Screw type for welsh slate roof

Rotor

I am intending to re roof a building using screws to hold the welsh slates on. A roofer has said it is ok to use drywall screws as they don't get wet( only atmospheric moisture).
Do people think this will last 30 yrs plus or should I use stainless steel screws at 5 times the price?
If drywall ok then what is the difference in terms of longevity between black phosphate ones and BZP>

Thanks

Plasterer

Rotor wrote: »

I am intending to re roof a building using screws to hold the welsh slates on. A roofer has said it is ok to use drywall screws as they don't get wet( only atmospheric moisture).
Do people think this will last 30 yrs plus or should I use stainless steel screws at 5 times the price?
If drywall ok then what is the difference in terms of longevity between black phosphate ones and BZP>

Thanks

Not sure about the longevity between the two, however I do know that you can use drywalls for a lot of different jobs (Iv'e never used them outside however). If you do decide to use drywalls though be carefull when screwiing them in as they go in a lot quicker than a normal screw as they have twinfast threads (Go in too quick and you'll crack your slate) Have you considered decking screws if your after longevity?
Regards
P

Rotor

Thanks for that plasterer. The screws need to be about 32mm long and decking ones seem to be much longer. Plus they're not much cheaper than stainless if at all. I need roughly 3000 screws so drywall are about £15 and stainless £72 ( both from Screwfix)

Gloomendoom

I'd pay the extra. That way I wouldn't spend the next 30 years wondering if my roof was going to fall off for the sake of 60 quid.


Edit: Also, consider how hard it will be to remove the corroded steel screws if it turns out that they are not suitable after all. You might also find that the expansion of the screw due to rust cracks the slate.

ormus

i dont see why the screws would be any worse than normal nails that are traditionally used.
after saying that, i wouldnt ruin the whole roof job for the sake of just 60 quid.

ps
have you priced up brass screws?

vaio

I thought copper or ali nails were the way to go

ormus

ally nails are not really suitable. they will corrode over time.
copper or brass are far better than ally.

Moss5

http://www.toolstation.com/shop/Screws+Fixings/Paslode+Screws/Paslode+ProScrews+Quattro+Shank+Ext+40+X+30/d90/sd2220/p35113


http://www.toolstation.com/shop/Screws+Fixings/Stainless+Steel+Screws/Stainless+Single+Thread+Pozi+Screw+4x30/d90/sd810/p47194


http://www.diynot.com/forums/viewtopic.php?t=192967

iamcornholio

You need to use copper, aluminium alloy or stainless steel clout nails with slates - any of these are recommended and none corrode in this use.

Why do you want to screw these down?

That roofer really needs to stay on the ground. The nails will get wet - more so if you are centre fixing the slates. But more importantly, as the slates move slightly with wind, they will wear a little bit of the coating off the fixing, and then the steel will get exposed and rust.

That is why you don't use steel fixings - coated or galvanised

Rotor

Thanks for the replies folks. Reckon I will go with stainless steel. I am using screws because there is a possibility that the slates may have to come back off again

Gloomendoom

Rotor wrote: »

Thanks for the replies folks. Reckon I will go with stainless steel. I am using screws because there is a possibility that the slates may have to come back off again

Are you sure the heads will be big enough? IIRC roofing nails have dirty great big heads on them.