Insulation for a loft conversion
Loft insulation is the most cost effective energy efficiency measure and the easiest to
install. Standards of loft insulation have increased in recent times. Some previously insulated lofts should be
‘topped-up’ as building regulations now specify a minimum of 250mm thick insulation.
UK Building regulations impose minimum insulation standards for loft conversions, which are considered to be
'material alterations'. The thermal transmittances (U-values) of exposed walls, roofs and openings must not exceed
set maximum values.
Best Practice insulation standards set out in Table 1 provide for a better overall standard of insulation, thus
reducing fuel use, fuel costs and carbon emissions.These cost savings (and the chance to buy smaller heating
systems because of reduced heat losses) will offset higher expenditure on insulation.
Three types of insulation are commonly used in roofspace conversions:
• rigid insulation;
• flexible insulation;
• thermal lining boards.
Rigid insulation is usually a form of plastic foam board, e.g. polyisocyanurate board. Glass fibre and mineral
fibre quilts are examples of flexible insulation.Thermal lining board usually consists of mineral wool or plastic
foam insulation bonded to plasterboard and contains an integral vapour check.
Insulation materials are readily available and can be installed by DIYers.
Installing loft insulation can save (on average) £80 to £100 on annual heating bills.
For a given thickness, rigid insulants usually have better insulating properties (i.e. lower thermal
conductivity) than flexible types.
The U-value of a construction is its thermal transmittance, in W/m2K.The more insulation a construction
contains, the lower the U-value.Thus thermal insulation standards for building elements are usually expressed as
maximum permissible U-values.