Hi all, I recently had a trench dug around our mid to late Victorian 3-bedroom semi, to address rising damp from high ground levels. The builders cut through the concrete hardstanding and then removed some earth below. I am a bit concerned that they went too deep and it may cause structural movement: they dug to roughly the top of the foundations, (in fact a couple of centimetres below this - see first pic). The trench was then infilled with pebbles, see second pic. The foundations start about 50cm below the top of the plinth/30cm below the old ground level. So will it be a problem structurally that the trench has been dug this deep? The trench width is at max 30cm, possibly a bit less. Thanks in advance
From that one picture it looks like they did it right. The gravel level should be at least 150 mm (ideally more) below the damp proof course or the level of an interior floor. You will find that on a lot of Victorian houses the plinth doesn't relate to the finished floor level and is mainly decorative.
Ok thanks. I take your point about going below the DPC but am worried that displacing that much earth (albeit only down to where the foundation starts) might allow the house walls to bow outwards - that's my real concern, more serious than damp!
You should be fine, if your house depended on a few inches of dirt you would be a precarious position anyway. The biggest danger to properties of this age are trees and bushes growing too close to a house
That's absolutely no problem at all. The house was designed to be built off of the foundation - Not supported by 6" of loose soil.
Hi all Sorry to resurrect this thread - a structural engineer has commented that because the house is built on clay subsoil, and the above trench has no lining or drainage (the shingles sit straight on top of the soil below, with no barrier inbetween), that rain water might ‘pool’ in this trench and soak into the clay subsoil below, thereby causing subsidence over time. Seems a bit much to me: surely when this (Victorian) house was built with much lower ground levels all round, rain would have been falling onto the grass/soil and soaking it anyway? Long before people installed patios around, dug trenches, etc. Thanks in advance!