Green Building Forum - Insulating concrete slab Tue, 19 Dec 2023 08:32:25 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297641#Comment_297641 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297641#Comment_297641 Sat, 17 Sep 2022 12:58:53 +0100 michaelf
https://ibb.co/YhVksGX

The room is early 20th century, solid walls (approx. 330mm) and a double layer of slate damp proof course (the concrete slab appears to breach this looking from at heights from the outside. There are two visible air bricks, one above and one below the slates so I assume the concrete was a late addition.

Without wanting to rip up the slab, does anyone have suggestions as the best way to insulate - ideally reusing as many floorboards as possible and replacing the ones that are damaged when lifting but happy for alternative recommendations.

Thanks]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297643#Comment_297643 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297643#Comment_297643 Sat, 17 Sep 2022 13:12:49 +0100 tony Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297645#Comment_297645 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297645#Comment_297645 Sat, 17 Sep 2022 14:04:44 +0100 michaelf
Initial hope was to use as many of existing floorboards as possible so place celotex between battens and fix floorboards to those.

If there are other ideas/approaches that would a) allow me to reuse floorboards or b) not reuse floorboards but be better from an insulation/effort perspective happy to hear them!]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297646#Comment_297646 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297646#Comment_297646 Sat, 17 Sep 2022 14:57:23 +0100 tony Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297650#Comment_297650 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297650#Comment_297650 Sat, 17 Sep 2022 17:41:56 +0100 Peter_in_Hungary Posted By: michaelfWithout wanting to rip up the slab, does anyone have suggestions as the best way to insulate - ideally reusing as many floorboards as possible and replacing the ones that are damaged when lifting but happy for alternative recommendations.
What I have done in the past is
Posted By: michaelfInitial hope was to use as many of existing floorboards as possible so place celotex between battens and fix floorboards to those.

Except that I have used EPS and XPS.
I would replace the battens and use a thickness that matches the insulation thickness and fix the battens to the slab and space them to match the insulation slabs (500mm ?). I use hammer in fixings (combined screw and plastic dowel) which makes fixing quite quick.
If the batten and insulation thickness match then the boards are fully supported.
You could put a DPC down first if you wanted or thought it needed.]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297654#Comment_297654 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297654#Comment_297654 Sat, 17 Sep 2022 20:12:32 +0100 michaelf
Digging up the concrete and replacing with a limecrete slab and ufh would be the dream but time/money/current heating system don't allow!

Should there be a membrane both below and above the insulation?]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297655#Comment_297655 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297655#Comment_297655 Sat, 17 Sep 2022 20:28:37 +0100 tony
I like combined airtightness and vapour barrier on the warm side of the insulation.]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297656#Comment_297656 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297656#Comment_297656 Sun, 18 Sep 2022 08:55:00 +0100 WillInAberdeen
https://omnie.co.uk/foilboard-batten/
https://www.theunderfloorheatingstore.com/prowarm-foiled-faced-in-joist-batten-system

Not fitted these products myself (yet!) and others are available...

Tapered oak thresholds are available to take up height differences between rooms without tripping over, we had iirc 40mm difference between different parts of our last house, which were taken up by two 20mm tapers at either end of a hallway.]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297811#Comment_297811 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=297811#Comment_297811 Tue, 27 Sep 2022 06:49:16 +0100 michaelf
He said this would leave the battens open to dry rot. Given that this solution is suggested in the links above seemed odd but does anyone have thoughts on this?]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=298164#Comment_298164 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=298164#Comment_298164 Sun, 09 Oct 2022 17:59:32 +0100 wookey Membrane on top to prevent air and moisture movement (The concrete is probably just sat on the ground so not all that dry) sealed round the edges: OrconF and/or tape. Then flooring. Either these boards or something which clips together and avoids spreading at the gaps. If you keep the current boards then you may need to cut a 20-25mm batten into the insulation (rout out a space) above the membrane to keep it dry, so you have something to attach the boards to and stop them slopping about.

Tony is right that digging it all out and putting 200-300mm of insulation down there is a much better job (and doing something about the bridge at the wall - external perimeter insulation or cutting in insulating blocks). But that's a lot of work and mess. As you have a convenient batten+board height of 55mm just sticking 40mm of insulation down with 20mm of boards on top (and maybe shaving a few door bottoms to make it fit) would be easy and effective. If you can raise the floor a bit more (would another 20mm really be a problem with e.g. external thresholds?) then that's half as good again (60mm insulation is not bad in a floor - might even be good enough for UFH?).]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=298165#Comment_298165 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=298165#Comment_298165 Sun, 09 Oct 2022 18:05:49 +0100 Peter_in_Hungary Posted By: wookeyI would scrap the battens and just put down PUR or XPS of suitable compressive strength (both materials are available in 'flooring' grades which are stronger than normal). I think stronger XPS is available than PUR. That avoids both rot and bridging issues.
+1
I have also used 80grade EPS without problems.

