Insulation - the best route for an energy efficienct home extension

The building regulations in the UK impose ‘minimum’ insulation standards for domestic extensions. However, the recommended Best Practice insulation standards (maximum U-values) set out in Table 1 provide for a better overall standard of insulation, thus reducing fuel use, fuel costs and carbon dioxide emissions.

What are U-values?

A U-value is a measure of the overall rate of heat transfer under standard conditions, through a particular section of construction (units = W/m2K). Lower U-values indicate better thermal insulation. For example, a wall with a U-value of 0.4W/m2K loses heat at half the rate of a wall with a U-value of 0.8W/m2K.

The cost of additional insulation may be offset against the savings from needing a smaller heating system (e.g. a smaller boiler and fewer, smaller radiators) resulting from the reduced heat loss.

Three types of insulation are commonly used in domestic extensions:

• rigid insulation;

• flexible insulation;

• thermal lining boards.

Rigid insulation is usually a form of plastic foam board, e.g. polyisocyanurate board. Examples of the flexible type are glass fibre and mineral fibre quilts. Thermal lining board usually consists of mineral wool or plastic foam insulation bonded to plasterboard, and containing an integral vapour check.

For a given thickness the rigid insulants usually have better insulating properties (i.e. lower thermal conductivity) than flexible types.