cavity walls and insulation

Millions of homes have external walls made with two layers and a small gap (cavity) between them, that is, they have ‘cavity walls’... Filling these cavities with insulation (or in some cases adding insulation to the existing) is an excellent way to get a more comfortable home and to reduce heating and cooling bills.

Cavity wall insulation vs. sheathing

Cavity wall insulation is very important, but it doesn't prevent heat and cold to pass through studs and other non-insulated wall components.

That makes insulated sheathing - applied to the exterior walls - also important. That is, outer walls will benefit hugely from a continuous layer of insulation over their surface, behind the siding.

See: Insulated Sheathing Basics.

Look into your walls

Cavity Walls Without Insulation If you are planning to paint your walls or to replace their siding, consider also cavity wall insulation and insulated sheathing. In case you don't know the situation of your walls in terms of insulation, you may demand a professional audit to them (see: Home Insulation Audit Basics), or make a quick assessment yourself.

Checking the wall insulation

To inspect the wall insulation you may remove one (or a few) small sections of the exterior siding, or you may drill a hole in a hidden and convenient location - away from electrical wiring - and use a plastic crochet hook or something equivalent to check for the wall insulation. Insulated Cavity Wall

Another technique involves the electrical outlets on the wall (be sure to turn off the power, first of all). Just remove the cover plate of an outlet and inspect the crack around it: shine a flashlight into the crack; repeat the same inspection in other separate outlets, to assess the situation in other parts of the house.

Obviously, these simple methods do not replace a professional audit in more demanding cases, involving different degrees of insulation in the walls…

Holes and installation

To insulate the cavity walls, the contractor will drill small holes (around 1 inch; 2-3 cm in size) at regular intervals (of around 3-5 feet; 1 m - 1.5 m) and blow insulation into the cavity, using proper equipment.

The contractor will then fill the holes in the walls and apply sheathing and/or a matching finish.

Costs

Cavity wall insulation prices vary a lot. They depend on the type of walls, access to them, parallel remodeling works, etc. But prices around $1,50 per square foot ($0,75 for ceiling and attics) are common.