I plan to redirect our ground floor front room next year.
Currently, the walls are unplastered, and we've rewired so floorboards are loose, so any option is possible at this point.
My question is what, if anything to do about draughts from under the floor.
We live at a T junction, with a road running off our road straight in front of our house. This road is a bit of a wind tunnel, and the room we plan to decorate gets the brunt of it.
The house is Victorian, and slightly raised with large cavities under the floor-boards. There is also a metal decorated air-grill at the front of our house which ventilates the space under this room.
Net result is that it is seriously cold and draughty at the moment, and I can feel quite strong cold draughts if I put my hands over the floorboard gaps in this room.
When we've decorated the room, I plan to get an underlayed berber style carpet, which should prevent the draughts, but I'd like it to be as cosy as possible for my children.
Is there anything else I can do to improve insulation/carpet warmth?
I presume blocking up the air vent completely would be a bad thing? Is it worthwhile attempting any other sort of under-floor insulation?
The idea on the ground floor is to stop draughts coming up through the boards, but allow a free flow of air under them via the air bricks, so your carpet should be enough. You don't lose heat downwards, so I'd say there's no point in insulating.
Yes. The airflow prevents the joists from rotting. Don't do it.
Perhaps put down a layer of thick polythene tucked under the skirting boards if there is enough of a gap, then the underlay, then the carpet?
FWIW, I live in s similar house to that you have described. The floors are stripped and varnished, and I love the look, but it's too draughty and difficult to heat, especially in this weather, so I'll also be putting carpet down when I get round to decorating.
I don't think that's a good idea. The whole point of under floor ventilation is to eliminate stagnant air which promotes rot, which affects not only the joists but the floorboards as well. If you're going to wrap (even just the under-side of) the floorboards in a vapour proof skin, you are *creating* pockets of stagnant air, defeating the purpose of the ventilation, thereby putting the floor boards at risk.
You need to remember that a certain amount of draught is actually a good thing, otherwise the room becomes too stuffy.
I think it's best not to insulate with anything non-permeable. Use underlay if you must, but with beautifully varnished floorboards, the in-character thing is to have rugs, not wall-to-wall carpet. With rugs you don't want an underlay that's too thick, or you'll keep tripping over the rug edges. Worth a try is thin cardboard.
If you can identify any spots where the draught is excessive, caulking the gaps with ordinary string may be effective.
How thick is a layer of celotex/kingspan? Also, what do you mean by foil tape?
Also, only some of the boards are already up, so I'd rather not lift them all unless I had to. Would a combination of your's and Mike's suggestions work?
That is to say, fix all the floorboards, then lay celotex/kingspan (I'll have to look those up), then foil tape on top of that, and then let the fitters lay underlay and carpet ontop of that? That would be a lot less effort intensive.
The point of underfloor ventilation is to conduct away the damp that evaporates from the earth below, so RH doesnt rise high enough to cause rot. If you insulate between the josits with no VB, you'd be right, condensation and rot could occur. But with insulation and VB above all is well.
Celotex is a foil-backed insulation mat, about an inch thick. It wouldn't stand up to being walked on, even with underlay and carpet on top. It's used for things like insulation between the roof joists during a loft conversion, for example.
I don't agree with TNP here. There would be some heat loss through the floor, but not much, certainly not worth the effort of following his suggestion of lifting the boards and fitting celotex between the joists, then re-laying. As others have said, you'd also be creating pockets of stagnant air between the celotex and the floorboards.
Can the small amount of vapour in the floorboards breath up through the underlay and carpet?
Unless there is a vapour barrier, I would have thought so.
I see no problems with this approach as long as there is a breathing path from everything above the celotext into the room, and what's under the celotex being open to the underfloor vents.
I'm in a similar position and this is what I plan to do.
