I talk a lot about dealing with damp so I’ve been practising what I preach at the 1900 house we’re renovating in America. Virtually everyone with an old house will experience some sort of damp problem. The most important rule is to diagnose the actual cause and tackle the problem at source, rather than simply treat the symptoms.
There are a number of causes of damp but, in the case of our house, it appears to be rising damp caused by excessively wet conditions at the base of the wall resulting from a combination of factors. The key issue seems to have been that a rainwater downpipe was discharging straight onto the ground. Although the soil is not particularly heavy, the discharge was in a corner between two walls with the ground sloping towards the walls. The problem was exacerbated by the fact that very little sun or wind gets to this corner so neither the soil nor the wall had much chance to dry out. An added issue was the impermeability of the surface due to a layer of bitumen which, at some point, had clearly been dumped by a contractor working on the felt roof above.
My first step was to take the ‘shoe’ off the bottom of the downpipe and replace it with a right angle piece that directed the water away from the house. Onto its end I wedged a piece of old soil pipe which I laid with a slight ‘fall’. At the end of this I dug a hole to create a soakaway which I filled with course gravel. I covered this with a permeable membrane and then, on top, leveled the area with soil.
Next I cleared away the bitumen. At the base of the wall I dug a trench. In doing this I discovered a mass of roots from the nearby privet hedge which had clearly grown to this spot seeking out the damp conditions. Once I had cut these away I backfilled the trench with more gravel. A word of caution here, normally I wouldn’t dig right next to an old wall for fear of destabilizing the foundations but, in this case, the stonework is deep because there’s a cellar. Something else working in my favour is the fact that the sub-soil is pure sand so there’s good natural drainage below the surface and neither the hole for the soakaway or the trench had to be particularly deep.
Hopefully the damp problem has now been rectified but I will be monitoring the wall for some time. Especially, as above the stone plinth, it’s the traditional American East Coast style of timber frame, clad with wooden shingles.