Four days of speaking and answering questions at the National Homebuilding & Renovating Show in Birmingham has only strengthened my concerns about the issues relating to the insulation of walls in old buildings. Twelve months ago the subject was barely on most people’s radar but, this year, the volume of questions relating to the topic was staggering and was only equalled by those about damp. Indeed, many of the questions embraced both topics; a fact that in itself is worrying.
I tried to give a broad overview of the subject in my seminar ‘Solving damp and improving energy efficiency in an old home’. The problem is that there’s no easy, one-fits-all solution and we have to question whether wall insulation is a good idea in any solid walled building.
My last post ‘old walls perform better’ highlighted the recent research by the Society for the Protection of Ancient Buildings (SPAB) into the energy performance of old buildings and I’m sure it’s going to be a subject I’ll be writing a lot about in the future. For now it’s worth reiterating some of the key issues about wall insulation.
Importantly, walls can be prevented from breathing and interstitial condensation may occur, resulting in rotten joist ends and general decay. Internal insulation separates the building’s thermal mass from the interior; takes up valuable living space; means features such as dado rails, cornices and so on are lost; while windows are set back due to the thickness of the insulation. If a dry lining system is used there is the added factor that the walls will appear flat and lifeless and the acoustics of the room may become rather ‘sharp’. Adding external insulation to walls is likely to ruin the aesthetics of an old buildings.
Natural ‘breathable’ options for internal wall insulation may include wood fibre, reed board or hemp fibre overlaid with lime plaster but we are still learning and, whatever method is used, great care needs to be taken to avoid potential problems with thermal bridging. An understanding of the way individual buildings work and the accurate detailing of junctions with other elements of the building is vital.
Quite understandably the well meaning owners of thousands of homes – be they of any period from medieval timber frame to Edwardian terrace – want to insulate their walls. At the moment there is still uncertainty about the best way forward and there needs to be further research so that good advice is offered which makes homes more energy efficient without storing up problems for the future.
Image credit: PRP Architects