the shower this morning and I thought someone else might want to take a stab at it.