Insulating a Stone Walled House

Following on from my thread about heating, can you let me have your thoughts please on the following.

The scenario is two terraced houses, front and rear external walls of about 500mm stone, plastered inside and out , with similar party walls between them and the neighbours on both sides.

The ground floors are concrete and tiled.

The bedrooms are on the first floor, timber joists and floor boards, with an attic overhead.

How would you approach insulating such houses?

Doublage (Dry lining) - a metal framework is built preferably 200mm inside the walls, the cavity is filled with fibreglass insulation, plasterboard fixed to the metal framework then taped & jointed. It is a very common thing to do.

Polystytene extruded is better than expanded and needs about 50% of the thickness of spun fibre insulation. Fibre glass is cheap but doesnt last as it hydrophilic and once damp collapses its structure. Rockwook is much better as it is hydrophobic and doesnt attract damp also doesnt collapse so lasts longer. Rockwool also prevents the spread of fire should it occur much better than the others. You should use a vapour barrier to prevent moisture getting into the insulation space and creating mold.
External insulation is generally better as it stops thermal bridging but usually more expensive and planning may not allow it.

First on the list is to insulate the attic with at least 30cm of good quality insulation, and if the party walls do not go all the way up to the ridge, then construct a fire retardant wall to divide your attic from that of the neighbour’s.

For the walls, changing the exterior appearance needs planning permission which is a pain in the neck, and is often subject to the personal whims of local officials.
Insulating the inside is much cheaper, far less hassle, and easily within the capabilities of most folk who can use basic tools.
Polystyrene panels glued directly to the existing (sound) surface work well. Plasterboard is available with the polystyrene already glued onto the back, and a sheet of 10mm board with 40mm polystyrene glued thereon is actually lighter to handle than a standard sheet of 13mm thick board.
I used a base layer of just plain polystyrene panels first. They come in different thicknesses, so by using combinations it was easy to make the walls vertical.
This also allowed the easy cutting of channels for pipes and cables to be hidden behind the final surface. The final layer had the joints offset to the under layer in order to create a completely waterproof surface. Fill and sand the joints, and then direct decoration onto the board surface preceded by a couple of coats of sealer to keep paint costs down. (I make my own sealer from the cheapest white emulsion I can find with some PVA adhesive added.)

For the ground floors, if there is sufficient headroom available, I would basically construct a wooden stud partition frame laid across the floor on top of a continuous damp proof membrane (plastic sheeting). Drill through the frame for whatever pipes and cables are needed and then fill the spaces in the frame with insulation, then OSB board onto the frame, and then the final surface to your preference. I found that laminate flooring onto a 3mm cushioning layer works really well for various reasons.
It will of course be necessary to adjust the doors to accommodate the raised floor level.

With appropriate planning you will be able to cover and hide all the cables and pipework as the insulating process proceeds.

What you will end up with is an insulated box within the pre-existing structure that has smooth, clean, sound, vertical, and flat surfaces that make installing cupboards and fitted wardrobes so much easier.
Good idea to insulate the party walls as well. Not only will it reduce damp and noise transmission, but an empty house next door can rapidly end up being markedly colder inside than the air outside in the street.

The question of insulating between the living rooms and the bedrooms on the upper floor is more a matter of reducing sound transmission than anything else. You may wish to consider the inconveniences of the sound of the TV rising up into the bedrooms, or indeed the noise of other activities permeating downwards. It’s a question that is greatly affected by who is going to be living there.

Complete insulation will of course substantially change the appearance of the interior of the building. I know some folks who just love the look of the old stone, but then they have deep pockets that can afford the heating and dehumidifying costs that go with that medieval look.
Personally, I like clean, dry, warm, straight, and cheap to run.

Some of your suggestions are sensible and helpful for a DIY enthusiast but your insulated floor idea creates more problems than it answers. A floor section you propose would be at least 100mm thick and to simply adjust doors to suit isnt going to work. Factor in door frame head hieght, new skirting boards, the inconvenience of lower door handles, electric wall sockets/light switches, lower window cills and a view through them that you have to stoop to enjoy and many more hiccups it creates…

There are many imaginative ways to insulate to create a cheap to run property without the need to sit looking at an insulated box.

