UKC

We are in a 100+ year old tiny cottage. Gradually making improvements. It's solid stone walls (approx 2 feet thick), with render on the road side aspect (the next side im Insulating).

I'm replacing a partion wall to basically look behind it and block up any mouse holes .. but when rebuilding it will Insulate it. 

I want to use the Sisal ECO Insulation as I've used somewhere else. 

I'm just confused about vapour barriers or not. I'd have the wool boards in the frame, then plaster board with the silver backing.

 Will this be fine, or does it need a vapour barrier, and if so where? There will obviously be a 4 - 6" gap between the inside of the external wall, and the partion frame. There is some airflow in the gap.  Thanks

I'm not sure if I'm being slow but I'm finding it hard to understand your question.

Are you basically asking if internal wall insulation on an external wall should have a moisture barrier or not? Sorry, I didn't quite understand what your sentence about the partition wall was trying to say.

To answer my interpretation of the question, if the external render lets moisture in (which most do) you need to allow the wall to dry out. In this case a moisture barrier will be a bad idea. You want to choose permeable internal insulation that allows that moisture to escape.

If however the external render is impermeable, then provided your wall has had time to dry out, then you can include a moisture barrier which stops warm water within the house air from condensing on the cold wall behind the insulation.

What's there now, false lath and plaster stud wall, airgap, stone? I'd be surprised if the heat leaking through your existing false wall is the difference between having a condensation problem and not on the stone.

jk

In the UK, the VCL (vapour control layer) should always go on the 'warm side' of the insulation as it helps prevent any warm, humid air in the room transferring into the wall construction. You should fix it to the inner side of your timber studs before you erect the foil-backed plasterboard.

Hi, the inside of the stone wall is plastered (very old, pink! Then a 4-6 " gap and an old partition,  many decades old, made from wood frame, with old plaster board on it. I know some of it is in very poor condition as I've looked through where an electrical socket is.

Very helpful, thanks. 

Might as well add the vapour barrier while you can it's cheap and easy (getting the details right so it works, less so!). You'll need to give some attention to the electrical penetrations, done wrong they'll make more difference than whether you have a plastic sheet behind your plasterboard or not (particularly if it's foiled).

jk

Thanks. There's only 1 x plastic socket on this wall. I know it makes sense to do the job right, but wonder if it really matters how well the vapour barrier is around the socket as there are 3 other partion walls in the room (2 are old as described like the one I'm replacing. The back wall partition was rebuild when we moved in and has 40mm celotex insulation in it, no vapour barrier. New silver backed plaster board. Theres free airflow around the whole cavity,  and god knows where else!)

You definitely don't want a vapour barrier, your foil backed plaster board will also act as a vapour barrier as well and will cause the same problems. 

Lath and lime plaster will allow the wall to breath, but it's hard finding a plasterer who can do it well. There are also a lot of builders who just have no idea how to deal with historic buildings and will try and apply modern solutions with short life spans and potentially damaging your walls. 

If you have a modern non-breathable cement based render on the outside, then this may well be the cause of the poor condition you are finding your walls in, although more than likely it is traditional and breathable and you just need to match this with breathable insulation (like your wool insulation), lime plaster and breathable paint and you will have a nice dry warm house for years to come. 

edit: historic england website have some resources which will point you in the right direction

I'm not saying you are wrong but I can't see why having a vapour barrier on the inside of the external wall would matter for what you are describing. If the external wall has absorbed moisture then what will dry it out is heat escaping from within the house (obviously less once the internal insulation is in place) or from outside /(during warm dry periods). Adding water vapour to the heat escaping from within won't do anything to improve the drying process.

If using external insulation then obviously that changes things a bit.

I'm far from expert, more "interested beginner" but from what I understand it's really quite hard to give general advice on old buildings and it really depends on what you are aiming for. 

Does your wall have any driven rain? What is the external render? What type of stone is it?

It seems like you have inherited a hodge-podge of various renovations, which is always fun! 

Again, I'm not trying to give advice, but if I were doing a similar project I'd be considering some things like:

• What are your moisture sources? Is it open plan to a kitchen, or very much a "living room".
• How is the ventilation? 
• How airtight is the room? 
• Will you end up with nasty cold bridges if you insulate? (cold windows that end up soaked with condensation). 
• How is the floor insulated and are there any high soil levels that could lead to pentrating damp?

If you don't suffer too much from outside moisture coming inwards, then I'd be (personally) be looking into ripping out the battens (that you call "stud wall") and just plastering on the hard with something like ecocork or diasen thermo active. They are breathable, so allow any built up moisture in the wall to slowly escape, insulating and will be in keeping with the style of an old stone cottage.

Caveat - I'm only away of those products in principle, but planning to use then for similar on a limestone wall soon. 

