Suspended-floor insulation

[seasickstevie]

To avoid the recent experience of struggling to keep the house warm, I'm going to insulate under the suspended ground floor. Particularly as we've gone for the stripped floor look with a few rugs. This has given us a few drafts and a generally cold feel to the floor.

I'm planning to use 60mm Kingspan (the stuff with no foil-face).

Should I use a membrane barrier of some sorts? I don't think it should be necessary, but would be interested in anyone else's opinion.

And is 60mm sufficient would you say?

 

[Deluks]

Obviously the thicker the better, but 60mm isn't too shabby and is a vast improvement on nothing at all.
Fit the boards flush with the tops of the joists and you won't need any membranes.

 

[noseall]

Th floor space should be full vented so condensation will not be an issue.

 

[seasickstevie]

Thanks for replies.

Yes there are two air bricks at the front, but because of a french window alteration about twenty years ago the air brick at the back is blocked off.

I've kept an eye on the situation in the intervening years, and although I've considered putting a small fan in to improve the air circulation (from one front air-brick to the other), it hasn't appeared necessary.

 

[alittlerespect]

I assume that you will be taking up the flooring to install the insulation? 60mm is bare bones stuff, especially if you have the flooring removed you should as a minimum be considering an insulation thickness of 100mm - 50-60mm would have been fine 15 years ago, but standards have moved on!!

You can buy polythene netting that you can drape over the floor joists, then infill with the insulation material.

On a personal note I would recommend installing a vapour barrier before re-fitting the flooring, as you will want to retain the vapour contained in the warm air on the warm side of the construction element. Also insulating between the joists will make the floor void a lot colder (as less/no heat is escaping from the room) which in certain conditions will encourage condensation.

Regards

 

[seasickstevie]

No, I'm afraid lifting the boards is out of the question.

Going to have to do it from underneath lying on my back

I realise that the joists will create a cold bridge, and is virtually unavoidable. Unless of course the joists were rapped in insulation - not going that far though.

As warm air rises, I would have thought 60mm underfloor would have been acceptable, but as you say, standards have changed.

Will make a thorough job of sealing all the joints etc.

 

[suts89]

No, I'm afraid lifting the boards is out of the question.

Going to have to do it from underneath lying on my back

I realise that the joists will create a cold bridge, and is virtually unavoidable. Unless of course the joists were rapped in insulation - not going that far though.

As warm air rises, I would have thought 60mm underfloor would have been acceptable, but as you say, standards have changed.

Will make a thorough job of sealing all the joints etc.

I,m planning on doing the same job myself.

Anychance of you posting a few pictures from under the floor as you do the job

 

[seasickstevie]

Will do

 

[seasickstevie]

Anychance of you posting a few pictures from under the floor as you do the job...

Finally made a start, but using rigid PIR in a confined space, getting around pipework etc is a nightmare!

Tried uploading pics, but just wouldn't work for some reason - What am I doing wrong?

As it's taken a considerable length of time to do just 20% of the area, we've decided to do the rest with Rockwool slabs which should be a lot quicker.

Still need to fill the edges of the PIR with expanding foam. This is something that shouldn't need doing with Rockwool.

Wouldn't recommend PIR in such awkward confined space to anyone! Too much cutting and trimming required.

 

[mointainwalker]

Fibre wool is much better for this type of situation as you can cut it wider than the joists and squeeze it in to eliminate gaps and is only 25+ of the cost of insulation boards.

I wouldn't think panels of the material is the best idea either. It is probably too heavy to hold itself between the joists and may need cutting to size which will be a nuisance.

Use ordinary fibre-wool rolls which will be half the price, so you can then afford to fill the joists to full depth and hold it in place by nailing/stapling/screwing some kind of mesh across the joists.

 

[Blagard]

I think your approach to this is fine - Fit in as much insulation you can afford since you are going to benefit in the end and certainly this will improve your home. As far as levels of insulation are concerned, the standards today are higher than before and will increase again as time goes on. The Awkward bit is crawling around under there - so make it worthwhile!