Help With Options Regarding A Single Skinned Wall

[lazybass@yahoo.co.uk]

Hi

My parents have purchased an old cob cottage in Mid Devon dating from the 1650's which requires some work to bring it back to its former glory, they desperately need some advice regarding the back wall of the house which is single skinned it is a later extension built in around 1850 which has an asbestos tiled sloping roof above, they would like to work from the inside so would battens / insulation / plasterboard be sufficiant or would it require breeze block then plastering or what other options do they have as they want to make it 100% mortgageable should they ever decide to sell. Also they require a heating system as there is no gas in the village and are looking at multifuel burners with back boilers to run around 8-10 radiators off any help with good burners much appreciated.

Thanks again

 

[NT]

Many properties with 4" walls are sold annually. It is an issue but still saleable and mortgageable.

> would battens / insulation / plasterboard be sufficiant

yes


NT

 

[MdB]

> would battens / insulation / plasterboard be sufficiant

yes

If the wall is suffering a little from damp then would this still be a good idea? Would there not be an issue with condensation in the cavity?

The end wall in my house is stone rubble construction approx 300mm thick which has about 10 layers of paint on the outside. The paint is full of holes and is good at letting the water in but not so good at letting it out so needs removing. This should hopefully cure the damp problem but I don't want to plaster board the inside walls if its going to stop the wall from breathing. I assume the foil backed plasterboard would be a bad idea for the same reason.

Ventilation for the cavity has been suggested but I'm unsure as to how to do this without removing the advantage that the insulation is giving.

 

[Penners]

Would there not be an issue with condensation in the cavity?

The trick is to leave an air gap between the insulation and the outside wall, with a damp-proof membrane on the insulation side of the gap. So (starting from the outside) you have outside wall, air gap, membrane, insulation, plasterboard. Measures should be taken to allow air circulation in the air gap.

 

[lazybass@yahoo.co.uk]

Hi

Thanks for your comments and advice.

 

[Sal]

for multifuel burner options i would approach Dean forge who are in your area to discuss your options. no doubt there are other suppliers nearby too


Sal

 

[MdB]

Would there not be an issue with condensation in the cavity?

The trick is to leave an air gap between the insulation and the outside wall, with a damp-proof membrane on the insulation side of the gap. So (starting from the outside) you have outside wall, air gap, membrane, insulation, plasterboard. Measures should be taken to allow air circulation in the air gap.

Thanks Penners very useful, that was what I was thinking. Any guides as to what sort of size vents should be fitted? One at top, one at bottom? Gaps in battens to allow air through? Any vents are going to be fairly visible in this wall so I want to keep them small as possible.

I would also assume that tanalised battens would be a good idea to help stop rot if it does get damp in the air gap.

(and sorry Lazybass for the thread hijack)

 

[GK]

Penners, have you got the membrane in the right place? I've always fitted a vapour barrier on the warm side of any insulation so the saturated air can't get to the cooler parts and condense. In your scenario I would worry that moisture-laden air can pass through the insulated structure, cooling on its travels, until it reaches the dewpoint which will be where the membrane is, whereupon it may run down in rivulets wetting the insulation and battens. (deep breath)

I rely on the ventilation to the cavity and the knowledge that the cooler air within it won't contain much moisture - but even so, take precautions to isolate treated timber from masonry anyway. The external wall could be damp on the interior face.

must teach the spell checker Penners, vapour and dewpoint

 

[MdB]

:? Me thinking aloud here - this is all new to me :?

Wouldn't the position of the membrane depend on the situation it is in?

i.e.
Showroom - Moisture in air in room. Cavity air is dry.
In this situation you would want the membrane next to the plaster board (wall - air gap - insulation - membrane - plaster board). This will as GK says stop the moist air reaching the cool side of the insulation and condensing.

