Replies

1. GBA Editor
   Martin Holladay | Jun 05, 2018 09:42am | #1

   Joseph,
   Roofs with valleys can't be vented, so you are restricted to unvented options.

   There are two basic approaches. Either:

   (a) Install an adequately thick layer of rigid foam above the roof sheathing, with or without supplemental fluffy insulation under the roof sheathing (and in direct contact with the roof sheathing), or

   (b) Install an adequately thick layer of closed-cell spray foam against the underside of the roof sheathing, with or without supplemental fluffy insulation under the cured spray foam (and in direct contact with the cured spray foam).

   Both options are fully explained in this article: How to Build an Insulated Cathedral Ceiling.

   You asked, "What would be best?" The answer to that question is to install rigid foam above the roof sheathing.

2. 
   jw54 | Jun 05, 2018 10:33am | #2

   Thanks Martin, Would u advise with option B given they are 5 pitch scissor trusses to only spray foam up to the point of having space between upper and lower chords. Also, if using foam can I still use 3/4 polyiso between furring strips on bottom ? How about a gable vent to go with the ridge vent?

3. GBA Editor
   Martin Holladay | Jun 05, 2018 11:37am | #3

   Joseph,
   Your questions are confusing. Time to post a sketch of what you have in mind, showing how the various roof slopes and trusses meet.