Insulating floor of an old stone house

[mcna1]

I’m renovating an old stone cottage in North Wales and I wish to upgrade the insulation as much as possible and I’m planning to use more natural materials in order to allow the house to ‘breath’.

The place seems to have suffered with damp in the past as there is a strong smell of mildew. I believe this may be to do with the fact that the place was renovated in the 70’s with cement render on the external walls, cement pointing to the stone work. Cement/ plaster internally and concrete floor slabs with no insulation (but it does have a plastic sheet under the slab).

The roof needs to be stripped off completely, re-slated and timbers replaced, so I’m planning to use wood fibre insulation sarking over the new rafters with either wood fibre or wool between the rafters.

The walls (about 600mm thick) will have all the cement render/ plaster and pointing hacked off and re plastered with Lime. I may also fix wood fibre board internally.

With the floor, I would like to insulate the floor and have UFH and am prepared to break up the existing concrete to lay new floors but have read conflicting advice on how to proceed.

Some claim that an old stone building should have a breathable floor so that moisture from the ground is not pushed into the walls.

Whereas elsewhere i have read that a modern floor (DPM, insulation & concrete) will be better as it prevents water vapour entering from the ground through the floor which will create internal humidity.

I am far from an expert on the matter and am seeking to learn more. If anyone has experience in this area I would appreciate all comments. Thank you

[Triumph Man]

The way I've done one recently is a Limecrete Floor system, which you can use with underfloor heating. The product we used was Ty Mawr "SubLime" https://www.lime.org.uk/applications/retrofit-insu...

which insulates as well as allowing the floor to breathe. There is, as you say, the school of thought that introducing DPMs and concrete to an older building can introduce issues. I've done insulated concrete floors in the past with no ill effects, however. In that scenario though we lined the inside of the external walls with a multifoil insulation system which stopped the warm moist air hitting the cold wall surface which would lead to condensation issues. If you are looking to simply re-plaster the walls in lime plastering, I'd consider the Ty Mawr Limecrete system above as the walls will be breathing into the room, and so will the floor.

Other issues can stem from the use of older buildings. If you understand that they are naturally "leaky" (in terms of air) you should be fine, and understand that they breathe. The multi foil scenario I mention above will still let a building's walls breathe . The issues come when people try to hermetically seal them, and use them badly, and you end up with a metric fkton of warm moist air hitting the cold surfaces.

Edited by Triumph Man on Tuesday 18th February 13:19

Edited by Triumph Man on Tuesday 18th February 13:19

[snowandrocks]

Fitting underfloor heating to a breathable floor slab with no damp proof course sounds potentially disastrous to me.

The subsoil beneath your house is an effectively unlimited source of moisture which is free to reach the surface of your new floor, where it'll then evaporate off.

Heating this surface will speed up that evaporation dramatically, the floor will probably feel dry to the touch but will be pumping lots of water vapour into the interior of your cottage.

My recommendation would be to avoid trying to make your floor breathable - if you're worried about moisture levels in the external walls, lower the external ground levels where possible, even dig French drains around the base of the walls if it's really wet. Then keep the place well ventilated and well heated.

[Triumph Man]

snowandrocks said:

Fitting underfloor heating to a breathable floor slab with no damp proof course sounds potentially disastrous to me.

The subsoil beneath your house is an effectively unlimited source of moisture which is free to reach the surface of your new floor, where it'll then evaporate off.

Heating this surface will speed up that evaporation dramatically, the floor will probably feel dry to the touch but will be pumping lots of water vapour into the interior of your cottage.

My recommendation would be to avoid trying to make your floor breathable - if you're worried about moisture levels in the external walls, lower the external ground levels where possible, even dig French drains around the base of the walls if it's really wet. Then keep the place well ventilated and well heated.

I agree with pretty much everything you've said (barring re. breathable floors) - French drains (or land drains - French drain with perforated pipe in the base) are a very good idea, and indeed we did them at the afore mentioned project with the SubLime Limecrete system. My caveat is that in the end we did not install underfloor heating, but Ty Mawr had no issues if we had wanted to (have a look at the link, it gives a detail of the build up) as we originally intended to do underfloor heating. I must admit I had my initial scepticism about Limecrete, but the sublime system seems to be doing its job, and our Client reports good comfort levels.

