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Up to half of the heat loss from a house occurs through the walls. This can be reduced by two-thirds by insulating the walls.
Most houses built before about 1980 have no wall insulation.
Many (though not all) houses built during the 1980s have some wall insulation. Houses built since the 1991 Building Regulations came into effect are required to have wall insulation.
Insulation may be placed on the outside, in the cavity or on the inside of a wall, without altering the overall insulation properties.
External or cavity insulation allows the internal wall to act as a thermal store, absorbing heat during the day and releasing it at night-time, reducing fluctuations in room temperature throughout the day. Internal insulation isolates the thermal mass from the room. This reduces both the response time of he heating system and the energy required to reach comfort levels in the room. Occupancy patterns, the response time of the central heating and its controls, and the optimal thermal ass of the building will determine the appropriate action.
When considering wall insulation, first you should find out whether your house has cavity walls or solid walls. A building contractor or architect will be able to tell you if you have cavity walls in your new or older house. If you have cavity walls, then cavity insulation is likely to be the most cost- effective insulation method. If cavity insulation is not an option, then the more expensive options of either internal or external insulation may be considered. It is not possible to fill the cavity in a wall constructed simply of 9-inch hollow blocks.
The walls of many houses consist of two `leaves' of brick or concrete block with a cavity or space between them to resist rain penetration. This is called cavity wall construction
In new housing, i t is standard practice when building to insulate this cavity as the wall is being constructed, with either full-fill batts, or partial-fill boards.
For cavity walls a minimum of 78mm rigid insulation board, with a thermal conductivity of 0.25W/mK must be used, unless there is additional insulation outside the cavity.
Initially the architect or installer will carry out an assessment of the walls to check their suitability for cavity insulation, particularly for full-fill insulation. This assessment will determine the degree of exposure of the house to wind- driven rain and the construction details of the walls.
Materials used for cavity insulation include mineral wool (glass or rock), polystyrene beads or granules and cellulose fibre.
The thermal properties of these materials do not differ greatly (in technical terms, their thermal conductivities tend to fall within the range 0.025 to 0.04 W/m K).
Insulating the cavity with such materials will typically reduce heat loss through the wall to one-third of its original value. Such cavity insulation materials are generally water-repellent and rot-proof and some are non-combustible.
It is most important before deciding to insulate existing cavity walls that you check their suitability for cavity insulation. This assessment will take account of the degree of exposure of the house to wind-driven rain and the construction details and condition of the walls. Any ventilation openings in the wall will also be checked to ensure that these will not be blocked by the insulation.
If the walls suffer from rain penetration at times, this problem must be remedied first. In some cases, the walls may be found to be unsuitable for cavity insulation or may require some remedial work beforehand.
The Irish Agrément Board (IAB) provides independent certification of cavity wall insulation systems and maintains a register of approved installers for certified systems. These installers should be able to show you an IAB certificate for the insulation system they propose to use and proof of their reputation as approved installers.
The cost of cavity wall insulation depends on a number of factors, including the width of the cavity, but is typically in the region of m5 to m7 per square metre. For a typical semi-detached house, this gives a total cost of about m550 - €1000.
With annual fuel savings of m100 to m160, the pay-back period will be in the region of 4 to 7 years.
You may be able to negotiate a lower price if you can persuade some of your neighbours to have their walls insulated at the same time.
When full-fill cavity insulation is being used, it is essential that such walls are designed and constructed to incorporate the normal precautions to prevent moisture penetration.
Insulation thickness should remain constant and should any change in vertical thickness occur, a horizontal damp-proof cavity tray should separate each thickness change.
It is important to ensure during installation that wall ties are fitted correctly and cleaned, excess mortar is cleaned from the inside faces of the wall, mortar droppings removed from the cavity and cleaned from the exposed edges of the insulation slabs. All insulating materials should be installed in accordance with manufacturers' instructions and procedures.
In older houses insulation can be injected into this cavity through holes drilled through the outer leaf, by means of a blowing or pumping machine.
Since the work is done from the outside, it causes minimum disturbance inside. The drilled holes, which are typically about 25 mm (1 inch) in diameter and spaced a metre or so apart, are then filled to match the wall appearance as closely as possible. The job typically takes less than a day.
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