Insulating old stone building

Please STW save me from going mad. I have an old (c. 200yo) stable block I want to insulate. Its been converted into an annex already but the job was clearly done on a budget/by idiots. Its freezing in the winter, boiling in the summer. They partitioned it with breeze blocks, threw up some plasterboard and called it done. Looks pretty with vaulted ceilings etc, is crap.

So I am gutting it and starting over. Walls are 10-12″ thick min with good solid Durham stone, and have been repointed with lime mortar to a high standard. Roof is solid and dry, so the outer fabric of the building is sound.

Inside where it was a stable some walls have what is probably a cement based render on them then a thick layer of paint behind the plasterboard, some are bare stone.

In an ideal world I would simply knock down the breeze walls, rebuild a stud frame inside the building to the shape I want, insulate that and Im away. However Im concerned about adding a damp problem to what is otherwise a very undamp building. Its breathable because its like a sieve with no insulation, but that’s got to change. Two options seem to be:

– fully breathable (woodfibre etc) right up to the wall with lime over the top. Pros: breathable, in keeping with building, cons: price, ability to alter / add stuff later / hang things on it is limited.
– Full sealed – Stud with insulation/vapour barrier set off the wall. Pros: Cheap, well within my skill set, Cons: Loss of space, and now I would be worried about air movement between inner and outer walls and I lose space too.

Has anyone had experience with a hybrid of the two maybe? How worried do I need to be about whats going on between wall and inner wall? I can leave it open to the roof space (as its a one story building) and then vent that easily enough, effectively building a building inside a building.

I’m not an expert at all, but I’m trying to work out what to do with our victorian house, this is a really good resource… https://www.thepebbletrust.org/wp-content/uploads/2023/08/230814_SRG-ed2_Digital-V2_compressed.pdf .  Also look at the Historic England site, there’s a really good talk on retrofitting old properties https://historicengland.org.uk/services-skills/training-skills/training/webinars/recordings/webinar-on-retrofit-fundamentals/  as well as a load more stuff to read. Generally speaking I think you want vapour permeable membranes and breathable insulation, but it has to be done properly or it’s not worth doing at all, and that seems to be the difficult part. I keep meaning to start a thread on here for advice.

You’ll need to do U value and interstitial condensation calculations for the existing structure and whatever you propose to insulate it with. There are online calculators or some suppliers will do the calcs for you based on their products.
If those are done properly you should be able to eliminate any potential dampness issues.
Maybe worth paying an architect to spec it up for you?

Have a look at some of the insulating lime plasters. Keeps the building looking period and the walls will still perform as they should without installing vapour barriers etc.

Fully vapour open, remove cement render internally from external walls and wood fibre or insulated lime plaster is probably best bet. If you can afford to loose the space you could make a box within a box and leave the external walls vented. The risk of going insulation and membrane route is condensation and interstitial condensation in stone walls. As above Wufi analysis from an insulation provider such as back to earth. These can be free. Ensure ventilation is up to spec as insulation without proper ventilation is a disaster. Also be aware that stables with urine in the walls can have a hydroscopic salts issue and then problems with damp. Key to a decent job is continuity of insulation layer, eg wall insulation meeting roof insulation. Attention to detail at junctions including window openings.

– fully breathable (woodfibre etc) right up to the wall with lime over the top. Pros: breathable, in keeping with building, cons: price, ability to alter / add stuff later / hang things on it is limited.

We have a Georgian house with about 12″ thick walls of stone and mortar, and like yours, breathable by design.
We went with a sort of hybrid – the ground floor boards and joists were rotten, so dug down, lined, insulated then laid a concrete slab and tanked up the walls about 18″ or so.
Beyond that, we went with fully breathable insulation (Gutex board) with lime over the top. Kept it internal to retain the exterior dimensions/ proportions; it’s about 4″ thick with a decent U value.
Hanging things on walls isn’t too problematic: we’ve used a mix of big anchor screws (100mm rawl plug with a screw you hammer in then screw) and just regular picture hooks. Obviously on the internal walls it’s regular plasterboard – the insulation’s only on the exterior walls.

For fully sealed often the preferred approach is to do it all on the <b>outside</b>, so that the stone walls are inside the warm dry envelope. In theory it reduces the risk of dampness in the walls, and means they become part of the thermal mass.

Honestly it’s not a big enough space to warrant the architect getting involved, it will only be a studio/bathroom. As for U calcs as its not a change of use building regs don’t apply so its only the space Im willing to give to the insulation and the price Im willing to pay that dictates how much I use. I will of course be paying attention to what gives me the most bang for buck, but I will be going from nowt to a decent amount, so its all good 😉 Secondly my experience is that with buildings like this (our house is even older) they just suck air through their teeth, tell you the ten different ways you could do it then say ‘well its really down to your budget’.