[strath44]

We had an ash / dirt floor in our house which the previous owner dug out in the 70s and replaced with a joist based floor supported by dwarf walls. I took the chipboard up which was bone dry and insulated this from above with Kingspan. I am not a fan of wool etc under the floor due to the large number of mice we have they would just wreck it. The floor is ventilated with a large number of air bricks and is covered at ground level in a thin layer of sand then liquid bitumen.
I dug in 300/400mm french drains round the full house and we get no issues with damp apart from one wall which still has the ground to high above floor level and this will be an easy fix.
The thing with a lot of these houses is that people used to just put up with the cold and damp, now we come along with our modern ways and want to tame the beast and have it all nice and dry and warm which is very difficult due to how much you have to change the fabric of the building to make it work. I have seen the Limecrete system discussed a fair bit and practically speaking a lot of people have good results, it looks a pita to me and the installer would need to make sure they are on it as far as bridging details etc go but I wouldn't knock it unless there is practical evidence of it causing issues.
The best you can do is research it to death and make the best decision you can and ignore anyone that give advice either way without any practical or practiced methodology to back it up!

Edited by strath44 on Tuesday 18th February 15:00

[mcna1]

snowandrocks said:

Fitting underfloor heating to a breathable floor slab with no damp proof course sounds potentially disastrous to me.

The subsoil beneath your house is an effectively unlimited source of moisture which is free to reach the surface of your new floor, where it'll then evaporate off.

Heating this surface will speed up that evaporation dramatically, the floor will probably feel dry to the touch but will be pumping lots of water vapour into the interior of your cottage.

My recommendation would be to avoid trying to make your floor breathable - if you're worried about moisture levels in the external walls, lower the external ground levels where possible, even dig French drains around the base of the walls if it's really wet. Then keep the place well ventilated and well heated.

Yes, I've read this elsewhere on the Interwebs.

I'm basically trying to understand which is the less damaging side effect, go with a breathable floor but suffer the water vapour or go with a dpm and risk pushing moisture to the walls.

And obviously, being a layman, i'm simply parroting what i've heard/ read about these options....

[C Lee Farquar]

mcna1 said:

I'm basically trying to understand which is the less damaging side effect, go with a breathable floor but suffer the water vapour or go with a dpm and risk pushing moisture to the walls.

This has been debated a number of times on here and I would suggest answered very simply.

Water will always obey the lays of physics, it can only be pushed if there is a force on it. The water is not under pressure (unless you have a high external ground level), so it cannot be pushed into the walls.

Furthermore, as other posters have mentioned, the soil beneath your floor has an inexhaustible supply of water for you to heat and evaporate off. This can then condense ad lib on your colder walls.

[mcna1]

So dpm, insulation, concrete slab is less potential risk, particularly if i make sure the external ground is lower/ drained?

I think what was clouding things for me regarding the breathable floor is that if the roof and walls are breathable then the vapour from the floor is sent out through those areas.

[C Lee Farquar]

mcna1 said:

So dpm, insulation, concrete slab is less potential risk, particularly if i make sure the external ground is lower/ drained?

I think what was clouding things for me regarding the breathable floor is that if the roof and walls are breathable then the vapour from the floor is sent out through those areas.

I can think of no circumstance that a dpm wouldn't give you a drier house.

Vapour can't be sent if there's no force acting on it, which there isn't.

I think you'd be asking too much to assume any vapour given off by your floor would 'breathe' through the walls and roof. Your underfloor heating would give off moist warm air that would condense when reaching a colder surface, like your walls. Unless your subfloor is bone dry I think there's a good chance you'd need additional ventilation to get rid of the water.

[foxoles]

mcna1 said:

The roof needs to be stripped off completely, re-slated and timbers replaced, so I’m planning to use wood fibre insulation sarking over the new rafters with either wood fibre or wool between the rafters.

There have been reports of moth infestation with the wool insulation.

[mcna1]

foxoles said:

There have been reports of moth infestation with the wool insulation.

oh, not good!

[Vanity Projects]

We had a similar problem with our house.

Bare earth foundation that had quarry tiles on it and then modern tiles with a top dressing of lino (one of our mistakes as a temporary fix). Net result, the water went up the walls and battered everything. Amusingly, the previous occupiers had injected the bricks around the floor level as if that would fix the fact there was no dpc across the whole inside of the floor.

Anyway, as ours is listed and figuring out the right approach to avoid just dropping in a cement slab and hoping it didn't go up the walls again, which it probably would, we went with a limecrete slab sitting on top of foamed glass insulation.

Foamed glass is interesting as it provides decent thermal performance but has zero capillary action so it doesn't wick moisture up from the ground into the house. The small amount of water vapour that does come from the subsoil is only evaporative and travels through the gaps, not the insulation. Insultation works both ways so the subsoil is insulated from the heat of the slab so the amount of evaporation is not that great. Certianly, we never notice the slabs wet or come downstairs to find a turkish baths in the kitchen.

