Insulating floor of an old stone house
Discussion
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 chickens
t.
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.
Thank you so much for posting this- You have basically just described our house- except we're not listed, thank god. 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 chickens
t.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.
was the limecrete slab harder to lay (ignoring the levels) than a concerete slab and was it much more expensive?
PugwasHDJ80 said:
Thank you so much for posting this- You have basically just described our house- except we're not listed, thank god.
was the limecrete slab harder to lay (ignoring the levels) than a concerete slab and was it much more expensive?
It's not really any harder to lay but the science of lime is different. you can't just pur the slab and then dry it out in three days and crack on.was the limecrete slab harder to lay (ignoring the levels) than a concerete slab and was it much more expensive?
The slab needs to be exposed to air for at least 48 hours ideally with so much a couple of weeks to carbonate beofre it cures otherwise it doesn't work properly and can fail.
It is more expensive as a bag of lime if about £11-£12 verus £7 for cement and when doing a floor, few compaines do cement mixer trucks that can just pipe it in so it's a case of a days labour for three lads and a s
t load of wheelbarrow and spazzling.The foamed glass is also more expensive in as much as you need more of it to get the same thermal efficiency.
I don't remember the exact costs but I think we didn't see change out of £1500 in material for the insulation, limecrete slab and screed.
the webiste mentioned in an earlier post has an online materials calculator so once you've put the numbers in there you can go to Mike Wye, Travis Perkins or womersleys, etc and price up the materials.
As Equus mentioned earlier though, I went this route as the best way to stop damp in the existing building, if I could have lifted the whole kitchen up and slid a proper dpc through the bottom of the brickwork to the great outdoors and then chucked kingspan and cement down, that would have been my preferred choice.
There is no damp in the victorian sections downstairs as they are floating beam and wooden floorboards. However, they are draughty!
What with storm Ciara and Dennis, it's like being Kelly Le Brock in *that* Lady in Red scene every morning in my dressing gown - the dog is traumatised.
As for breathable walls, they're a good idea - Although using non-breathable latex paint is better at telling you there's a leak on the the outside wall because all the efferfesence helpfully bubbles up under the paint so the blisters help you find another place to burn some cash...
Vanity Projects said:
The foamed glass is also more expensive in as much as you need more of it to get the same thermal efficiency.
There is, of course, the distinct possibility that where it works, it's not working for the reasons you might think it is.As discussed above, there's no basis in terms of building physics to think that a DPM will 'force' damp up the walls, and there's a very good basis in terms of building physics to assume that a breathable floor will actually admit more moisture to the building, and make things worse.
Provided the water table is not too high, though, the mere act of digging out the damp soil and replacing it with a layer of non-absorbent, non-capillary material (the foamglass) would dramatically improve the situation on its own... nothing to do with the breathable limecrete floor over the top of it, and it's possible that a modern DPM and concrete floor over the foamglass might improve things still further.
Vanity Projects said:
if I could have lifted the whole kitchen up and slid a proper dpc through the bottom of the brickwork to the great outdoors and then chucked kingspan and cement down, that would have been my preferred choice.
I have seen this done to the rear part of a Victorian house. A high water table and no sign of an existing dpc meant all attempts to keep the walls dry had failed.They installed a lead dpc by removing bricks and rolling out a lead dpc, rebuilding the disturbed bricks and moving along. Similar process to underpinning. Should solve the problem for a few hundred years. Time consuming and you need some patience buy very low material cost.
I had an ash lime floor without dpm, dug it up, dpm, insulated underneath and around the perimeters, and put concrete in.
Stuff doing this foamed glass nonsense. It’s touted as the best thing in the lime render “sustainable” world, it’s just a money making scam imo. Think about it, it’s all wrong imo, outside walls ok with lime, inside not so much, batten out with wood or metal and plasterboard. Easy
Stuff doing this foamed glass nonsense. It’s touted as the best thing in the lime render “sustainable” world, it’s just a money making scam imo. Think about it, it’s all wrong imo, outside walls ok with lime, inside not so much, batten out with wood or metal and plasterboard. Easy
When we moved in we were advised ‘the cellar sometimes gets a bit of water in’ and I’d certainly suggest before anyone goes batst crazy on their flooring they check for underlying issues with water.
The cellar is full height and a level lower than the kitchen (obviously but not under the kitchen directly.