The question is what to use and how though as its that interstitial condensation thats the problem… If lime plastering wasn’t so damned expensive it would be a no brainer to go that route.

The other option is to install a proper heat recovery ventilation system to actively extract the moisture from the building (combined with venting the air gap on a framed silution.

Concrete slab to replace rotten joists is a very high risk approach, especially if root cause of joist rot is not sorted. Moisture gets pushed sideways under slab and up walls just moving the problem around

Cement based render on the inside has probably killed off any hope of going down the breathable route. I’ve gone for the fully sealed route in ours as there’s so much draught behind the studs I’m not worried about damp on the stone, but am concerned about interstitial condensation arising from vapour coming from inside the house.

Like you, we have a 170yr old Durham barn conversion converted by a total cockwomble. The 50mm of kingspan is fitted to a an atrocious standard and in most instance may as well not be there.

I’m currently working though room by room removing the plasterboard, refitting the old Kingspan correctly (with bodge foam to seal the big gaps) and then taping the edges, the studs and any surface damage. I’m then gluing a further 50mm of Kingspan to that, foaming the edges and taping it all before adding new plasterboard.

On the lower floors, I’m removing the current floors, putting a DPM down extending 400mm up the walls behind the studs, loading that up with screed and then a new floor will be floated on top on about 100mm of kingspan.

We have a few window reveals where space is at a premium and damp has previously lurked. I managed to source some relatively cheap aerogel mat which I’ve put behind new reveals. This is truly awful stuff: it is exactly how I remember the white asbestos matting you’d find on old ship and railway engines, needing lots of ventilation (I had two industrial air movers pulling the dust out of the room) and full ppe when fitting. Scared me stupid. It is however extremely effective. I’ve fitted this behind a layer of the basic superfoil which I then foam edged taped and taped again to encapsulate it. I don’t want any of it to escape, ever.

I’m looking to do something to my house in the next few months as well. Old granite house with 22″ wall and lath and plaster. The previous owner has done one room where the plaster has been stripped but the lath left in place and insulation placed between the lath and new stud work and plasterboard and it’s noticeable warmer. But going buy some of the other stuff I’ve found since I moved in last year there’s no guarantee this has been done correctly

Like you, we have a 170yr old Durham barn conversion converted by a total cockwomble.

At least yours attempted insulation.

If you can afford to loose the space you could make a box within a box and leave the external walls vented.

This describes our house, was previously a threshing mill with +2ft thick stone walls and slate roofs.  It’d had a concrete slab installed over 100 years ago when it was extended.  Basically an internal frame built with 4″ CLS set away from the inner side of the stone with some fibreboard, then Cellotex inset and plasterboard.

Same approach when we converted one of our smaller barns as a place for my Mum.

It is worth understanding that adding too much insulation greatly increases the risk of damage to the stone wall and damp problems. Chasing high U values is risky in old buildings hence the recommendation of Wufi analysis. Normally with solid walls 60mm woodfibre or less would be low risk.

Following with interest as we’ll be going through this at some point

Following with interest as we ought to be going through this at some point

I may go for the hybrid of direct to wall woodfibre and plasterboard TBH. The lime plaster thing seems a bit over-egged as plasterboard + plaster is definitely not vapour-proof. I tried to find some numbers and to illustrate that point here’s some sort of graphs someone did – https://www.conservationphysics.org/wallbuff/wallbuff.php

What it claims/shows is that the performance of lime vs gypsum isn’t really that different. Externally lime’s ability to cope with moisture is important, but internally in a fundamentally dry house its not going to be used like that, and as long as I keep away from latex paints etc. I think it would be fine. My stone walls (like 99% of stone built houses, and contrary to what damp ‘specialists’ might say) are not damp inside so I don’t need to have something that can move moisture from the wall and away, just something that wont trap it in and create a problem that didn’t exist.

Investing a few £s into a hygrostatic heat exchanging external ventilation system to keep the internal moisture content down would seem like the cheaper more sensible way to insure no problems occur down the line as well as providing a drier (and so warmer feeling) environment.

Yep MVHR will be key. I’ve got two big MRXbox units to go in the loft (they’re 150m^2 capacity each, we’re just under 300 total). Will be driving them based off realtime humidity readings in various rooms (netatmo kit and a couple of homepod minis in the kid’s rooms).

Generally, like you I’ve found the internal stone to be bone dry.

We should meet up and compare money pits.

