combination of insulations

[Dan Mack]

I was considering using 2"of formular 250 with r-19 fiberglass in my 2 x 8 stud walls. is this ok and what insulation should I put against my outside sheathing? A vapor barrier will be installed just inside my drywall wall.

[Michael Thomas]

Depends on your location the construction of the wall.

Here in Chicago I see many buildings where single wyeth concrete masonry unit + fiberglass + A poly vapor retarder + drywall is a recipe for disaster.

OTOH, the same insulation / vapor retarder behind siding + a membrane such as Tyvek + Plywood or OSB sheathing works acceptably.

For starters, you might want to take a look at Vapor Barriers and Wall Design by Joseph Lstiburek (http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design).

[Dan Mack]

Thanks for your feedback. I appreciate any feedback on this matter. I need good constructive criticism.

[Jim Robinson]

Personally, I would use 2x6 with R-19 and put the two inch foam on the outside of the OSB, followed by the house wrap on the exterior of the foam. You can get a nice tight seal around the house by taking your time with the foam.