Insulate under floorboards or thick underlay?

[mondeoman]

As the title says really..

Lounge carpet is coming up shortly and its a suspended wooden floor, with about 2' clearance underneath, fully vented with air-bricks, and its always been a bit draughty and cool under-foot, even though it is carpeted. Do I go to the hassle of fitting insulation under the floorboards, or will a decent modern underlay (12mm Cloud9 or similar) do the job just as well (and a lot easier). I can do 12mm as there are no doors to trim.

[B17NNS]

Why not do both? Chicken wire, staples and rock wool are cheap.

If you buy your underlay on-line the savings will probably pay for the insulation.

[paulrockliffe]

I fitted 100mm of celotex between my joists, it was pretty straightforward and has probably made a big difference (I did it between buying the house and winter, so don't know the exact impact. If you're taking the boards up you'll be better off going the extra yard and fitting celotex rather than rockwool I'd think.

[mondeoman]

Celotex sounds interesting, how did you fix it in place?

[nightwalker]

mondeoman said:

Celotex sounds interesting, how did you fix it in place?

Celotex/kingspan/eco therm, they're all very expensive but do offer the best thermal barrier. Roughly around £25-30 per 2.4x1.2 sheet.

[B17NNS]

mondeoman said:

Celotex sounds interesting, how did you fix it in place?

As above, Celotex/Kingspan will be better than rock wool but it's a case of diminishing returns. To fit just knock a few nails in the joists for the boards to sit on. Make sure the boards are a snug fit or there's no point doing it.

If you want to take that route have a look at www.secondsandco.co.uk. Big savings to be had on imperfect boards (functionality not affected).

[bigdom]

Not sure on the savings, just bought 20 boards,cheaper to buy brand new than the quote they provided.

[Grandad Gaz]

Interesting topic, thanks.

I shall be doing exactly this to the ground floor of our next house. The insulation part is the easy bit, it's ripping up all the old T+G boards that's the difficult and messy part!

I shall probably put new T+G chipboard sheets down and engineered flooring on top of that, unless someone can think of a better option!

[mondeoman]

oooh there's an idea - can I rip up the old T&G, put the insulation in, then replace with flooring sheets??

[paulrockliffe]

I put a couple of nails in each side to sit the insulation boards on, though with a tight fit they were more of a backup just in case really. I filled the gaps with expanding foam, which when set will hold the boards without the nails. Vapour barrier over the top, then 22mm Egger chipboard over the top.

I've not done the maths, but the boards I took up are making great kindling, so there's another bit of a 'saving' to feed into the Man Maths if you have a fire or stove.

[C Lee Farquar]

Personally I wouldn't replace t&g with chipboard, it never feels as good underfoot IMO. But I also detest engineered wood.

Surely a good underlay would be fine?

[GuinnessMK]

We insulated under the floor boards, using 50mm polystyrene, with foil tape across the joints. Made a huge difference to the warmth of the room and heating bills. In fact we just ended up sanding and staining the floor boards.

[Welshbeef]

Ripping up lots of floorboards to put in underfloor insulation - lot of extra work and the boards will never sit perfectly again /creek.

Put the best underlay you can down leave the floorboards untouched job done.