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I know this came up in another thread but I wanted to ask specifically in case any builders and insulation people are around.
Void under a concrete floor, by the look of it maybe 0.5-1m high. How to insulate if I cannot gain access? I thought I could get in through the garage floor but I actually don't think the void goes under the garage.
- I could drill a few holes and pour in loads of expanding foam mix*.
- I could drill a few holes and buy tons of polystyrene balls and pour them in through a giant funnel*.
- I could consult a professional - but who? Is this even a thing?
* not serious - although the foam one would be great fun I don't want to explode my house 🙂
You probably don't. The block and beam is likely over a bed of gravel/shingle below that just dirt. it needs to maintain airflow underneath ideally. You would go over the top with kingspan type board, then screed over that ... in normal circumstances.
I am not a builder, but do own a block and beam floor Im currently working with and this was my conclusion.
I think what he said sounds about right ^
The void may also be there for very good reason, e.g. for ground gas protection, so filling it up may lead to bad things. Insulating over the top is likely your best bet.
There is definitely a void - the floor is hollow when you stamp on it. The front of the house is above the ground on the right hand side, with steps up to the front door.
I don't want to put Kingspan over the top of the floor and then more screed, that's going to take too much height from the doorways and might even require a whole kitchen refit.
We have tiles down now, which are clearly very cold feeling. The only over-floor option I can think of would be to remove the tiles and then underlay underneath vinyl. If we were to put vinyl down, because it's so thin we would probably be able to fit another 20-30mm of insulation, but I think Kingspan is not rigid enough to be put under vinyl and walked on, or even directly under thin laminate?
so filling it up may lead to bad things
Yes, of course. Ideally I'd get under there and stick a thick layer of kingspan underneath - but thinking about it, the concrete above would still have a high thermal mass.
The void may also be there for very good reason, e.g. for ground gas protection, so filling it up may lead to bad things. Insulating over the top is likely your best bet.
generally its for either:
clay soils which can lift or sink a normal floor slab, so instead the floor spans between the main buiding foundations, which will be at the required depth.
property built on a slope, large amounts of backfilling would be required to level a traditional slab, so quicker and easier to use B+B.
the bottom of the B+B floor should be ventilated, which means not completely filling the void with foam (cant imagine how much foam this would need!) or polystyrene
insulate on the top.
If you have 30mm then a 15mm XPS base and a 13mm laminate would be my choice.
How thick is the floor?
I suspect insulating underneath it would be pretty pointless, unless you're actively heating the floor, as there's not 'that much' heat lost from the air into the floor.
(Walls are different matter)
If you're talking about "UFH" then you might be better adding insulation on top of the concrete.
but I think Kingspan is not rigid enough to be put under vinyl and walked on, or even directly under thin laminate?
I agree.... It's not made for that kind of loading.
I'm not sure anything would be OK under vinyl as it's got too much "give" and needs to be on a hard surface.
Got the same issue here, there is insulation under our floor but only 50mm and very poorly fitted from the access photo I had when the extension was added a couple of years ago. The only thing I have read on someone improving it was blowing the cavity polystyrene beads in and I assume glue maybe. This is not advisable apparently as others have stated, gases need to be ventilated away even if you have a radon gas barrier (I have) and also I've read a few opinions on the concrete beams not sitting there saturated from condensation due to no ventilation. You would need to get clearance/advice from the local council to be honest and I doubt they will have a clue.
My only option is to dig up the screed we have sat on top of our beams, potentially somehow pull our the blocks between beams and lay insulated blocks of some description and then pir board and then concrete/screed/whatever and floor finish on top. Issue with this is I do not know how much depth I have and this will cost a fortune plus the mess on top of it.
Floor in this cold weather is at 11C at one end of the kitchen and by the front door, and 14C at it's warmest. Always cold to walk on at any time of year. It does help in summer though!
House is on a slope yes.
