Mike writes from Bonham, Texas: "I am remodeling a house for my daughter and her family. The house was built around the early 60's and has very thin cedar or cypress siding. Before the siding was installed, the house was wrapped in 30# black felt paper, there is no insulation in the outside walls. To rewire the house, I have removed all the sheetrock on the exterior walls. I was thinking of putting in 1/2" foam board between the studs and then putting in the 3 1/2" fiberglass insulation over that. Would that compact the fiberglass insulation too much? Would it help?"

I assume you are trying to achieve a higher R-Value by adding FOAMULAR insulation with the fiberglass insulation. If you have 2 x 4 studs, you would normally use an R-13 (3 1/2") insulation. If you looking to achieve a higher R-Value, keep in mind that Owens Corning also manufactures a high density R-15 (3 1/2") insulation which would fit into a 2 x 4 cavity.

If you still want to use the 1/2" FOAMULAR product, I do NOT suggest cutting it into every stud cavity behind the fiberglass. This would be very labor intensive and would compress the fiberglass. I suggest installing the fiberglass insulation first and then attaching the 1/2" FOAMULAR directly to the studs. Keep in mind the drywall must be attached directly to the studs also. Make sure you have a fastener long enough to penetrate both the drywall and FOAMULAR.

The 1/2" FOAMULAR will give you an added R-Value of 3.