Confusion regarding how to build a floor on concrete

[JS7319]

Our detached garage that is being converted is at the stage of having its floor built.

We understand that from our research it's a DPM, foil faced insulation (we can only do 25mm due to height), tongue and groove OSB, underlay and then laminate floor. My research shows that the OSB will move with the seasons, and I don't know what impact this will have on the laminate stability.

We have found other polystyrene boards in DIY stores that are 5mm purporting to be suitable to ultra cold concrete floors, and no additional OSB or underlay needed, so laminate would to directly ontop. I have attached the image of the product

I'm confused how such boards that are 5mm would out perform 25mm of insulation in the traditional way.

What's the best approach for stability and heat retention.

Note, our garage is detached and is small, around 12m2 and doesn't need building regs.

 

[^woody^]

My research shows that the OSB will move with the seasons,

Where have you been researching?

OSB is stable, used on roofs, and as wall panels particularly for its stability. However its not really designed for floors, but in this case as its going to be fully supported it will be OK.

In any case where is it going to move to? Glue all the joints, cork perimeter, and its a standard floating deck.

No other product will beat the 25mm of foil faced insulation that you proposed.

 

[JS7319]

Almost all videos I have seen where contractors have done work have used t&g boarding. Kingspan technical have also advised 18mm as a minimum ontop of their foil faced boards.

The movement document is the natural.expansion and contraction over the seasons where the perimeter gap widens and narrows.

 

[mikeey84]

That 5mm underlay will not outperform 25mm of celotex or similar. Its worth using, but in addition to, not instead of, the 25mm.

The only thing that outperforms celotex or other PIR type boards is ultra expensive aerogel, which I don't think is suitable for floors as its quite fragile

 

[JS7319]

Is it possible to put the laminate floor on top of the celotex boards with the use of underlay? Can we do without the tongue and groove OSB boarding?

 

[Tigercubrider]

Not an expert but..
The thin boards are likely a pressed material. The OSB is far stronger. It should provide a flat surface that's easy to lay laminate on. Once all the T&G has been glued, a garage sized piece of OSB will weigh a bit and won't really move.
Think what happens when you walk on snow, it compresses. The OSD acts like a snow shoe and distributes the weight.
You might need that thin underlay that looks like white fabric between the OSB and Laminate? Thinking that it might add some slippage for both surfaces?

 

[mikeey84]

Not an expert either, but feel you would need the osb

 

[^woody^]

The movement document is the natural.expansion and contraction over the seasons where the perimeter gap widens and narrows.

It not as if it expands or contracts by much. Its theoretical fractions of a mm with man made boards, and imperceptible in use, as once the room humidity has stabilised following any construction work there is not a lot to cause expansion anyway.

You don't see perimeter gaps due to skirtings, and cork packers or dense foam are used to keep the whole deck centralised and prevent it sliding.

 

[endecotp]

we can only do 25mm due to height

That’s really not very much. What limits the height?

I have experience with 18mm T&G OSB over PIR insulation boards. The result is a good solid floor. It is recommended to put timber supports at the perimeter and under thresholds, but honestly if I were doing it again I wouldn’t

I'm confused how such boards that are 5mm would out perform 25mm of insulation in the traditional way.

I think that’s an alternative to the underlay that you need between the OSB and the laminate.

 

[catlad]

If you don't put the osb down then you will have problems with the laminate flooring.

 

[Dallypro]

We understand that from our research it's a DPM, foil faced insulation (we can only do 25mm due to height), tongue and groove OSB, underlay and then laminate floor. My research shows that the OSB will move with the seasons, and I don't know what impact this will have on the laminate stability.

View attachment 217234

I have very recently DIY'd a floor exactly as you have described:

Concrete - DPM - 25mm PIR - OSB (Glued joints) - Underlay - Laminate.

10mm Expansion gap round the edges to allow the floor to expand/contract - this is covered by either skirting or threshold.

OSB flooring doesn't move significantly and is essential to lay the laminate properly. PIR is the only cost effective insulation worth considering.

Your stated plan is the way to go for stability and heat retention.

 

[Bodgedbuild]

If your concrete is just standard garage floor I would consider a layer of sand on top before you lay DPM to avoid the risk of puncturing it.