Does Floor Insulation Performance Meet Expectations?
If they are insulated at all, floors over crawlspaces or unconditioned spaces are insulated with fiberglass blankets or batts. The ideal installation includes a uniform, uncompressed layer of insulation in contact with the subfloor and the sides of the floor joists (see Figure 1A). How does reality differ from this ideal? Insulating underneath floors is complicated by the fact that, unlike inside walls and above ceilings, there is no surface below the insulation to hold it in place. Two main methods are used to hold up insulation. In new construction, plastic netting is draped over the floor joists before the subfloor is installed; the netting is typically stapled to the top of every second or third joist. Once the netting is installed, the insulation is placed in the hammock-like support baskets, and then the subfloor is installed (see Figure 1B). In retrofits, springy metal rods placed every couple of feet are typically used to hold the insulation. These rods, sometimes called “tiger
