Fixing firrings

[PaulH13]

Hi,

I’m in the process for building a timber framed conservatory and am getting towards the flat roof part.

I’m fitting the joists to which I will attach firrings then 18mm t&g OSB with an epdm roof.

I’ve search the forums and read that the firrings can be nailed to the joists but sparingly to avoid hitting anything when fixing the osb deck but does the osb deck fix into or through the firrings.

At the thin firring end, a 50mm screw (what I’ve read should be used for osb fixing) will go into the joist but at the thicker firring parts the screw will only just reach the joist or be just in the firring which I’ve lightly tacked?

Is nailing the firring recommended to avoid splitting but then I’m screwing through it?

Should I use a longer screw to fix osb through firrings into joist?

Any guidance would be gratefully received.

 

[JohnD]

To avoid splitting you can drill pilot holes.

 

[PaulH13]

Thanks John, so fix the firrings to joists (I was going to used annular nails spaced out quite a bit) then pilot through firrings and fix to joists using something like a 100mm screw (for the thicker firring end) and taper screw size down to 50mm at the thin end?