Replies

1. 
   Jon R|Oct 08, 2021 10:03pm|#1

   To convince them, look up your code, specifically something like:

   In Climate Zones 5, 6, 7 and 8, any air-impermeable insulation shall be a Class II vapor retarder, or shall have a Class II vapor retarder coating or covering in direct contact with the underside of the insulation.

   Also investigate encapsulating the ducts with closed cell spray foam, leaving the attic unconditioned.

   https://basc.pnnl.gov/resource-guides/ducts-buried-attic-insulation-and-encapsulated#quicktabs-guides=0

2. Expert Member
   Zephyr7|Oct 08, 2021 10:25pm|#2

   It's safer to just use closed cell spray foam under the roof sheathing. If you want to build up a thick layer, you can use several inches of closed cell to get the barrier you need, then fill the rest with open cell. This saves a little money compared to using exclusively closed cell spray foam.

   Jon's idea about sealing up the ducts in closed cell spray foam could work, but that would make maintenance a huge problem. I wouldn't go that route myself.

   BTW, don't let the contractors get away with "we always do it this way". It's entirely possible to always do something incorrectly.

   Bill

1. Expert Member
   Malcolm Taylor|Oct 08, 2021 10:35pm|#3

   Bill,

   It's funny how some parts of the construction industry think it's a positive when they say they have been doing things the same way for decades. I'm trying to think of how that approach would sound if said by dentists? doctors? automotive designers? appliance manufacturers?