Plasterboard and gypsum plaster will pretty much eliminate any moisture buffering and moisture transfer benefits of the wood fibre. The plasterboard and gypsum plaster are unable to allow the free movement of liquid water. The risk is that water vapour passes through the plasterboard, becomes intistitial condensation in the wood fibre /cold wall junction and then cannot leave the wall in a liquid form back through the plasterboard. It is worth speaking to back to earth, ecomerchant or similar about your requirements . High humidity rooms like bathrooms may need a slightly different approach. Calsitherm bonded to the stone is very good in high humidity areas.

It is worth speaking to back to earth, ecomerchant or similar about your requirements . High humidity rooms like bathrooms may need a slightly different approach. Calsitherm bonded to the stone is very good in high humidity areas.

It was Back To Earth that started me down the hybrid path:

“Contrary to what some believe, plasterboard and gypsum plasters are just as breathable as the most permeable of lime plasters and so is perfectly useable on this type of construction. When painting the plastered surface once it has been skimmed, you should only use acrylic or other breathable paints and no vinyl paints.”

Internal Wall Insulation – Wood fibre insulation with a plasterboard finish

Two things to this approach thats worthy of a note (maybe):

They insert a permeable membrane between the layers of insulation, presumably to try and keep the cooler/warmer air masses from freely circulating with each other.

You dont have to use plasterboard and skim. Ive done drywall with just filling the tapers and sanding and if you’re willing to spray paint the finish can be excellent. Thats going to improve the breathability no end.

Knock the whole bloody thing down and put a proper building up in its place using modern methods and materials. Stone has no place as a modern building material. It’s just what was easily and cheaply available at the time.

They have put a membrane in that build up I suspect to reduce the risk of interstitial condensation at the wall woodfibre junction. If it is a build up they recommend then it should be fine, but make sure you do all the layers not just pick and choose as they will be there for a reason. The nature of the stone externally could also effect the build up especially if it is soft and porous. In their build up there is a lot of use of tapes and other products that are not going to make it a cheap alternative to just lime plaster straight over the fully bonded wood fibre which would be just as airtight and at least as breathable.

“As for U calcs as its not a change of use building regs don’t apply so its only the space Im willing to give to the insulation and the price Im willing to pay that dictates how much I use.”

Are you sure? I needed building regs when I stripped our loft room back to brick and re insulated it. I can’t see how you don’t need regs given what you’re doing (a thermal element is external walls, the floor, or the ceiling/roof).

https://www.tameside.gov.uk/buildingcontrol/guidancenotes/note24guide2.pdf

https://www.eastsuffolk.gov.uk/assets/Planning/Building-Control/Common-projects-guidance/Thermal-upgrades-to-your-house.pdf

“Renovation of a Thermal Element.
Renovation of a thermal element through:
The provision of a new layer means either of the following:
a. Cladding or rendering the external surface of the thermal element; or
b. Dry-lining the internal surface of a thermal element.

Replacement of a Thermal Element.
The replacement of an existing layer means either of the following activities:
a. Stripping down the element to expose the basic structural components (brick / blockwork, timber / metal frame, joists, rafters, etc) and then rebuilding to achieve all the necessary
performance requirements
”

Sorry for the rubbish quotes – the buttons has disappeared again for me.

Yeah I was told by DCC that any change to the insulation in the fabric of the building would require building regs.

They have put a membrane in that build up I suspect to reduce the risk of interstitial condensation at the wall woodfibre junction.

It’s a ‘Smart’ membrane it would appear to stop moisture entering the wall space when its cold but opening up during warmer days months to allow for residual moisture in the wall to escape… I think. However it works there’s equivalents with similar SD ranges that are a bit cheaper. I reckon you need to allow £15 pm2 tops for plasterboard / VCL / Tapes vs £30? + for lime. The other advantage is I end up with a sacrificial layer on the outside that can easily be changed by me, rather than a specialist job, as well as a services cavity possibly/hopefully (I have emailed BtoE to ask about that).

Are you sure? I needed building regs when I stripped our loft room back to brick and re insulated it. I can’t see how you don’t need regs given what you’re doing (a thermal element is external walls, the floor, or the ceiling/roof).

