Fixings into woodwool/cement slabs

[Tipper]

Can anyone suggest the best way of fixing new metal roofing sheet system onto an existing woodwool/cement slab roof deck? (10 deg low pitch roof)

Will they take some type of coarse threaded screw or expanding plug or is the only way hollow/cavity fixings right through the slabs?

I'm keen not to have to remove the slabs and lay ply as they are in good condition and are contributing to both the thermal insulation and fire/rot resistance.

 

[hardmetalking]

I have fitted both in the past. The wood wool slab had galvanised tongue and groove top and bottom but we still installed 18mm ply over the top and fixed into the galv with self tappers. Then tyvek over the top and finally copper on top of that.
Couldn't believe that they still use the stuff as its horrible to cut and weighs a ton!
The only other option would be to install galvanised strips as set intervals and maybe bituthene over the top and this would give you a regular fixing point.
Hope this helps.

 

[Xenon]

Not all woodwall slab has the channels down the side. Best way to get a fix if they are the older type is straight through with a washr/nut.

 

[Tipper]

Just to close this out we didn't go for sheet metal roofing in the end but chose 'Dryseal' dry fix GRP system roofing. We added 50mm of insulation over the existing roof structure before the new system.
This was fixed to the wood-wool substrate using long peel rivets by SFS Intec. It worked really well although the rivets were on the expensive side they did a good job.