Unvented low slope roof detail, Zone 6
Hello all, A quick intro:
First time poster here. I’ve been a lurker on FHB and this site for some time now and have always had a passive interest in construction/building science outside of my “real” job. Currently I have the opportunity/time to tackle a few larger scale projects on our circa 1900 New Englander style home located in Southern Maine (zone 6). I want to do things “the right way” and also maintain the charm and character of this old house within reason.
Current project: Deconstruct 12’x16’ single story section under flat roof extending from north gable end of main 24’x28’ 1-1/2 story house and reconstruct an addition in same location. Deconstruction is complete. I saved as much material as possible and will re-use elsewhere.
A few key details for the planned addition:
Single story, approx. 15’ x 16’ Low slope shed roof, ~1/12, unvented (low slope due to need for peak to fall under 2nd floor window elevation).
.060 EPDM single sheet
ICF foundation, pinned to shallow bedrock (6-30” deep), tied to existing main house brick/stone foundation.
There is no room for an accessible crawlspace, I plan to have a slab with radiant heat.
I’m in the process of working through the key construction details in all of the critical areas with the aid of this site, codes, and various other resources. I’m hoping that some of you might share your feedback / expertise as I progress…
For the unvented, ~1/12 shed roof this is my plan:
Roof from inside to outside:
LVL rafters R24 batts tight to underside of roof sheathing
ZIP roof sheathing, taped
~R26 over roof sheathing: 3″ Polyiso with 2″ Toprock DD on top of Polyiso EPDM roofing, .060, over Toprock Total roof assembly
Walls from inside to outside:
2×6 batt insulation (likely R23 Rockwool)
ZIP sheathing, taped
1.5″ Polyiso, taped, over sheathing
3/4″ Rainscreen cavity
I plan to run the sheathing and exterior wall insulation up to the roof sheathing, over the rafter ends. The roof sheathing is planned to extend into the built-up roof overhang as shown in the detail. This is a hybrid plan from some of the details in the detail library on this site. This is a preliminary detail with many components not shown. Any glaring issues or things that I should reconsider? Thanks in advance.
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