There are various underlay things for UFH use with an R of 0.19. A rough calc suggests that would result in a reduction of about 400W ish at typical temps.i reckon there's about 1.5kW going in there when the heating is on. So potentially significant.
I could fit that underlay and click-fit flooring this year then next year, funds allowing, I could lift it up and put UFH under and refit the flooring.
the concrete above would still have a high thermal mass.
Excellent, the more the better as it brings temerature stability.
As ajaydoubleyou says the void is probably there to compensate for the house being on a slope. You're in an area which has moderate radon levels but I doubt that's the reason for the void, if it was there would be so many vents you'd find one you could see in through. So it's just a void and you'd like to get in to insulate whcich seems like a good idea if you can.
If there were really no vent at all I'd drill an inspection hole to see what's there and take it from there. If I could see a place where I could cut an access hole without destroying the structural integrity of the floor I'd then get a diamond disc spinning, fit a 650mm wide trap and get down there digging and insulating under the floor.
That's what I'd like, I think. I could fit much thicker insulation. But Id need to be very careful with the hole cutting.
All of the floors we install are beam n block all have a 200 m void minimum under all are insulated and screeded over b n b
Some need gas barriers but none are insulated under most blocks are standard sizes so could be broken out to allow access (440mm)and replaced easily you can get through 440mm can’t you? TLDR insulation over b n b
Should I have insulation under the flooring already?
Are you suggesting removing the blocks like you would bricks?
The pictures on the internet look like the blocks go in dry but they are a bit close together!
Rather than go through the floor take some bricks out?
How old is the floor/house. You should have insulation on top of the floor them a screed to bring you up to finished floor level..
As mentioned above the void would be there to serve two purposes. Firstly to allow ventilation for ground gases, CO2, methane, radon etc. 2nd is to provide a void for expansive soils to expand into, called ground heave. Is it possible to insulate from above? Appreciate this will probably raise finished floor levels. Load bearing insulation is a thing and it’s something I used to help architects specify.
Rather than go through the floor take some bricks out?
Considered it, but.. dunno.. the inner wall is thermolite block and seems awfully fragile.
I am now thinking of the insulating above. There are tiles down there now, they could be removed I guess (and are part of the problem tbh). I wouldn't have to remove the kitchen cupboards, I don't think, because they were laid before the tiles went down anyway. I can insulate under the kickboards however I want.
I can look for load bearing insulation if that's what it's called, then thin clickboard on top.
Client of mine used Aerogel matting under the timber floor, ie they lifted the boards, laid the aerogel and replaced boards. Im not sure on the detail but the mat is approx 10mm thick with phenomenal insulation properties. Sadly the cost was also phenomenal too but the building was vastly improved - solid concrete floor
We have a new build with beam and block floor (for clay soil) and a very well ventilated void. Then a massive foam slab and thin concrete on top which seems a great way of making a floor. Not cold under foot, decently air tight and a good overlap with the cavity wall insulation. Over floor is the way to go but you unfortunately lose height. Would woodfibre insulation boards be any good? I think Mattoutandabout has experience as a supplier of Pavatex boards.
In our old house (60's wood suspended floor) I slithered flat on my back in a max. 12" gap under the entire house fitting mineral wool insulation held up by netting. It was a horrible dank place and I really wouldn't do anything that impaired ventilation (and was very careful making dpc trays to stop moisture tracking into the insulation where it met any masonry).
Brief stay in a rental house between the two was 80's uninsulated solid floor that just sucked all body heat out through your feet....
This looks alright..? It doesn't specifically say it's for flooring but it does make a reference to underfloor heating so I guess it can be walked on.
https://www.victorianplumbing.co.uk/tilemaster-adhesives-thermal-construction-board-various-sizes
1cm of polystyrene is about R=0.3, which is next to useless. 4cm is R=1.2 which is getting there. The specific underfloor polystyrene insulation I've go for my extension is 100mm and R=2.85. It still requires a good thickness of concrete or wooden boards over it. I haven't got that far yet so I'm not up to speed on the details.
