Drywall Screw Length

[norris309]

Hi All,

Hopefully a very simple answer to this.
I need to Plasterboard a ceiling below a flat roof, in a newly built extension.

Currently have Insulation between the Joists & have screwed 30mm celotex under the joists & now need to fix the 12.5mm Plasterboard under the celotex.
What is the ideal Depth the screws should penetrate the joists in this situation, I was thinking 25mm?

So, 12.5 + 30 + 25 = 67.5mm

Looking around locally it seems you get either 65mm or 75mm, 65mm being very slightly under but 75mm possibly being over kill?

What would you use?
I have found you can get 70mm online if that's the ideal size?

Cheers

 

[jj4091]

Do you mean plasterboard over the celotex rather than under it. I would think 60 or 65mm would be more than enough given there will be many fixings

 

[norris309]

lol.. yeah Over the celotex (finished ceiling if you will).. but as it's a ceiling.. it's kinda 'under' it in my head lol

I just wasn't sure how far the screws should go into the wood being it's heavy plasterboard on a ceiling, don't want anything falling down.. but realistically the ceiling is just under 2m x 2.5m with a skylight in the middle.. so not that much board & plenty of joists to screw to.

So a 65mm screw will go 22.5mm into the timber joists.. gotta be fine.. surely

 

[blup]

It used to be twice the depth of the fixing, I would use 70mm

 

[norris309]

It used to be twice the depth of the fixing, I would use 70mm

damn don't complicate things now lol..

Maybe i'll just order some 70mm & have done with it.
Just gotta hope i actually hit the joists/noggins' with the screws now they're covered in PIR.. hopefully i've marked the locations accurately enough on the walls all around (not easy to mark pebbledash!!)

Cheers

 

[johnny2007]

65mm