Walls adjoining houses – a source of damp

Many homes have garden boundary walls
that butt into the main external wall of the house. The continuity of
the materials can look really attractive, especially where it is an
old stone wall. There can be complications though with the junction
between the two structures.

We look to keep our houses dry and free
from damp, but we do not expect the same from our walls. So we tend
to turn a blind eye to the water that seeps into the garden wall,
whilst desperately trying to keep water from entering the wall.

This has led us to applying waterproof
render to our house walls and nothing on the boundary wall. The
trouble is that if there is no capping on the garden wall, water will
seep into it and this can then be transferred through the junction of
the two walls and thence behind the water proof render.

This is normally ‘cured’ by injecting
silicon vertically into the house wall, but it stands little real
chance, especially in stone. So what to do?

Well, ideally your house walls are
treated with lime render and so can breathe and let the water out,
however this is making the lime do a lot of work. The best two scenarios
is that you either reduce the amount of water entering the garden wall in
the first place, via a simple capping system; or that you create a physical gap between the two walls.

If you choose the latter then be aware
that the house wall would be giving the garden wall some inherent
strength and stability and so this will probably have to be replaced
by the use of a buttress type support in order to stop it all from
falling over!!