Insulation boards

30 Dec 2014
Reaction score
United Kingdom
Hi guys,

In 3 bedrooms upstairs, I have just laid laminate flooring on top of fibre board underlay and a vapour barrier.
I am now moving onto downstairs and am in the process of trying to get quotes for sub floor insulation. If this turns out not to be cost effective in terms of what it will save me (I'm not sure if I'm confident tackling it myself) or even if I do do it or get it done I'm considering laying insulation boards on top of the sub floor as an extra layer of insulation.
I'm just wondering that if I do this whether I can happily use the same flooring/ underlay combination on top? I've read that it's not a good idea to use 2 layers of fibre board as the sub floor will then be too wobbly/ springy.

These are the boards I'm considering:

And this underlay:

Sponsored Links
Oh OK lol, I got the impression that laying boards on top was an alternative to the method shown in the picture but obviously not!
Hopefully I will get some good quotes for this next week but I may just do it myself if not.
Is there anything better than the fibre board underlay for floors in terms of thermal insulation?

Anything you put on top of the floor will prevent the doors opening,

If you are insulating under the floor, then you can use Celotex or Kingspan or mineral wool.

For the same depth, the foam boards have better insulation, but are not so good at sealing draught gaps, whereas you can stuff in the fibre wool to fill gaps. Cold from floors is mostly from draughts, there is no convection loss at all, and very little conduction loss.

Mineral wool is cheaper and does not require precise cutting.

Do you have floorboards made of planks, or chipboard <vom> sheets?
Sponsored Links
Thanks for the info John. I hadn't considered the issue with draughts from fibre boards. I think I will go with the mineral wool, whether I get it done or do it myself.
The floorboards are made of planks.
Also, I was wondering if the estimates of potential savings are realistic? I've seen anything from about £40 to £80 per year though obviously it all depends on the particular property. I had one quote from someone without seeing the job of £900 materials and labour so hopefully when I have people in to see it this week it will be considerably less so as to have a decent payback time in years.

the heat loss through uninsulated floors is far far less than through uninsulated lofts or walls; which are bigger and exposed to outside temperatures, so spend your money there first.

The main problem with floors, if you do not have carpets, is that they are draughty and feel cold to the touch.

So in terms of energy costs savings as a return on investment, it is not economic to spend a lot on insulating floors. However, if you are taking up the floor for some other reason, it is an excellent opportunity to insulate and draught-proof before relaying it.

Floorboards that are "planks" do not need ply or chipboard under them. Some overlay floorings, like laminates or ornamental "engineered" boards, that are too thin or in short pieces so do not have adequate strength, need a floor under them.
Thanks John, I will certainly consider that then when working out if it's worth getting done at all once I get the quotes.
I already have cavity wall and loft insulation at 200mm and floor insulation was on the EPC taken just before I bought the house as the biggest improvement that could be made beyond that already done.
I guess I could increase the loft insulation further as 270mm seems to be recommended these days. Would that be more worthwhile than doing the floor?
I was only really considering the floor insulation as currently all I have is floorboards that I will soon be laying vapour barrier, fibre board and laminate on so if I'm going to do insulation at any point it should be now.
try calculating heat loss for your house here

do it twice, once with the extra insulation, once without.

But I agree that if you are planning to take the floor up, now's the time to do it. The extra cost and labour will be much less than if dome at any other time.

Insulate underfloor pipes at the same time.
Thanks John.
I will have to do it more accurately when I get back bu it's currently coming up as 4.4kW compared with 4.5kW. I'm trying to work out the savings based on that. From a search, it looks like 100W costs around £1.30 per week so £67.60 per year if I'm working that out correctly?
100W means that in 10 hours it uses 1kWh, which probably costs you about 13p

Lets assume you heat the room for 10 hours a day, for 6 months a year

so 365 days divided by 2 = 182 heating days

at 1 kWh per heating day

182 x 13p = £24 ish a year

Not worth it for money-saving, but if you intend to have bare boards with no carpet, and like to crawl around the floor naked, you will appreciate the comfort.
Ah OK, thank you for the help in the calculations!
I may as well get the quotes anyway but at this point it looks like it's not gonna be worth it.

the heat loss through uninsulated floors is far far less than through uninsulated lofts or walls; which are bigger and exposed to outside temperatures, so spend your money there first.

I would sincerely hope that a suspended timber floor IS exposed to outside temperatures. If your underfloor void is not ventilated then you are going to have problems down the line.

Typically heat loss through the floor is around 10 to 15% of the total, and insulating the floor will make a noticeable difference.[/b]
As it turned out, I got the quotes and they were anywhere from £1-1.5k depending on the insulation I went for and whether I replaced the floor.
Compared to potential savings, it would have taken too long to earn back.

Thanks John.
I have cavity wall and a fair amount of loft insulation (200mm). I may add to that at some point but I think I've done all the main things I can with insulation for now.


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links