Under floor insulation (over crawl spaces)

Inadequate under floor insulation is a common problem, expressed in heat losses and drafts. Millions of homes - in colder climates - lack adequate under floor insulation...

The thermal gains provided by under floor insulation aren’t as large as those granted by attic or wall insulation, but it can be important to block air infiltration, and to avoid drafts and to get a more comfortable home with less energy consumption (at least in colder climates).

When not to apply Under floor insulation

Floor Insulation for Soundproofing
Floor insulation can be great to block air infiltration and to avoid drafts and heat loss. But it can also be a soundproofing strategy in intermediate floors, in two-story homes. In this case you can use blanket of batt fiberglass or rock wool and proceed the same way as for insulating for thermal reasons (see Installing Floor Insulation).

Not all under floors require insulation. If the floor is over a heated basement or other conditioned space, then floor insulation is useless (unless for some specific reasons or for soundproofing). Floor insulation only makes really sense for floors over vented crawl spaces.

But be also careful when insulating a floor over a poor vented crawl space. That can pose problems, since water and moisture can easily damage the floor and the insulation layer. Adequate ground-floor drainage is crucially important.

Insulating under sill and sole plates

Under sill and sole plates insulation can stop air infiltration and is advantageous for energy savings and efficiency. But that's mainly a job for the during-construction-period.

Under Floor Insulation Materials

Rigid insulation (Extruded polystyrene foam, Polyurethane foam…) is excellent for under floor insulation material. Blankets (rock wool, fiberglass…) are also largely used. In some cases you may also use fiberglass, cellulose or rock-wool fibers (loose-fill insulation).

Reflective foil was, some years ago, a common under floor insulation material. But, today it is little used. It demands a careful and precise installation to be truly effective, and poses some safety risks, namely whenever there is electric cabling under the floor (foil can be a cause of electrical conduction and possible electrocution hazards).

See: Insulation Materials

A do-it-yourself job

Under floor insulation over crawl spaces can be a Do-It-Yourself job, but unless electrical cables and pipes advise otherwise. In such cases, it’s better to hire a professional installer.

See: Installing Underfloor Insulation

Under-floor Dampness and insulation

Undrfloor insulation can help reduce dampness and moisture, but if the area underneath your floor is damp, the problem should be previously checked and fixed.