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Actually, that isn’t the case. I used 50mm square timber resulting in a total rise in finished height of 75mm. By keeping the frame spacing fairly close together it enables the use of thinner OSB panels (14mm).
The other factors you mention may, or indeed may not, be relevant depending on the way the building was constructed in the first place.
Insulating the inside of the walls means new skirting boards in any case, and makes it very easy to site electrical outlets and switches at whatever height is desired.
The existing door frame head height was 2m10 in my home, so losing 75mm was not a problem.
The upper edge of our window openings is beyond my reach ( I’m 6ft 1) so there is no way I need to stoop to see out. Slightly lower window sill – Yes, but then at what height is the old one in the first place, and does the renovation involve replacing the windows anyway ?
As for the doors, well some doors lend themselves to just having 75mm cut off the bottom. Others will no longer be needed at all if the householder prefers open plan, and sometimes doors are just ancient and knackered and need replacing anyway.
Our solid, tiled, and very cold ground floors were actually at slightly different levels in different areas and were a considerable ‘trip’ hazard, so using the timber frame method was good not only for insulating, but also for creating one level all the way through.

All of these old stone houses are very individual in their structure, and so a concept that will work well in one building may not be suited to another.
@Mike313 has the right idea in asking for different views, because with these old houses it is always like doing a jig-saw when it comes to finding the right pieces to fit in the right places for the particular building concerned.

I do entirely agree that well insulated does not have to be visually boring. Original beams can be left visible, and old windows, doors, and cupboards can be refurbished and re-used if that is the desired style. New moldings can be fitted and fireplaces revamped.
However, I have always found that the more twiddly bits that are included, then the higher is the cost and the longer the job takes. So it just becomes a matter of personal preference coupled with having to cut one’s cloth according to one’s means.

Thank you very much indeed for such comprehensive replies. Very helpful :slight_smile:

The owner of an old (100 years +) stone house just a few doors away from me is in the process of insulating the building by using polystyrene blocks attached to the outside walls. May be worth investigating further?

My home has stone walls ranging in thickness from half to one meter.
In most parts the previous owners constructed metal studs frames with plasterboard. The result is tremendous heat loss and very cold surfaces. The only good thing is that any damp from the walls and earth floor can arise through gap between the walls and plasterboard.
To remedy this I intend to fix plasterboard back with a polystyrene layer onto the existing plasterboard.
Depending upon the results of that I may then use thermal wallpaper.

Ideally when the renovations were first carried out, the previous owners should have left a gap between the walls and a OSB-rockwool-polystyrene/plasterboard sandwich.

I recently bought a Black & Decker Thermal Leak Detector from Amazon France - worth every cent!

A rather different approach, based on vernacular traditional work and eco-building techniques:

  • walls plastered with two coats of chaux/chanvre lime and hemp mix, 5cm thick each; except the party wall and any internal walls which you can keep bare stone if you like. Big advantage if you have an older house and walls are not 100% straight, you can easily fit the odd angles.

The attic is easy if you’re not planning to use it. Wood cellulose fibre or even wool ; plenty of different materials that are easy to install.

Floor: this may be too much trouble, but it is fabulously toasty. Get rid of the concrete and dig out to 50cm depth; then lay gravel herisson, dalle de chaux or pozzolane, and terracotta tile on top. (That’s a very rough description, there are various details… but masons differ in exactly how they work. The broad plan is pretty much the same.)


Dont forget the DPM under the build up materials as moisture will reduce the insulation properties.
Personally I wouldnt dig out as much and would DPM and ridgid insulation, what are your thoughts?

Isn’t the whole point of using the materials that @Andrea_Kirby mention is to absorb the damp, rather than drive it into the walls which would be the case if a DMP was used?

The DPM is to stop damp from excavated ground from rising into the material above rotting the floor or causing a cold floor and a huge condensation problem.

DPM always essential in my book. Good overlaps and proper sealing, plus bringing it up the walls to well above finished floor level.

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At a rather different price as well.

I’m with you. Chaux/chanvre or terre/chanvre (from the garden if your soil has enough clay). Stone walls need to breathe.


I used this for the walls and and interior roofing, which had already been insulated with some other material, (can’t recall what exactly). It is fabulous. I have a chartreuse some 30 metres long x 6m wide. Parts of the building are 3 floors high and one Jotul log burning stove keeps the place really snug thanks to the insulation. Before the insulation it was cold…cold…cold

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Sorry, forgot to add the link from Point P to my post. Here it is: Doublage isolant Prégytherm R1,15 - polystyrène graphité - 2600x1200 mm - ép. 10+40 mm - R = 1,15 m².K/W