Under floor insulation

Joined
30 Aug 2010
Messages
699
Reaction score
4
Location
London
Country
United Kingdom
I'm due to relay my upstairs floor and I'm using reclaimed pine floorboards. What would people recommend I use as under-floor insulation material? Shall I use Celotex or is there a more efficient insolation that I can use
 
Sponsored Links
Do you mean for sound insulation? Or thermal? What is on the other side, and is it heated?
 
Do you mean for sound insulation? Or thermal? What is on the other side, and is it heated?
Mostly thermal. Downstairs is heated but the cold might be creeping in from the external front wall of the house and the floor is cold in the winter
 
I'd use mineral wool quilt, as sold for loft insulation. It can be stuffed tightly around the edges of the room to prevent draughts blowing in from gappy brickwork or around joists, and can be laid under the rest of the floor to cut any potential heat transfer through the ceiling below (there will not be much) and it will slightly muffle noise.

It is cheaper, and easier to cut and lay, than foam slabs. Since Grenfell, I would not want foam inside my house. Mineral wool does not burn or emit poisonous fumes.

Get the stuff treated with Ecose, it does not shed irritant dust or fibres, and is comfortable to handle. It is brown, not like the old yellow fibreglass.
 
Sponsored Links
Heat loss is low through floors due to convection. Draughts are more common so stuffing round the edges of the room will do the most good. A layer of quilt on the rest will block draughts round light fittings and pipes, and cut any residual losses.

Losses by conduction through the floor are low so no point in paying extra for a fancy product. I find heat losses through a kitchen floor above an unheated garage are imperceptible with 100mm loft roll (plus extra round the edges of the room to stuff tightly).

If you find any visible gaps or cracks while you are working, fill them with pink expanding foam (fire grade) just in case.

You may find end-of-winter price cuts on insulation in the DIY sheds. Knauf also make many own-brands but you will see "Ecose" on the packaging.

Compare this price
https://www.wickes.co.uk/Knauf-100mm-Space-Loft-Roll-Bottom-Layer-Roll---8-3m2/p/166877

And this

https://www.diy.com/departments/kna...n-roll-l-7-28m-w-1-14-m-t-100mm/182146_BQ.prd

The cavity wall grade is usually denser so a bit better for muffling sound. Travis perkins link seems to be for that.

Looking at the price you could probably fit 170mm loft roll for less, but I wouldn't bother
 
Last edited:
I find heat losses through a kitchen floor above an unheated garage are imperceptible with 100mm loft roll
How do you judge /perceive heat loss through a floor over an unheated garage , and surely thermal insulation must be better and heat loss reduced with 200mm thickness of loft roll ?!
 
The floor is now not cold to the touch.
I obviously misunderstood the original comment - ' I find heat losses through a kitchen floor above an unheated garage are imperceptible with 100mm loft roll ' ,for some reason I took that to mean you didn't think insulation any thicker than 100mm would make any difference. :oops:
 
I think 100mm is plenty, it does the job and I don't think you need more.

Once you have blocked the draughts round the edges, and muffled air movement with a layer of quilt, the coldest air will lie against the ceiling below, and will not rise up to the floor at the top of the void.

Ceiling heat loss is much worse because convection carries the warmth up into the cold loft.



20180108_172001.jpg
 
My floors are coming up on our first floor as we are having some wiring done. For thermal & sound insulation I have used 100mm Rockwool RW3. I will be using it again when the loft floors come up too.
 

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
Back
Top