Green Building Forum - Insulating existing concrete floor in building with low ceilings

Insulating existing concrete floor in building with low ceilings

jwd — Fri, 06 Jan 2023 11:50:14 +0000

Hi

We have a stone 1800s terraced cottage in SW Scotland. It is listed and in a conservation area. I have a very low budget but I need to replace carpets on the ground floor after a flood from a burst pipe. It seems like a good opportunity to add at least some insulation. Because ceilings are low already I am limited to a couple of inches maximum for the total build up. I cant afford to dig up the slab and also wouldnt be able to cope with the disruption as we would need to move out and there is no alternative temporary housing in the area.
My plan is to use a foam or wood fibre insulation covered by a chip board or fibreboard layer. What I am not sure about is what would be the best insulation to use (pur, polystyrene, wood fibre) and where to put the vapour barrier.

Any help would be very gratefully received.

Thanks

Insulating existing concrete floor in building with low ceilings

lngn2 — Fri, 06 Jan 2023 12:35:10 +0000

You'll get a better U-Value for the thickness with PIR. Vapour barrier on top of it.

Insulating existing concrete floor in building with low ceilings

jwd — Fri, 06 Jan 2023 12:39:25 +0000

Thanks Ingn2. Do you have any suggestions for a good top layer to go on top of the PIR and vapour barrier - is chipboard the only choice?

Also would it be best to try to tape the vapour barrier to the existing DPC ?

Insulating existing concrete floor in building with low ceilings

philedge — Fri, 06 Jan 2023 13:33:32 +0000

Make sure the existing floor is flat or your new floor/insulation will be bouncy over any dips. A skim of floor leveller may be all thats needed, but get it flat if you want a solid floor.

Insulating existing concrete floor in building with low ceilings

Nick Parsons — Fri, 06 Jan 2023 14:12:35 +0000

I prefer OSB to chipboard - slightly less horrible and less likely to fall apart in the presence of water. I have done a few such floating floors with 25 or 50mm PIR and have always used heavy duty polythene rather than thin VCL - less chance of putting a work-boot through it. +1 to philedge in principle, though one of my floating floors (18mm T&G OSB on DPM(VCL) on 50mm taped PIR) is on a less-than-perfect slab and doesn't have any discernible 'boing'.

Insulating existing concrete floor in building with low ceilings

Jeff B — Fri, 06 Jan 2023 15:00:56 +0000

I agree with Nick P regarding the VCL - definitely use DPM quality polythene sheeting. We used polystyrene (EPS 100 grade not the usual EPS 70 grade). Cheaper than Celotex but less U value of course. Horses for courses etc!

Insulating existing concrete floor in building with low ceilings

lngn2 — Fri, 06 Jan 2023 16:43:22 +0000

jwd - not really placed to comment on whether OSB or Chipboard is best I'm afraid.

Your query re. taping to the DPC is a good one - I think ideally you'd put down a damp proof membrane under the insulation (if there isn't already one in the floor), tape that to the DPC and then heavy VCL (1000/1200 gauge) on top of the insulation.

Good luck with it - I sympathise as we're in the midst of relaying 100m2 of downstair floor, moving from suspended wooden floors to concrete slab, loads of insulation and underfloor heating. Indeed I'll be on my knees all weekend..

Insulating existing concrete floor in building with low ceilings

Peter_in_Hungary — Fri, 06 Jan 2023 22:25:39 +0000

+1 to the comments about insulation and DPC. Definitely worth self leveling screed. If you are strapped for cash consider click fit flooring to whatever the funds allow. This may be cheaper than OSB plus carpet.

Insulating existing concrete floor in building with low ceilings

Dominic Cooney — Sat, 07 Jan 2023 07:15:54 +0000

I am surprised that a Listed Building from the 1800s has a concrete slab, and/or a DPC (unless itâ€™s an injection DPC)
Or is there an existing DPM under the concrete slab that you are thinking of taping to?
I hate to be the one to point out that the work should probably have Listed Building Consent, itâ€™s up to you whether you contact the Council about it. The concrete slab should have had it too (unless it was put in before it was Listed)
Then you may be up against the Conservation Officer wanting breathable materials (which is pointless over a concrete floor with DPM)

Insulating existing concrete floor in building with low ceilings

Nick Parsons — Sat, 07 Jan 2023 11:10:07 +0000

Good point re Listed Bldg Consent, Dominic. I had sort of missed that in skipping to practical details.

