Thu, 23 Apr 2026 11:18:20 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310510#Comment_310510 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310510#Comment_310510 Wed, 15 Apr 2026 10:35:53 +0100 andyman99
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]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310511#Comment_310511 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310511#Comment_310511 Wed, 15 Apr 2026 10:39:22 +0100 andyman99 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310514#Comment_310514 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310514#Comment_310514 Wed, 15 Apr 2026 13:01:35 +0100 tony
Nice to see you again]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310515#Comment_310515 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310515#Comment_310515 Wed, 15 Apr 2026 15:18:37 +0100 andyman99 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310516#Comment_310516 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310516#Comment_310516 Wed, 15 Apr 2026 16:16:16 +0100 djh
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?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310517#Comment_310517 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310517#Comment_310517 Wed, 15 Apr 2026 16:17:39 +0100 tony
For the shower room/bathroom I would seriously consider fail safe design and go wetroom style]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310518#Comment_310518 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310518#Comment_310518 Wed, 15 Apr 2026 18:37:05 +0100 GreenPaddy
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.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310519#Comment_310519 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310519#Comment_310519 Wed, 15 Apr 2026 21:26:21 +0100 andyman99 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310520#Comment_310520 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310520#Comment_310520 Wed, 15 Apr 2026 21:49:59 +0100 tony
Pretty rare to see problems like this too.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310523#Comment_310523 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310523#Comment_310523 Thu, 16 Apr 2026 08:34:57 +0100 GreenPaddy
Checking Doc C...5.15 onwards - explains that a ventilated and draining cavity is required for external framed walls, and a VCL internally, as I read it, and matches the Scottish Regs which I know pretty well.

Some scenarios might get away with insulation against the cladding, but being PVC plus felt, vapour's completely trapped, and being a high humidity room, it's pretty likely there'll be rot in the timbers.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310525#Comment_310525 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310525#Comment_310525 Thu, 16 Apr 2026 10:40:49 +0100 djh Posted By: tonyI have noted before that although roofs need to be ventilated, there no building regulations requirement for any ventilation in wallsWhat 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)."]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310528#Comment_310528 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310528#Comment_310528 Thu, 16 Apr 2026 13:35:17 +0100 philedge
A couple of years ago we stripped the cladding to insulate between and over the outside of the studs and fitted new cladding with a 25mm drainage/ventilation gap. When we stripped the exterior walls to the ensuite and family bathroom there was no evidence of damp even though there was no moisture barrier on the inside. I don't think the lack of a moisture barrier on the inside necessarily leads to excessive moisture within the wall.

Was the tiled exterior wall part of a shower enclosure? If so then I'd suspect moisture ingress from splashing through tiles/grouting rather than vapour ingress condensing within the wall.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310532#Comment_310532 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310532#Comment_310532 Fri, 17 Apr 2026 06:57:31 +0100 andyman99 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]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310541#Comment_310541 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310541#Comment_310541 Sat, 18 Apr 2026 10:07:39 +0100 djh Posted By: andyman99Wondering if there's a way to put in a few vents to outsidePVC cladding vents seem to be easily available. Just replace the bottom and top cladding planks?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310542#Comment_310542 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310542#Comment_310542 Sun, 19 Apr 2026 14:42:54 +0100 philedge
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]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310543#Comment_310543 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310543#Comment_310543 Sun, 19 Apr 2026 18:09:40 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310544#Comment_310544 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310544#Comment_310544 Sun, 19 Apr 2026 20:32:22 +0100 philedge https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310545#Comment_310545 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310545#Comment_310545 Sun, 19 Apr 2026 20:54:20 +0100 djh https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310546#Comment_310546 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310546#Comment_310546 Sun, 19 Apr 2026 22:21:39 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310548#Comment_310548 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310548#Comment_310548 Mon, 20 Apr 2026 08:33:49 +0100 philedge https://www.diy.com/departments/expamet-mini-mesh-steel-angle-bead-l-2-4m-w-25mm/35790_BQ.prd

With 25mm mesh they fit over the ends of 25mm perfectly:)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310551#Comment_310551 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=18423&Focus=310551#Comment_310551 Mon, 20 Apr 2026 11:54:48 +0100 Dominic Cooney