If that board is intended for tiles then they are rigid so will spread load. Maybe not so good for vinyl and more point loading.
40mm of this gives an r of 0.9 and can take a lot of compressive load.
https://www.soprema.ie/en/product/insulation/wood-fibre/natural-wood-fibre-insulation/pavaboard
Just thought of a huge problem. We have to keep the floor in washing machine and dishwasher nook the same level as the main floor, obviously, but if that gets raised they won't fit under the worktop. So the kitchen would all have to come out.
In our old house (60’s wood suspended floor) I slithered flat on my back in a max. 12″ gap under the entire house fitting mineral wool insulation held up by netting.
Just done this. Not the most pleasant experience of my life...made a big difference to perceived temperatures underfoot though.
I am now thinking of the insulating above. There are tiles down there now, they could be removed I guess (and are part of the problem tbh). I wouldn’t have to remove the kitchen cupboards, I don’t think, because they were laid before the tiles went down anyway.
Question. Is it actually significantly colder in the room compared with other rooms, or are you just getting cold feet?
How thick are the floor tiles and cement - you may get some thickness of insulation under vinyl.
Question. Is it actually significantly colder in the room compared with other rooms, or are you just getting cold feet?
Bit of both. It's colder down there because of course it's downstairs, and the doors are down there too. I don't have an air thermometer to compare the rooms. But with the floor at those temperatures in contact with the air it must be chilling the room.
It's worth checking before you start spending vast amounts (not to mention the likely disruption) to try to insulate just one surface.
Cold air does tend to pool in certain rooms, plus stuff like hob extractor vents and even apparently well-sealed doors can introduce or encourage this air flow.
I really think it's just perceived coldness because of the type of floor finish. Tiles will always feel cold compared to most other surfaces in the house, if you replaced it with vinyl or laminate you would instantly notice a difference.
Trying to retrofit more insulation to a block and beam floor without raising the finished floor level is not really possible. It's definitely not worth ripping a kitchen out for.
I'm concerned you'll got to a lot of effort and expense for not much noticeable difference, or you'll achieve a similar outcome to what you'll feel by just changing the floor covering.
I had a spare pack of vinyl strips left over from the caravan so I put those down. Slight improvement but still cold.
Now though I think that the draught is the problem under the tiles because the air temp under the washing machine is 10C!
I couldn't figure out how to address this but I am thinking I can lift the tiles and I am expecting to find a huge hole that I can fill with foam.
If it was built correctly you won't see any void, you should see plywood under the tiles, then under that should be any insulation that was installed, then under the insulation would be a vapour control layer. Under that again would be a very thin layer of cement poured over the blocks and beams to 'seal' any gaps between them.
If it hasn't been done like that, who knows what you'll find, it's been done very wrong though by cowboys if it doesn't have a similar build up to that.
It was built by Taylor Wimpey. One of the tiles rings hollow and the drain pipe from the sink goes under it. I think the void is linked to the cavity by the utility holes.
Anyway. Pulled the kickboards odd and found the boiler condensate pipe leaking....
Molgrips, how old is your place?
2007
Similar to mine. My main issue where the y didn't fit the plastic sheet tight up to the walls for the floor to be poured and it's now ripped where it's pulled away and nice cold air from the space under the floor gets in the house. It takes hours to seal these up as not much sticks to the sheet. I use tiny pieces of airtight tape to line the exposed sheet and then fire airtight flexible foam in the ripped sections and once the foam has hardened I trim anything that got through the rip and tape over that. I then foam the gaps above the sheet and use airtight paint over the floor to wall junction. I then ask the plasterer to not step anywhere near the work I did when he boards the walls. I just have to accept the floor will never feel warm in these much colder spells.
What I am trying to pay attention to is the wind direction and how the house feels as this can be a giveaway as to locations of gaps in the house and draughts.
Ps. Don't let it consume you like I have let it. Ive made huge improvements, whether it's all worth it I don't know as the house can still feel cold.