Hi all, delighted to have a chance to join this neighborhood and thank you beforehand.
I remain in the northeast, in zone 5. This question follows some guidance I received from a green building centric contractor that likewise weighs practicality when considering constructing information, in addition to budget. Here it goes:
1. My task is a restoration and addition. As part of the restoration, offered the need to tie in the addition roofing system, I restored the existing attic roof. This was done with 7.25 ″ LVL in order to retain the height as 2x10s would have dramatically reduced the use of the attic. Note that this space WILL be conditioned.
2. Relating to insulation, the recommendation for the vented part of the roof was to utilize 2 inch broad strips of 1 ″ XPS on either side of the bay, with 1 ″ board over it. On top of that is Rockwool 5.5 insulation (.25 ″ too big, I understand) to develop a total R value of 28. The foam’s purpose is to crate (a) a strong air baffle, and (b) a thermal break so that the ceiling inside the attic doesn’t become very hot and radiate heat. I am normally ok with this method offered the vent, and it has been performed so actually no going back on this front.
3. On the other side of the roofing are valleys, so no vent. I am inclined to use a full” 2 ″ foam, with 5.5 Rockwool (now getting me ~ R33), but some research study has me worried that without a vent I may have some type of condensation concern as the foam isn’t enough to handle the roof temperature.
CONCERN: Relating to # 3– am I ok with the 2 ″ XPS plus 5.5 ″ of Rockwool? If not, should I (a) go pure Rockwool (painful modification), (b) include another 2 ″ of XPS which would then get me 4 ″ XPS and then R15 Rockwool, which gets me ~ R35?
Thank you!