Green Building Forum - Installing new floor and replastering, building regulations/control advice Wed, 22 Apr 2026 10:31:22 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274339#Comment_274339 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274339#Comment_274339 Tue, 25 Jun 2019 09:47:49 +0100 thebeacon
i have just purchased a Victorian terrace house, built 1890. It's in need of some renovation, for starters we will be taking the entire ground level floor boars up to insulate between the joists and then lay a new tongue and groove wood floor. We will also lay a new floor upstairs.

We would also like to re-plaster the walls, this would include taking the plaster off the walls (it was plastered in the early 2000s with a non-breathable plaster) and applying a breathable lime plaster. We want to use Breathaplasta, a newish lime based plaster: https://www.celticsustainables.co.uk/adaptavate-breathaplasta/

We are planning to take the floors up and lay the insulation ourselves, and then have a flooring company lay the boards. And with the plaster we will take the plaster back to the walls and then have a contractor in to plaster.

My question is with regards to Building control, i have read that if you are taking up more than 25% of a floor or more than 25% of plaster off a wall, it must then be inline with building regulations. By insulating the floor we will achieve better than the thermal target, but my concern is with the plastering of the walls on to bare brick. We really don't want to build a stud wall.

Having never done this before, what is the best route to getting approval/ when should i contact building control, before i start? Would an independent inspector be able to approve the works? It would be good to have it approved/ certificated in case we want to sell the house in the future.


Any advice would be much appreciated.


Thanks,]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274343#Comment_274343 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274343#Comment_274343 Tue, 25 Jun 2019 14:50:56 +0100 DarylP Look online, table 5 Wales,
or table 3 England.
cheers]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274344#Comment_274344 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274344#Comment_274344 Tue, 25 Jun 2019 15:01:48 +0100 djh Posted By: thebeaconWe want to use Breathaplasta, a newish lime based plaster
Seems to be over double the price of other lime plasters. Why that product specifically?

My question is with regards to Building control, i have read that if you are taking up more than 25% of a floor or more than 25% of plaster off a wall, it must then be inline with building regulations. By insulating the floor we will achieve better than the thermal target, but my concern is with the plastering of the walls on to bare brick. We really don't want to build a stud wall.

Unless you are in a conservation area, or a listed building, you will need to meet the insulation requirements of Part L for the walls, and hopefully improve on them. So either EWI or IWI. Others on here will be able to better advise. You will be able to use the council building control or an independent firm, but I don't think you're there yet.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274345#Comment_274345 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274345#Comment_274345 Tue, 25 Jun 2019 17:20:06 +0100 philedge Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274346#Comment_274346 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274346#Comment_274346 Tue, 25 Jun 2019 17:46:50 +0100 GreenPaddy
That said, I wouldn't consider going to all the trouble, and just living with cold brick walls. If you are concerned about breathability, perhaps a layer of wood fibre insulation, then your lime plaster. Got to make a big impact to what I'm guessing is a solid 9 inch wall?

You may not even then have to fully meet the regs, as the effect on the building structure of too much insulation could be argued, as an "historic" building.

Please do consider insulation, it would be such a missed opportunity, not to mention additional carbon into our blighted atmosphere. It's terraced so only 2 external walls (end terrace...3 ?)]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274349#Comment_274349 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274349#Comment_274349 Tue, 25 Jun 2019 20:55:09 +0100 WillInAberdeen
Terraces don't have a lot of external wall to breathe through, at the front you've probably got some area of door/windows/bay etc and the brick /stone finish probably matches all the neighbours. Its definitely worth internal insulation on this wall, espc if you are going to all the trouble/mess of replastering.
At the back you may have extensions kitchen/bathroom etc which may lend themselves to external insulation without disturbing the plaster.

Probably no point replastering the side party walls, or insulating them.

If you make the house warm (insulation, fix draughts) but ventilated, maybe any damp issue will be resolved without wholesale replastering?

You may need to repoint the walls externally with lime if you want to make them breathable again.

NB when insulating the floor, many people advocate laying a plastic air/vapour barrier under the floorboards, this will stop draughts but it will negate any breathability of the existing floor, so add ventilation to compensate. (We didn't use one)]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274358#Comment_274358 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274358#Comment_274358 Wed, 26 Jun 2019 09:10:20 +0100 revor Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274366#Comment_274366 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274366#Comment_274366 Wed, 26 Jun 2019 17:28:50 +0100 thebeacon
Thanks for the comments and input. Its really useful to get advice. I will do my best to answer your comments.


Posted By: djh
Seems to be over double the price of other lime plasters. Why that product specifically?


Specifically it’s a much quicker drying time.


Posted By: GreenPaddy perhaps a layer of wood fibre insulation, then your lime plaster.


This is now the plan. Thanks for signalling it. I have been reading up on wood fibre insulation. We will insulate internally on the exterior facing walls. I have been looking at:

1. Warmshell interior insulation https://www.lime-green.co.uk/warmshell/warmshell-interior.

2. Pavatex Pavadento http://www.pavatex.com/en/products/wall/pavadentro/

3. Steico https://www.steico.com/en/products/wood-fibre-insulation/


Will look at placing 40mm of wood fibre board then lime plaster. From the looks of it the Pavatex Pavadento seems pretty good. Does anyone have experience using any of these?

Should I be considering painting a breathable waterproofing on the bricks before we insulate?


