Cabin roof with exposed rafters & EPS foam?
Hi there, I’m looking for comments on a roof I’m planning to put on a small cabin I’m building. The cabin will be framed using round poles (peeled logs) with a simple gable roof, using round peeled logs for the rafters which I want to be exposed to the space below. (Cathedral ceilings) On top of the rafters will be T&G cedar 1×6 planks, 4″ of rigid EPS foam insulation, some sort of decking, felt paper or a moisture barrier and then a standing seam metal roof. My questions are as follows: 1. Roof decking: I’m going to frame up the cavities for the rigid foam on top of the cedar out of 2x stock and am weighing options for the decking. 1/2″ ply is an obvious choice, but I’ve been considering the venting options and I also have a source of salvaged 1×6 siding (not beveled) that I’ve been considering of using as purlins across the 2x’s. I’m figuring that if I use plywood I’ll need to leave an air gap above the insulation to prevent the ply from potential condensation damage. On the other hand, if I used the salvaged wood I already have, I might be able to eliminate the air gap since there will be air circulation on the sides of the boards. 2. Venting. In general there seems to be mixed opinions regarding the need to vent a cathedral roof. Most of the unvented options deal with standard 2×12 rafters and cellulose, fiberglass or spray foam insulation, but not rigid foam (from what I’ve found so far). Should I bother venting this roof or just make sure the rigid foam is sealed around the edges and no air gets into the cavities from the room below? Thanks
Replies
try asking the question here
http://forums.delphiforums.com/breaktimeclass
it's where most of the regulars have moved to untill this abortion gets sorted
no need to vent, but if you have a heavy sun load, you may want ot vent under the shingles to extend their life.
Have you considered stressed skin panels? OSB on both sides, finish nail the cedar on the underside, nail the shingles on the top, done.
Hunter panel makes a vented panel, but they have minimum orders and shipping charges.
Not sure how far north your cabin is, but if you total up the square footage of the 2x material and figure about R-4, that is not very much insulation in between the EPS foam.
The Hunter panels are also available in ISO foam with OSB on top to nail roofing on. Way better insulating at about R-25 for 4".
Atlas also makes the same type of nailbase insulation.