High Damp Meter Readings & Failing Render on External Garage Wall

[HelloDave]

Hi all. We recently bought a house and had a structural survey. The Chartered Survey came back with

1) Damp extracts pdf (with pictures).

I then sought advice from several damp specialists, but perhaps made the mistake of telling them what the surveyor thought was the cause. You can see the vendor has tried to re dash the failing render (badly!).

2) Damp Specialist Findings pdf with pics and drawings

Basically damp is apparently caused by rain run off from neighbours roof, and their drive.

3) It was settled pre exchange that, with the neighbours permission they would put in a aco drain and to stop the water running up against the wall, and put in some lead flashing where the neighbours garage met our wall.... (see 2 pictures)

4) Since moving in there was a day of torrential rain. In this video you can see that it's pretty obvious that the initial diagnosis of the cause of the damp is wrong.... the water doesn't run off anywhere near that wall.

https://drive.google.com/file/d/12zR1Mz9O3i8BQWQetWbSFdcx5xMV6O-K/view?usp=sharing

I don't really want to pay the damp people to tank the internal wall, when the cause of the damp is totally uncertain. Has anyone seen this before? Can anyone give any thoughts on possibilities of the cause for us to explore? Could it just be driving rain hitting that side of the house and over time the render has cracked and given up? (see image 4). Just the way it has spread out from that low part up is interesting to me.

Happy to supply more pics / info if it helps. I'm just stuck with where to go next with this issue.

 

[RandomGrinch]

I'm just a DIY'er, so feel free to ignore

How I read the reports, is that a lot of the problem is caused by the higher ground level of the neighbouring property.
If there was a DPC on the garage wall it is most probably bridged.
This will cause a load of damp issues, even if a lot of the surface run-off has now been taken away by drains; the ground below will still be damp!
The report also states why dampness from here could lead to the cracked render.
The suggested solution only involves tanking up to a new DPC, so that shouldn't be a huge expense.

Personally, I would install a new DPC and the tanking.

The render should also be removed between the ground and (slightly above) the level of the new DPC (to avoid bridging).
The tanking should also be bonded into your existing DPM.

...and fix the cracks in the render.

Also consider, that after years of dampness, the wall may take a considerable amount of time to dry out (many months!).

I hope that makes sense

 

[HelloDave]

Hi Mr Grinch. Thank you very much for your reply and for taking the time to read my lengthy post!!

What you say is very interesting. If I am understanding correctly, just because the water isn't directly slopping up against the wall, doesn't mean that the ground below isn't retaining water. The key issue here is that the neighbours drive is above the level of 'water protection' (DPC) of that wall. So that wall is now at the mercy of any water sitting around above or below ground, because it touches the wall above the old DPC?

This makes sense now, because using google maps history, that wall was there in the 60s. In 2005 next doors drive way got redone - clearly by professionals who understood DPC levels / cared about the consequences of their work ha ha). Then you can see the slow progression on street view images attached. A very good example really of the slow 'creep' of damp.

So if I move this forward. Is this my plan of action in the right order......

1) Employ the pro Damp specialist to tank the internal wall and create a new DPC that is higher than the neighbours 'new' existing drive.

2) WAIT WAIT WAIT (But for how long? a few months? Years?)

3) Employ a renderer to do the outside of the wall - making sure they 'tank' / bridge externally up to the new DPC level, then nice render finish above that.

Have I got that right?

 

[RandomGrinch]

If I am understanding correctly, just because the water isn't directly slopping up against the wall, doesn't mean that the ground below isn't retaining water. The key issue here is that the neighbours drive is above the level of 'water protection' (DPC) of that wall. So that wall is now at the mercy of any water sitting around above or below ground, because it touches the wall above the old DPC?

Precisely!

1). The DPC should be installed 150mm above your neighbours drive level.
Internally the tanking should be bonded to your existing DPM and extend in height to your new DPC.

2). I can't remember how long it will take to dry out, but it can take a while (months). However, this will only be relevant to the area above the new DPC. The bricks below the DPC will probably remain permanently wet! But this wont matter; the tanking will protect your new internal surfaces!

3). The new render should stop above the new DPC with a drip bead. Something like:

There may be methods of tidying up the bare bricks/blocks but I don't have the details.

I hope that makes sense

Interesting detective work on street view!

 

[HelloDave]

ha ha. Thank you so much. Damp is a bitch, and you have really helped me here.