Suitable fixings for chipboard floor in loft

[blup]

Hi,

Is it safe to screw chipboard flooring into ceiling joists in the loft and, if so, how deep into the joist?

The chipboard is 18mm, the joists 6 x 2 with a span of approx 3.5 metres.

What size screws/nails are recommended?

The floor will be used for light storage e.g. Christmas decorations, photo albums etc.

Cheers,

Blup

 

[motorbiking]

I'd probably use an M3.5 or M4 in a 45 - 50mm screw. As long as the beams can take the weight (and thats more about spacing and how they are mounted) then its really just a plug to hold them in place.
The thing you need to consider is your roof is under insulated 150mm, so you might consider adding another 100mm and raising the floor before boarding over. e.g.

 

[JohnD]

I've used counterbattens in the past to fit in extra insulation under loft flooring (it also improves rigidity a bit when well-screwed together, and you can space them to match the board size) but you can also lay rigid foam slabs over the joists, then your flooring over that, and use extra-long screws to go right through the slabs into the joists.

Foam has about twice the insulating power as the same thickness of mineral wool, but is more expensive.

 

[blup]

Thanks, both, for the suggestions, the floor will need raising to accommodate the pipes and cables clipped to it, and this would, as you suggest, be an opportunity to improve the insulation.

Cheers

Blup