As well as being a repository for all things creeping, crawling and slithering, Alicia’s house also has a few problems with water moving through the walls. We got to talking about this a few months ago when I pointed out the ground levels around her house were rather high, how I could tell, and what it meant was happening inside the walls. It all led to a conversation about water movement in old buildings which was either:
a) a riveting discourse in building philosophy, or;
b) a mind-melting boredom festival- depending upon whom you ask. I shall summarise…
Rising damp is a peculiarly English ailment of solid-walled house stock built before cavity walls became a standard and the philosophy of building houses changed from allowing water to move through the walls to keeping it out at all costs. So what is rising damp? That depends upon who you ask?
There is a physical process known as capillary action wherein water moves up a tube a distance proportional to the diameter of the tube. The finer the tube, the higher the water will rise. It’s why lemonade inside a drinking straw is at a higher level than the lemonade in the surrounding glass. Think of a brick as a series of tubes.For one group of people this is rising damp: the process of capillary action in walls made of porous stone or clan. It doesn’t matter what the source of the water is, just that it rises.
For another group of people rising damp is water that has moved up through a by capillary action and that the sole source of the water is the ground itself. This group argues that if a homeowner removes the factors that cause capillary action rising damp is a very rare problem, if it exists at all.
These are subtly different definitions, and it looks initially like these groups are arguing about whether rising damp exists. They aren’t: they are arguing over the definition of what they think rising damp actually is. It is all rather tedious, even for me, but feel free to run it through Google if you have trouble sleeping.
The builders of old solid-walled Victorian houses knew that water would rise through a solid wall and damage a homeowner’s lovely paintwork if given the chance, so they designed the problem out. If the ground level outside your house is lower than the floors inside, any water that gets into the base of the walls will evaporate outside before it gets to the plaster on the inside and make a mess of it by evaporating through that. For this reason you should always step up into a Victorian house. The 150mm (6″ in old money) difference between the outside ground and the inside floor is enough (usually) to ensure that water doesn’t rise up the level of the plaster inside your ground floor rooms, instead it evaporates outside or under the floor.
All of which is a long-winded way of saying that you should always step up into an old house with solid walls in order to avoid long-term bother.