Insulating under floorboards

koradma

We want to insulate under our pine floorboards and our boards have been nailed in a lot of places, making removing them means we will lose a few boards in the process.

Is it possible to lift only a few boards and pull through an insulation sheet(breathable membrane) under just to prevent the draughts if anything. We asked a few builders most seemed clueless. Some did want to pull up all the boards, which we are not keen on doing if we can avoid to save the old floor boards.

Any ideas of how to get insulation(min of a breathable membrane for 80-90% of the area). Nice to have would be to get insulation(rockwool style) above this membrane. There is about a feet of space between the joists and the ground below(concrete). It means we cant really wander down there, but have to use some tools to pull through membranes or cables underneath.

Ideas?

dracthelad

I'm afraid if you want to install insulation in there it's a case of pull up floor boards or get underneath. You can't pull insulaton underneath the joists for lack of suitable fixings -the insulation would just sag. Even rigid boards won't work as again how would you fix them to the underside of the joists? Whatever you do don't block the void under the joists as you'll get a rotten floor.

koradma

dracthelad

Agree with you if i wanted to cover the entire area under the floorboards. Will i be able to pull a breathable membrane by lifting only some floorboards(already some are lifted for the radiator work we did recently). Am hoping I can cut the direct draft for say 70-80% of the area even though its not fully sealed. Will that help?

Appreciate i will not fill the void as I understand air is required for ventilation below.

dracthelad

I suppose there's only one way to find out.... Are you just trying to stop the draft rather than provide insulation? The breathable membrane won't really achieve much (I take it you mean of the roofing felt variety?) as you won't be able to seal the joints and it's only usually available in 1.5m wide rolls. If you do manage to get a good seal you'll prevent your joists from getting sufficient ventilation!

If you just want to stop the draft try sealing around the junction between floor boards and skirting (silicone sealant) and properly fix down any loose boards.

koradma

dracthelad

There is a breathable membrane that should prevent straight drafts and also allow for venitlation.
Was hoping to overlap them a little. Sure it wont be a perfect seal.

I do like your idea about sealing the junctions with saw dust etc. Just that it doesnt look that great. The missus doesnt like it

I guess my approach wont really work is what you are saying. Thanks for your reply.

dracthelad

Do you have a link to the breathable membrane? Be interested to see what it is.

Are you leaving the timber floor exposed? Usually timber floors are laid with gaps for expansion around the perimeter and this can cause drafts from under the skirting boards. Seal it with clear silicone (not saw dust!!?!) and it should help a little.

koradma

Solitex Plus (Small rolls) 1.5m x 15m -
PC-TV-60 Tescon Vana 60mm x 30m
PC-O Orcon F Size - 310ml Cartridge

These were the items recommended. The top one being the membrane. You are right they are narrow which means they have to be taped tight. Am still wondering can i get 70% drafts stopped even if i overlapped the membranes from one end to another without lifting all the boards. Even better still i can tape them all to form a big carpet like and slide under from one side of the room to the other. This way i prevent the drafts.

Knows its a big shot.

dracthelad

Hi Koradma,

The felt appears to be straightforward breathable felt used on roofs and with timber frame buildings. The tape is jointing tape designed to make structures air tight to reduce heat loss through convection.

If you feel it will help then give it a go. I don't feel it will make much if any difference. It will also potentially prevent correct ventilation of the timber floor if you do manage to get a good seal - the felt is breathable to moisture vapour but not air as such - certainly not as much as a timber floor needs!

If you are wanting to prevent drafts rather than insulate then seal under your skirting boards with silicone. If you want to insulate correctly, then the floor boards have to come up!