It is therefore a good way to gauge where the water table is/was. It’s peaked at my kneecaps in the past (burst water pipe) but whilst the damp were having in the kitchen walls was going on, the cellar floor was dry, as much as a cellar is ever actually ’dry‘.
We certainly did a lot of water resolution and over the years have addressed...
- A water leak (via a request for a £7000 water bill from Yorkshire water - they wrote that down to £100)
- Fixing the down pipe that drained direct to ground,
- Fixing the underground pipe that had been cracked by a tree root and was draining under the house,
- Fixed the fall of the slabs to be away from the building instead of guiding water into it,
- Fixed the gaps right through in the pointing from the outside that were helpfully telegraphed to us by the wife stepping on a massive slug one morning...
Having eradicated all that, nothing was going up the the newly plastered kitchen walls (this part of the house has engineered colliery bricks so it was plasterboard not lime on the walls) but the floor had areas that were very cold and damp.
As a stop gap to getting a new floor, we rolled a Lino out. Within a few months of doing that, the lower few feet of the plasterboard went manky as hell and when eventually the Lino up for work to be done, it was a bit ‘sweaty’ under there.
I’d have suspected external factors again were it not for the fact the chimney breast that sits well inside the house, has no external walls near it (as it abuts the old property) and the only place moisture could get to for that was from the ground.
TLDR, damp isn’t magic, it comes from water so check all obvious sources first before undertaking more expensive invasive stuff, etc.
It’s worked for me, ymmv.
t crazy on their flooring they check for underlying issues with water.The cellar is full height and a level lower than the kitchen (obviously
but not under the kitchen directly.It is therefore a good way to gauge where the water table is/was. It’s peaked at my kneecaps in the past (burst water pipe) but whilst the damp were having in the kitchen walls was going on, the cellar floor was dry, as much as a cellar is ever actually ’dry‘.
We certainly did a lot of water resolution and over the years have addressed...
- A water leak (via a request for a £7000 water bill from Yorkshire water - they wrote that down to £100)
- Fixing the down pipe that drained direct to ground,
- Fixing the underground pipe that had been cracked by a tree root and was draining under the house,
- Fixed the fall of the slabs to be away from the building instead of guiding water into it,
- Fixed the gaps right through in the pointing from the outside that were helpfully telegraphed to us by the wife stepping on a massive slug one morning...
Having eradicated all that, nothing was going up the the newly plastered kitchen walls (this part of the house has engineered colliery bricks so it was plasterboard not lime on the walls) but the floor had areas that were very cold and damp.
As a stop gap to getting a new floor, we rolled a Lino out. Within a few months of doing that, the lower few feet of the plasterboard went manky as hell and when eventually the Lino up for work to be done, it was a bit ‘sweaty’ under there.
I’d have suspected external factors again were it not for the fact the chimney breast that sits well inside the house, has no external walls near it (as it abuts the old property) and the only place moisture could get to for that was from the ground.
TLDR, damp isn’t magic, it comes from water so check all obvious sources first before undertaking more expensive invasive stuff, etc.
It’s worked for me, ymmv.
Edited by Vanity Projects on Friday 21st February 23:49
Equus said:
There is, of course, the distinct possibility that where it works, it's not working for the reasons you might think it is.
True but at least it’s working somehow 
Equus said:
As discussed above, there's no basis in terms of building physics to think that a DPM will 'force' damp up the walls, and there's a very good basis in terms of building physics to assume that a breathable floor will actually admit more moisture to the building, and make things worse.
I’d agree in principle, particularly since the affected bricks were engineering bricks and nowhere near as porous as the handmade parts of the house but ’I seen it with my own eyes m’lud’ so science be damned, something weird was happening.Equus said:
Provided the water table is not too high, though, the mere act of digging out the damp soil and replacing it with a layer of non-absorbent, non-capillary material (the foamglass) would dramatically improve the situation on its own...
Agree, and I kind of wanted this for partly that reason anyway, even if the breathability and slab etc is snake oil at least the reduction in capillary action and the drier void have has created ‘breathing space’ (in a different sense of the word) from damp ingress.
Equus said:
Nothing to do with the breathable limecrete floor over the top of it, and it's possible that a modern DPM and concrete floor over the foamglass might improve things still further.
It was possible a modern dpc and slab would work and both I and the builder (the proper conservation one - long story, see thread) debated the two options and everything in between.In the end it was my gut that said to go with breathable because I was sure it would be the least open to failure. I was perversely afraid of going modern and having it f
k up and having to explain to the wife we’d have to hack it up and off the walls and do it again.Then it was simply a case of rationalising the extra costs away in my head, not unlike buying a car...
