Insulating Suspended Wooden Floor

[SadieLovatt]

Hi,

I had an idea re the above and could do with some feedback as to whether I am completely barking or whether this is a sensible suggestion.

In our house we have suspended wooden flooring on the ground floor and B&Q (ww.diy.com) are currently doing top-up loft insulation (200mm) for £9 for 3 rolls - to cover the living room would therefore only take £27-35 of insulation. My idea is to have the loft insulation between the joists that support the floorboards and be held in place (the loft insulation that is) with something like chicken wire.

So, is this a good idea or are there some fundamental reasons why this is a bad idea?

Sadie.

 

[Fluffster]

As long as you maintain airflow ventalation to the joists and boards this would be ok.
Do not expect a big difference in heat though as insulating floors is usually related to slabs where they have direct contact to the sub surface.

Pete

 

[^woody^]

The only issue would be if you tend to have damp under the floor, and then there may be a potential for moist air to get in between the fibres and cause the insulation to loose effectiveness.

If the floor void is normally quite dry, then it should be OK.

It should also reduce draughts

It will be hard work, but it should pay for itself quickly at that price, and worth doing

 

[tryitandsee]

I like the idea but lifting and relaying floorboards etc is quite a lot of hard work. I saw some of those rolls in B & Q, but I also saw they were selling 'space blankets' as well. They look like thin layers of tin foil. Could this not be rolled out under the underfelt
I should think it would work as it wouldn't matter if it was compressed. A lot more easier pulling up carpet!

 

[tryitandsee]

Sorry, I have reread your post and perhaps you have exposed polished floorboards

 

[stuart45]

There are a few different methods that have been tried over the years for insulating timber floors. One was to lay a quilt on top of the joists and then fix the boards on top. This led to cold bridging and an uneven finish on the floor. Another way is to fix netting to the bottom of the joists and lay the insulation on top. You need to put some between the end joist and the exterior wall to prevent a cold bridge.

 

[SadieLovatt]

Having done a little research on floor U values and feeling a little out of my depth on building terms ("cold bridging"..? What's that..?) I thought it was time to step back a little and check that I am not using a sledgehammer to crack a nut.

Just to put this into context; Considering that the U value of the uninsulated floor (0.7-0.8) is going to be one of the lowest U values in the house (the solid walls for example have U values of 2.1), our yearly gas bills are < £400/year and the floorboards are not the kind you want to show off then is this actually worth doing or should I just replace the 10 year old carpet and cardboard underlay with a nice deep-pile and the thickest underlay I can buy?

Sadie.

 

[^woody^]

Don't worry about cold bridging - that's irrelevant and confusing in this instance - and you don't lay insulation on the joists (this would prevent a cold bridge not cause one, incidently )

Typically, about 15% of heat (fuel bills) will be lost through the floor and it could be up to 40% depending on construction.

There is also the draughts and air leakage to consider

You will not get anywhere near the savings or comfort levels by using a thick carpet.

If you have the access, then its worth doing

 

[stuart45]

Insulation can be layed on top of the joists. When rigid boards are used then there is no cold bridging. The problem is that the floor level is raised. When a quilt was used it was crushed by the floorboards and there was the possibility of cold bridging. I have seen both types used in the past.

 

[^woody^]

Quilt is never laid between joists and the floor deck (it will bounce) - it is between joists only. In any case it can not cause a cold bridge as it is a thermal break between the joist and floor board

Rigid board is typically between or under timber joists. I can't think of a situation where it would be fitted on top of joists unless in a warm roof situation.

 

[stuart45]

I agree that quilt should not be laid over the top of the joists. It does give a poor finish. However it is a method that has been used in the past. I have taken up floors done like this. The quilt has been crushed to the point were its thermal properties would be lost.
I have worked on refurbs where rigid boards were specified to be laid on top of the joists. I am not saying that its a good design but just the fact that it has been done. You can only follow the spec on the job.

 

[wms]

I agree that quilt should not be laid over the top of the joists. It does give a poor finish. However it is a method that has been used in the past. I have taken up floors done like this. The quilt has been crushed to the point were its thermal properties would be lost.
I have worked on refurbs where rigid boards were specified to be laid on top of the joists. I am not saying that its a good design but just the fact that it has been done. You can only follow the spec on the job.

the only time ive come across this method is on sound insulation rather than thermal and this is usually between floors?