Stone built internal wall insulation advice please

[sb1202]

Thanks for adding me.

Looking for advice on how to best insulate the internal walls of a stone built cottage. It's single storey with some modernisation from the 1980s. Walls are 600mm (not 400mm). Internal walls are drywall with vapour barrier on 50mm batten frame and at 150mm gap from the walls. Roof is insulated with about 300mm knauf type wool. Floor is concrete/dpm and chipboard on 50mm and not insulated. I upgraded the anel rads to columns a couple of years ago and this made a difference but it's still difficult to retain heat. There's no damp and I've taken the drywall out in one room, and again, everything bone dry. The humidity sits around 50% in winter.

 

I'm installing UFH in the next month  and looking to finish it off with internal insulation. I've read as much as I can but I need advice as I've read so many different ways.

This will be DIY (I'm an electrical engineer and pretty competent when it comes to carpentry and most general building works)

Photos attached give an idea of the rooms. 

This is aberdeenshire.

Thanks for any help.
 

[JamesP]

I would recommend wood fibre board insulation. Had a similar stone built barn, battened, wood fibre then lime plaster.

 

Have a read at https://www.mikewye.co.uk/product-category/natural-insulation/wood-fibre-insulation/steico-wood-fibre-insulation/

[Redbeard]

+1 for WF, but the existing structure will make it difficult for you to get a membrane on the *cold* side between the stone and the insulation, I think. It's ar*e-covering, but I would not want to risk moisture in the  wall  being 'wicked out' by the insulation. I would use flexi WF with a lambda of 0.039W/mK. Get one of the merchants who offers them (I am not sure Mike Wye does) to do a WUFI dynamic condensation risk assessment. Knowing nothing of your building I'd guess that 100mm maximum would be deemed 'safe', and possibly as little as 60-80. Intelligent VCL (e.g. Pro Clima Intello) on the warm side. Then plasterboard, 20mm rigid WF or 15mm woodwool.

 

What about the window reveals?

 

''Floor is concrete/dpm and chipboard on 50mm (battens??) and not insulated'' . Is that to come up and be insulated? Could do a floating floor and lose the thermal bridge of the battens, and get tight insulation-insulation contact between floor and walls. **Ah, sorry, just re-read re UFH. How much insulation underneath. Remember the greater delta T at the floor level.

 

Don't forget to ensure the wall ins touches the roof ins too.

 

Any egg-sucking tuition is not intended!

[saveasteading]

You might be able to staple a membrane behind the stud if you are a contortionist. Then fill between studs.

Then a service gap and a finish. That adds up to a half decent insulation. The wall itself is contributing if the outside is well pointed.

[sb1202]

1 hour ago, Redbeard said:

"Any egg-sucking tuition is not intended!" - Go for it - I'm a novice where this is concerned so I won't be offended. I'm also dyslexic so I'm struggling with all the acronym stuff. 

"membrane on the *cold* side between the stone and the insulation" - why is this required? Will it not trap moisture from the warm side? 

"Knowing nothing of your building I'd guess that 100mm maximum" - is this the Gap? The building goes back to the 1800s. I was a former croft, granite stone at 600mm. It was renovated in 1982. Stnework all pointed, internal plasterboard skin. Concrete floor was put in at the same time. Chipboard on batten. 

(e.g. Pro Clima Intello) on the warm side. Then plasterboard, 20mm rigid WF or 15mm woodwool.

 

"What about the window reveals?" - I'll be doing these as well so advice needed. 

 

"Don't forget to ensure the wall ins touches the roof ins too." - sorry. Not sure what this means.

Thanks for taking the tine to reply

 

 

 

Edited Thursday at 11:46 by sb1202

[sb1202]

42 minutes ago, saveasteading said:

You might be able to staple a membrane behind the stud if you are a contortionist. Then fill between studs.

Then a service gap and a finish. That adds up to a half decent insulation. The wall itself is contributing if the outside is well pointed.

This is the part that's confusing me - why is a membrane required for the cold side?  What do you mean by a service gap?  yeah, outside it well pointed.

I can take out the studs easily enough and start afresh.

[lookseehear]

Welcome! You'll find lots of people doing similar things to you on here - I'm one of them. Definitely have a read through this thread when you get a minute. 

 

 

I, too, am confused by the membrane on the cold side - I think the idea is that because wood fibre insulation is very hygroscopic (will absorb moisture), it will act like a bit of a sponge making your walls stay relatively dry but your insulation becomes wet. This goes against the idea that wood fibre should be able to buffer moisture in the walls, and will inevitably create air gaps between the membrane and the wall. Seems unnecessary to me!