Fine for a floating floor but if michaelf is wanting to use the original floor boards then battens will be needed to fix the boards]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=298169#Comment_298169 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=298169#Comment_298169 Sun, 09 Oct 2022 20:28:18 +0100 djh
PS Using a jackhammer is good fun if you do decide to dig up the slab, very therapeutic, but as others have said that is more work and mess.]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299002#Comment_299002 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299002#Comment_299002 Fri, 25 Nov 2022 10:45:14 +0000 michaelf
As far as I can work out there are two options:

1) Battens fixed to concrete (I've seen composite ones that could be better than timber) with insulation between, fix cement board over the top and pour self levelling compound.

2) Fix jackoboard (or similar) straight onto concrete floor and pour self levelling compound over.

Any thoughts? Is there a third (or fourth) option?]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299008#Comment_299008 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299008#Comment_299008 Fri, 25 Nov 2022 17:26:09 +0000 philedge Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299022#Comment_299022 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299022#Comment_299022 Sat, 26 Nov 2022 21:23:13 +0000 tony Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299034#Comment_299034 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299034#Comment_299034 Mon, 28 Nov 2022 14:44:24 +0000 michaelf Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299035#Comment_299035 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299035#Comment_299035 Mon, 28 Nov 2022 16:27:51 +0000 philedge
I think you can get some high performance screeds that would go over your insulation but how thin these go down to I dont know]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299067#Comment_299067 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299067#Comment_299067 Wed, 30 Nov 2022 09:29:34 +0000 michaelf Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299070#Comment_299070 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299070#Comment_299070 Wed, 30 Nov 2022 15:38:05 +0000 philedge Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299074#Comment_299074 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299074#Comment_299074 Thu, 01 Dec 2022 10:42:51 +0000 michaelf Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299157#Comment_299157 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299157#Comment_299157 Wed, 07 Dec 2022 10:59:50 +0000 michaelf
Putting a micro cement on top of a SLC on a foam cementitious board can lead to failure particularly when wheeled loads are being rolled over the top or point loading, since the board could compress.

You can apply micro cement finishes directly to concrete or over SLC applied over concrete such as Ardex K301 if left to cure for several days to achieve maximum hardness.]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299268#Comment_299268 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299268#Comment_299268 Sat, 17 Dec 2022 06:13:18 +0000 cjard
Not sure that's actually true..]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299279#Comment_299279 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299279#Comment_299279 Sat, 17 Dec 2022 23:53:07 +0000 Rick_M Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299281#Comment_299281 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=299281#Comment_299281 Sun, 18 Dec 2022 06:07:05 +0000 tony
My view is that radon barriers are not as effective as thought. The radon has escaped through hundreds of meters of rock, often granite. It is a tiny atom that can and does go through polythene! A better plan is to design in a labyrinth with a sump, then use a part time fan to suck or blow the radon out. It is a heavy atom that it tends to sink in air and can be collected and removed safely to outside.]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=300670#Comment_300670 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=300670#Comment_300670 Thu, 09 Mar 2023 12:31:56 +0000 michaelf https://www.kingspan.com/gb/en/knowledge-articles/a-guide-to-constructing-a-floating-floor/

So I'd end up with:

- Floor finish - LVT
- Tongue and Groove flooring (typically 18 mm T&G chipboard or cement/gypsum fibre boards)
- Separation layer (500 gauge polythene)
- Insulation laid continuously
- Damp proof membrane if required
- Screed (if existing)
- Concrete slab

Above I see lots of suggestions for XPS/EPS instead of PIR? What are the pro's and con's of each?

The linked guide suggests a DPC on the slab before laying the insulation, but I think I read somewhere else on the forum that this could lead to a 'bucket' effect and so better just to place above the insulation. Also, some of the guides I've seen for XPS/EPS talk about securing it to the floor with flexible adhesive which obviously wouldn't be possible if there was a dpc? Or is it fine just 'floating'?]]> Insulating concrete slab http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=301716#Comment_301716 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17570&Focus=301716#Comment_301716 Fri, 26 May 2023 14:53:04 +0100 wookey XPS pro is stronger grades, T&G edges to help keep it all flat. EPS is lowest embodied carbon. Not sure if the low-carbon stuff is available in flooring grades. EPS and XPS approx same insulation value - the denser flooring grades tend to be slightly worse insulation.

PUR/PIR is less waterproof than XPS/EPS and may get waterlogged over decades if it's soggy enough down there. If using that you'd want it above the DPC rather than below it, notwithstanding the mentioned 'bucket' risk. That's presumably why kingspan recommend that DPC location.

Floating floor is fine so long as the base is flat enough. If it isn't you will get 'bouncy' spots. Basically add some material to make it flat within 3-5mm before laying DPC and insulation. Self-levelling compound is good. Sand blinding has been suggested too. Presumably also fine so long as the ants never find it.

For the flooring layer the Cellecta gypsum boards seem good screedboard 20 or hideck 18. Immune to water unlike chipboard but no doubt much expense. They also transmit heat very well so good over UFH but you are not proposing that.]]>