Air Barrier for Unvented Roof Assembly
Hi all. I’m in the process of building my house with Faswall blocks, a type of ICF. All blocks are placed and filled with concrete and we’ll drop in the roof beams in a few weeks. I’m trying to get my roof assembly dialed in and have several questions. I’ve read the articles posted here on rigid foam roof insulation as well as on buildingscience.com and have consulted with a few friends in the energy efficiency/weatherization business. I still have few questions as this is my first build and I want to get it right. I live in Wenatchee, WA, which is climate zone 5, at 1,400 ft elevation. Snow in the winter is hit or miss at this elevation. Some winters, such as this past one and the winter of 2018-19 bring 2 foot snow loads and other winters have minimal accumulations.
Following my structural plan and Joe’s “Robust Unvented Roof” here https://www.buildingscience.com/documents/insights/bsi083-mea-culpa-roofs, I have the following layers for my roof assembly, from bottom to top:
per the architectural plans, the minimum value for this roof is R-38 (because it’s a vaulted roof, according to my architect).
My questions are:
1) to create an air barrier, should I tape the seams on both plywood layers, or just the top or the bottom layer? Joe’s assembly only has plywood on top of the foam and he recommends taping the seams or applying a fully adhered membrane.
2) should I tape the poly-iso or the EPS seams? If so, with what?
3) should I vent the roof to account for ice dams?
4) the standing seam metal roof screws will penetrate the top layer of plywood and into the EPS rigid foam layer. Will the gaskets provided with these screws provide an air barrier, or should I take a further precaution?
I’ve attached several photos of the roof detail.
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