Making garage floor up

[thomp1983]

Hi all,

We knocked our downstairs bedroom through into the old single garage.

As you'd expect the old garage floor is lower than the bedroom by 120mm. The garage floor is roughly 50mm thick.

What floor make up will I need? I'm guessing the old floor will have to be dug up. Our building notice went in in 2021 so the insulation thickness will be the old rules.

I'm assuming it's dig out, lay mot 1, fit celotex, lay dpm, pour concrete on top?

I just need a hand with what thickness of mot I need and what thickness of insulation? The building inspector will be out tomorrow and could advise on the insulation but I'd rather get started today and order the stuff.

Thanks
Chris

 

[matlob]

Not sure exactly, but if the current floor is flat enough and concrete you could you put a 100mm pir board down over a dpm and chipboard flooring over it without any digging.

 

[thomp1983]

Building inspectors been out,

Options are either dig out current floor then 75mm of celotex and 4 inches of concrete or retain current floor, dpm, 100mm of celotex then a floating chipboard floor finished with self levelling compound to match the existing floor heights.

As you might guess I'll be going for the second setup.

Thanks
Chris

 

[matlob]

Winner

Nice that the difference is 120mm too!

 

[Ivor Windybottom]

The idea of self levelling compound on top of chipboard would be extremely unusual, I'd imagine that ending up as a load of cracked shrapnel.

You should put the self levelling compound on the concrete so that the celotex + chipboard ends up at the matching height, after calculating it.

It sounds weird, but my concrete was about the right height and I just used kiln-dried sand on mine, just skimmed it over dry with a float to fill the voids in the concrete, leaving just the peaks poking through. It's all still there as dry sand, holding me up. Then whatever thickness of Celotex, then a vapour barrier (not sure if strictly necessary), then chipboard glued together with a gap all round. It's all as solid as a rock, despite the room being used for storage with literally tons of business stock on steel racking on top of it.

You may be able to get the floor height right by using thicker insulation if there's a suitable size.

I used heavy duty 22mm chipboard instead of the standard 18mm to give me the extra 4mm I was short by. It's also much better, well worth paying the extra if you have the height for it.

 

[matlob]

Out of interest as I may need to do this, could you have 200mm of pir under the chipboard or will this not be study enough.

 

[thomp1983]

I doubt you'd meet the u value with 200mm but you'd have to ask a building inspector

 

[Ivor Windybottom]

There would be no problem with the U-value, 200mm would be massive.

Check with Celotex if you have concerns about rigidity vs depth. I phoned their tech enquiries people before doing mine to ask about loading. I hadn't had a floating floor before, I thought it would be like a bouncy castle but it's actually rock solid.

I'm sure the 22mm chipboard improves it, as it's very resistant to bending. If you can fit this in then use it, it's well worth the small amount extra.