 

"Knowing nothing of your building I'd guess that 100mm maximum" - I'm fairly sure this is referencing how much insulation you can use. If you are insulating internally you are limited on how much you can use, because the more insulation you put in, the warmer your house but the colder the stone walls become which increases risks of condensation within the structure. I think that what Redbeard was saying is that 100mm of insulation might be on the edge of being too much internally for a solid walled property. If you are familiar with U values, it would seem sensible to aim for something in the region of 0.4-0.5 rather than trying to get to modern standards (below 0.2) with internal wall insulation.

 

"What about the window reveals?" - I'm probably going to use something like a thin layer of wood fibre or mineral wool to take up the unevenness of the stonework, then a thin layer of modern PIR insulation on top, all fully taped to the windows and any airtightness/vapour control membranes but this is open to critique. Low thickness is important here to avoid impacting window size.

 

"Don't forget to ensure the wall ins touches the roof ins too." - this means that your wall insulation should be continuous with roof insulation to avoid any cold gaps or bridges. It looks like you're wanting to retain the cornice detail from your photos so not exactly sure what you'll do here but probably just careful attention to detail around the edges to avoid gaps. 

[lookseehear]

43 minutes ago, sb1202 said:

What do you mean by a service gap?

 

Ideally you would have your insulation layer with a membrane, then more battens to create a void where you can run services (pipes, wires) to avoid having them puncture your vapour control membrane, then plasterboard over the top (or dense WF and lime plaster).

[sb1202]

1 hour ago, lookseehear said:

Welcome! - Thanks

 

 

"I, too, am confused by the membrane on the cold side" - yeah, this seems counter intuitive to me at least. My thinking/guessing is that the WF will retain moisture over winter and release it during summer through the walls. As I understand it, my cottage is a typical thick walled scottish/irish construct of stone and rubble that's meant to behave like this over the seasons. 

 

"Knowing nothing of your building I'd guess that 100mm maximum" - I'm fairly sure this is referencing how much insulation you can use." - Ah! Got you. I'm only vaguely familiar with U values but I can brush up. 

 

"What about the window reveals?" - I'm probably going to use something like a thin layer of wood fibre or mineral wool to take up the unevenness of the stonework, then a thin layer of modern PIR insulation on top, all fully taped to the windows and any airtightness/vapour control membranes but this is open to critique. Low thickness is important here to avoid impacting window size."

I've seen some YT videos that use 6 or 12mm Jackoboard that can be plastered over.

 

"Don't forget to ensure the wall ins touches the roof ins too." - this means that your wall insulation should be continuous with roof insulation to avoid any cold gaps or bridges. It looks like you're wanting to retain the cornice detail from your photos so not exactly sure what you'll do here but probably just careful attention to detail around the edges to avoid gaps. "

Not bothered about the cornice - this was just left in whislt I was taking down the plasterboard. I can pop this off no probs. 

See attached pics - during the renovation, they've raised the ceiling height and you can see where the roof insutlation has been laid over. 

 

 

[lookseehear]

It's hard to tell but the most important thing with the loft insulation is to make sure you retain ventilation at the eaves - it looks suspiciously like the loft roll is pushed up against the underside of the roof.

[Redbeard]

Seem to have lost the 'quote' function:

 

OP asked why membrane on cold side and whether it would trap moisture. I had said:

 

''+1 for WF, but the existing structure will make it difficult for you to get a membrane on the *cold* side between the stone and the insulation, I think. It's ar*e-covering, but I would not want to risk moisture in the  wall  being 'wicked out' by the insulation. I would use flexi WF with a lambda of 0.039W/mK. Get one of the merchants who offers them (I am not sure Mike Wye does) to do a WUFI dynamic condensation risk assessment. Knowing nothing of your building I'd guess that 100mm maximum would be deemed 'safe', and possibly as little as 60-80. Intelligent VCL (e.g. Pro Clima Intello) on the warm side. Then plasterboard, 20mm rigid WF or 15mm woodwool.

 

The membrane would be breathable ('Gore-tex for Buildings') letting the building breathe out but keeping *liquid water* at bay. Yes, it is for a worst-case scenario, but worst-case scenarios are why sometimes work has to be undone.

 

100mm is not the gap, as queried, but the suggested maximum depth of insulation. As stated others may be even more conservative and suggest 60-80mm Thanks, @lookseehear, that's what I was saying. Remember that when you add or replace a layer to a thermal element (any bit of the building fabric which gives onto a cold outside - such as walls - or even a cold space - such as a ventilated roof void) you are within the remit of Bldg Regs and have either to meet the target U value (0.3 for walls) or come up with a jolly good reason why you cannot (interstitial condensation risk in this case. (Sorry, that's English Regs - I have just read that you are a former croft. Not sure of Scottish regs just now.

