Screwing down plywood subfloor for laminate

[liamruairi]

Is there a 'rule' for screwing ply down into floorboards? Am getting 18mm and 12mm ply to screw into floorboards. Am thinking 6' intervals along the edges but do I have to screw through the middle as well? Or will edges be enough? Also is 12mm ply thick enough to level wonky floorboards? Floors are different heights hence 18+12 mm to try and even this out 6mm fibreboard will go on top of all this before laminate
Cheers!

 

[liamruairi]

Sorry I should add that the different flooring thicknesses (12+18mm) are for different rooms not on floor in the same room! A reducer bar will be still required on thresholds

 

[ree]

The laminate has underlay below, and the underlay can be laid on whatever floor boards you have down at the moment. There's no need for ply.

FWIW: sheet boards of almost any material should be fixed at 100mm edges and 150mm in the field. Care must be taken not to use too long fixings or to fix down thro the floorboards into the joists - pinning to the joists will restrict movement and cause possible problems.

 

[liamruairi]

Ok great thanks. Floors are very uneven throughout with hearths and a large hole where a chimney breast once stood so thought it better to ply down