Chris writes from Spokane, Washington: "Is there any benefit in insulating under a basement slab and if so, how much?" Answer: Good question. I had to have my technical friends at Owens Corning help answer this one.

Yes, there is a benefit to insulating under a slab. The best way to illustrate the benefit is to do a comparison between a floor with insulation and one without. If you figure the ground temp at 50 degrees F and the inside temp at 70 degrees F and the R-value of four inches of concrete at R-1, you will have the following BTU loss for a 1000sf slab.

 SF x temp diff / R-value = BTU

1000sf x 20F / R-1 = 20,000 BTU loss. Add just two inches of R-10 PINK FOAMULAR® Insulation and the BTU loss goes to 2,000 BTUs.

Unless you are in the south where the cooling benefits outweigh the heat savings, then you should insulate the slab if you can.