How much can you screw into the roof trusses?

[Lego Pusselsson]

I was thinking of installing a new ceiling over the old ceiling and screwing directly through the old ceiling into the rafters. The new ceiling is panel, boards in pine.

So it will be about 5cm screws approximately every 15cm in the rafters throughout an entire room.

Is that okay? Or is there any risk that the load-bearing capacity of the rafters will be weakened?

In another room, I also plan to install a strong double metal curtain rail with heavy curtains, so there might be a need for slightly longer screws into the rafters.

 

[Plutus]

No problem, but how will you find the roof trusses? Are there nail rows today that can be followed?

 

[Lego Pusselsson]

No problem, but how will you find the roof trusses? Are there nail lines today that one can follow?

Thanks! Yes, the old ceiling (some kind of masonite with grooves around) seems to have the joints at the roof trusses where I assume they are nailed.