Foamed glass aggregate has been compacted here to form an insulated, breathable subfloor. Above right: The stonework on this old property has been repointed using an earth/ lime mortar
Traditionally constructed houses (ie those built before 1919) were created from soft, permeable and flexible materials - typically earth, lime or clay mortars and plasters binding soft bricks, stone or timber. These buildings don’t have vapour barriers or damp proof membranes like modern structures do, but manage damp and moisture in a different way, through absorption and evaporation. This is known as breathability and before you undertake any renovation work on a heritage property, it’s vitally important that you understand this concept.
You must make sure that the materials you use maintain the breathable performance of the building fabric. Most modern products don’t do this because they are designed to restrict moisture movement. As a result, incorporating materials such as cement, gypsum plaster, vinyl paints, impermeable membranes or vapour closed insulation could result in very serious long-term damp problems in old buildings, leading to decay and mould growth.