Insulating timber framed walls
Energy Efficiency and Historic Buildings
Insulating timber-framed walls
This guidance note provides advice on the methods, materials and risks involved with insulating the walls of timber framed buildings. The benefits of making improvements will include improved comfort for occupants as well as lower fuel bills and carbon emissions. However, such improvements can have conservation and planning implications.
It can be difficult and relatively expensive to insulate the timber framed walls of traditional buildings reliably and to achieve worthwhile gains in thermal efficiency without compromising their appearance, character and performance and possibly creating additional problems in the longer term.
Great care is needed to ensure that highly sensitive and very rare fabric and finishes are not damaged or lost. The historic fabric can include wattle and daub infill panels, historic render finishes, brick infill panels and finishes such as traditional lath and plaster. Care also needs to be taken to use materials and methods that are compatible with the performance of the building. There are increasingly a greater number of materials available that have similar performance characteristics to traditional materials and these can, with care, be used to improve the thermal performance of these buildings. Such materials include wood fibreboard, sheep’s wool, hemp insulation and vapour permeable felts.
The following areas could be considered for thermal upgrading depending on the nature of the building:
Gap filling
One of the characteristics of timber framed buildings is that there can be a high number of cracks and gaps in the fabric between the timber frame and infill panels. Filling these with a compatible material, such as a lime putty mortar, can eradicate draughts.
Removed infill panels
Where infill panels have been removed possibly to facilitate structural repair this often provides the opportunity to replace them with insulated panels.
Insulating within the thickness of the timber frame
Where a building is clad externally, and there are no historic infill panels, this can provide the opportunity to insulate within the thickness of the timber frame.
If the building is rendered and the render is to be removed, for example where it has failed or is an inappropriate later cement render, there is an opportunity to insert insulation between the elements of the timber frame before the render is reinstated.
Similarly if cladding, tile hanging or weatherboarding is to be removed for repair this can also provide the opportunity to install insulation within the thickness of the timber frame.
Insulating outside the timber frame
Insulation on the outside of the timber frame may be the only alternative if there are historic infill panels present. The disadvantage of this approach is that it will make the wall thicker with consequential changes in window reveals, eaves projections which could create an unacceptable impact on the appearance of the building.
Internal lining
Internal insulation is a possibility for most timber framed walls but it can have major implications on the internal appearance of the walls and will reduce the floor area of the internal rooms/spaces.
Inserting some form of insulation into a timber framed building should only occur after a thoroughly detailed assessment has been made of the particular building taking into account the often complex performance characteristics. Any solutions may need to be adapted to take account of the location, orientation, exposure and condition of an individual wall.