Green Building Forum - Insulating solid floor, with minimal cost/disruption? Wed, 10 Jun 2026 09:30:58 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286190#Comment_286190 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286190#Comment_286190 Sun, 10 Jan 2021 10:00:41 +0000 Ebeneezer
My question is what low cost/disruption options are available for the solid floor. Digging out the concrete, insulating and covering with a new screed would be outside of the budget so is there anything worth doing that would be a significant upgrade on just using very good underlay?

These rooms will be be carpeted so if there was product with was [x]mm of “good” insulation that could have carpet laid directly on top of it that would be ideal.

I have seen the Sempafloor product but when I asked about the U-Values I wasn’t impressed. Is there anything you would recommend?


We are doing quiet a bit of improvement and these rooms will probably be the last things we do but I want to keep the floor (mostly) level across the house so if that is going to be 25mm (or whatever) higher I’d like to plan for it before we start on the other rooms.]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286193#Comment_286193 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286193#Comment_286193 Sun, 10 Jan 2021 11:02:39 +0000 Peter_in_Hungary Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286195#Comment_286195 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286195#Comment_286195 Sun, 10 Jan 2021 11:58:06 +0000 Fred56 Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286197#Comment_286197 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286197#Comment_286197 Sun, 10 Jan 2021 12:19:38 +0000 tony
I would go for external perimeter insulation and EWI too]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286202#Comment_286202 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286202#Comment_286202 Sun, 10 Jan 2021 14:18:59 +0000 Ebeneezer Posted By: Peter_in_Hungary20mm EPS then T&G OSB under the carpet will make a big difference. About 40mm rise, door threshold might be a problem but you could cut the bottom of the door to suit
Hi Peter,

Thank you , this looks like a possible option, I assume 18mm OSB?

To reduce the height difference, would fitting OSB over the floorboards in the connecting rooms be a silly idea?]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286203#Comment_286203 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286203#Comment_286203 Sun, 10 Jan 2021 14:24:34 +0000 Ebeneezer Posted By: tonyNot good on floors unless in rigid sheet form

I would go for external perimeter insulation and EWI too

Hi Tony,

In an ideal world that is what I would do. The solid floor exists where the house was extended and is on the North and East sides, which never see the sun so EWI would be great, but the extended area also has a “flat” roof and the eaves leave no overhang. So adding EWI would then involve work to the roof and costs start escalating.

Thanks]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286205#Comment_286205 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286205#Comment_286205 Sun, 10 Jan 2021 14:32:24 +0000 Ebeneezer Posted By: Fred56Aerogel
Hi Fred,

That sounds expensive, though it is something I have considered for window reveals.

Is there a supplier you would recommend for Spacetherm?

Thanks]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286208#Comment_286208 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286208#Comment_286208 Sun, 10 Jan 2021 15:34:52 +0000 tony Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286209#Comment_286209 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286209#Comment_286209 Sun, 10 Jan 2021 15:38:17 +0000 WillInAberdeen
Depending what shape your floor is, you will have a
bigger or smaller existing heat loss, so you top up the insulation to get to the legal u value or better.

If you use a basic insulation like EPS you will need a lot of it (70-100mm) So it is worth considering higher performance insulation materials like phenolic or even aerogel if you need to keep the height down.

Most of the cold comes in from the perimeter of a solid floor, so turn the insulation up the wall behind the skirting as far as possible to stop cold from bridging into your floor from the edges.

If your existing floor has a cement screed over a concrete slab, you can remove the screed to gain some depth.

Instead of plain OSB on top, you can get boards that have channels cut in them, so you can lay underfloor heating pipes while you are at it!

We found that insulating and draughtproofing the floors was a transformation for the 'livability' of our house, having warm feet makes everything else feel warmer!]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286210#Comment_286210 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286210#Comment_286210 Sun, 10 Jan 2021 15:40:25 +0000 CWatters Posted By: Peter_in_Hungary20mm EPS then T&G OSB under the carpet will make a big difference. About 40mm rise, door threshold might be a problem but you could cut the bottom of the door to suit

I would recommend fixing down 20mm battens to take the load as otherwise the EPS will break up over time.

