Retaining Wall/Damp Issues

[JustAnotherDave]

Hoping someone might offer some help with damp issues, some of which I think might be related to a retaining wall (might also be other things in play).

 

The house is a terraced 3-bed built around 1904. Uncovered damp in the dining room about 6 months ago: ends of floor joists damp and rotting along rear wall (wall with French doors in 2nd picture), damp in pantry (room with small window on left of 2nd picture) and a damp spot in the corner of the room (1st picture and outside view with red arrow).

 

The previous owners had covered the air brick, laid laminate flooring, and the ground level was above the slate damp course.

 

Side note: along the entire wall in left of 2nd picture, I can't find any evidence of damp course (I've investigated either side of the brickwork). Is this common? I can see damp course everywhere else except this wall.

 

Anyway, I've lowered the ground level, taken up laminate, freed air brick, removed some of the black paint from the lower parts of the walls etc. and joists have dried out. However, I'm starting to think the spot in the corner, which rotted out a half joist completely, might be related to the earth that's against the wall of my neighbour's property (4th pic is the same corner pointed to by red arrow in 2nd pic). I live on a hill and their ground level is a couple of feet higher, and the earth is being retained by a failing flagstone 'wall'. The earth all around the house, including what I think are the pile? foundations, seems to be clay - did down and it gets prgressively stickier and more orange - if that's relevant.

 

I'm wondering if anyone has any other ideas? I only uncovered the retaining wall over the weekend as it was completely covered by a fence; I know some work will be needed to repair or replace this in future. My main priority at the moment is fixing the damp so I can make the dining room habitable again...I've had various people tell me that the damp is due to condensation, failed damp course, beetle infestation etc. Some have tried to sell me DPC injections, tanking and the like, which I've resisted as none of these seem to address the cause(s).

 

Happy to give more info/posts more pics if it will help. This is slowly driving me insane!

[Redbeard]

I think your theory that the damp in the corner is being 'transmitted' via the neighbour's masonry is a good one. All of the 'solutions' which come to mind immediately are compromises rather than true solutions. I shall ponder a bit more.

[MikeGrahamT21]

Are your neighbours against removal of the flagstones and the soil? could help to solve the issue, and the placement is bang on

[ProDave]

It's a tricky one.

 

It has taken probably over 100 years for that end joist to rot out.  A quick solution would just be replace that end joist having given the new joust lots of coats of wood preservative.  you have solved all the easy problems on your own land.

 

To do anything with that retaining wall is going to need cooperation with your neighbour and work on their land.

[Redbeard]

 

10 minutes ago, MikeGrahamT21 said:

Are your neighbours against removal of the flagstones and the soil? could help to solve the issue, and the placement is bang on

 

I'm not sure what the permanent solution would be. Permanent removal of the soil on the neighbour's land would require construction of another retaining wall at right-angles (and it'd need to be a hell of a lot more chunky than those slabs to meet Regs) and it would have exposed their footing wall. Subject to a structural assessment of that exposure, back-filling with pea-gravel might help the 'moisture management' but, like any French drain it becomes a maintenance liability in terms of potential 'silting'. This can be mitigated by layers of horticultural membrane, though. 

 

To get a really good idea of what is going on you really need to see in your neighbour's sub-floor void. If their 'arrangement' (solum - 'soil' under the suspended floor - about 300mm below joists, AFAICS) is the same as yours then their solum is against your back-room wall because of the height of the 'step' (the flagstone 'retainers'), so your chances of that bit of wall being, and staying, dry are poor.

 

Interim solution for the rotten joist is simply not to 'pocket' it in the wall. Build a 'footing' out of your solum and sit the joist (protected by a DPC) on that.

[saveasteading]

Well done. The airbrick and ground level will sort all that and perhaps even dry the other area up , if you have airflow.

How many airbricks have you found?

 

I would plan on a spliced joist resting in the wall. Tanalised timber and an extra coat of rot preventer on nes and old timbers. and maybe bitumen on it too.