 

I would normally do a parge (air-tightness) coat of lime plaster over the wall (when I am doing rigid wood-fibre), but your wall is a lot more uneven than a brick wall (e my suggestion for flexible insulation between/behind studs) , and it does seem to be well pointed (is it sand/cement, though?), and if you do a breathable membrane (taped at all joints and perimeters) there would be less need.

 

 

 

[sb1202]

2 hours ago, Redbeard said:

"I have just read that you are a former croft. Not sure of Scottish regs just now." - Regs are here but I'm struggling to find anything for retrofit old buildings.  https://www.gov.scot/publications/building-standards-technical-handbook-2022-domestic/6-energy/6-2-building-insulation-envelope/

Historic scotland provide a doc for retrofit but don't specify any max values. Page 56 onwards for walls  - Energy Retrofit Guide

 

"I would normally do a parge (air-tightness) coat of lime plaster over the wall (when I am doing rigid wood-fibre), but your wall is a lot more uneven than a brick wall (e my suggestion for flexible insulation between/behind studs) , and it does seem to be well pointed (is it sand/cement, though?), and if you do a breathable membrane (taped at all joints and perimeters) there would be less need."

Yeah, it's very uneven large granite boulders from the local area. Pointing on the outside is lime and pointing on the internal is sand/cement. 

From what I can gather, lots of cottages on the west coast of Scotland/Ireland were renovated this way but were never insulated. Before renovations, the walls would have been bare but when they came to renovate in the 80s, due to the un-eveness, they built the studwork stood off the wall in order to get a flat/plumb surface to attach plasterboard to.  

 

I've only taken down the plasterboard in one room so far. (I have 3 rooms in total to do) but I'm getting bogged down researching and I keep ending up down another rabbit hole and not being able to get started. 

Is the solution this - breathable vapour barrier on the cold side, 50-60mm insulation between the battens then a breathable vapour barrier on the warm side, plasterboard and breathable paint?

 

Or would a more simple solution be aerogell or a wallrock type covering over the top of the existing plasterboard? 

Cheers 
 

 

 

 

 

[sb1202]

3 hours ago, lookseehear said:

It's hard to tell but the most important thing with the loft insulation is to make sure you retain ventilation at the eaves - it looks suspiciously like the loft roll is pushed up against the underside of the roof.

Yeah, they just seem to have shoved it in.  There's plenty air flowing through the roof void though  - quite a big roof space actually.

[JamesP]

We used one of the Ungerdiffutherm boards, sourced from https://www.backtoearth.co.uk

I would give them a call, very helpful. 

Did not use a vapour barrier if I remember correctly, lots of layers and cost but great final product.

 

 

[Redbeard]

Note that (unless stone was at great risk of becoming moist) I would not necessarily have been suggesting membranes if I were suggesting rigid (140-180kg/m3) WF. Flexi WF is about 50kg/m3; a different proposition and with a great deal less scope for moisture buffering.

 

I was, however, not suggesting rigid as the stone sub-strate seems v uneven. What max depth do you think a parge coat would have to go to to flatten those walls? Hard to tell with photos.

 

sb1202 said: "Is the solution this - breathable vapour barrier on the cold side, 50-60mm insulation between the battens then a breathable vapour barrier on the warm side, plasterboard and breathable paint?"

 

The membrane on the cold side (if required) would not be a VCL, but a breathable membrane ('gore-tex for buildings') rather like roofing membrane). The inner membrane is an Intelligent VCL (such as Pro Clima's Intello). Final finish for me would be lime plaster on 20mm rigid WF or wood-wool ('Heraklith')

 

 

 

[saveasteading]

I notice that your stud is only 45mm deep. that isn't strong enough for normal stiffness (it will bend if shouldered, and cracks could appear or pictures fall off.

So either add to it or replace.

100mm stud will do but more will allow more insulation but lose floor space.

I have no issue with having 100mm or more insulation. if you leave a gap from stud to stone it will look after itself. There is only so much you can do with an old stone wall.

 

Also, the roof has planked sarking boards. These have gaps between them so there is loads of ventilation.

 

3 skin stone walls have decent inbuilt properties for losing the dampness. Yours is presumably granite which is waterproof, but needs good pointing.

 

So I suggest you have the following 

600mm stone wall

gap, 25mm minimum, but it will be very variable.

vapour barrier on stud

100mm stud, containing 50mm pir board and 50mm knauf mineral wool (100mm pi is difficult to fit accurately)

polyethene layer

30mm battens

plasterboard.

 

This is likely to be how your stone walls are built, with the middle having lots of mortar.

 

 

 

[ProDave]

10 hours ago, saveasteading said:

I notice that your stud is only 45mm deep. that isn't strong enough for normal stiffness (it will bend if shouldered, and cracks could appear or pictures fall off.