PIR instead of EPS would give a slight improvement.

Posted By: Ebeneezer
Posted By: Peter_in_Hungary20mm EPS then T&G OSB under the carpet will make a big difference. About 40mm rise, door threshold might be a problem but you could cut the bottom of the door to suit

Hi Peter,

Thank you , this looks like a possible option, I assume 18mm OSB?

To reduce the height difference, would fitting OSB over the floorboards in the connecting rooms be a silly idea?


18mm T&G is the minimum normally recommended for floors. Personally I like my floors solid so I would go with 21mm.

Putting OSB over the existing floor boards would be fine.

If you want to tile some rooms then WBP plywood screwed down is better as the floor needs to be quite rigid.]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286211#Comment_286211 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286211#Comment_286211 Sun, 10 Jan 2021 15:49:08 +0000 Peter_in_Hungary Posted By: EbeneezerThank you , this looks like a possible option, I assume 18mm OSB?

To reduce the height difference, would fitting OSB over the floorboards in the connecting rooms be a silly idea?
Yes 18mm OSB thiner if you can get T&G - I think you might be able to get 12mm but the OSB must be T&G. It is just to spread the point loads on the EPS.

OSB on the adjacent room would reduce the difference but unless you are wheeling stuff around (or have a wheel chair) I would not expect a problem.I have a 40mm floor difference between 2 rooms with a 50mm threshold from the lower floor and don't have problems (2 year old grandson tripped a couple of times when first toddling but takes it in his stride now)

Posted By: EbeneezerIn an ideal world that is what I would do. The solid floor exists where the house was extended and is on the North and East sides, which never see the sun so EWI would be great, but the extended area also has a “flat” roof and the eaves leave no overhang. So adding EWI would then involve work to the roof and costs start escalating.


You can add EWI without roofing work by putting flashing (angled slightly to the outside) on the upper edge of the EWI, but for the EWI to work the cavity must be properly filled so first good CWI then EWI.

Edit - Cross posted with CW. If the floor is flat (without dips) then IMO a thinner OSB should be OK. A 100 grade EPS is what is used under concrete so should be OK on the floor or use XPS which is denser and harder. (over here 100 grade EPS is used under engineered wood floating flooring)]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286215#Comment_286215 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286215#Comment_286215 Sun, 10 Jan 2021 17:49:18 +0000 WillInAberdeen
So P/A = 0.5

The existing U value is from the BRE formula

U = 0.05 + 1.65(P/A) – 0.6(P/A)² = 0.725W/mK
And existing R value = 1/U = 1.38 mK/W

The max legal U value from Scottish building stds tech handbook is 0.18 W/mK. (Is subject to various getouts, but who are we trying to cheat here!)

So required R = 1/U = 1/0.18 = 5.55 mK/W

We need to add insulation to improve the R value, by 5.55 - 1.38 = 4.17 mK/ W

Using EPS with a conductivity of 0.037, we would need 4.17*0.037 = 150mm

Using phenolic with a conductivity of 0.018, we would need 4.17*0.018 = 75mm

Using aerogel with conductivity of 0.014 we would need 4.17*0.014 = 60 mm

Plus whatever surface layer on top - OSB+carpet, or more likely cementboard+ufh+vinyl in our case.]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286217#Comment_286217 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286217#Comment_286217 Sun, 10 Jan 2021 18:21:52 +0000 Ebeneezer
I agree it is job that I only want to once but aiming to achieve the higher U value’s will probably lead to a situation where perfect is the enemy of done and no improvement happens. I’ll have to weigh up the options.]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286224#Comment_286224 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286224#Comment_286224 Mon, 11 Jan 2021 00:05:55 +0000 Jeff B
Regarding the difference in level between rooms. On a different job to the one above, we made a ramp from a piece of varnished 6" timber at the threshold. It looked as though it was a part of the door frame and worked a treat.]]> Insulating solid floor, with minimal cost/disruption? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286225#Comment_286225 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16880&Focus=286225#Comment_286225 Mon, 11 Jan 2021 09:03:38 +0000 Pile-o-Stone
https://www.thermablok.co.uk/our-products/thermablok-aerogel-magnesium-floor-board/]]>