Vanity Projects said:
Equus said:
As discussed above, there's no basis in terms of building physics to think that a DPM will 'force' damp up the walls, and there's a very good basis in terms of building physics to assume that a breathable floor will actually admit more moisture to the building, and make things worse.
I’d agree in principle, particularly since the affected bricks were engineering bricks and nowhere near as porous as the handmade parts of the house but ’I seen it with my own eyes m’lud’ so science be damned, something weird was happening.From your description, you've told me nothing that suggests that it was an un-breathable floor that was 'forcing' the moisture up into the walls and causing the problem. The fact that you had walls without an effective DPC sitting in damp ground would have been enough on its own.
Contrary to Peter Ward's rabid ramblings, rising damp very much does exist. And if that's what you were suffering, simply the act of digging out the damp soil and replacing it with foamglass (or some other insulation material that doesn't transmit moisture) may well have cured the problem in itself. It is entirely probable that the 'breathable' limecrete floor is at best a red herring, and at worst is actually performing less well than a modern floor with a DPM would at preventing admission of moisture to the building. It is least open to failure, because it has 'failed' already (a concrete floor would admit less moisture to the building, even with a failed DPM... that's a simple, incontrovertible fact, based on its measurable vapour resistivity).
If I told you that a sure and certain cure for your headache was to drink a glass of water steeped in willow bark, then strangle a small chicken to death while dancing naked thrice widdershins around blackberry bush at midnight, it would very probably work. Point being, of course, that it would be the willow bark (aspirin) that did the trick, and an innocent chicken would have died entirely unnecessarily.
There are tribes in Peru who are firmly convinced that their Shaman blowing smoke up the nose of a small crocodile will cure asthma... until someone can explain to me a scientific mechanism why this should be so, I'm as reluctant to believe that as I am to believe Peter Ward.
I’m not disputing your expertise or experience (I have a sample size of 1 and therefore not statistically significant).
I’m just pointing out that I’d pretty much thought I’d covered every eventuality or root cause I could think off so was a bit baffled, the only thing I could identify that changed was the putting down of Lino that prevented moisture escaping the floor and when that was taken up again (it was up a few months (in autumn/winter) for a period before the work, the walls dried again.
It’s an isolated case that we can’t evidentially investigate on an Internet forum so let’s park it.
I’m not saying you’re wrong (and that’s written straight, not in the condescending way I say that sentence to the wife). I’d love to know the root cause as understanding this stuff interests me.
I don’t subscribe to the Heritage House, do it all old school and don’t forget the pagan goat rituals to be 100% certain, but tried to research as thoroughly and diversely as I could before going this way.
If anything it highlights the challengers older building owners have in finding the right (reliable) sources for info for this stuff, the local conservation team added little in terms of insight for this phase.
I’m just pointing out that I’d pretty much thought I’d covered every eventuality or root cause I could think off so was a bit baffled, the only thing I could identify that changed was the putting down of Lino that prevented moisture escaping the floor and when that was taken up again (it was up a few months (in autumn/winter) for a period before the work, the walls dried again.
It’s an isolated case that we can’t evidentially investigate on an Internet forum so let’s park it.
I’m not saying you’re wrong (and that’s written straight, not in the condescending way I say that sentence to the wife
). I’d love to know the root cause as understanding this stuff interests me.I don’t subscribe to the Heritage House, do it all old school and don’t forget the pagan goat rituals to be 100% certain, but tried to research as thoroughly and diversely as I could before going this way.
If anything it highlights the challengers older building owners have in finding the right (reliable) sources for info for this stuff, the local conservation team added little in terms of insight for this phase.
Just a quick follow up regarding the underfloor heating.
So the floor build up will go:
1. hardcore
2. sand blinding
3. dpm
4. concrete slab
5. insulation
6. screed with UFH pipes
Which is better, having the insulation above or below the concrete slab?
And, any suggestions for floor insulation,? I've read Kingspan is very good.
thanks
So the floor build up will go:
1. hardcore
2. sand blinding
3. dpm
4. concrete slab
5. insulation
6. screed with UFH pipes
Which is better, having the insulation above or below the concrete slab?
And, any suggestions for floor insulation,? I've read Kingspan is very good.
thanks
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