I have wanted a living roof for my studio since I started. Preferably a butterfly garden.
3 16' poles2 10' poles40 6' poles
A living roof is obviously heavier than a normal roof. That means over engineering for safety. The log beam site I posted above takes roofing variables such as span, spacing, combined dead and live loads and commonly used species of tree. At 50 psf for a shallow soil roof, I am getting a minimum that ranges from just over 2 inches to just under 2.25 inches. So, I plan to go with a minimum diameter of 2.5 inches for the rafters and a minimum of 3 inches for the ridgepole and headers.
The end two rafters on the top of the short walls will be triangular trusses.
I can harvest five or six from our yard, and some from my in-laws. I will need to figure out how to scrounge the rest. I want to season the wood before I build. I still need to plan how to deck it. I will probably end up using a tarp for a couple seasons to a year. I will need galvanized lag bolts and nuts to connect assemble the two trusses and to attach rafters or trusses to ridgepole and to headers. Scraps can be used inside the wall to create anchor points for the headers.
I will likely make a ferrocement shell out of chicken wire and bags of Portland cement, but wonder how living roofs were created before cement and concrete. Does the soil layer need to be a couple feet thick for that to work, such as the Scandinavian long houses I have seen and built strong enough to support trees growing on them? Clay can seal ponds with a bit of help, but usually needs to be kept under water. Would lime plaster work for the roof deck instead of cement? Would lime plaster erode? It would be a risk, unless I could watch for problems for a season or several before adding the rest of the living roof, or having to remove sections of plants, soil and drainage to repair.
A 2" layer of small gravel and sand. A 2-4" layer of fallen leaves. A 2-4" layer of grass clippings. A 2" layer of soil. A 2" layer of mulch. Seed and plants including milkweeds.
The end result would be an organic organic roof. Organic architecture and chemical free growing plants. Sand and gravel to have a drainage layer to drain water away from the roof. Plant material to create an organic sponge to hold water up and away from the roof. Soil and plants to use the water. Mulch to keep the soil from blowing away in Oklahoma winds before the seeds can take root. So, using water, trapping water and allowing excess water to drain before the roof decking needs to prevent water from seeping through. I would want to assemble the roof in spring so that I would have minimal erosion as plants are getting established. Or have to water. Frequently.
So, tarp roof or roof deck from wall completion until the next spring comes around. It might take a while to get and season all the rafters I will need, even though I don't plan to start cobbing the walls until late spring when it starts warming and drying up. Or until I can get good rain gear to work in, cold and wet is miserable, while cold, wet and windy is a dangerous health risk without the right clothing.
So much to think about. Slow and steady, plan, plan, plan. It WILL happen.