Township Building Department & Unvented Roof Assembly
I am a few weeks away from beginning a roofing/insulation project on a cape. I went into my local code enforcement office to pull permits and the official told me that the code requires ventilation unless I am using spray foam.
The proposed roof section goes like this, from the top: shingles, 15 pound felt, Hunter Nail Base (2 inches of polyiso laminated to half-inch CDX) installed over old roof deck , old roof deck, 2 x 10 rafter bays dense packed, sheet rock. At the rafter/top plate intersection we will be installing CCSF to join ( as best as possible) the thermal and air pressure boundaries. The cellulose will be installed from the roof, not from the interior. We will also be adding overhangs to the entire house.
When I explained the proposed assembly, he seemed to understand and asked me to provide a roof section. Reading between the lines, it seemed as though he was prepared to accept this assembly with some documentation.
My goal here is to provide a meaningful, thorough, and repeatable energy upgrade to this 1950s Cape. There are thousands of these homes locally. I want it to be minimally invasive and will be doing as much of the work as possible from the topside on the roof. The small second floor attics will require gaining access from the interior knee walls. In these small attics we will be packing out the 2×8’s by 2 inches and installing foam blocking and sheet rock to contain the dense packed cellulose. The R-value of this assembly is 50 (not the Whole Roof R-value).
1. Can anyone direct me to a similar roof section that I could alter or use as is for the purposes of obtaining building permits? I will sketch one if needed, but providing one from a known source would carry more weight.
2. Does anyone have ideas on how to minimize the invasive nature of this work? It seems to me that the work behind the knee walls is the only reason we have to go inside. In a perfect world everything would be done from above. There is also the RRP rule consideration. If I could figure out how to retrofit these homes, as illustrated above, without subjecting myself to the RRP rule or having to go inside, I think I could keep the costs down and have a better chance at selling this approach.
3. Any comments on the effectiveness of this strategy, the assembly itself, or tactics would be greatly appreciated.
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