Loft conversion options

Some conversions are inherently easier to make energy efficient than others.The most efficient forms minimise heat losses by reducing the ratio of heat loss area (i.e. exposed walls and roofs) to floor area. They also allow easy installation of insulation.The main choices are as follows.

• Use of dormer windows. This provides good headroom over more of the floorspace than other options, and allows conventional windows to be used. However, the roof form is complex, with more complicated construction and greater heat loss area.

• Incorporation of roof windows, within the pitch of the existing roof. This produces a 'cathedral' type conversion, with relatively simple form and construction. Figures 3 and 4 illustrate ways in which this type of conversion may be insulated.

• Conversion of a loft that already has vertical walls (usually between 0.6 m and 1.8 m high) beneath the roof itself.This option is rare today, as most such lofts have already been converted. Figure 5 illustrates a typical 'half-wall' conversion.

Many roofs constructed during the last 30 years are supported by 'trussed rafters'. Here the lofts are criss-crossed by timber ties that brace the thin timber rafters.These ties cannot easily be removed, which makes conversion of the roofspace more difficult and expensive, usually involving either very limited additional accommodation or re-building the roof. A garage conversion or an extension is likely to be a more cost-effective option.