Replies

1. GBA Editor
   Martin Holladay | Feb 06, 2017 06:21am | #1

   You now have an excellent opportunity to solve a fundamental problem of the Cape Cod style. (That fundamental problem is an awkward shape with a thermal barrier that is often unclear.) If you need new roof sheathing, now is the best opportunity to solve your problems -- by installing one or more layers of thick rigid foam on the exterior side of your roof sheathing, or by installing a layer of nailbase.

   Empty your bank account or borrow the money; you won't regret it. If you don't do it now, you never will.

   Here are links to two articles to guide you:

   Insulating a Cape Cod House

   How to Install Rigid Foam On Top of Roof Sheathing

2. 
   Dana1 | Feb 06, 2017 08:31am | #2

   R20-ish fluff in the rafters and 4" of polyiso or 5" of EPS above the roof deck will get you to current code-min performance on a U-factor basis for climate zones 4 & higher, and would have very decent dew-point margins in zones 4-6. In zone 7 you'd need a bit more foam on the exterior, or a class-II vapor retarder on the interior. If you use reclaimed foam from commercial building re-roofing/demolition the material cost can be well-bounded, but depending on the complexity of the roof lines there can be a significant labor cost, if say, you have a bunch of gabled dormers creating compound-angle valleys and hipped roof rather than flat rectangular planes.