Damp in alleyway wall

kev25v6

My neighbours wall on the right is full of damp but we can’t figure out where from. Their house site around 5 feet lower than ours and their dining room wall paint is peeling off. There isn’t much water that runs between the houses and any that does seems to run more towards mine as you can see in the picture where the green algae line is. There is salts coming out of some of his bricks, the house is about 110 years old with no cavity. Could it just be ground water as his house is built so much lower than ours? 

stuart45

If his floor is well below ground level then this could well be the cause of the dampness.

Woolsery

If his house is that deep, nothing other than tanking would be likely to stop water penetration. Ground water will move sideways even if the surface is essentially covered with flags, tarmac, or whatever.

DRP

what is their internal floor level relative to the alley? 

We had similar issues with a house that was only about 30cm lower than the neighbour.

We tanked the wall and put in a concrete floor. THis solved the symptoms at least.

stuart45

That's the problem when the floor is lower than the external ground level, the room becomes a semi basement and the same construction methods need to be applied. It is in effect a swimming pool in reverse.
Doing the methods retro is much more difficult than on a new build, and often fail in time. Normally it's better to do the waterproofing on the positive side, as hydrostatic pressure can force though when done on the inside.
One of the best methods done years ago on basement was to tank the external wall with asphalt and link it to the floor to form a continuous skin.
It depends how much they want to spend on the work. A proper French drain might help if the ground water is quite high. 

kev25v6

There isn’t much water that goes down the alley but he said about a French drain. Would that not just let more water through the concrete and into the soil next to his house? The floor outside is about chest height inside. 

stuart45

A proper French drain takes ground water away from the area, but it needs to go in below floor level, so may not be practical if it's that far below ground level. 

DRP

That was my thought - a french drain won't stop sideways movement of water below it. 

Tanking seems the effective solution