Cavity Wall Insulation could be a remedy for the energy poverty undergone by many homes in Ireland. Available statistics show over 60,000 low income and 160,000 other homes suffer from energy poverty. This invariably affects their health, indoor comforts while causing huge wastage of limited earnings. Insulation In general and cavity wall insulation in particular will help you if you are one of the above house holders.

SEAI offers special grants for up to Euro 400 to meet your home improvements by cavity wall insulation. The installations have to be carried out by qualified installers as special tools are required to carry this out. Under no circumstance this is a DIY job even for a person good with their hands.

Cavity walls

A cavity wall can be a construction of two walls with an air gap in between or a wall constructed of hollow blocks .The air gap in this manner should be continuous for any effective cavity wall insulation to be carried out.

How are the Cavity walls insulated?

The cavity wall insulation is applied in several ways depending on the type and construction of wall, type of insulation selected etc. What ever the material selected the idea is to cut off heat transfer by cutting off the heat transfer primarily, by conduction ( ie. by physical contact) and convection (ie. by the movement of hot air (molecules) due to air currents) . Naturally unless there is a continuous cavity this process has limited detrimental affect as the heat by air movement is limited to a small wall cavity portion. (The conduction though not hindered in this scenario but is a slow process).

Thus the filling of the wall cavity by an insulation material addresses both these heat loss processes conveniently.

What material can be used to insulate cavity walls?

There are several insulation products which can be used for cavity wall insulation. Popular materials include Glass fibres, rock wool, expanded and extruded polystyrene (EPS and XPS) panels and beads and cellulose material. Though cellulose material is not very popular here in Ireland, in some countries such as USA it is widely used as it has a high R factor (at least initially), low price and made using recycled material and is therefore environmentally friendly). Each type has good as well as bad qualities, some having more of each than the others.

While during construction it is possible to insulate cavity walls with almost all the above material (though not done generally) after construction or in old buildings only polystyrene beads or glass fibres can be installed only by the special process of "bowing in". The polystyrene bead insulation is done if during construction through the inside walls while it is done from out side walls in existing homes. Holes are drilled on the walls right through and checked whether existing insulation is present and if so in what condition. If the cavity is not filled, insulation beads or fibres are blown in through a hose inserted in through the drilled holes. A special adhesive is blown through along with polystyrene beads which keep the beads bonded after curing.

Moisture, air leaks and insulation

Moisture and, air leaks, though not the main cause has a role in the loss of home heat energy in addition to damaging the insulation, lowering insulation properties of the core fill, damaging the wall material and promoting mould growth. A good vapour barrier therefore should be applied even with cavity wall insulation. An aluminium foil vapour barrier applied with a water resistant adhesive or a liquid type vapor barrier are good solutions (regional fire codes permitting). In addition, an aluminium vapor barrier will act as a radiant heat barrier too improving the energy conservation further.

On the other hand the air leakage is not advisable because with the leaked cold out door air warm indoor air leaks out to neutralize the pressure built up in the indoors. Also t moisture too gets in along with the chilled air to condense on inner walls causing damages. (How ever it is difficult to totally eliminate these as some openings to outside as weep holes to drain out any leaked in water should be kept).