Nope I’m not sure and reading up it looks like you’re right. Its pretty ludicrous that you can add cavity insulation to very low standard but if you go from zero insulation on a solid wall you need best part of half the u value. If I did I would probably point out that I can’t meet these with a U value of .30 and still have breathability

“Assess the impact on internal floor area. In
general it is reasonable to accept a reduction
not exceeding 5% in the area of a room.
However, the use of the room, and the space
needed for people to move around and
for fixtures, fittings and furniture should be
assessed

Assess condensation and other moisture
risks and make appropriate provision in
accordance with the requirements of Part C
relating to the control of condensation
(BS 5250 and BS EN ISO 13788). This
will usually require the provision of
vapour control and damp protection
of components. Guidance on the risks
involved is provided in the Building Research
Establishment’s BR 262 and, on the technical
options, in Energy Saving Trust publications”

The building regs look like they’ve been specifically designed to prevent people from upgrading their insulation! Its no wonder we’re overrun by dodgy ‘government backed’ insulation schemes charging fortunes to screw up peoples houses.

@hot_fiat that looks like a very tall space you’re refurbing! If you want to borrow it I have a 7m platform (can be less than 7m) you can borrow.

Worth noting that if you’re renovating the building regs people are pragmatic in practice (they have a lot of discretion) as long as it’s an improvement on what was there before, if you can bring it up to regs fine, but if you can’t for a good reason (e.g. floor space being encroached, low ceiling height) they will accept a lower U value.

When doing my loft I found the building controls guy (a council guy) extremely reasonable and helpful. It’s not like they come out once at the end and give you a pass or fail, you book an initial appointment and they’ll come out. You give them the general idea of what you’re doing and they will tell you if they’ll accept it or what you need to change to get accepted – they certainly appreciate that people doing conversion / renovation themselves are not experts. Obviously no one will know if you don’t get building regs, but if it is obvious and substantial you will have a problem when you come to sell, so on balance i’d get them in.

The system described in this video looks good: https://www.youtube.com/watch?v=Ou1CjwflZtM&list=PLGLW0V-dOcLqiat24cTlcdHESDkJASA-n&index=16

Thanks for the offer Benpinnick, fortunately my brother in law is an IPAF instructor so access to towers isn’t an issue.  Should Really have got my arse in gear and got one dropped off on Saturday.

I like the look of that SWIP system though it’s probably not as high an insulating value as K118 but if i had solid walls or an older property then it’s probably what I would go for.

I did our 1960 flat with 65mm of K118 (72mm inc the plasterboard bit) and the difference it made was huge. the walls are mostly cavity with one solid wall with a huge 5m long Crittall window in it but it’s tile faced so no issues with moisture transmission. 65mm was the sweet spot and going any thicker was into the law of diminishing returns. I used foam adhesive with 3 fixing per board as per the guidelines, they are only there to stop the boards falling off the wall and blocking your exit in a fire.

I did check if it was a notifiable work but it wasn’t, there were guidelines that suggested if you were insulating then you had to have a certain depth/U value and under insulating was frowned upon. As stated above it’s not a huge issue if you can’t bring the building up to spec 100% due to size/construction/access etc.

Whatever you do take lots of photographs and keep receipts of materials for when you get a new EPC or come to sell.

You don’t need to meet the building regs backstop u values for refurb as it is an historic building of vapour open construction. A risk based approach should be taken.  Most building control officers are aware of this.

I’ve used wood fibre insulation in various thicknesses but only in places where I am pretty sure it won’t get wet. I’ve seen what happens when it does get wet, it loses its structural integrity and swells. In places where there’s high humidity and/or water around I’ve used kingspan type boards and/or polyester wool.

If the inside covering over the wood fiber is breathable there’s the risk of condensation within the insulation as the dew point will be somewhere in there. If in doubt, Kingspan or multi-layer stuff. In some places I’ve used Kingspan over woodfiber, I can only say it’s gone though one Winter OK as I did it last Autumn and have recently checked.

The SWIP system does look great. Might cost it up for a few rooms.

Sealing socket boxes is a good shout. I bodge foamed the last room’s in and then taped up any foam present on the inside.

If I wasn’t literally painting the plasterboard right now I could have shown you my accidental almost swip system I put into another more modern part of the house. Its cavity walled with a full cavity but because I live on top of a windy, often wet, often snowy hill and it’s a north facing room I just made up a way of doing it that used the exact same layup and products (knauf eco/intello vcl) just with wooden stud framing which I think is fine as it’s onto the insulated side of my cavity wall.

Not convinced I want to replicate the knauf into my next job though, hence looking at stieco or similar, but the knauf is cheap, available at my local b&q and nice to work with.

It’s worth pointing out it’s why I was saying I’d appreciate the service cavity in what I do in the stables. What I’ve done in the utility is somewhat pointless in terms of the intello as the room hosts a 300L thermal store with more pipework than the titanic. Trying to seal it up was ultimately a fruitless exercise so next time I want to build it with a. Sealed perimeter and then a service cavity in front of that ideally. Lesson learned!

