Bob writes from West Orange, New Jersey: "My friend compressed R19 fiberglass batts intended for a 2x6 wall cavity into a smaller 2x4 wall cavity. The wall is now covered with wall board. What is the effective R value of this improper installation? What problems will this cause? What do you recommend?"

Answer: Stuffing a 2x4 wall with R-19 will decrease the R-Value to about R-13, so your friend will not receive the full benefit of the insulating value he or she purchased. High Density R-15 insulation would have been a better choice. The insulation shouldn’t cause any problems and replacing it will be a hassle since the cavity is already covered. With walls, we typically have only one opportunity to insulate them for maximum energy efficiency.