 

Where you can't see a dpc there may be a slate layer just behind the pointing.

[JustAnotherDave]

On 13/08/2024 at 09:15, MikeGrahamT21 said:

Are your neighbours against removal of the flagstones and the soil? could help to solve the issue, and the placement is bang on

No, thankfully. The neighbour's house is rented and the landlord leaves all maintenance to a builder he employs. The builder has been and had a look, and suggested more or less the same. He's going to price up the cost of a new wall, in which case the soil would be removed up to the flagstones on the ground, proper drainage installed etc. To help drainage, He said he could cut a channel and install an 'eco drain' (whatever that is) against the wall of the neighbour's house - perpendicular to the retaining wall.

[JustAnotherDave]

On 13/08/2024 at 09:40, Redbeard said:

 

 

I'm not sure what the permanent solution would be. Permanent removal of the soil on the neighbour's land would require construction of another retaining wall at right-angles (and it'd need to be a hell of a lot more chunky than those slabs to meet Regs) and it would have exposed their footing wall. Subject to a structural assessment of that exposure, back-filling with pea-gravel might help the 'moisture management' but, like any French drain it becomes a maintenance liability in terms of potential 'silting'. This can be mitigated by layers of horticultural membrane, though. 

 

To get a really good idea of what is going on you really need to see in your neighbour's sub-floor void. If their 'arrangement' (solum - 'soil' under the suspended floor - about 300mm below joists, AFAICS) is the same as yours then their solum is against your back-room wall because of the height of the 'step' (the flagstone 'retainers'), so your chances of that bit of wall being, and staying, dry are poor.

 

Interim solution for the rotten joist is simply not to 'pocket' it in the wall. Build a 'footing' out of your solum and sit the joist (protected by a DPC) on that.

Thanks for the insight. I like the idea about not pocketing the joist, I think I'll do that.

 

I see little chance of building a retaining wall at right angles. Unless the owner of the house next door is willing to stump up a contribution to what would, presumably, be a hefty sum for all involved with that, it'll likely be too costly for me. I've replied to someone else above about what a builder has suggested - any thoughts on whether that would help?

[JustAnotherDave]

On 13/08/2024 at 10:38, saveasteading said:

Well done. The airbrick and ground level will sort all that and perhaps even dry the other area up , if you have airflow.

How many airbricks have you found?

 

I would plan on a spliced joist resting in the wall. Tanalised timber and an extra coat of rot preventer on nes and old timbers. and maybe bitumen on it too.

 

Where you can't see a dpc there may be a slate layer just behind the pointing.

That's the only airbrick on the whole of the back face of the house 🤯. I've just installed another in the wall under the little window in the 2nd pic of my original post, and I've bought 2 more (one is double sized). I'm thinking about putting another one in on left-hand wall and the double brick in the corner where the joist rotted out. I'm a little concerned about removing too many bricks though. Obviously, a large part of the wall was removed for the French doors so removing another 4 bricks close might not be the wisest. What do you think?

 

Many thanks for the advice. I've looked at repair kits for joists - there's some here that look promising: cut the rotten ends of, bolt steel repair plates to the ends of the joists, and the trailing parts of the metal sit in the wall pockets. No need to add additional wood even.

 

Re. the dpc: you might be right. I haven't seen any sight of dpc along that wall but doesn't mean it's not there. The bricks up to about 2 courses above the foundations (or whatever they are) are soaking wet though, and some previous owner has tanked the wall the other side so damp along that wall has definitely been a problem in the past.

[saveasteading]

You are on the right lines. 2 front and 2 back will cause plenty of airflow. If a pair of them is within say 1.5m of the side wall I'd think that will cause enough that you don't need a side one.

If these are perforated  bricks, made of clay, then there is no concern about strength. 

[saveasteading]

He means  or meant to mean, an Aco drain. It is a trade name for a channel drain...a grating at ground level. Overused where the underlying problem should be sorted.