Replies

1. 
   Malcolm_Taylor | Jan 11, 2022 05:39pm | #1

   Bobb,

   Yes that will work fine.

2. 
   b3lbittner | Jan 11, 2022 05:50pm | #2

   Well, that was much easier than I was expecting (fearing).

   Thank you so much for the help, Martin!

1. 
   Malcolm_Taylor | Jan 11, 2022 07:54pm | #4

   Bobb,

   To address Bill's concerns, make sure to adhere to the ratios Martin calls out in assembly #5 in this link: https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work

3. Expert Member
   BILL WICHERS | Jan 11, 2022 07:38pm | #3

   Note that flash and batt could potentially be a problem in those unvented rafter bays. You need to make sure you have sufficient spray foam for dew point control, and you want that to be closed cell spray foam. Exactly how much spray foam you need for dew point control depends on your climate zone. As long as you put in enough spray foam to keep condensation issues at bay, you're safe filling the remaining space with batts.

   I personally would probably fill the remainder of the space with open cell spray foam though, since it's cheaper than a full fill of closed cell spray foam, and it's easier than trying to stuff batts into the irregular spaces that you have after you do a partial fill of closed cell spray foam.

   Edit: when I reread that, it occurred to me that what I said might not be entirely clear. When I said “fill the remainder of the space with open cell spray foam”, I meant first apply sufficient closed cell spray for dew point control, then fill the remaining space with open cell cell spray foam and trim it flush. You don’t want to fill the entire cavity with only open cell spray foam.

   Bill

4. 
   b3lbittner | Jan 15, 2022 01:35pm | #5

   Bill and Malcolm --

   Thank you for the follow-up! I have read that article, and it is already my plan to maintain an appropriate ratio between closed cell and fiberglass.