Looking to do a partial garage conversion on a new build integrated garage so the dogs have somewhere to sleep.

 

Existing internal door from utility room with a 150mm step down into the garage. I'm planning to partition off with a stud wall.

 

To bring the garage finished floor level up with the house I was thinking 100mm PIR boards, ~25mm thick battens at 400mm centres topped with 22mm thick floorboards.

 

Concrete screws to secure battens and PIR to the concrete floor and then screw the floorboards onto the battens.

 

Any issues with this approach? Specifically, is inch thick battens sufficient and do I need a DPM under the PIR (on top of concrete)?

 

Any suggestions for alternatives if this is rubbish?

 

Thanks

 

Why are you bothering with battens over the PIR? Just do a solid layer of 125mm PIR (you could bond this to the floor with foam or certain tile adhesives), taped at the joins and perimeter, then float 22mm t&g glued flooring over the top.

As to whether you need a dpm - depends on the concrete floor you've got there. Do you know if it has a dpm underneath already? If not, you could do a liquid DPM.

Thanks, the reason for the battens is I can get a very good price on 100mm but not so much on 125mm PIR (almost double, would be 100mm and 25mm separately)

 

If going down the no batten route does both the PIR to concrete and PIR to floorboards need glued/adhesive or can anything float? I was hoping to go for a "dry" construction method as far as possible 

Edited March 18, 20242 yr by ryfly

Just now, ryfly said:

Thanks, the reason for the battens is I can get a very good price on 100mm but not so much on 125mm PIR (almost double)

 

If going down the no batten route does both the PIR to concrete and PIR to floorboards need glued/adhesive or can anything float? I was hoping to go for a "dry" construction method as far as possible 

Personally with the battens I'd be a little worried about them locally compressing the PIR over time unless you did pretty narrow centres. Especially if you put any significant dead load on top.

 

If you're dead set on 100mm PIR, I'd probably change direction and go with a framed floor using 5x2s on 400 centres, infilled with 100mm PIR raised up on 25mm battens. Then t&g across the top. Rock solid.

 

Are you also insulating the walls and ceiling?

 

If you're after cheap insulation check out seconds and co. They buy b-grade PIR from manufacturers and sell it off cheap.

And to actually answer your question - if you go down the no batten route and want the entire thing can be dry, it can. The only thing that needs gluing is the 22mm t&g to itself along the tongues using 5 minute woodglue (the expanding foam-like stuff). Very quick and easy, but an important step. Also you can create a decent dpm using the foil top of the PIR if you do a good job of taping using foil tape (both the joins between sheets and the perimeter to the walls).

Our garage floor sloped away to the outside so check that as you may need to level (we did framed floor for this reason). Building inspector wanted a couple of courses of brickwork under the stud wall to prevent spills in the remaining garage contaminating below new floor or creating fire risk. Dpm is cheap and saves risk of more expensive problems later