Damp in victorian terrace. Piglet John?

[LadyCurd]

We renovated our victorian house top to bottom two years ago. The back wall of the house had problems (half of the wall is joined to the kitchen extension, the other half is outside). The builder stripped back the damp plaster and I thought he did something to the wall before re plastering (not sure though and need to check!) the damp started to creep back but we thought it was a roof or a gutter problem (the neighbours extension guttering was crap so water ran down our wall) which have both been fixed and it's not made it any better. Now we are at the point where there is half a metre or more up the wall all along the back of the house! (Weirdly there are two doors in that wall one into kitchen and one into side and the damp is in the wall between the doors too but not as bad.

I know airflow is a problem as the previous owners partially blocked a air brick to make a step down for the outside door. We need to get at least 1 possibly two more put in. Not sure about the wall going into the extension though.

There is no damp proof course at the back of the house (or in the crappy kitchen extension which also has damp in places there) so pondering about that. The annoying thing is when we thought the roof and guttering had fixed the issues and while it wasn't an obvious problem we also had our garden landscaped and a beautiful sandstone patio laid on top of the crappy concrete that was there before. It has been laid properly so water run off is correct so don't think that is the problem so much.

Any ideas what we can do preferably without digging up the patio although I worry this is only option (if we do it for extension too it means digging up neighbours garden- utter nightmare!)

Also got damp in one of the bedrooms top walls where it meets neightpbours wall, again not fixed by fixing the guttering but is where the neighbours will have a corner chimney breast and that room is there bathroom, the chimney is capped off but does have a small ventilation brick in it, presumably the chimney needs better ventilation or maybe it's the neighbours bathroom causing issues in that wall.

Any ideas or advice gratefully received, unsure about calling "damp specialists" as suspect I may pay loads and not ultimately fix issue! So would like ideas here first!

If it is wet 500mm up the wall, I would suspect gutter or downpipe problem. Is the wet patch flat-topped, or semi-circular, or mountain shaped? draw a pencil line round it so you can see if it gets bigger or smaller, especially if that is related to rainfall. Presumably the wet patch starts at floor level. Is it a wooden or concrete floor? I presume this is a solid, nine-inch thick Victorian brick wall?

How long ago were the roof and gutter fixed? If you go outside on a rainy day, does the outside of the wall have water on it?

Did the person who replastered it tell you what he thought the cause was?

Have you got a water meter?

It is mountain shaped. No down pipe on one side but neighbours down pipe has been checked and is clear.. Gutters all fixed and sorted and have been since last nov- roof fixed in feb. wall dried out outside (was really damp outside but internal wall has got worse.) haven't noticed water on walls but will check- shouldn't be as we have eaves protectors all along into the gutters.
Pencil tip is a good one thanks will do that.

Is a bare wooden floor plenty of gaps and breeze! (concrete in extension where part of damp is). There is a decent subfloor space. A metre or so.

We have a soil pipe running under the floor and outside from a loo we put in upstairs. Plus hot and cold water pipes but obvs unlikely to be a prob as not running along entire wall. Just trying to give you most info I can!

Will check with builder what he did too! Oddly the problem seems to have gotten worse after the gutter prob was sorted! Pretty sure they did a good job though as outside wall dried out.

if it is mountain shaped there may be a problem at the top of the mountain, for example a leaking pipe buried in the wall, or a downpipe outside, or a defect in the brickwork or render outside, or a fastening in the wall.

Thanks for all the feedback piglet John. I really appreciate it. Sorry When I said mountain shaped I actually meant hill shaped! (Rolling hills of damp the entire width of the house- it is the whole back wall! There are definitely no pipes or down pipes causing a downwards spray triangle.
Will draw on with pencil tomorrow and try and take a pic!

if it's all along the wall, have a look under the floor next to the wall. See how wet the bricks are. The might (or not) be a Slate DPC embedded in the mortar joint about two courses above where ground level used to be when the house was built. If so, see if the bricks are wetter or drier above or below. Also, see how high they are compared with the outside paving as it now stands.

The ground under the floor is probably bare earth but might be weak concrete. Is it wet?

Please measure the thickness of the wall and confirm that it is the nine-inch solid brick Victorian wall. If a cavity wall, something quite different has happened.

Have you got a water meter?

Hullo,
Thanks so much for replying on this. Yes to 9inch brickwall, no to a water meter.
Will try me work out how to get floorboards up without knackering the floor to have a look underneath.

Spoke to builder he is fairly sure he will have put a treatment on the brick when he stripped it back and re plastered so odd it is coming through again. Though I'm always a bit doubtful about chemical sealants.
Thanks
LC

there does seem to be a lot of water, so I would suspect either a leaking pipe or drain; or a splashing gutter; or else that rain is running towards the house due to a slope.