Def add vapour barrier as per Fraser's post.

If there's good airflow in the cavity this can make up for the vapour barrier not being 100%. There will inevitably be something that punctures the barrier somewhere. Like a picture hook nail or suchlike.

In essence, moisture needs to escape quicker than it can get in. Otherwise the timber studwork will eventually go mouldy and rot. Form a wood rot pov, you can not have too much airflow here! Need through draft, high and low vents. I'm a bit worried your anti mouse work might stop up the airflow.

It's still highly recommend to tape up the socket box and avoid cold bridging. Even if the moisture in the cavity escapes quick enough you can still end up with a localised cold spot inside the room where condensation and mould might become an issue. In a slightly ironic way, the more you insulate the higher the temperature difference you can generate between the room in general and a cold spot that's been missed.

Make sure your insul is held in place well and can't fall out during or after putting up the plasterboard. Need to account for a bit of sturdyness should anything bump the wall.

Good luck, and happy warming. 

You raise valid points and considerations, but I'm not going to delve into the hodge potch you have correctly highlighted as its too nuanced and individual to actually get one answer to on here! But I do appreciate all of the advice. I did consider just going back to the plastered wall, but want to desperately warm it up by insulating. I think that sure there may be some moisture in the cavity, but the original cavity frame could have been there 20- 30 years (or longer , I've no idea), so frankly I only need my repair/modification to last 10 - 20 years or whatever because there is no way to Insulate the house / room flawlessly due to many factors without gutting the whole room/house, which I can't do as I have to live in it

Ha, yes the mouse/ rat hole investigation may impact matters,  but does need addressing.  I suspect there's a hole in the ground behind the partion which rodents use as I found one behind an inbuild cupboard in the same room and had to concrete it up. The room did have a suspended floor, the older gentleman who lived here told us he used to put his terrier under the floor to get rats. Due to damp issues on the back wall rotting the floor timbers (the land is higher this side externally) we had a concrete slab put in along with insulation and proper membranes along the back wall etc. But I suspect the odd hole between the slab and external wall, as I don't think it quite reached it due to the partition on the wall side I'm now going to work on! 

The foil backing of the plasterboard you're planning to use is the vapour barrier. The foil on the cellotex in the other walls is the vapour barrier.

Once it's skimmed and painted a partition wall, with or without a foil backed board, is a pretty good vapour barrier.

The reason to particular about insulating and sealing the penetrations such as electrical boxes is because once the rest of the wall is insulated the space behind will be colder and moisture will condense onto cold things crossing the insulated layer.

If you have the money you may do better to buy cellotex backed plasterboard and fill the partition with cellotex bats as it is a lot more insulating than this sisal eco (I'm sure that tracing paper bog roll you'd get in school was sisal) or use the cellotex backed board and the wool bats if you want a halfway house.

While you're pulling the wall down think about if you want to add plug sockets as it's a lot easier to do it at this point.

If the render is permeable, is it not better to let moisture escape the same way it came in, rather than adding moist internal air into the mix?

If the render is impermeable, with an old stone building are you not potentially trapping in rising damp if you don't let it breathe internally?

There's no way to know about the render's permeability that I know of unfortunately 

A builder will quickly tell you whether the render is lime based (breathable, softer) or cement based (effectively impermeable). 
 

Dig out some from an existing loose bit (you're bound to find a bit somewhere) and drop I tin vinegar, if it doesn't fizz it's cement based and therefore waterproof (I think this is true, someone correct me if wrong) and if it fizzes it's lime based. Our rende lr is lime based and fizzes! 

Vapour barriers are not to prevent water seeping in from outside, but to prevent moisture laden (from people, cooking etc) inside the room passing through interior insulation where it would meet cold surface or air and condense causing damage

It's worth thinking about what your house was like when it was built - It probably had an earth floor and no damp proof course in the walls and no external render. It would have been very well ventilated and occupants would have lived with damp walls in the winter with everything drying out somewhat in the summer. As Sharp has said damp proofing old houses is tricky with many traps for the unwary. I suggest you avoid a damp proof membrane or non breathing construction on the inside wall unless you can guarantee that the cavity between the inside of the stone wall and stud partition and insulation is very well ventilated over the whole wall area, otherwise you will have a wood rot problem besides a damp problem. It would be worth getting some local advice from houses with similar construction if you can. For better or worse dealing with damp is part of the character of old houses and you can't turn it into a modern house just with stud partition and damp proofing. Good luck. Our house is 150 yrs old and I'm looking at several damp patches on the walls thinking they need a bit of replastering (with lime plaster) ...

