HOW TO BUILD AN ENERGY EFFICIENT WALL
QUESTION FROM CHRIS FROM AUSTIN, UTAH:
I am trying to figure out which wall design would provide the best overall insulation value.
I can either build a wall out of 2X6 studs on 24" on center filled with blown in insulation plus 1" rigid foam insulation on the exterior.
I can build the wall using 2X6 top and bottom plate but use 2X4 studs 16" on center but have twice as many and offset them so that there is a 2" gap between the outer sheathing and the sheetrock. This space would also be filled with blown in insulation, but without the rigid foam insulation on the exterior.
Both construction designs are trying to prevent thermal bridgeing. If you know of any other resources who may be able to provide help with this I would appreciate it.
ANSWER FROM THE INSULATION DOCTOR:
My recommendation would be to use your second method consisting of the staggered wall system. I have personal experience with this type of system and have found it to be very efficient. You mentioned you are going to forego the outside foam sheeting, but I assume that you are still going to use a tyvek type wrap on the exterior?
I have some reservations in your use of a blown-in insulation due to the fact that over time vibration is liable to cause a slight settlement approximately 1/2" from the top. I would strongly recommend the use of a blanket or rolled type insulation with the outer layer being unfaced material. This unfaced insulation can be secured with insulation supports which are attached to the outer wall with a protruding inward point that you can hang the insulation on. The inside layer (next to the drywall) would then be a kraft-backed insulation with the paper facing the drywall.
Hope this helps.
The Insulation Doctor