timber framed wall missing a breathable membrane

[mountain1985]

Right folks. Usually use this website as a source for home DIY but need a hand with work related stuff now. My client has gone and built a timber framed wall on the inside of there garage with the intent to make it a habitable area. Now they didn't put in a breathable membrane in on the back of the timber frame in the cavity space, and its at final finish stage now. they haven't left the end of the wall open so you can see down the cavity about 2/3 meters.

Now the planner has spotted that there isn't a membrane and is basically asking for the timber wall to be ripped down and to put one in. Please tell me someone on here knows a cheaper alternative? I'll owe a bottle of wine to someone out there if they do.

 

[Deluks]

So it's plasterboarded and insulated already?


If it was just the bare studwork you'd have more luck.

When I built my shed up against the garage wall, membrane was an afterthought. I was still at the studwork stage, so I stapled membrane to treated roofing batten, carefully spaced to match the studs, then fixed short lengths of galv metal band to each batten. Folded it all up concertina style and fed it down the back of the shed, fixing each batten in turn by wrapping the band around the stud and screwing it in. I did it backwards, so that the batten was on the outside.

I'm not convinced that membrane is necessary in an application such as this though, if the stud wall is spaced from the exterior wall, then any ingress cannot bridge to the inner wall and remains in the cavity, the back of the insulation is still able to breath and transmit moisture to the outside (assuming the air inside is warmer) And if you do a good job with the internal vapour barrier then this won't be an issue anyway.

If the studs are fixed to the wall and insulation completely fills the cavity then your ferked. In which case see if he'll accept external cladding to the exterior as a 'let you off' Assuming the entire wall is accessible.

 

[^woody^]

There is a high risk of dampness and condensation affecting the sheathing or the frame from the cavity, and that is what the membrane would prevent.

And that is what the BCO is trying to prevent

There would be an argument that for this type of conversion, with a non-load bearing internal wall, then the risk is not only reduced, but the consequences of some rot are not of structural significance.

However, that argument would go against the majority of current thinking (BRE, TRADA etc) and would take a really good expert and report to convince the BCO or the Secretary of State on any appeal

If the property is not in an exposed location, and impregnated sheathing has been used then a membrane wont be required. If the frame is of treated/impregnated timber then you could also argue that a membrane wont be doing much.

If its just plain old ply/OSB sheathing and CLS studs, then it may have to come down

 

[mountain1985]

the insulation is foil backed but thats about it in terms of protection. the wood isn't treated and the edges of the insulation haven't been tapped up to prevent moisture ingress.

Nothing bridging the cavity and the insulation is between the timber frame though which is good. Its is a slightly smaller cavity than standard though (30-40mm)

Deluks, Like the concertina idea. May be able to just remove the plasterboard and do that. How did you seal the edges though?

The room on the inside is intended to be a utility room, soooo high miosture levels aswell. there is an extractor but they never solve the problem completely. See I was contemplating foil backed timber board on the inside so you can say moisture won't penetrate the wall from the inside and accept that the wall will get some rot but as it's not load barring its not the end of the world.

Woody, the wall itself isn't exposed. There is a small path along it then it has a high mound of earth topped with a dense tree line. I would have thought that the area being sheltered would have caused more good than bad and prevented direct rain penetration?

 

[Deluks]

AFAIK breather membrane doesn't need strictly need taping in walls (water can't run uphill right?) although the manufacturers do spec it, maybe so they can sell overlap tape.
I used 2 layers running horizontally with a 100mm overlap and taped that seam, the bottom was left loose but overlapped the timber (it's raised up on 2 brick courses) I was able to wrap each end around the final stud, and overlapped more membrane which covered the rest of the (accessible) frame.

I don't see the lack of membrane being a massive problem here. The trees will dissipate any horizontal driving rain, the cavity won't bridge any ingress, the extractor will do it's job assuming it's used often enough and at the right times (full on if drying clothes inside) There should be some form of heating in the room to maintain a higher temperature then the outside.
I'd say the lack of treated timber is more of an issue here and btw ANY form of rot is unacceptable and just to accept it as a problem that can be ignored is unwise.

 

[mountain1985]

yeah. The main issues are though if there will be enough water ingress to cause rot on the untreated wood. If yes (which I suspect the planner will say there will) then the only options open are to pull down the wall and stick in a membrane or find an alternative solution to breather membranes out there. Ideally like to stay on the clients good side the are a repeat customer so if there is an alternative method out there it'd be a top find. Starting to seem like the will have to tear the thing down though. may have to break the "happy" news to them.

 

[Deluks]

As mentioned earlier, see if exterior render would be an acceptable alternative.