Roofs are an underutilized asset in the suburban garden. When I was studying Permaculture Design at Oregon State University, we calculated how much water would run off of our roofs in an average year. The results: our 1800 sq foot house sheds a staggering 15,572 gallons per year! It’s begging for a rainwater harvesting system beyond the little barrels most of us use. I’m still looking for an aesthetically pleasing option. The Rainwater HOG systems look pretty good, but they’re pricey. If I were a real permie, I would install a huge cistern and be done with it. I just can’t go there yet. If you want to calculate how much water runs off your roof, Texas A&M can help you here.
The roof can theoretically generate some of our electricity needs as well. I had done some research into purchasing versus leasing at Dominion Power when it occurred to me that all the trees around our place could be a liability. Here in Northern Virginia there is a website called Nova Solar that analyzes each home’s capacity to generate electricity using satellite images.
Our results are a little better than I thought. Even though our roof is only 35% usable, it could hold a 7.2 kW system. The average system in the U.S. is 5 kW. So now the question is pricing, which is way too complicated to go into here. I don’t understand it fully myself yet. I did see that some community organizations are setting up central solar power stations that neighbors can then purchase from, so that’s another option.
For an even more unusual roof use, check out rooftop beekeeping on the Beekeeping Like a Girl blog . It would have the advantage of not having bees swarming our small yard as much, but the very real risk of one of us falling off the roof and dying. We’re still weighing the pros and cons of that one.