Insulate a floor in old house - raised floor boards

dryan · 13-11-2009 05:48PM #1

Have been getting some work done on insulation lately on my parents house (3 bed bungalo) to try and make it more comfy.

The bedrooms are freezing.
The floors are a raised timber floor that are well ventilated underneath. On a windy night, one can feel the breeze coming through it.
There is loads of room to get insulation in there.

Whats the best way to tackle it?

Im not a builder an i was thinking of:
- taking up the old floorboards
- pack in insulation between floor joyces
- Lay a good thick layer of heavy duty polythene - sealed around edges
- lay a floor of say 1/2" ply wood
- Finish with a good quality carpet.

what ye think? Is this a good/bad idea?

Any alternative suggestions?

Any advice on what materials to use would be much appreciated.

MicktheMan · 13-11-2009 06:01PM

Not a bad detail.
I would use some light weight netting draped between the joists and use this to hold the fibreglass insulation between the floor joists. Finish as you describe with polythene, ply & carpet.

stedeb · 13-11-2009 07:24PM

hi guys just wondering what thicknessfiberglass would you use under the floorboards and if replacing the floorboards is it better to use mdf or chipboard which is better ?
sorry for hogging the thread
ste

holdfast · 13-11-2009 07:36PM

I would say go with a soild floor construction rather than suspend timber floor and would not go with poly if you go for the other if could lead to future problems, dry rot etc. a good carpet should reduce draft anyway, should reduce your problems a good bit anyway. but if you are going to lift the boards just take out the joists and dwarf walls fill with some hardcore, sand, DPM, 150mm min insulation and screed to finish. the job will be oxo after that better insualtion and reduced draft. cover with you want then

decdoc · 13-11-2009 09:59PM

I've just finished doing this job in my own house. I kept in fairly simple, just took up the floorboards, draped a breathable roofing membrane accross the joists and packed with 125mm of rockwool and then screwed 18mm plywood. I stayed away from the polythene as I was worried about dry rot and condensation, and the breathable roofing membrane should stop any drafts anyway. There feels to be a hugh difference, but I'll see come the end of the winter when I'll see how much oil its saved!

dryan · 16-11-2009 10:56PM

Thanks for all the info there.

So, what thickness/type of fibreglass should be used under the floor boards?

Should i pack the insulation in from the top of the joists down to the solid ground?

d2ww · 17-11-2009 02:46PM

The previous owner of my place used chicken wire nailed to the underside of the joists to hold the insulation in place. I suspect that this was done from below, definitely not a nice job!!

Adja · 30-01-2021 11:20PM

I am thinking of insulating timber raised floor from the top,over already existing floors.anyone has any experience in this?

Gumbo · 30-01-2021 11:49PM

Adja wrote: »

I am thinking of insulating timber raised floor from the top,over already existing floors.anyone has any experience in this?

Not really as it’s not a good way of doing it. You will then have to add floor finishes. Compression of the insulation will mean the floor will dip. Then you have to remove all the skit-ratings, all the doors, frames and architraves.

Much cheaper to insulate between the existing joists. I’ve given an example in your thread you started.

BryanF · 31-01-2021 12:02AM

Adja wrote: »

I am thinking of insulating timber raised floor from the top,over already existing floors.anyone has any experience in this?

Hi one post/one thread per topic is enough. have a read of the forum charter. Thanks

Insulate a floor in old house - raised floor boards

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