I sanded and varnished several of my downstairs floors last year, and am now kicking myself for not taking the opportunity to take all or most of the boards up and insulate underneath first. Not only are the boards cold under foot (even through rugs), but despite the greatest care I have gaps and draughts where boards have had to come up for plumbing and electrics (someone said in a similar thread in an other place that they'd totted up all the gaps and holes in their floor, and if they were all in once place they'd amount to an eight inch square hole).
I have one more room to do, and I'm going to start by lifting all the boards. It's a job, but a job you only have to do once. I might cut the tongues out first, to get them up easier, as once I've insulated, tongues won't matter.
What you need to do is insulate between the joists, putting the floorboards into the warm zone of the room.
The easiest way to insulate is probably to use space blanket, which is a roll insulation encapsulated in plastic to avoid mess. It is rolled out between the joists and supported on netting or similar. My problem with this is that the standard size is 370mm wide, and assumes that your joists are at 400 centres, whereas mine, annoyingly, are at 430 centres, so I'd have a gap. This leaves me the option of using messier, unencapsulated roll insulation, or what I'll probably do which is buy seconds of 50mm Kingspan, cut to size and fix in place with PU foam.
Where my previously-sanded floors are concerned, I had a plan to lift a couple of floorboards in four or five places across the floor, and pull space blanket through, under the floor, between the joists, supporting it where I could. Unfortunately I have this width issue so I'm not sure what approach I'll take to that now - possibly pull up a lot more boards than I had intended, and use Kingspan again.
Important issues are electric cabling and central heating pipes - cable should not be buried in insulation as it can theoretically overheat and become a fire hazard, so it needs to run above it. I also need access to my central heating pipework (in case I want to reconfigure the radiators or access the Speedfit connectors, so I need to make sure that's abpve the insulation too - which has an obvious other benefit).
As people have said, on no account block up your air bricks, as air circulation to the bottom of the joists is essential for the avoidance of rot. I think worrying about the floorboards is unnecessary, as Tim Watts says.
I've had three winters here now and dealt with a lot of the other insulation issues that the house has - I'm convinced now that a major part of the cold feel that is left is down to the floors. Especially when outside is minus fifteen. I've yet to hear anyone say they insulated their floor, but considered it a waste of time. You can't build anything new without insulating the floor...
That's a bit misleading. There is more than one Celotex product, but the most common is a rigid foam board, usually foil backed, that comes in sizes from one inch up to - actually I don't know, but certainly more than seven inches. It's not a mat that you can lay on top of floorboards and fix carpet to.
Do the calculations before you make such opinions.
Would you want a wall the size of your floor, cosnsisting of leaky floorboards just covered with a carpet and underlay with a -5C 15mph wind the other side?
yet a well vented underfloor space is just that.
Compared with a solid floor, where the ground itself acts as an insulator, suspended wood is a complete heat loss disaster area especially when its well ventilated. .
As others have said, you'd also be creating pockets of
The celotex is flush with the top of the boards.
BUT creating pockets if stagnant air is precisely what an insulation material does anyway, so its a silly thing for you to say, twice over.
If they are vapour barriered, modest ventilation the works.
If you're
Utter tosh. You neither understand how the insulation is applied, nor why.
Celotex is made and approved for exactly this scenario: roof joists with eaves venting behind, and habitable space inside.
Absolete tosh.
That room air change ion a modern insulated house is controlled by specific deliberate and known sized ventilation. Nit by random icy draughts.
More complete rubbish.
If its permeable, the wind gets in and destroys the properties. You don't go out in an icy wind with JUST a jumper on. You need a windproof covering over it.
My advice to the OP is to disregard everything this idiot says. he appears to have no clue about insulation, damp or heat loss whatsoever.
Some have mentioned a vapour barrier but I'm not convinced this is essential within a floor. Moisture in the air underneath will be carried away by the ventilation. If moisture in the warm air in the room was going to condense into the floor, that would be more likely in a colder uninsulated floor. I just don't think condensation is an issue in either case, if under-floor ventilation is present. Though as it happens, if you use foil-backed Celotex or Kingspan you'd have a pretty good vapour barrier in any case.
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