Damp wall - Air in room is dry. Cavity air is moist due to damp wall.
In this situation you would want the membrane next to the cavity (wall - air gap - membrane - insulation - plaster board). This will stop the moist air reaching the warm side of the insulation. I guess this doesn't matter though as it won't condense. Hmm. Thinking whilst typing suggests that this isn't such a good idea and GK it right for this situation also.

Comments please.

 

[GK]

The air in the dwelling will almost always have a greater moisture content than outside and the natural pressure is (i think) for it to migrate outwards. You think its dry air but it soon reveals its true colours in contact with a cool surface.

To be honest, if you have a room which isn't producing a lot of moisture and your level of insulation isn't that great you can probably do without a vapour barrier and hope that natural air movement will clear any moisture. But if you fit one on the cold side, my money says that everything on the inside of it will be permanently damp.

Biff has cited sheeps wool as the natural insulation material, I think it tolerates moisture and is vapour permeable, but I haven't used it. And you've still got to fix your plasterboard to something. Or reed and lime if you're faking it as I have.


vapour=no, vapor=yes. since when did PPUK become PPUS?

edit: worked it out. latest Firefox has built in spell checker. just need to set it for English

 

[Penners]

Penners, have you got the membrane in the right place? I've always fitted a vapour barrier on the warm side of any insulation so the saturated air can't get to the cooler parts and condense. In your scenario I would worry that moisture-laden air can pass through the insulated structure, cooling on its travels, until it reaches the dewpoint which will be where the membrane is, whereupon it may run down in rivulets wetting the insulation and battens. (deep breath)

I rely on the ventilation to the cavity and the knowledge that the cooler air within it won't contain much moisture - but even so, take precautions to isolate treated timber from masonry anyway. The external wall could be damp on the interior face.

Actually GK, when I typed my post I was a bit unsure about that, so I popped across the road to talk to a builder who is putting a timberframe extension on a neighbour's house. What I typed was what he told me.

However, judging from past experience of your posts, I think I would rely on your views, rather than his!

 

[GK]

Penners, if it's a modern build timber frame I'll bet he's thinking you meant breather paper. Some types are quite black and look a bit like dpm but they're actually vapour permeable from the inside and waterproof from the outside. They are fixed on the outside (cool) side of the frame. There will almost certainly be a vapour barrier on the room side behind the plasterboard, though.

This fits perfectly with what you describe.

 

[MdB]

I can see there is one big advantage from a builders point of view of having wall - air gap - membrane - insulation - plaster board. It allows you to use the membrane to hold the insulation in place as you assemble it. (I would assume not ever having tried it :wink If you go wall - air gap - insulation - membrane - plaster board then you will need some sort of spacer to create the air gap. Any hints as to what to use?

(edit - GK just beat me to the post)
Would the breather paper be used to hold the insulation in place hence no need for spacers?

PS Thanks for all the comments - learning all the time...

 

[Nemesis]

GK - IE now has ver 7, which apparently makes it much better, apart from the fact the menu bar vanishes and you have to hit alt to use it.

Hmmmm....

 

[lazybass@yahoo.co.uk]

Hi

Gk when you say reed and lime what exactly do you mean ? do you mean you would use reed boards instead of plasterboard and then a lime plaster finish ?

 

[GK]

Nemesis - My ie7 menu bar doesn't vanish ... you've broken it again, haven't you?

Tabs browsing at last and the control-Q thingy is good.

 

[Nemesis]

Oh - I just read about it! That's what it said... yesterday...

Hmmm. You are right - I'm rubbish with the technology.

 

[GK]

Reed matting is fine for a ceiling but does a seems a bit flimsy for a wall. But I've still done it successfully in two large rooms. Reed matting and two coats of lime plaster over an insulated frame. You end up with a finish that's visually very close to lime plaster on masonry.

 

[Penners]

Nemesis - My ie7 menu bar doesn't vanish ... you've broken it again, haven't you?

Tabs browsing at last and the control-Q thingy is good.

GK - is IE7 now in its full version? Last I heard it was still in beta.

 

[GK]

Full version 7 I think, not meant to be a beta.