Posted By: WillInAberdeen
NB when insulating the floor, many people advocate laying a plastic air/vapour barrier under the floorboards, this will stop draughts but it will negate any breathability of the existing floor, so add ventilation to compensate. (We didn't use one)


For the floor insulation I am considering using Tyvek® Supro breather membrane to hang over the joists and sit the insulation in. Then insulating with a natural breathable insulation like therma fleece sheep’s woo between the joists: https://www.thermafleece.com/. And then solid oak T+G floor boards on top. Does this sound sensible?



Posted By: revorDon't miss the opportunity to insulate the external walls. There is a chance you may have a cavity wall do you know for sure.


I dont know for sure.

Thanks so much for the responses so far.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274367#Comment_274367 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274367#Comment_274367 Wed, 26 Jun 2019 17:43:18 +0100 Nick Parsons
Ref the floor insulation, you want a VCL on the warm side. I would use Pro Clima Intello. (Other intelligent membranes probably exist).

I have used Pavadentro quite a lot, in case you want to whisper (or ask publicly, I don't mind) any Qs.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274369#Comment_274369 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274369#Comment_274369 Thu, 27 Jun 2019 01:40:07 +0100 djh Posted By: thebeaconSpecifically it’s a much quicker drying time.
Why do you want that? And again, even if you do it seems to be double the price of other hydraulic lime plasters (e.g. https://www.lime-mortars.co.uk/lime-plaster/hydraulic )

The reason I'm asking is that if you're planning to do the work yourself, and given that you say you are new to it, then I'd think that a longer working time would be more important. If you're not planning to do the work yourself, then I'd recommend letting your chosen lime plasterer specify the product to be used.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274370#Comment_274370 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274370#Comment_274370 Thu, 27 Jun 2019 08:49:30 +0100 jfb
No need to paint walls first. If putting IWI on the external walls have you considered the ceiling/wall junctions. Ideally the insulation would run all the way up the walls through the ceiling. But that is more invasive and might need the joist nearest the wall being brought in a bit to allow for the IWI to fit (if the joists run parallel to the wall). But if you are doing the floors upstairs as well might be possible. I would use inorganic insulation in the floor not sheep's wool.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274371#Comment_274371 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274371#Comment_274371 Thu, 27 Jun 2019 09:55:16 +0100 djh Posted By: thebeaconShould I be considering painting a breathable waterproofing on the bricks before we insulate?
Each of the insulation manufacturers provides specifications for how to use their insulation.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274376#Comment_274376 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274376#Comment_274376 Thu, 27 Jun 2019 14:46:32 +0100 thebeacon


Posted By: Nick ParsonsTaking the new SAP 'base case' U value for a solid 225mm wall as 1.7


what’s the SAP Base case?

Thanks i might ask some more questions re pavadentro. Are there alternative products? just pricing it up and its pretty pricey. i have 60sm of wall to do.



Posted By: djh If you're not planning to do the work yourself, then I'd recommend letting your chosen lime plasterer specify the product to be used.


We won’t plaster ourselves, so will speak with a plasterer re what product to use. Have been trying to research a good lime plaster to use. I spoke with Mike Wye and they suggested a lime plaster that works with Pavadentro.



Posted By: jfbIf putting IWI on the external walls have you considered the ceiling/wall junctions. Ideally the insulation would run all the way up the walls through the ceiling. But that is more invasive and might need the joist nearest the wall being brought in a bit to allow for the IWI to fit (if the joists run parallel to the wall). But if you are doing the floors upstairs as well might be possible.


I haven’t considered this. Thanks for bringing it up. Would i be able to insulate to the ceiling and then under the floor boards in the room above to the topside of the downstair ceiling, without removing the ground floor ceiling?



Posted By: Nick ParsonsRef the floor insulation, you want a VCL on the warm side. I would use Pro Clima Intello. (Other intelligent membranes probably exist).




Posted By: jfb I would use inorganic insulation in the floor not sheep's wool.




We want to use a breathable and hygroscopic insulation. Sheep wool is both of these, but i am weary of using it. what suggestions do you have?

Floor wise, will go with

Solid wood t+g oak floor
Pro Clima Intello VLC
joists with insulation (breathable hygroscopic)
layer hanging over joists to sit insulation in (what should this be)
additional layer required under joists?


What should i hang over the joists to sit the insulation in? And does there need to be another airtightness layer under the joists?



Thanks again.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274377#Comment_274377 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274377#Comment_274377 Thu, 27 Jun 2019 16:32:14 +0100 djh Posted By: thebeaconWould i be able to insulate to the ceiling and then under the floor boards in the room above to the topside of the downstair ceiling, without removing the ground floor ceiling?
It depends which way the joists & floorboards run. If the joists run into the external wall then you can take up a few boards to add insulation. If they run the other way you would have to cut the ends off all the boards and it would probably be simpler to cut the edge of the ceiling plaster out and replace that instead. Cutting out plaster and making good afterwards is relatively straightforward unless there are cornices or suchlike and if you're doing IWI you would have to deal with those anyway.

We want to use a breathable and hygroscopic insulation.

Hygroscopic usually means organic, which means it can rot, which is usually not a good idea under floors. There are mineral insulants such as (uncoated) perlite, vermiculite and leca but most people don't see a need for hygroscopicity so tend to use mineral wool or suchlike.]]> Installing new floor and replastering, building regulations/control advice https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274382#Comment_274382 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16161&Focus=274382#Comment_274382 Thu, 27 Jun 2019 22:32:32 +0100 Nick Parsons
There are other makes of wood-fibre available. Steico and Gutex are both, I think, cheaper than the Pavatex range. The methods of manufacture are slightly different and I think Pavadentro has been shown to be rather better at moisture-buffering, though I cannot remember the source for that assertion.]]>