Dry lining - advice needed

[BlueC]

Hi, I saw a similar thread but for clarity thought it best to open a new discussion.

We are renovating our kitchen in our 1890 ground floor flat. It is 3 course brick and cement construction and the kitchen is in an outrigger with a recently laid concrete floor. The walls are 3 courses brick construction. We've hacked off the patchwork of concrete/plaster/plasterboard and taken it back to brick throughout.

I intend to batten and board the walls then have them skimmed. Originally we were thinking 2 x 1 battens with a 12.5mm plasterboard and 25mm polystyrene between the battens as this would give us a bit better insulation without widening the walls too much. However we were then advised that we'd be better to keep an air gap between the battens and line with thermal board (e.g. gyproc thermaline). Does this sound right? And if so, how important is it to have a vapour control layer on the back of the thermal board? Clearly this method is more expensive and reduces the room size a little bit more too so I want to ensure this is the right thing to do.

In case it matters - the walls are nicely dry although there is a little rising damp in the bottom of two external corners but it is not rising above the injected DPC. Its hard to know the cause of this damp - it could be from the poor/old plumbing - a leadlock was leaking a little and a cast iron waste pipe had rotted through near to these corners. These will all be replaced. It could also be coming through the walls below ground level because the troughs around the outside of the walls had become filled with organic matter which we have now dug out. Or it could be something else - maybe caused by the recent concrete floor and DPC forcing the water out and to the sides.

Anyway, any suggestions about how we should dry line would be most appreciated. And where we can find the materials at competitive prices would also be very helpful!

Many thanks
Chris

 

[Moo]

where we can find the materials at competitive prices would also be very helpful!

Cue a suggestion that you add some idea of your whereabouts to your Profile page. You may then find that someone on this forum lives quite near you and can give you lots of local information about suppliers and such-like.

 

[Zebra]

Hi, I'm no expert but have a similar situation, solid brick walls which have shown some damp, I've made some alterations to stop the water getting in, don't yet know whether that has solved the problem, and still have to figure out which type of insulation to use.
Where there have been damp problems, I understand that walls only dry very slowly, a month per inch I believe I've heard, so it may take a while for damp problems which have been solved to dry out.
In any case, the wall may still need to breathe through the insulation to prevent damp being trapped in those corners. There are the breathable forms of insulation you could use, such as lime hemp, wood wool, wood fibre etc. Some of those can absorb quite a lot of moisture (20%? don't quote me) before their insulating value is affected.
Or if you were to batten and use polystyrene or the Kingspan type stuff then I believe (again I'm no expert) that strips of vapour barrier on the backs of the timbers to keep them from rotting would do. Any vapour barrier against the bricks will cause moisture to build up behind it. Depends how bad the damp problem is of course, which you perhaps won't know yet! If you had a recent concrete floor and DPC, why was this not lapped with the injected DPM? Why was a gap left where damp can penetrate through? Doesn't seem to make any sense!
I know it's so hard knowing what the right thing to do is, there seem to be so many products on the market and so many ways to approach the problem. I find slowing down and not rushing decisions helps (though I've had my house a year now, and it's still only bare bricks and frame with no insulation!)

 

[AMc]

Our walls were battened to create an even surface & air gap then we used insulated plasterboard (12.5mm with 50mm of insulation IIRC) fixed to the battens.
Unless the room is very small the 50mm of foam insulation is equivalent to 150mm of mineral wool and will be worth the effort. The foil backing and foam insulation provides a fairly strong DPM but the joins are potentially vulnerable - ours were just scrim taped but then our walls were bone dry.
Obviously the battens even though tanilised are at some risk, you could seat them on strips of black plastic DPM run up the wall behind them to provide more protection.

Using insulation bonded to the plasterboard makes it much quicker and easier to get a good solid wall of insulation - it's also quicker then infilling and then boarding so should be worth the small increase in cost of materials.

I got my board from Sheffield Insulations who are a major supplier of all sorts of building related insulation products. Any only builders merchant should be able to order in what you need but cost may be higher. There is also a supplier of "seconds" in foam board insulation who get enthusiastic praise from those who've used them - a google will find the name.

 

[BlueC]

Hi Zebra and AMc, thanks for the replies!

Hi, I'm no expert but have a similar situation [...] Or if you were to batten and use polystyrene or the Kingspan type stuff then I believe (again I'm no expert) that strips of vapour barrier on the backs of the timbers to keep them from rotting would do.

We're using treated timber to prevent rotting but I like your idea as it would prevent any damp from penetrating through. Will give it some thought.

I know it's so hard knowing what the right thing to do is, there seem to be so many products on the market and so many ways to approach the problem. I find slowing down and not rushing decisions helps (though I've had my house a year now, and it's still only bare bricks and frame with no insulation!)

Indeed the number of products on the market is astonishing and very confusing! Similarly everyone seems to have a different opinion about what is the best thing to do! We are going pretty slowly but we're living without a kitchen right now so I do need to get this finished.

Our walls were battened to create an even surface & air gap then we used insulated plasterboard (12.5mm with 50mm of insulation IIRC) fixed to the battens.
Unless the room is very small the 50mm of foam insulation is equivalent to 150mm of mineral wool and will be worth the effort. The foil backing and foam insulation provides a fairly strong DPM but the joins are potentially vulnerable - ours were just scrim taped but then our walls were bone dry.
Obviously the battens even though tanilised are at some risk, you could seat them on strips of black plastic DPM run up the wall behind them to provide more protection.

I got my board from Sheffield Insulations who are a major supplier of all sorts of building related insulation products. Any only builders merchant should be able to order in what you need but cost may be higher. There is also a supplier of "seconds" in foam board insulation who get enthusiastic praise from those who've used them - a google will find the name.

Thanks this is useful. I actually ordered (indirectly) some 35mm Gyproc Thermaline Plus from Sheffield Insulations - very quick service but when it arrived it was all torn up on the edges - looked like a lorry wheel had spun against it and ripped it up. The driver said I should reject it which I did hoping they could send out something better but they said all their stock is like that. Seems a bit fishy but maybe I was unlucky. Had to cancel it in the end and we're having to go with 27mm instead now as its all I can get hold of within a reasonable time.

 

[MdB]

A bit of direct experience which you might find useful regarding dry lining:

One room of our house was dry lined 20 to 30 years ago due to dampness in the wall. After this period of time it was failing along the bottom edge where the damp had got to the plasterboard (One section was famously repaired with a piece of cardboard and then wallpapered over). I removed the lot to find out what was going on underneath and under the majority of sections it was absolutely black with mould but not all. One section was fine - the one that had ventilation into the void. The timber used was treated and separated from the wall by a strip of black DPM as AMc has suggested. Despite all the mould, none of the wood had been affected at all and I've reused it elsewhere. I also cured the damp problem via the standard tricks (and some more radical) and now have a warm dry room.

Conclusion, if you can avoid dry lining - do so by curing the damp issue. If you do dry line then ventilate the void and use treated wood / DPM strips.

 

[AMc]

Conclusion, if you can avoid dry lining - do so by curing the damp issue. If you do dry line then ventilate the void and use treated wood / DPM strips.

In our case dry lining was the only option for meeting building regs and had nothing to do with damp.
I could have externally insulated the wall (and ruined the appearance of the house).
I could have used wool behind a stud wall and lath and plastered but given the complexity, cost and loss of 300mm of room space (a.k.a. a foot) on all sides this seemed like a poor option.

Glad to hear the battens will last though