Problems with Cavity wall Insulation

Pay attention to cavity wall insulation problems. Unprofessional installation or wrong choices involving the insulation materials, will diminish the energy-efficiency of the walls and can be a source of problems.

Problems with cavity wall Insulation

Cavity wall insulation demands proper installation and suitable materials to avoid typical problems like 1) voids and compression, 2) fluffing and settling, 3) moisture and 4) insects.

Cavity Wall insulation voids

A common problem with cavity insulation is voids and gaps A major problem with cavity insulation is voids, that may result from fluffing and settling problems (in the case of loose-fill and sprayed insulation materials) or from an unproperly installation (when using other insulation materials).

In the case of batt and blanke insulation (fiberglass, rockwool, cellulose), gaps are very common. The insulation batts should fill the cavity completely, from top to bottom, without gaps or splits for a full insulation value. With gaps the insulation performance will be reduced.

Compressed and split insulation batts

Also do not compress the batts, or split them - to accommodate electrical, ducts, etc. As stressed above, the batts should fill the cavity completely, from top to bottom, without leaving gaps, but also without being compressed or split... Otherwise, batts will perform poorly. Cavity walls without insulation are

Settling and fluffing

Settling is also common in cavity wall insulation retrofits using blown in insulation materials (loose fill fiberglass and mineral wool, and most of all, cellulose).

All these materials are subject to settling after installation, but while fiberglass and mineral wall settling is usually less than 5%, cellulose settling may amount to 15 to 20%, which can be a significant problem in wall cavities (and not a so big one in attics, where we always can easily add more insulation material, or adding it in advance).

The easiest way to solve the settling problem is to take it into account in advance, adding more insulation (in the case of attics) or using specific machinery and expertise in order to get fully filled cavities.

Another way to solve these cavity wall problems is to use insulation materials resistant to settling and fluffing, like sprayed foam.

Moisture

Moisture is another common problem in walls cavities. Leaky pipes, and problems with roofs, painting or siding can be causes of moisture in the cavities

But a bad choice of the insulation material (cellulose is too prone to water damages, and should not be used whenever the risk of dampness is high) and its wrong installation can also cause unwanted moisture in the wall cavities.

Choosing water-resistant or waterproofing insulation materials can avoid many problems: vapor barriers, polythene sheets, reflective foils, high-efficient foams with water-resistant membranes...

See: Moisture and Insulation

Insects

Insects can also cause problems in wall cavities insulated with some materials (cellulose...). Insecticide-treated materials can avoid them.

Professional Contractors

Retrofit cavity wall insulation demands well tested techniques, special equipment for blowing the insulation into cavities (for loose-fill and sprayed-on insulation materials) and professional knowledge of the problems posed by cavity insulation. That's the best way to avoid problems when insulating cavities.

To look for qualified installers, consider…

USA and Canada:
Home Energy Rater (to find contractors in your area), or a member of the Insulation Contractors Association of America

UK:
The National Insulation Association (NIA), The Cavity Insulation Guarantee Agency (CIGA), The British Board of Agreement (BBA)

Australia:
The Thermal Insulation Contractors Association

Image above:Dow Chemical