That is common for old stone houses here, and you will note from the pictures the studwork is pegged to the stone wall in several places.

[scottishjohn]

I know some will say i,m making a bigger job than required

youdo not need 150mm space behind studs  50mm +is fine 

 and yes studs look very small 

 you could replace them with  larger ones and reduce space behind 

then fill with what ever your choice of insulation

 

me i would go PIR jam them in the studs and fill any gaps with foam 

 

then your vapour barier on inside of insulation  and if space and money allow  insulated plaster board --  

- foil backed pir will not absorb any moisture and will reflect cold back to the outer wall

 the most of the moisture will come from you living in there so thats why i say put it on inside of insulation and if done right there should be no cold spots to cause condensation

 attention around window reaveals  is important - behind the uprights  and under the lower  internal widow  ledge 

 

sealing it all this stage is the key so no cold spots to cause  condensation

 

you only spend once on insulation --and it pays back forever 

 

Edited Friday at 10:50 by scottishjohn

[sb1202]

11 hours ago, saveasteading said:

30mm battens

What are these for?

 

11 hours ago, saveasteading said:

I notice that your stud is only 45mm deep. that isn't strong enough for normal stiffness (it will bend if shouldered, and cracks could appear or pictures fall off.

So either add to it or replace

This is really common in these type of renovations. The studs are tied to the walls with pegs so its pretty rigid. The cottage throughout has heavy wall cabinets, bathroom is fully tiled etc and the studs are bang on plumb after 40 years. Agree that some more depth will help for thicker insulation. 

 

12 hours ago, saveasteading said:

100mm stud will do but more will allow more insulation but lose floor space.

There's enough wiggle room to sister the studs towards the wall and keep the floor space intact - will be a pain in the proverbial though

Thanks for the reply - it helps a lot.

[sb1202]

1 hour ago, scottishjohn said:

me i would go PIR jam them in the studs and fill any gaps with foam 

I've seen videos using a foil edging tape. Apparently this works better than foam. 

 

1 hour ago, scottishjohn said:

youdo not need 150mm space behind studs  50mm +is fine

Yeah, the problem is the high and low spots in the wall. I took measurements and the gap from stud to wall varies from 60mm-160mm on this one room. I'm presuming there will be similar deviations in the other rooms. 

[Ferdinand]

3 minutes ago, sb1202 said:

I've seen videos using a foil edging tape. Apparently this works better than foam. 

 

Yeah, the problem is the high and low spots in the wall. I took measurements and the gap from stud to wall varies from 60mm-160mm on this one room. I'm presuming there will be similar deviations in the other rooms. 

You arguably need both - foil edging tape does not insulate, so if you get convection currents within the gap that can bleed hear away.

If your foam bulges like Lord Bufton-Tufton's eyebrows, you can just trim it back.

[sb1202]

2 hours ago, ProDave said:

That is common for old stone houses here, and you will note from the pictures the studwork is pegged to the stone wall in several places.

Yeah - very common. I've seen this in lots of other houses I've worked on.

I found the old plans and it was spec'd by the architect for 50x45mm studs and 60mm "pillow" insulation. I've since learned that the previous owner who did the renovation was as tight as the proverbial duck's bahookie.  

[sb1202]

26 minutes ago, Ferdinand said:

If your foam bulges like Lord Bufton-Tufton's eyebrows, you can just trim it back.

This got me thinking - If wool insulation is used instead of PIR, then how do you keep the wool from bulging and falling out the back of the stud frame into the gap? String? Some king of wire tie? Is there something for this?

[saveasteading]

The vapour barrier goes on the back of the stud and holds it all in place.

We went for 50mm pir because 100 is difficult to push in precisely and leaves gaps. But squirty foam is banned by me. 

The gaps should be tiny closed pockets and mot too much heat loss. 

Don't be tempted to cut the pir well  short for ease and foam it all....I've read this is the norm by some  builders for their convenience.

50mm fits pir well enough with small air gaps.

The 50mm rockwool squeezes in over the pir and covers the gaps. Half as good insulation but a decent compromise.

 

Re the wall profile, that's as I predicted above, based on ours. You don't have to make it all the same thickness eg if one smsll area of stone is sticking out, it's ok to bridge past it in smaller stud, to keep more room area.

[Beau]

I've battened out over old wobbly stone walls a few times. I use 25mmx50mm battens fixed back to the wall with adjustable screws like this. Even though the battens are thin I've had no problems with movement. https://www.efixings.com/adjustable-screws-tx-flat-countersunk-zinc/ You can quickly create a fair wall without any complicated packing out. I will leave advise on insulation and vapour barriers to others