Looking for a bit of advice please.

Whilst starting to help my son renovate his bathroom we came across a rather unpleasant problem. The tiles on an external wall pretty much fell off and everything behind is very wet.
Construction: this “front” wall appears to be a simple timber frame structure. From outside to in: PVC cladding - roofing felt (what I would call old style felt not a breathable membrane) - timber frame filled with fibreglass type insulation - plasterboard. The water ingress does appear to have come from the inside. The timber structure is very wet, the insulation a sodden mess and the roofing felt disintegrates as you touch it. We have an insurance assessment this Friday but I would like to understand a way forward if possible before then. I think the main structural walls are brick, left and right whilst front and back appear to be this timber frame structure. 2 rooms across the front, bathroom and bedroom. No obvious signs of a problem in the bedroom front wall. I’m wondering how fixing this would best be approached? Any ideas welcomed

Was there a vapour barrier anywhere or foil backed plasterboard?

Nice to see you again

The PVC cladding components on the outside will prevent outward movement of water vapour, although there may well be gaps in between that allow movement. Similarly, the roofing felt is probably impermeable and may well have fewer gaps. You didn't mention a ventilated gap behind the roofing felt. So it'd be no surprise if water has made its way from a bathroom to the outside of the wall and structure.

A vapour barrier on the inside would help, as would a ventilation-gap/drainage-plane behind the outer cladding (PVC and roofing felt). How old is the PVC cladding?

my assessment, (like DJH has mentioned above) would be the vapour in the bathroom has been condensing on the felt and been trapped with no ventilation void. The bedroom may have managed to avoid an issue being less vapour generation in the room, but it's still a very bad wall build up.

The timbers look like 50x50?? Presumably you don't want to remove those, as they are supporting the cladding, which you've said you want to keep in place. It would be better to remove it and start again, but in absence of that approach, I would do the following....

- remove the insulation/felt/mould
- treat the timbers which are remaining, assuming they aren't completely nackered
- ensure there is a ventilation path below and above the cladding, in the vertical voids created by the timber structure (may have to cut/drill in vents/mesh)
- fix OSB to the back side of the existing 50x50 timbers (forms a 50mm cavity).
- assumption again... the brick walls each side are 100/50cav/100, and the OSB layer takes you flush with the outer face of the inner brick leaf
- add PIR insulation board against the OSB to bring the new build-up flush with the existing brick wall (may be 100mm, may be 90mm or even 80mm PIR).
- if you've space add another layer of let's say 50mm PIR covering brick and the first layer of PIR.
- use spray PU adhesive from a can to stick the PIR boards over the surfaces and all butt edges.
- fit a VCL over the lot, catching the ceiling, floor, and perp walls.
- strap out the wall with 22x100 treated offsaw timber vertically at 600 cntrs, fixing into the brickwork with concrete screws, and into the original stimber studs with timber screws (might be 180mm or longer)
- plasterboard over.

You might have to replace windows cills as internally the wall will now be deeper. Catch window reveals (and cills) with 25mm PIR all around and plasterboard over if that doesn't prevent window opening or look too daft with no window frame left.

Whatever method you use, the key is venting the back of the cladding.

I have noted before that although roofs need to be ventilated, there no building regulations requirement for any ventilation in walls

Pretty rare to see problems like this too.

Posted By: tonyI have noted before that although roofs need to be ventilated, there no building regulations requirement for any ventilation in walls

What is Part C para 5.17 about then? :

"5.17 Any framed external wall will meet the
requirement if the cladding is separated from the
insulation or sheathing by a vented and drained
cavity with a membrane that is vapour open, but
resists the passage of liquid water, on the inside
of the cavity (see Diagram 11)."

>philedge

Sounds a vey similar construction. Yes the wall was tiled (around a bath). My son took the tiles off but said they came off very easily, so ingress here is certainly high on the list as the culprit. The cladding does appear to be a fairly complete barrier and less likely to allow the level of water ingress we have. I'm back today.
Subject to opinions of the assessor, my current thoughts are:

strengthen timber structure where necessary
create some vertical ventilation throughout the timbers (drill some holes!)
insulate (celotex?) leaving 25mm gap to cladding
OSB /vapour barrier, but on inside wall
I think the timbers are at least 3x2 so should be able to use 50mm insulation.
Wondering if there's a way to put in a few vents to outside

To vent the 25mm cavity behind the cladding we ran a length of stainless plasterers skim angle bead along the top and bottom of the vertical battens. Once the cladding is on the cavity is closed to all but the smallest insects but nicely vented.

I appreciate it's a load of extra work but if you're reworking the cladding on the exterior then consider insulating between and over the outside of the studs in the wall. With 75x50 studs we had 65mm PIR between the studs and 75mm PIR over the outside

The ones we used are skim beads with a very fine mesh.....much smaller gaps than typical eaves vents. The angle beads for basecoat plaster or render have a much coarser mesh

Thanks philedge, will look into it. And Dave.

What a great solution.