I am hoping to cull the collective knowledge base here for some ideas on roofing an octagonal, roundwood-framed barn/out-building. The building uses a beefy (~18") cedar trunk as a centerpole. The roof pitch came out to be about 2.8 in 12. We had planned on a 3+ in 12 pitch but circumstances conspired against us & we ended up with a bit shallower pitch, limiting our options somewhat.
Really don't want to use asphalt shingles (from a financial & aesthetic perspective). Thought about metal (actually have some around that might work), but was STRONGLY caution against this by a builder we trust (said wind blown rain will keep the hip rafters wet & rot them). Thought about the velacreations latex concrete roof (even bought the Knott/Nez book: 'Latex Concrete Habitat'). When I calculated the amount of latex & the cost, however, decided to look for other alternatives. Latex is expensive & there is very little info about this approach online. Thought about cedar shingles. We live on an island in the PNW & there is a lot of cedar available. However, most resources suggest a pitch of at least 3 in 12.
This leads me to looking at a living roof or a simpler (?), lighter weight (?) moss roof. This is not an engineered structure. This has been and will continue to be true design-build (and not all of it that well thought out at times as I am learning as I go). I have no idea what kinds of loads my round wood framing can take. Plan would be to sheet the roof using boards or plywood, add EPDM (or similar, ideas encouraged), add media & some kind of drainage, then add moss/sedums/other. We are looking for simple, inexpensive, using as little purchased/manufactured product as possible. We are very puzzled by drainage issues & media/substrate. Any thoughts & ideas are appreciated. Right now all we have is the framed structure (tarped for the winter to minimize damage). We are open to possibilities & constantly limited by imagination! I will try to attach some pictures... I hope this works! Note for the pictures: each of the 8 pie shapes in the roof consist of 2 hip rafters (these go directly over the 8 outer posts to the cedar centerpost), 1 mid-rafter (these go from the centerpost to the mid-point of the beam (half way between each outer post)), and 2 jack-rafters (these attach to each of the hip rafters and span the distance between the hip rafter and the mid-rafter). With the addition of the jack rafters (not shown in the pix), the maximum distance between rafters is a bit over 2-feet at the bottom of the slope.
Here are some pictures. Thanks in advance for any ideas!!!
(tried to post 3 pix, but no luck. Trying again with one...)