Slightly off-topic (but not entirely) has anyone ever experimented with PIR/GRP composites? I believe these may actually exist as a 'thing' (though I am not sure in what context). Where space is at a premium such as here it occurs to me that (DPM)/PIR/GRP bonded to PIR could (a) perform the VCL function and (b) obviate the need for floorboard. Very smelly, but technically feasible...?

Insulating existing concrete floor in building with low ceilings

Jeff B — Sat, 07 Jan 2023 12:15:51 +0000

Posted By: Dominic CooneyI am surprised that a Listed Building from the 1800s has a concrete slab, and/or a DPC (unless itâ€™s an injection DPC)
Or is there an existing DPM under the concrete slab that you are thinking of taping to?
I hate to be the one to point out that the work should probably have Listed Building Consent, itâ€™s up to you whether you contact the Council about it. The concrete slab should have had it too (unless it was put in before it was Listed)
Then you may be up against the Conservation Officer wanting breathable materials (which is pointless over a concrete floor with DPM)

Pardon my ignorance, but does changing the makeup of the underfloor require consent just because it is a listed building? I'm guessing but a stone cottage built in 1800 is likely to have had stone slabs for flooring laid directly on the earth not exactly conducive to energy conservation! What's done is done (I'm assuming here the OP bought the cottage with the concrete slab already in place) and I would carry on with his plan.

Admittedly not a listed building here, but I had a similar situation here when we insulated our dormer bedrooms with IWI. In theory I should have installed sufficient insulation to meet the latest building regs for U values but it was simply not practical. I had a face-to-face discussion with one of the BCO's and he basically said just get on with it and do the best you can! I guess it all depends on how pramatic your local conservation officer is?

Insulating existing concrete floor in building with low ceilings

Peter_in_Hungary — Sat, 07 Jan 2023 13:25:03 +0000

Posted By: Jeff Ba stone cottage built in 1800 is likely to have had stone slabs for flooring laid directly on the earth not exactly conducive to energy conservation!

Unfortunately with listed buildings conservation officers don't care about energy conservation, efficiency or saving the planet - it's more important to keep everything as it was when the building was listed. Note that it is what is there when it is listed not when the building was built. So if a 1800s house has a 1950s single brick extension with a corrugated asbestos roof when it is listed then that is listed along with the original building. IMO crazy)

What jwd is doing is replacing a flood damaged carpet with a couple of inches of insulation then perhaps a new carpet. As far as I know soft furnishings (carpets, curtains etc.) are not included in the listing schedule.

In jwd position I would put down the insulation and floor covering without consulting anyone. As planned none of the floor covering will be a permanent change to the building and none of it will be attached to the building (even the click fit flooring I suggested above would be a loose laid floor)

Edit to add it also depends upon what classification of listing the building has e.g.external construction or external and internal

Insulating existing concrete floor in building with low ceilings

Jeff B — Sat, 07 Jan 2023 19:07:51 +0000

Posted By: Peter_in_Hungary
Posted By: Jeff Ba stone cottage built in 1800 is likely to have had stone slabs for flooring laid directly on the earth not exactly conducive to energy conservation!

Unfortunately with listed buildings conservation officers don't care about energy conservation, efficiency or saving the planet - it's more important to keep everything as it was when the building was listed. Note that it is what is there when it is listed not when the building was built. So if a 1800s house has a 1950s single brick extension with a corrugated asbestos roof when it is listed then that is listed along with the original building. IMO crazy)

What jwd is doing is replacing a flood damaged carpet with a couple of inches of insulation then perhaps a new carpet. As far as I know soft furnishings (carpets, curtains etc.) are not included in the listing schedule.

