Low-slope “warm” roof build-up clarification
We are advancing on the planning stages of a new build project in climate 4C (near Vancouver, Canada). Thanks to the many articles and Q&As on this site I’ve got myself comfortable with most outstanding issues we are facing in developing our roof and wall build ups. This is a small building used as a holiday home, not fully occupied in Winter.
With that in mind any feedback from your good selves would be appreciated.
The roof is a mono pitch (shed style) front to back at just 1:12 with no “rafter” space to hold insulation
– Exposed 3X8 Douglas fir beams
– Exposed 2×6 Douglas fir T&G boards
– Vapour barrier – BIGGEST QUESTION – Just want to confirm that what we need is a fully-adhered air and vapour barrier, such as Ice & Water (I believe this qualifies?) or another similar product? Any product suggestions?
– 1″ poly iso foam (to boost the R Value of the assembly) We may need to drop this however due to budget.
– 2 layers of 3″ EPS (offset seams etc). Total R value is only R37 ish but our code for flat roofs is only R26
– 1/2″ ply sheathing, long screws down into 2×8″ beams to hold together assembly.
– EPDM membrane (possibly torch on).
The house designer (not necessary a qualified architect or experienced builder) says we need Ice and Water for ice dam protection, I fail to see in what layer of the build up that would go in the “warm” unvented assembly we are proposing and what it would achieve when one has a fully-adhered type roof like an EPDM membrane.
This is still in the planning stages so also open to suggestions for a low-slope roof with exposed rafters if you see us going wrong with the above in mind.
Thanks in advance.
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