floor insulation

In colder climates, there are millions of homes with inadequate under-floor insulation, with the consequent heat loss and drafts.

The gains provided by floor insulation aren’t as large as those related with attic insulation or wall insulation, but they still may deserve the investment.

When not to apply floor insulation

If the floor is over a heated basement or other conditioned space, then floor insulation is useless. Also insulating a floor when the crawl space below isn’t well-vented can be a mistake …

Pay also attention to problems with moisture and water that may affect the floor and the insulation layer. You should provide adequate floor drainage before insulating the floor.

Insulation Floor Goals

Insulation is usually used on the underside of concrete and suspended timber floors, and on the underside and edge of concrete floor slabs.

Reflective foil

Reflective foil was, some years ago, a common floor insulation material. If well installed and stapled along the floor joists, it reflects the heat back into the house, reduces moisture associated with the floor and traps the air between the floor and the foil. In other words: it works as a good insulator though it isn’t exactly an insulator (its R-Value is 0).

Nowadays, reflective foil is little used in floor insulation. It demands a careful and precise installation to be truly effective, and whenever there is electric cabling under the floor it poses safety risks (foil involves metal, which may cause electrical conduction and the possibility of electrocution).

Materials

Rigid insulation (Extruded polystyrene foam, Polyurethane foam…) is the most common floor insulation material today. Blankets (rock wool, fibreglass…) are also used. These materials have the advantages of being much more easy to install correctly than foil reflective products…

See Insulation Materials

A do-it-yourself job

Floor insulation is a do-it-yourself job, but whenever there is a risk associated with the existence of electrical cables and pipes, it’s better to hire a professional installer.

The installation

When using rigid insulation, you have to cut carefully the pieces of insulation and fit them in the under-floor, more exactly in the bays between the floor joists. The pieces should fit tightly, and the job usually involves two layers of material: the first insulation pieces layer is usually covered with a second layer of insulation (also caulk the seam where the floor joists and the insulation meets).

When using insulation blankets, the materials should also be fitted between the floor joists. They can be installed hard against the underside of the floor, but some installers also let a small gap between the top of the insulation and the bottom of the floor. In many cases the installers use fixings (clips…) but in some cases they simply slightly squash the product between the joists.

Be careful and avoid electric shock hazards. Staples should be kept well clear of any power cables when stapling. Safe work practices are crucial.

Water pipes and electrical wiring and boxes should also be carefully insulated.

R-Value

The floor insulation requirements (in other words, its R-Value) depends on climate. See Insulation R-values.

Under-floor Dampness and insulation

Floor insulation can help reduce dampness (and moisture), but if the area underneath your floor is damp, that should be previously checked and fixed.