In jwd position I would put down the insulation and floor covering without consulting anyone. As planned none of the floor covering will be a permanent change to the building and none of it will be attached to the building (even the click fit flooring I suggested above would be a loose laid floor)

Edit to add it also depends upon what classification of listing the building has e.g.external construction or external and internal

I find it hard to believe that a 200 year old stone-built terrace cottage in Scotland would be listed for both external and internal construction. The former yes but internal? It is hardly a Georgian mansion is it! However as you say these conservation chaps are probably not interested in conserving energy. I agree the OP should just get on with it and keep his head down (which he might have to do anyway with the ceiling becoming even lower than it was before).

Insulating existing concrete floor in building with low ceilings

Dominic Cooney — Sun, 08 Jan 2023 07:33:07 +0000

Sorry to put the cat amongst the pigeons! but I did think it warranted a mention, and it is very much a technicality.
There are some very good comments here above. If it was mine I would just carry on (until such time as I could dig out and insulate - we are about to do that here after 8 years)
Now is a good time to take lots of photos to show that the concrete slab was there when you moved in.
Some other points of clarification:
BCO is Building Control Officer - deals with Building Regulations compliance which is concerned with safety and energy efficiency (not planning permission or Listed Building Consent)
Conservation Officer - looks after the Listed Buildings and is concerned mainly with how they look (and how this affects their significance) but also the long term health of the fabric of the building itself.
Planning Officer - deals with planning applications but some of them know a bit about Listed Buildings (what you are doing doesnâ€™t need planning permission)

So 3 different people, and the BCO rarely talks to the other 2 (in fact they are quite commonly a consultancy business outside of the Council)

Listed Buildings - the whole of the building is listed, inside and out, and anything attached to it. Outbuildings are normally â€œcurtilage listedâ€ because they are in the curtilage at the time of listing, so they can also be protected even though they are not mentioned in the listing.

The description in the listing is to identify the building, it does not state the only parts that are listed (a common misunderstanding)

P-i-H makes a good point about it all floating on the top of the floor. However, the Conservation Officer would be concerned about impermeable insulation driving moisture up the walls, but the concrete slab and DPM will already be doing that.

I see a lot of concrete slabs in listed buildings, most went in many years after the building was built but before the date of listing.

Insulating existing concrete floor in building with low ceilings

Dominic Cooney — Sun, 08 Jan 2023 07:36:34 +0000

Also more generally we should all be aware that there is no time period for immunity from works that should have had Listed Building Consent, like there is with planning permission.

Insulating existing concrete floor in building with low ceilings

Jeff B — Sun, 08 Jan 2023 23:10:54 +0000

Dominic - thank you for the comprehensive reply regarding listed buildings. One thing I was surprised to read is that the designation of "listed" status can take place at any time. I had assumed that all listed buildings were listed a long time ago so things like adding concrete slabs would inevitably take place after the building was listed but apparently not then?

Insulating existing concrete floor in building with low ceilings

jwd — Mon, 09 Jan 2023 11:14:09 +0000

Many thanks to all of you for your very useful comments. Ill group my responses by topic

Listed building status--
The building is Category B (equivalent to Grade 2 in England) and the interiors are not part of the listing although technically speaking that doesnt matter (Dominic Cooney is absolutely correct on this and about the lack of a "statute of limitations" for LBC). Its generally advisable to clear alterations to the fabric with planners before you start. They dont always require consent but it is sensible to ask . The original floor was removed in the 1980s when the house was renovated (with planning and listed building consent). As an escaped planner myself I can confirm its a bit of a grey area if consent is officially required for my proposal but I will take the line that this is just a floor covering akin to thick underlay! and not bother telling the council . They are far too short staffed and overworked currently to proactively seek out extra work. I wont be talking to Building Control either and will try to keep under the radar.

In reply to Jeff B - many properties have been listed in recent years that are full of non original features ( concrete floors, extensions, etc and even UPVC windows). I had many cases where we required applicants to use timber windows when replacing UPVC - much to their annoyance. It is very much down to individual conservation officers, enforcement officers and the culture of each council as too how obstructive they can be. Historic Environment Scotland are quite pragmatic though.

