Annie writes from Fair Lawn, New Jersey: "What is the highest r-value roll of insulation can I put in a crawl space of an addition? I am NE NJ. I have an addition 15 x 25 (10 ft ceilings) facing north, three outside walls. The foundation of it is cinder block walls about 2.5 ft above grade. The floor of the foundation crawlspace is sealed with concrete so no soil is exposed. It has two vents on each side. Currently there is R-19 in between the 16" on ctr joists. It is hard to keep this room comfortable in the winter. The floor is always freezing. Can I put something like an R-49 in there, or two levels of something else? What about ventilation and vapor issues?"

Answer: Kraft-faced R-25 fiberglass insulation is recommended in your part of the country. However, you may increase the R-value if you have the space. R-49 could be achieved by layering Kraft-faced R-30 with unfaced R-19. The Kraft facing should be installed toward the warm-in-winter side of the framing.

We recommend a minimum of two vents, which will allow for airflow in and out of the crawl space. One square foot of free vent area is recommended for every 1500 sq. ft of floor area. (NOTE: Never cover these vents)