@edukator kingspan isn’t suitable in vapour open construction buildings. All current best practice advice is to use vapour open insulation  in buildings of vapour open construction. Eg solid walls and generally pre 1919. There is a lot of evidence of vapour closed insulation leading to damp and mould problems over time. Products like calcium silicate board Calsitherm, are good alternatives to woodfibre in high humidity environments. The only time to use a vapour closed insulation in the walls would be in a box in box scenario where the external wall is well ventilated to both sides.

So, Im thinking (having had the evening to mull it over, watch more Youtube!) of doing a hybrid of the hybrid. The SWIP is not that different to the B2E method I posted above, but I do like the levelling/no bridging of the SWIP studs which the B2E woodbatts screwed to the wall only can do half, as the woodbatts wont level the surface that effectively.

So I reckon I might:

Bond some OSB to 50mm kingspan and rip some studs, affixing them horizontally on the walls at 600 mm centres.
Infill that with Knauf party wall slabs @60mm or something like that. I will ask Knauf what they recommend.

Cover that, and the rafters (now also insulated) with a continous layer of Intello or similar. There’s other brands available too, after I bought the roll of intello I found Vara Plus which is an Irish made product with slightly different variable SD numbers (Slightly less breathable at the low end, more watertight at the high end), Im not sure which is better, more research needed! Which ever it is though the principle is the same to wrap the walls such that the vapour barrier is continous around the whole space. I will look into whether I could/should use an open membrane roof insulation instead of the smart one, allowing moisture to easily exit the roof space (since its vaulted ceilings).

One wall is a party wall, and one affords me the option to externally insulate relatively cheaply, on those two walls I will build a thin stud frame, no further insulation, in order to provide a services void. On the other two walls build 4″ stud walls (all of which I may end up stick-building).

Affixing that as infrequently to the hybrid studs I made as possible attach my stud walls. I’ll probably use something like a mastic tape at the intersections so that when I screw through the vapour layer theres a self sealing layer already in place that will seal the holes I’m making.

Once the 4″ walls are up I will add 60mm batts to those too, and that gives me room for back boxes, cables etc. .

According to this calculator (https://www.changeplan.co.uk/u_value_calculator.php) two 60mm layers @ 0.036 conductivity gives me a building regs friendly 0.288. I lost around 120mm on two sides and around 90 on the the other two (relative to what was there) but that’s liveable.

What do you think?

Update: So I decided to improve on the design a little to make it nicer to install. rather than ripping solid strips from a full board of ply/XPS I will use smaller XPS panels spaced apart to allow me to create slots in which to have verticals slot in. The horizontal spacing and verticals height will be matched to a Knauf RS45 slab for easy installation, 1 slab per gap formed. I will probably do 3 verticals per beam, 2 one way one the other, alternating, but that does depend on slab size of course.

As my install is horizontal it means there’s less chance of the insulation slumping, which is nice, but also means that for my rather triangular walls I will have the option to increase batten thickness as I go upwards to maintain a more constant vertical plane. I will also make a few corner beams where I leave off the face for 60mm so the beams can form a corner without the wood touching the wall at the end of a run.

For anyone interested this is what the SWIP system is based on – https://www.foamseal-insulation.co.uk/images/brochures/knauf-brochure.pdf

Its worth a read. The only difference being the Knauf one isn’t using a smart vapour control layer/fastidious sealing.

Much better to have a service zone behind the plasterboard. Air leakage points from sockets or fixings for shelves etc will allow air movement and a point for warm moist air to then cause condensation and mould behind the plasterboard. The link above does talk about the importance of controlling air leakage around joist ends in the inter floor zone and also insulating in it. This is important to not have a thermal bridge right where the joist ends are in the wall which can cause moisture from condensation and rotting of joist ends.

Knock the whole bloody thing down and put a proper building up in its place using modern methods and materials. Stone has no place as a modern building material. It’s just what was easily and cheaply available at the time.

Yeah, right. *rollseyes*. Clearly you’re of the same mindset as those who destroyed countless lovely old buildings in the 60’s, or the cockwombles who destroyed the leaning pub recently. Either that, or you left off the /s from your statement.

A very close friend of mine owns an old farmhouse on the Fosseway near Castle Combe. When she wanted to rebuild and convert an old milking shed out the back, for self catering, (the house is a hotel, tearoom and restaurant), she had to match the Cotswold Stone the house is built from. The quarry the stone was sourced from is very close by, but the council refused permission to extract stone from the quarry ‘on environmental grounds’!
The house is 18th century, and perfectly solid – I’m wondering just how many modern houses built to current standards, will still be standing in 350 years time.

Caron’s farmhouse, 350 years old…