OSB vs Chipboard and DPCs
Thanks to Nick Parsons for the comment about using OSB - I hate chipboard with a vengeance and I hadnt thought of OSB. I also think the idea of a thicker membrane is very sensible and incurs minimal penalties in cost and thickness while gaining a great deal in terms of durability/ resistance to puncture.

Floor covering -
The Jury (SAF or spousal acceptance factor is an issue here!) is out on the use of laminate or similar hard flooring but I can see lots of advantages. There are 5 rooms involved - a living room, a bed room, a bathroom, a hall and a kitchen. The bathroom and entrance hall had lino in them before the flood and are likely to be either lino or laminate. My main worry is the kitchen which has a tiled floor (therefor no damage from leak ). I have to say I dont fancy the hassle of lifting the tiles and moving kitchen units. I was thinking of leaving it as is but I am a bit concerned with level differences between the kitchen and living room to avoid creating a trip hazard and may have to bite the bullet.

Many thanks again.

JWD

Insulating existing concrete floor in building with low ceilings

Peter_in_Hungary — Mon, 09 Jan 2023 12:05:42 +0000

Posted By: jwdbut I will take the line that this is just a floor covering akin to thick underlay! and not bother telling the council .

A very sensible approach

Posted By: jwdMy main worry is the kitchen which has a tiled floor (therefor no damage from leak ). I have to say I dont fancy the hassle of lifting the tiles and moving kitchen units. I was thinking of leaving it as is but I am a bit concerned with level differences between the kitchen and living room to avoid creating a trip hazard and may have to bite the bullet.

About half of my doors have thresholds that vary between 1" and 2" the rest are flush through. no one has a problem caused by tripping over them. You very quickly get used to a 2" difference and you will take it in your stride.
I would leave the kitchen floor as it is and avoid the expense and hassle.

Insulating existing concrete floor in building with low ceilings

jwd — Mon, 09 Jan 2023 13:45:27 +0000

Posted By: Dominic CooneyI am surprised that a Listed Building from the 1800s has a concrete slab, and/or a DPC (unless itâ€™s an injection DPC)
Or is there an existing DPM under the concrete slab that you are thinking of taping to?

I meant DPM under the concrete slab..It doesnt have a DPC or if it does its unlikely to function given that the walls are rubble stone.

Insulating existing concrete floor in building with low ceilings

Dominic Cooney — Mon, 09 Jan 2023 15:34:00 +0000

I thought that might be the case, and the 1980s permission means that you won't get blamed for the concrete floor!

Posted By: Jeff Bthe designation of "listed" status can take place at any time

yes the date that it was added to the list is shown in the "official listing" for each building/structure which can be found here:
https://historicengland.org.uk/listing/the-list/

buildings are still being added to the list, but they have to be exceptional. Britain' youngest listed building was built in 1997
https://www.dezeen.com/2022/12/01/will-alsop-la-fregate-cafe-awarded-grade-ii-listed-status/

and the Twentieth Century Society are campaigning for Peckham Library to be listed. It opened in 2000 so would be the first 21st Century Listed Building!
https://www.architectsjournal.co.uk/news/alsops-peckham-library-targeted-to-be-uks-first-21st-century-listed-building

Insulating existing concrete floor in building with low ceilings

jwd — Mon, 09 Jan 2023 15:44:41 +0000

Try this link for listed buildings in Scotland:
https://www.historicenvironment.scot/advice-and-support/listing-scheduling-and-designations/listed-buildings/search-for-a-listed-building/

Insulating existing concrete floor in building with low ceilings

Jeff B — Mon, 09 Jan 2023 22:33:41 +0000

Posted By: jwd

My main worry is the kitchen which has a tiled floor (therefor no damage from leak ). I have to say I dont fancy the hassle of lifting the tiles and moving kitchen units. I was thinking of leaving it as is but I am a bit concerned with level differences between the kitchen and living room to avoid creating a trip hazard and may have to bite the bullet.

JWD

We had this issue in my brother-in-laws house but we simply made a timber "ramp" at the threshold. It did the job and was scarcely noticeable.