Garage Floor Insulation and Finish

[Lung]

My garage workshop is nearly finished and the floor is the last thing I need to sort out. Now the sills and doors are fitted, I have a better idea of how much space I have to put down some flooring. Originally I didn't think i'd have much depth and was just going to have bare concrete with a rubber mat here and there, but I have approx 32mm to play with so now i think I could put down something more substantial.

For context, the floor is a DPM with new concrete slab on top and single block walls. I've painted Black Jack up one block in height, and 120mm out from the walls too. Concrete surface hasn't been smoothed off or any other finish, so is pretty level but very rough. Garage will be my 3D printing, telescope fiddling and general DIY and bike maintenance workshop.

Options I'm considering:
1) 10mm XPS, 9mm board (OSB, Ply etc), 10mm rubber on top
2) 20mm PIR, 10mm rubber
3) 20mm PIR, 10mm board, small pieces of rubber in specific places
4) 10mm XPS, 18mm P5 board, small pieces of rubber

Any thoughts?

 

[Ivor Windybottom]

It's a bit of an awkward height. You need at least 18mm of wood, ideally 22mm for a floating floor, leaving you with little or nothing for insulation. I'd put a polythene membrane under the insulation, and a vapour barrier on top. If you could handle a slightly higher floor then it would be worthwhile.

 

[Lung]

Higher floor would start to be a trip hazard unfortunately. I'm going for 12mm XPS and 18mm P5 chip boards I think. Seems the best solution for the space I have. Should I glue the t&g on a floating floor?

 

[Ivor Windybottom]

Definitely glue the joints, otherwise it will creak like mad forever when you walk around.

Put a polythene vapour barrier over the insulation, this is a thin membrane that won't add any measurable height...

Wickes Green Polythene Vapour Barrier - 2.5 x 20m | Wickes.co.uk

Wickes Green Polythene Vapour Barrier - 2.5 x 20m

www.wickes.co.uk

This is to prevent water vapour from the room condensing within the insulation. In your case it will also serve as a secondary damp proof membrane as a second line after the paint you've already used. It also stops the wood sticking to the insulation, leaving it free to slide as it naturally expands and contracts. You can spill as much glue as you like onto it, it will still slide underneath it. Ideally you should also have a thick polythene membrane under the insulation or under the concrete.

Leave a 10mm gap all round, use a plastic skirting to cover it, the sort of thing that's used in commercial units, e.g. this sort of thing...

Anthracite Grey Skirting Board Chamfered External Corners Pack of 2 - 150mm

Now it’s easier than ever to enjoy terrific looking skirting boards and architraves – thanks to Roomline skirting boards. With this high-quality uPVC solution, you can forget all of that time-consuming sanding and messy painting, not to mention the tricky mitring of skirting board corners. It’s...

www.eurocell.co.uk

I'd also put a commercial grade vinyl floor down. Domestic stuff is garbage, it's foamed so is mostly air bubbles. Commercial is solid, you may find roll ends going for next to nothing on ebay or elsewhere.