External Insulation for stone walls

[SimonNorthWales]

Hi All.

Just wondering if anyone here has had success with external insulation of a stone-walled property. Ours is not made of faced stone, is detached and is not listed or in any conservation area. Therefore the visual impact of EWI is of less concern to us. The upper walls of the building (above 1st story window cill level) are modern (1970s) with wood cladding.
The property is very cold downstairs but fine upstairs, leading to mould around windows (and therefore a tendency to want to open them for ventilation) and high heating bills to keep the downstairs at even 18 degres. I don't particularly want to go down an internal route so as to avoid ripping out all the interim, and to keep as much living space as possible. I also like the idea that the walls remain as warm as a heat store through the winter.
From what I have read, breathable materials are a must as who knows what the interior of the stone walls is like. We don't want to trap condensation inside the rubble. I have read about Woodboard, Rockwool or hemp board as being the most effective.

Has anyone tried this, how effective has it been and if so was it possible as a DIY job?

Cheers

Simon

 

[88v8]

Hello and welcome.

So the upper floor was added? Cavity? Or just cladding?

Which magazine had a feature on wall insulation in the October issue, you may find in your local library.
For a detached house the payback in fuel cost saving was 2-3%, and given that one can get 5% in cash or 7% in preference shares, in monetary terms that means the payback is actually negative.

However.... mould and cold are not nice to live with.

Your walls... are they rendered? Pointed with what? Cement render or pointing inside or out will prevent the walls from breathing and that definitely conduces to cold and damp.

Solid walls do leech the heat away, worse when wet. Is mould a problem on all walls, or more so on one side of the house? In terms of bang for buck one would derive the greatest benefit from insulating the wall that gets the most weather, ie the wettest wall. Part of the reason that your upstairs is warmer, is that the cladding keeps the rain off.
Could you replicate this on the ground floor? Even clad down to 2 feet above ground, it would have a noticeable effect.

 

[SimonNorthWales]

Thanks for the insite 88v8, I will track down a copy of Which.
Yes, motivation will be comfort rather than financial. We want the house to be as consistent as possible with the least amount of fule needed.
Upstairs was added of modern construction (mix of bloc and frame as far as I can tell) on top of the Stone wall (above window sill level) and seems to be pretty well insulated.
Current walls are not rendered, one side has been repointed with cement the other is original lime, both walls see equal temperature and Mold forms around window reveals on both sides.
Stone work is pretty rough as this was built as a Stables.
We run dehumidifier and allow plenty of ventilation and heating but those walls just stay cold all winter. (it's lovely and cool in summer).
Any insulation on outside would incorporate breathable render and or cladding so keeping rain off would be additional win. Would seem to be a wasted opportunity to clad but not insulate.
We plan to add a rear extension which would at least keep one large wall warm.
Still interested if anyone has tried external insulation over stone and the solution they decided on.

 

[paulc]

Current walls are not rendered, one side has been repointed with cement the other is original lime, both walls see equal temperature and Mold forms around window reveals on both sides.

The first thing to do is measure the thickness of your wall, and then calculate the u-value. The resulting number may not be too bad. Putting EWI on will improve the numbers, but unless you can wrap the insulation around the window reveals, I'm not sure you'll get rid of the condensation in those areas - It could be, that the windows are the source of most of your heat loss, so it may be more cost effective to replace the windows (or just the units if double glazed). The use of a thermal imaging camera on a cold day will highlight areas of greatest heat loss, so you can target your funds on the worst sections. Even if you have to pay someone to do a thermal survey, that would be money well spent.

I'm in the slow process of improving the thermal performance of my 1920s semi (a mix of cavity & solid wall construction). Fitting new windows and doors to current standards has made a huge difference in comfort levels. Used to get a lot of condensation on the glass, and the rooms were always difficult to heat. Now, only minimal condensation on really cold days, and I can keep the house warm without spending huge amounts on heating.
Also been insulating some of the solid brick walls - The loss of 75mm of floor space is not noticeable even in the smallest room. The replacement window frames are a little larger than the originals, so that has enabled me to use 25-50mm of insulation around the reveals. That has reduced the impact of any cold bridging, and gives the impression of a slim profile window.