Single brick garage wall and damp

[markaw]

I've a detached single brick thick garage. 2 sides of it form the boundaries with 2 neighbours.
It has a concrete slab, 2 courses of engineering (I understand to be water proof) bricks a DPC.

Now comes the problem. Both the neighbours gardens are approx 1 to 2 ft above my DPC. I figured out based on the height of the foundations of nearby buildings (the neighbours ' garages) that's how it was built, otherwise there'd be a huge angle to the ground between them.

Long story short can't do anything externally. The house was just inside the NHBC insurance/warranty and they wouldn't do anything because a garage is allowed to be damp. Something about classification.

So I've tanked the inside myself. I applied 2 coats of tanking slurry to the clean bricks within 24 hours of each other for a good bond. Now it's all dried (set) I still get water beading on it. I understand that to be condensation from the temperature difference between the air inside and the ground outside.
So it seems I now need to insulate internally.

How's best to do this? Timber frame and PIR between, ply/osb/plasterboard over the top of that?

I learnt early on that cast iron doesn't like cold garages in winter, so I've plasterboard and insulated the ceiling already (the door also has two sheets of PIR over it)

 

[Cabinetman]

Sounds like a good plan to me – the timber frame and insulation, but I bet an expert will be along in a second.

 

[AJB Temple]

Are you saying that you have 12" to 24" of soil against the walls of your garage on two sides, and that these soil levels go above the dpc. A plan & elevation sketch would help. And an indication of the size of the building.

Your garage, by the sound of it, is effectively acting as a retaining wall, and presumably has a slope upwards away from the wall on those two sides (or otherwise why sink the garage below the ground? Sounds like you are dealing with potentially water run off as well as wet soil.

It wasn't clear either whether you have two courses of engineering bricks and a dpc above them, or just the bricks.

I have somewhat got the T shirt on this as we had a barn once where the developer failed to deal with the elevated ground on one side, that breached the dpc. The work required to deal with this effectively was very extensive and expensive.

I am wondering if it is realistic to consider raising the floor to above ground level everywhere, and raising the roof.

 

[markaw]

Are you saying that you have 12" to 24" of soil against the walls of your garage on two sides, and that these soil levels go above the dpc.

Yes, exactly. I will try to attach a pic of it from my side which doesn't show the full extent of levels on the neighbours side

 

[markaw]

Sorry, that was the wrong picture. That was the inside. Below should be the outside

 

[AJB Temple]

I would, if you have not already, have a word with your neighbours, explaining that your garage is flooding and asking if you can dig a narrow water diversion trench and drain immediately adjacent to your garage walls. Stopping or greatly reducing the water from the outside will certainly assist in dealing with the inside.

 

[Trevanion]

One thing I'd be looking at closer is that gutter downpipe, does it drain into an underground pipe or just run into the ground, if that's the case that's most likely what's causing your excessive damp issues as all the roof rainwater is being diverted into your wall.

What I did with my own shed which is in a very similar situation, about 2ft of elevated ground up against a wall which was causing water ingress on wet days. About 25 years ago when the shed was built a plastic membrane was used against the wall, and a pipe with loads of drainage holes drilled into it put at the bottom to divert water to another pipe underneath the floor of the building and out the other side which runs off into a field, then there was a lot of drainage stone put on top with maybe 4-5" of top soil on top of that. It worked up until the membrane perished and was allowing water by it had gone really bad, you could poke holes in it with your fingers, a consequence of this which I didn't realise could happen was that the concrete blocks were actually rotting away from being constantly damp, some had turned completely to black sludge which you could scoop out with your hands as though it was mud.

The solution was that I dug out all the rotted sections of blockwork, filled it up with concrete, and created a sort of V- channel towards the pipe with the concrete as well so that water was directed towards the pipe rather than the wall, I then used a tanking render on the wall and also on the concrete, put new clean drainage stone in as the old stuff was very dirty and not very efficient and put the soil back in place. It's been a few years now and there have been no issues with damp walls or water in there.

I guess the neighbours won't approve of digging up their garden, but maybe they will so long as you put it back the way it was and don't cause too much of a mess.

 

[markaw]

Hi, yeah I've had a word with the neighbours, that being the "best" solution, to rectify at the source of the problem. Though many conversations, even owners later haven't been able to sort something out. One of the previous neighbours even paved up to the wall.

I've resigned myself to the fate of having to sort from the inside

The first picture I uploaded by mistake was before I cleaned and tanked it, but useful for understanding. It now looks a lot more grey.

So coming back to my original question, how to insulate over the (interior) tanked wall? And whether that will sort the hopefully condensation problem? I do appreciate you asking and challenging to understand the problem

 

[Mike G]

Yes insulate, but you will need airflow between the wall and the insulation......ideally top and bottom. So, if you were to build a 2x2 frame internally, spaced an inch off the wall, with a breather membrane on the outside, and a vapour barrier on the warm side of the insulation (obviously insulation between the studs), you'll give yourself a chance. It really does need a decent amount of airflow, and of course, it should be sitting on a DPC.

However, there really is no replacement for a retaining wall to take the soil back away from the wall on the outside. If that is the source of the moisture ingress, then any internal solution will fail in the end.

 

[toolsntat]

Sorry, that was the wrong picture. That was the inside. Below should be the outside

Am I seeing this wrong or is there not 2 course of engineering red bricks on both buildings?
Cheers, Andy
EDIT just re-read and the extra height may be behind the fence?

 

[Mike G]

That doesn't make much difference Andy if the source of the dampness is A/ from outside, above the top of the engineering bricks, or B/ condensation internally.

 

[toolsntat]

That doesn't make much difference Andy if the source of the dampness is A/ from outside, above the top of the engineering bricks, or B/ condensation internally.

Yes, just realised the shot was a good face Mike

 

[toolsntat]

Extreme action I know, but for a belt and braces answer I'd have looked into taking out the commons and replacing with engineering all the way along both walls.
Cheers, Andy

 

[markaw]

Thanks for the help all.
Seems I'll loose a fair bit of space, but I'll at least have somewhere warm to work in the winter. I'll update with pictures when done (won't be for a while)