Old houses need to be treated differently from modern ones. Keeping this in mind is important when you’re planning to repair, redecorate or alter one.
The main distinction is between solid wall and cavity wall construction. If your house was built before the early 20th century then it is almost certainly an example of solid wall construction. Legislation introduced in 1919 brought about a steep decline in this building method.
The most important characteristic of solid wall buildings is that they were not designed to present an impermeable face to the elements. In London, of course, the majority of domestic buildings are constructed with brick rather than stone. Rain can be absorbed into the masonry then naturally evaporate during the dry periods which follow. This is an oversimplification of a complicated process, but the principle is important. I remember grasping the counterintuitive reality – of old buildings not in any meaningful sense being waterproof – when I spoke to family friends living in a late 18th century farmhouse in Ayrshire, an area with more than twice the annual rainfall of London. Their home, with its two-foot-thick stone walls, coped perfectly well with this challenging climate despite the lack of waterproof membranes or barriers of any kind.
In contrast, a modern wall separates the inner and outer leaves with a cavity. The outer leaf is designed to act as a rain screen, with the cavity helping to prevent moisture reaching the interior. The materials used to repair these two types of construction are therefore not interchangeable. Problems in traditional buildings can arise when relatively impermeable modern materials are introduced where they aren’t appropriate, including cement-based mortar, acrylic paints, rigid PVC moisture barriers and silicone-based sealants.
A good way to think about a house that has reached 100 years old is that, like a good doctor, you should “do no harm”. Your building has almost certainly been repaired at some point in the past with inappropriate materials – ideally, you would remove them all, but this isn’t always feasible or affordable. It’s far easier, however, to make the commitment that you won’t add any more damaging materials to your house.
The widespread use of damaging materials in the repair of old buildings didn’t happen overnight. It’s always something I keep in mind, and I enjoy taking care over seemingly simple jobs, such as painting, and plaster and timber repairs on old houses. The right approach is rarely the newest material, or simply the one that happens to be suitable for a modern building.
Contact me at any time if you would like advice or a quote for a job: hello@siskinprojects.co.uk
Graeme