Advice on laying floorboards

[KLMC]

I am about to lay floorboards to a recent extension and need to match them (height wise) to the existing boards.

The old boards are sitting on a concrete floor, but due to current building regs the new boards need to sit on battens on the new concrete floor with insulation between them.

I have a question with regards to the laying of battens. Do they simply sit on the new concrete floor ready to take the floor boards? Or should they be fixed to the concrete prior to installation of the boards. If the concrete isn't perfectly flat then how should I compensate for changes in level (plane the battens accordingly or bed the battens onto something and then level?

The battens will be approx 2 inches deep with a 3/4 inch board on top.

Any advice greatly appreciated.

[Mike Halmarack]

I'd fix the battens by plugging and screwing them. I'd have some of the screws going through plywood packing shims that adjust for variations in the floor surface. I did once bed floor joists in mortar but i didn't like the effects or obstacles it caused to later work.

[G&M]

Hard one with no right answer - even from BCOs. In the past I've built a complete floor as you describe with the battens sitting on sprayed foam which is used to level the floor and also provide extra insulation to the Kingspan wedged between the battens. But this makes the whole floor 'floating' and so it takes some effort to get rid of that 'hollow' feel.