A reciprocal roof is a beautiful and simple self-supporting structure that can be composed of as few as three rafters, and up to any imaginable quantity (within reason, of course). Reciprocal roofs require no center support, they are quick to construct, and they can be built using round poles or dimensional lumber (perhaps with some creative notching). They are extremely strong, perfect for round buildings, and very appropriate for living roofs, as well. The reciprocal roof design was developed by Graham Brown in 1987.
- 14 primary rafters
- Black locust poles except for one pin oak (used green)
- All rafters have a diameter of roughly 5″ at the top end of the poles (heavy!)
- 14 secondary rafters
- Pin oak and a few black locust (used mostly green)
- Diameter of 3-4″ at top end of poles
In total, the roof frame is composed of 28 poles. This frame sits on the walls of my load-bearing cob house.
You will need a sturdy center post, or “charlie stick” to temporarily prop up the rafters. You can either find a pole with a natural Y at the top, or find a really sturdy pole and nail two 2×4s to the top to keep the first rafter from wanting to slide off. Saw the charlie stick to the desired height, based on what the pitch of your roof will be and the height of your walls. There’s a little bit of math there. Also, aim to leave it perhaps a little long, because the roof could settle when you take out the stick.
Prop up your post with some braces. Don’t worry about burying it — it will just be that much more difficult to get it out later. You should have someone standing by to watch the stick while the first few rafters go up to make sure it is steady.
Visit www.theyearofmud.com/2008/11/26/how-to-build-a-reciprocal-roof-frame for Ziggy’s entire post.