Floor insulation advice for garage conversion to office

[omega11]

Hi there,

I'm converting our garage into an office and the garage already has a false floor with a 46mm cavity but with no insulation.

I'm going to cover it with liquid DPM and wanted to add some insulation between the floor and the false floor, but not sure which is the best approach.

I can buy 25mm thick insulation panels, but this will leave a gap of around 20mm. The 50mm thick panels are just a little too thick or I was thinking using insulation wool but the thinest I can find is 100mm which will mean it will get heavily compressed and I hear this is not ideal for the wool to breathe.

What would be the best approach here?

Thanks in advance for any advice.

 

[Tigercubrider]

Loose insulation?
No expert but is it possible to inject foam ?

 

[Deleted member 174758]

I'm converting our garage into an office and the garage already has a false floor with a 46mm cavity but with no insulation.

I'm going to cover it with liquid DPM and wanted to add some insulation between the floor and the false floor, but not sure which is the best approach....

What would be the best approach here?

If possible skip the liquid DPM. Instead a layer of 1000 gauge Visqueen DPM (available from any builder's merchants) would be far more effective, but it does mean lifting the timberwork to get it in. If all you intend to do is put down liquid DPM between the existing timbers, then what you will do is keep the bottom of the insulation dry - but the timbers can still soak-up moisture from the concrete and can go rotten, so not really a great idea

If you need to leave the timbers in place, in terms of speed and simplicity I'd go for 40mm PIR insulation, cut very tight (e.g. Cellotex or Kingspan) so that it holds itself in place with a 6mm gap beneath. This stuff has a foil surface which in itself is a basic DPM. It also gets you nearer to your 46mm limit. As an insulating material it is more effective than mineral wool, sheeps wool or loose fill insulations, It is more expensive, though

I'd avoid spray foam like the plague. If your timber frame is sitting directly on the concrete without an intermediate DPM it will seal the timber brilliantly - so well that any moisture wicked up from the concrete will accumulate in the timber - and accelerate rotting of the timber. There's a video about why it is such bad news in attic timbers, here, but the same would apply in the case of floor timbers laid directly onto concrete without a DPM:

Note the comments about surveys, mortgages, etc

Maybe it's a bit of Irish ancestry in me, but if I were you going there, sir, I wouldn't be starting from here...

From my perspective I'd go a little bit more radical, but oddly enough I think is a heck of a lot less cutting and faffing about:

- Remove the timber framing (the timber can always be used elsewhere)
- Lay down a Visqueen DPM lapped 200 to 300mm up the walls and taped off
- Put down 40 or 50mm of PIR insulation over the entire floor (very few cuts)
- Lay a floating floor of P5 T&G chipboard (pulled and glued together) leaving a 5 to 10mm gap all around

and job's a good one, ready for vinyl or carpet. Add skirting to the walls and you can trim back the DPM at the same time