suspended timber floorboards, 6mm ply over for LVT - could I put insulation between ply and floorboards?

[Del-inquent]

Redoing the floor in one GF room, the existing floorboards are all sound but a bit gappy and VERY draughty, the ventilation is clearly doing its job very well.

I have to put 6mm ply down to prep for LVT which I know will take care of the major gap draughts but the floorboards are always very cold in winter, I'm wondering if I could put a thin insulation layer between the floorboards and the ply or if that would be a bad idea. 

If it is a good idea, what would be recommended?

[MikeGrahamT21]

You absolutely could, the ply would need to be screwed down in a tight grid format, through the insulation and into the floorboards. Ensure you aren't going all the way through in case of pipes/cables etc.

 

Alternatively you could use something like a Marmox board along with their fixings.

 

Any reason for not taking the floorboards up and insulating between the joists?

Edited 11 hours ago by MikeGrahamT21

[marshian]

32 minutes ago, MikeGrahamT21 said:

Any reason for not taking the floorboards up and insulating between the joists?

 

That's what I would be doing - a thin layer of foil insulation isn't going to have much impact on heat loss on a suspended ground floor

[Redbeard]

How thin is thin? My 'go-to overlay' used to be 25mm PIR and T&G OSB floating (not fixed) on top, but I always used 18mm. 9mm might just be OK (I don't know - I have never tried, and of course you don't get the T&G) but I think 6mm over PIR might feel a bit like walking on a blancmange. 

[Del-inquent]

8 minutes ago, MikeGrahamT21 said:

You absolutely could, the ply would need to be screwed down in a tight grid format, through the insulation and into the floorboards. Ensure you aren't going all the way through in case of pipes/cables etc.

 

Alternatively you could use something like a Marmox board along with their fixings.

 

Any reason for not taking the floorboards up and insulating between the joists?

Yes ply was going to be screwed down at 150 centres perimeter 300 centres, fortunately no pipes or cables that are less than 75mm below the floor so can go without caution.

Ideally I would have taken the floorboards up and insulated between them, however its a large room, the boards are solid but really don't like being lifted (they also appear to have used about 200 nails per plank...) and we have to have the room cleared, the ply down and the stuff back in all in one day.
 

[Del-inquent]

13 minutes ago, Redbeard said:

How thin is thin? My 'go-to overlay' used to be 25mm PIR and T&G OSB floating (not fixed) on top, but I always used 18mm. 9mm might just be OK (I don't know - I have never tried, and of course you don't get the T&G) but I think 6mm over PIR might feel a bit like walking on a blancmange. 

I was looking at Spacetherm which comes from 5mm thick upwards, in 5mm increments. 

I'm not expecting to create a miracle loss of heat through the floor, more just trying to stop the icy blasts coming up quite so easily and thinking that if something simple will be an improvement over just putting the ply down I might as well. 

[Big Jimbo]

At my daughters. 1930's butched floorboards, i glued, and screwed down 9mm ply. Just blocking all the gaps made a huge difference. After LVT floor obviously not warm, but much better that leaky old floorboards. Listen, i am not against insulation. Quite the opposite. But stop the airflow. It will make a big difference.

[TheMitchells]

9 hours ago, MikeGrahamT21 said:

You absolutely could, the ply would need to be screwed down in a tight grid format, through the insulation and into the floorboards. Ensure you aren't going all the way through in case of pipes/cables etc.

 

Got to tell you this - at my friends last week, the boss had left a young chap to fit the T&G osb boards, over new ground floor joists.  We heard a yell and looked though to see a jet of water shooting straight up to the ceiling!!  He had not taken complete note of where the water pipes went.  I doubt he'll make that mistake again...... 😆

[Oz07]

I'd say it wouldn't be worth the effort. As above once you stop the draughts with ply and have the lvt down it won't feel as cold. Insulation would have to be thick to make any difference 

[Oz07]

Also with ply you can staple it no risk of hitting anything below then