From memory we got our kitchen to u0.30 with three external walls and 150mm of insulation - would have liked more but would have had to get into potentially underpinning or supporting as we dug down and I'm a chickenst.

I think the details are on my thread around this point (https://www.pistonheads.com/gassing/topic.asp?h=0&f=207&t=1618510&i=450)

We did a geothermal membrane, 150mm of foamed glass, a 100mm limcrete slab, then laid electric UFH, with a 75mm lime screed on top and then natural stone tiles with lime mortar. The stones are impgregnated with a breathable sealer and have been like this now for about six months with no problems whatsoever.

Our challenges were all in the laying/time to go off/taking levels, etc.

You could take a look at foamedglass.co.uk to get an idea of the stuff we used.

[Triumph Man]

Vanity Projects said:

We had a similar problem with our house.

Bare earth foundation that had quarry tiles on it and then modern tiles with a top dressing of lino (one of our mistakes as a temporary fix). Net result, the water went up the walls and battered everything. Amusingly, the previous occupiers had injected the bricks around the floor level as if that would fix the fact there was no dpc across the whole inside of the floor.

Anyway, as ours is listed and figuring out the right approach to avoid just dropping in a cement slab and hoping it didn't go up the walls again, which it probably would, we went with a limecrete slab sitting on top of foamed glass insulation.

Foamed glass is interesting as it provides decent thermal performance but has zero capillary action so it doesn't wick moisture up from the ground into the house. The small amount of water vapour that does come from the subsoil is only evaporative and travels through the gaps, not the insulation. Insultation works both ways so the subsoil is insulated from the heat of the slab so the amount of evaporation is not that great. Certianly, we never notice the slabs wet or come downstairs to find a turkish baths in the kitchen.

From memory we got our kitchen to u0.30 with three external walls and 150mm of insulation - would have liked more but would have had to get into potentially underpinning or supporting as we dug down and I'm a chickenst.

I think the details are on my thread around this point (https://www.pistonheads.com/gassing/topic.asp?h=0&f=207&t=1618510&i=450)

We did a geothermal membrane, 150mm of foamed glass, a 100mm limcrete slab, then laid electric UFH, with a 75mm lime screed on top and then natural stone tiles with lime mortar. The stones are impgregnated with a breathable sealer and have been like this now for about six months with no problems whatsoever.

Our challenges were all in the laying/time to go off/taking levels, etc.

You could take a look at foamedglass.co.uk to get an idea of the stuff we used.

The foamed glass is weird - you look at it thinking it will weigh as much as a good lump of coal, then when you pick it up it's ridiculously light.

[Equus]

Vanity Projects said:

We had a similar problem with our house.

Bare earth foundation that had quarry tiles on it and then modern tiles with a top dressing of lino (one of our mistakes as a temporary fix). Net result, the water went up the walls and battered everything. Amusingly, the previous occupiers had injected the bricks around the floor level as if that would fix the fact there was no dpc across the whole inside of the floor.

Anyway, as ours is listed and figuring out the right approach to avoid just dropping in a cement slab and hoping it didn't go up the walls again, which it probably would, we went with a limecrete slab sitting on top of foamed glass insulation.

Foamed glass is interesting as it provides decent thermal performance but has zero capillary action so it doesn't wick moisture up from the ground into the house. The small amount of water vapour that does come from the subsoil is only evaporative and travels through the gaps, not the insulation. Insultation works both ways so the subsoil is insulated from the heat of the slab so the amount of evaporation is not that great. Certianly, we never notice the slabs wet or come downstairs to find a turkish baths in the kitchen.

From memory we got our kitchen to u0.30 with three external walls and 150mm of insulation - would have liked more but would have had to get into potentially underpinning or supporting as we dug down and I'm a chickenst.

I think the details are on my thread around this point (https://www.pistonheads.com/gassing/topic.asp?h=0&f=207&t=1618510&i=450)

We did a geothermal membrane, 150mm of foamed glass, a 100mm limcrete slab, then laid electric UFH, with a 75mm lime screed on top and then natural stone tiles with lime mortar. The stones are impgregnated with a breathable sealer and have been like this now for about six months with no problems whatsoever.

Our challenges were all in the laying/time to go off/taking levels, etc.

You could take a look at foamedglass.co.uk to get an idea of the stuff we used.

This is a good and useful post.

And yes, in theory the foamed glass insulation provides sufficient thermal insulation/separation from the UFH that the amount of ground moisture that is vapourised into the dwelling is minimal.

In practice, there is a possibility that it won't work that way (high water table or standing ground water and the voids between the foamed glass insulation can become a very nice reservoir, for example).

