Insulating thatched roofs

Energy Efficiency and Historic Buildings
Insulating thatched roofs

This guidance note provides advice on improving the energy efficiency of thatched roofs. The guidance stresses that changes to improve the energy performance of thatched roofs should only be attempted where necessary and where the traditional ‘breathable’ performance of the building will not be compromised.

Thatched roofs differ from tiled or slated roofs as they already have good insulating properties.  Only very rarely would it make sense to fix extra insulation to the underneath of a properly maintained thatch roof.

Some thatched roofs are draughty, with lots of air entering through the eaves, junctions with dormers and gables and through poorly maintained sections of thatch.  Basic maintenance and sealing of gaps will help reduce air infiltration to acceptable levels. Some thatched buildings without rooms in the roof space have well ventilated lofts that are almost as cold as the outside.  In such buildings it may be sensible and cost effective to add insulation above the ceiling as for a tiled or slated roof, whilst ensuring the cold roof space is kept well ventilated.  It is particularly important that any materials used to insulate or draught-proof thatched roofs are vapour permeable.  Changing humidity levels can lead to condensation within the thatch which must be able to evaporate easily to prevent decay.