Insulating floor advice needed

[Bibby1]

Hi. I’m looking to improve the insulation in our living room a little. Despite carpets being down, the floor is always cold due to a large area underneath the floor boards. At least a meter deep with good air circulation.

We’re having some new carpets down in a few weeks and a friend has suggested I use some foil sheeting he has left over to lay on top of floor boards before the underlay. He thinks it won’t offer by way of insulation but should help by acting as a bit of a barrier from the cold air coming up. Do you think this would do much?

I’ve been doing research online and two other options look to be using wool insulation with chicken wire or board insulation held in place with some foam. Both would need me to go under the floor and fit from underneath. (I’m making the assumption with these options that the insulation goes as tight to the floorboards as possible, rather than create a little compartment?).

I’m looking for the easiest option which offers some protection. Would love to hear any suggestions or thoughts if anybody has done this before.

Thanks in advance

 

[Stivino]

from the cold air coming up.

Cold air doesn’t rise, heat rises.

 

[Nozzle]

Cold air doesn’t rise, heat rises.

And the cold air replaces the heat

 

[Stivino]

And the cold air replaces the heat

Then, would it not be wise to insulate the ceiling to prevent the heat escaping?

 

[Nozzle]

Nope, as by the time it gets there it cools off and falls back again :-p

 

[Bibby1]

The issue we have is that the floor is so cold. You sometimes find that the room itself isn’t cold but you sit on the floor to play with the kids and the floor is really cold.

 

[plastic_peanut]

I am just in the process of insulating our ground floor from the void beneath. Sounds similar to your construction. We found the ground floor would lose heat quite quickly and the floor ( engineered wood 21mm with insulation) was cool.

I decided upon using 200mm knauf wool and plastic netting. I purchased the netting from amazon and was reasonably easy to use.

Considerations for me were getting the materials actually into the the void beneath the floor. The roll of netting and Knauf went through our hatch.
Tried a couple of different approaches but found the quickest option was to size the netting, cut, Fold out then staple to the joists furthest away. The insulation could then be rolled out and the netting pulled tight and stapled in place. Gem move onto the next joist etc
I have around 3-4m2 left to do but this is under our utility space. I feel the living space is noticeably warmer and retains heat better.
Any questions please ask

 

[plastic_peanut]

Oh just to add, if you do opt for the Knauf earthwool it comes pre slit. The end pieces are around 16” and the middle is slit into two 8” pieces.

This can be a pain in the arse trying to work with the thinner slits. I opted to cut off the ends and use the wider rolls as they are much easier to work with. This has left me with a number of the thinner rolls but I will be using these nearer the hatch where it is less critical.

The other option is to use the encapsulated space blanket which isn’t slit and can be cut to size by you. The encapsulation can then be removed leaving you with 3x hopefully correct size rolls. Big difference in price though

 

[Mr Chibs]

I did the knauf and plastic netting method it's worked well, I also used a building paper to cover the insulation before I put the floorboards down.
It's draft free and keeps the temperature well.

I also used zig zags of cable sheathing around joists where the netting was difficult to staple on.

 

[Bibby1]

Thank you for input. I like the idea of using earth wool. With it being quite an old property, presumably the fact it’s breathable will help reduce risk of damp or mould?

A few questions.

Did you pack the material in or keep it quite loose?
Did you insulate right up to the external walls or leave any gap?
Did you consider putting a foil vapour barrier down on top of floor boards, before underlay?

Thanks again

 

[plastic_peanut]

As you are fighting gravity in an enclosed space it is difficult to fully pack the voids.

As mentioned earlier if you are using a roll that you can cut to size it means you can make it wider so it will wedge between the joists. This makes it easier if installing yourself and can be pushed up closer to the floor.
I had some left over space blanket from my loft and found it easier to work with then the earthwool. I moved to earthwool which is significantly cheaper but as mentioned the pre-slit element meant they weren’t as tight in between the joists so you are then reliant on pulling the netting right to support it and prevent it falling.

I ensured the insulation was left well clear of air bricks around 12” or so to prevent blocking air flow.
I was conscious of blocking through the property so did leave some gaps and didn’t always insulate up to the eaves.

We have engineered wood flooring but I don’t intend to use a foil barrier when I replace the floor.
I am quite happy with the underfloor insulation performance now for not a lot of money.

 

[Mr Chibs]

I packed close to the wall, tried to fill all voids, but also to keep the insulation 'fluffy' try not to compress it.

Around the air vent (below joists) I used bits of celotex to keep the rockwool from blocking said vents.

Mine is an old property too.
I was laying solid hardwood floor, so after the insulation I stapled builders paper over the whole floor, before laying floorboards.
You could probably use roof membrane, maybe polythene, or foil.

Shouldn't have a problem with damp/mould as I also added more air vents, and re-connected the whole of the ground floor together, as previous person had blocked some up.

 

[ericmark]

In the main the air under the floor would replace the air used for combustion in an open fire, and reduced drafts under the doors, if your room does not have a open fire any more, it does not need to draw combustion air from under the floor.

I had problem and cure was to put a plastic sheet under the underlay and carpet, however over time it got holes in it. Moved house so never cured.