We also live in a 100year old house and are busy renovating it. We had to use a cavity drain system (eggbox sheeting) on one side of a wall as metre+ ground build up on other side (pavement so couldn't exactly sort this out!) and we covered this with celotex and plasterboard. The other two external walls we used Lime Green's warm shell insulation system. More expensive than celotex etc and a lot more work but we wanted to go down the breathable route. We don't have a DPC (not sure if you do or not) but everything is lovely and dry and much cosier than it was! 

Sorry, that didn't actually answer your question and threw yet more ideas your way!

Great tip,  I'll try that

Interesting to hear, the back of the house with higher earth, they did the same thing when they put the concrete slab in, egg box sheeting between slab and Wall and goes up a meter or so. 

Will look up the limes green warm shell

That does look a good solution,  but presume you put it on a bare wall???

My problem might be whether it would work on the old internal plaster, which I have no idea how old it is, or what it consists of, and I don't think trying to get that off is viable. 

Hello, yes - we really went for it with the DIY 🤣 back to stone on the walls (they were covered in a mixture of old lime plaster and/or cladding) before building it up. It was a lot of work and levelling the walls was awful (well for me, my partner is much better at that sort of thing) afterwards with lime. Happy to send details/pics if interested - it was a huge amount of work but very happy with results. We're now onto room two so get to do it all over again - woohoo! The only thing I would say is that whilst we have noticed a massive improvement in terms of insulation in the room, celotex does provide better insulation.

Good luck with the renovations! 

Edit to say: you could always contact Lime Green to ask if could build up from existing plaster, assuming it is lime plaster.

Thanks, I'll have a think about it all. Happy renovations 

As others have said foil is a vapour barrier .

Whatever system you use you need to make sure the internal stud wall is airtight otherwise no point . The air on the warm side rises and is less dense so pressure differential. So any small hole allows air to come blasting through with surprising force . The devil is in the detail. Mastic under floor plate etc . As they say, "Don't ask me how I know" ,,,,,,,,🤔.

Warm air in your house has a much higher capacity to hold water. Since people add significant moisture to the air, warm air in your house tends to have a high total water content.

That is until it hits something cold like your stone wall. This means that if you have sealed the outside of your wall, you seal the inside also otherwise that condensing water on the back of the insulation will saturate the wall over time.

Option B is to let the whole lot breath. 

So seal both ends, or neither.

Kingspan explain better than I here https://www.kingspan.com/gb/en/knowledge-articles/should-I-install-moisture...

The Kingspan page cunningly omits the impact of non existent or imperfect damp proof courses. Simon - unless you know otherwise  you are best off assuming your damp proofing is imperfect at best, so you will have damp rising up through the foundation into your wall that needs to be ventilated to prevent rotting of internal timber. 

You’re right, I misread the paragraph I quoted. 

So you think that I need vents into the partition from the room, Or that I should have a vapour barrier on the the internal part of the partition? Sorry, slightly unsure. 

I took down the old partition wall today. I guess it may be approx 15 - 20 years old (hard to say). The plasterboard was similar to current stuff with grey paper type material (no branding etc). The timbers, and plastered wall showed no sign of damage/rot/mould. 

I did find a scarely large rodent hole in the base of the wall. The stone walls have no foundations and are set on bare earth (I knew this already). The walls were built with lime mortar, and it looks like internal lime plaster. But I'm still not sure if the external render is permeable or not. 

If internally insulated properly the external wall becomes a cold wall and, therefore, subject to damp penetration. Depends how thick it is I guess. I used galv metal studs and fittings. Pretty sure the specs, for such a system, include periodically coating the outside wall with a waterproofer. I haven't done that but I do worry, occasionally, about my joist ends .

Simon - personally I'd go for Edges proposal and avoid a cavity completely for a long term solution - If you have a cavity I think you'll have damp problems unless the cavity is ventilated (particularly if the external render is impermeable). Read around the subject and get some local advice, and contact Fran - she's been there on a DIY basis.

Sorry - I meant Sharps message - not Edge!

I haven't the time to reply properly right now, but this is a useful group (yeah, fb, sorry). 

https://www.facebook.com/groups/youroldhouseuk/?ref=share

It's also next to impossible to advise without a lot more detail - photos inside and out would be useful. 

I'll try to write something later. Atb David (historic building conservator). 

P. S. Sharp's advice upthread is a good starting point. 

No problem, thanks for the reply. I'm going to rebuild the partition with insulation now I've filled the rodent holes at the wall base. The wooden frame was in excellent condition surprisingly despite being a few decades old. No point us just having the external wall as it's too cold. If I'd found any damp issues I may have reconsidered. I'm prepared to accept that the partition may need maintenance/checking every 20/30  years or so! 

Many thanks all. Rightly or wrongly, I think this internal partition system seems to be pretty standard on lots of these old croft style properties in Scotland.