As with most construction techniques, most of the time it works, but it's the times that it doesn't that you need to try to manage.

I'd also observe that ground is always damper than the inside of a house. This means that if you make floor construction breathable, the flow of moisture (even if it is not large) is always into the dwelling, not out of it. The opposite is true for breathable wall and roof elements, most of the time (unless it's pissing down or foggy outside).

For these reasons, I can see little benefit in a breathable floor, and personally I remain uncomfortable with the idea of UFH with a breathable floor construction... so far as I can see, even at best it's more a matter of how little harm it does, rather than being a positive benefit.

[mcna1]

Equus,

It was actually a post of yours on an earlier thread i came across that set me questioning the breathable floor idea.

And I’d originally started thinking about breathable floor slabs after watching You Tube videos of Peter Ward from Heritage House investigate old houses where he states that moisture can be pushed into the walls and that everything should be breathable.

May i ask, how did you arrive at this opinion?

My house is very cold. And even now, in the wet and cold climate of North Wales, it feels colder inside that out. The builders currently working on the job have commented several times that its warmer outside!

So i am seeking to improve things by 1-making it as breathable as possible (hacked off all the cement render inside and out) and 2- insulate as best i can with breathable materials (woodfibre in the roof and maybe wood panelling inside walls).

[Equus]

mcna1 said:

And I’d originally started thinking about breathable floor slabs after watching You Tube videos of Peter Ward from Heritage House

There was your first mistake.

The guy is a (very convincing) charlatan with a (very large) axe to grind. He has no real background, training or education in building technology.

There is a grain of truth behind his obsession - certainly, rising damp is over-diagnosed and there are a lot of cowboys in the damp-proofing industry - but he's developed it into a fixation that goes well beyond anything that can be supported by either the science or practical experience.

His website should be read with the same degree of skepticism you'd reserve for any other conspiracy theorist.

mcna1 said:

May i ask, how did you arrive at this opinion?

A B/TEC in Building Technology followed by a technology-biased Degree in Architecture, 4 decades interest in building science, and the same designing, surveying and altering buildings.

[mcna1]

Equus said:

The guy is a (very convincing) charlatan with a (very large) axe to grind. He has no real background, training or education in building technology.

There is a grain of truth behind his obsession - certainly, rising damp is over-diagnosed and there are a lot of cowboys in the damp-proofing industry - but he's developed it into a fixation that goes well beyond anything that can be supported by either the science or practical experience.

His website should be read with the same degree of skepticism you'd reserve for any other conspiracy theorist.

What about his opinions on making the walls and roof breathable?

I've already hacked off the render, so I hope that wasnt a waste of time! And i'm planning to cover the roof with wood fibre sarking plus woodfibre (or maybe wool) between the rafters. But that is pretty expensive

[C Lee Farquar]

I've used woodfibre fairly extensively, I have an unfounded dislike of plasterboard. It is good stuff, very fire resistant, but it does expand considerably if it gets damp, which might have a bearing if your roof isn't completely water tight.

[Equus]

mcna1 said:

What about his opinions on making the walls and roof breathable?

Breathabilty of walls and roof, I have no problem with (though again it's a lot more complicated and equivocal than Peter Ward would simplistically have you believe).

As I said above: walls and roofs are are (on average) almost always breathing moisture out of the building, which is in general a good thing. Ground bearing floors are always breathing it in, which is bad.

If you must believe in the 'wisdom-of-the-ancients-they-don't-build-'em-like-they-used-to' gnostic, then ask yourself why the Victorians (and earlier) moved to suspended and ventilated timber ground floors in their high quality, high status buildings, and left ground bearing floors to poorer-quality buildings, despite the fact that suspended timber floors are very draughty. We only reverted to solid, ground-bearing floors once we'd invented effective damp-proof membranes.

And if you must look at the overall approach simplistically, then what you should always be striving for is a thermal envelope that has its highest vapour resistance toward the inside (warm) face, and progressively less vapour resistance toward the outside. If you can achieve that, then the actual/total vapour resistance is of secondary importance (though condensation risk still needs to be calculated using dewpoint profiles, etc., if you want to be sure).

This is all basic building science, backed up by historical experience and simple common sense.

[mcna1]

C Lee Farquar said:

I've used woodfibre fairly extensively, I have an unfounded dislike of plasterboard. It is good stuff, very fire resistant, but it does expand considerably if it gets damp, which might have a bearing if your roof isn't completely water tight.

The roof is being completely redone, slates, timbers etc so at what its costing me it bl**dy well should be watertight....