Are these screws ok for OSB3 on my flatroof?

[SS-ProjectBuild]

Hi Guys,

As the title suggests...are these screws ok to use? I know they are designed for floor chipboard/osb but was think they would do the same job on the flat roof construction?

https://www.screwfix.com/p/spax-wirox-tx-countersunk-wirox-flooring-screw-4-5-x-60mm-300-pack/88716

Thanks.

 

[Funtimes]

Hi SS, I've done a couple of flat roofs and used decking screws (for OSB use a length of at least 2.5x the thickness of the board). Those linked are for internal use only.

 

[SS-ProjectBuild]

Thanks...something like this for 18mm TG boards

https://www.screwfix.com/p/deck-tite-double-countersunk-decking-screws-4-5-x-50mm-200-pack/26909

 

[Funtimes]

Yeah sound, something like that, think the ones I used were a shade longer at 65mm.

 

[SS-ProjectBuild]

The screws are going into the firrings i assume and they dont need to pass through to the joist?

 

[Funtimes]

You'll fix your firrings to the joist first and then the OSB on top so the screws will pass through to the joist at the thinner end. Towards the thicker end make sure the firrings are adequately fixed to the joist where your screws won't reach the joist.

Alternatively you could use longer screws as the firrings get thicker so it goes through to the joist.

 

[^woody^]

You need to avoid the screws indenting the surface too much unless you are countersinking each hole , so a screw with a wide "double countersunk" head (self cutting) would be better.

 

[SS-ProjectBuild]

You'll fix your firrings to the joist first and then the OSB on top so the screws will pass through to the joist at the thinner end. Towards the thicker end make sure the firrings are adequately fixed to the joist where your screws won't reach the joist.

Alternatively you could use longer screws as the firrings get thicker so it goes through to the joist.

What glue do you recommend?

 

[Funtimes]

What glue do you recommend?

I didn't use any glue for fixing the firrings, just screws and countersunk the ones where the firrings got thicker.

I'm not sure I'd trust glue on its own but I'm only a diyer so one of pros might suggest otherwise.