In traditionally built properties with solid walls, water vapour can usually move quite freely through the building. This is partly because of the high levels of ventilation and draughts, but also because water vapour can travel through the bricks and stones that the walls are made of. When you insulate an older building, you will change the way that water vapour behaves in several ways:
- adding wall insulation will usually cut down on draughts through the walls and round the windows
- the insulation may create a barrier to vapour movement, depending on what materials are used
- adding insulation to the inside of a wall will make the wall colder. This means that any water vapour entering the wall from inside will get a lot colder, and may condense inside the wall
Whenever you fit solid wall insulation to a building you need to take account of water vapour to make sure that you don’t create new damp problems in the future. This may involve using “breathable” insulation materials that will allow the vapour to carry on permeating the walls, or it could involve creating a continuous vapour barrier to make sure no vapour can get into the walls from the inside. You will need an experienced specialist installer to develop a moisture control strategy that is specific to your building.
You should check with your installer that the installation is covered by an appropriate 25 year guarantee. They may be members of the SWIGA guarantee scheme, or they may offer an independent insurance-backed guarantee. You can find a list of Ofgem approved guarantee schemes.