Lay Celotex / Kingspan over existing suspended floor - OK to do?

[Rodders66]

Hello all,

I need to raise the floor of an existing room to match the others by approx 140mm, the room is suspended and has a reasonable T&G floor but not insulated, is very well ventilated with multiple air bricks and bone dry.

Can I simply lay 100mm insulation slabs onto the existing T&G floor, then tape it all up, and sit some top boards to make up the height to match other rooms?

Do it as a floating floor as per concrete slab method?

My thoughts were, provided that the existing good ventilation is maintained beneath the existing floor there's no difference to what's there already and I benefit from the insulation without needing to spend time / £ on additional timberwork.

What do you reckon?

 

[Rodders66]

Hi

I've been told it's OK and also maybe not OK in another forum. ...all feedback welcome!!

 

[WabbitPoo]

Wont the new boards be a little, well, bouncy or, indeed, squidgy?

 

[Rodders66]

Apparently not, because its common practice to lay 100mm onto a concrete slab, and the existing floor is solid even though it's suspended ground floor.

That said really happy to get more feedback on my assumptions!

 

[Notch7]

Celetex is fine as a continuous layer under screed.

Its no good as floating floor with floorboards only over the top -I know sonebody that did it in a conservatory with oak floor over. Ended up really bouncy, had to be ripped up and re done

You need joists with celetex in between. Run joists at 90 degrees to existing floor joists.

 

[Rodders66]

Thanks,

So it's OK to lay the celotex / kingspan on top of the existing suspended floor but, I need to lay a screed down over the insulation before laying final boards?

 

[Notch7]

Thanks,

So it's OK to lay the celotex / kingspan on top of the existing suspended floor but, I need to lay a screed down over the insulation before laying final boards?

You cant lay screed over a suspended floor, its too heavy. Screed only goes over a concrete slab or concrete block and beam floor.

So your option is to counterbatten with say 100mm studs at 400mm centres and fit celetex inbetween. The floor boards will rest on the studs not the insulation.

for a screed finish you would have to convert your floor to solid -if thats possible.

 

[endecotp]

Celetex is fine as a continuous layer under screed.

Its no good as floating floor with floorboards only over the top

Not floorboards no, but you can use e.g T&G chipboard (22mm) or OSB or ply (18mm), with the T&G joints glued, floating.

 

[Rodders66]

Thanks for the info,

I'm getting differing views on this which means it's not normal to do, I guess?

Through DIYNOT I've advised it's OK as long as there's good underside ventilation, which there is.

The idea of the final floor being springy did cross my mind, but only because I was laying the whole thing on top of the existing suspended floor, and not because the Celotex would make is spongy if you get me?

I was also advised that I could lay a thick Ply base on the Celotex and then go on top with 20mm Engineered flooring....I'm now doubting it... any more experienced input welcome

 

[JohnD]

You can put sheet flooring, such as Ply or Chipboard, on top of rigid foam. Nothing new or controversial about that.

 

[Rodders66]

Thanks John..do you think theses a problem with doing that on top of an existing suspended floor though?

From a strength or flexible / springy perspective?...the existing floor certainly doesn't feel at all springy .

 

[JohnD]

no.