Jim’ll Fix it (if Jim’s a roofer)
According to British Standards a wind loading calculation should be carried out on every roof to determine how the tiles should be secured to resist wind uplift; in other words, to stop them being blown off in high winds. This is usually done on larger projects, but on many smaller, one-off jobs it could still be down to the roofer to decide how to fix the tiles.
Don’t be a shrinking violet
You should never be afraid to ask the roofer how he intends to fix your tiles - and there is no reason why you can’t specify how you, as the homeowner, want your tiles fixed. The choices are usually nail or clip, or both. Some roofers don’t even nail all the tiles, so a good starting point is to insist that every tile be fixed.
On my re-roofing project the calculations showed that all tiles should be clipped. Our house is in quite an exposed area so we nailed each tile and used Cassius plastic clips, to match the roof tiles and to make sure everything fit together nicely.
For some of the very small cut pieces at the valleys we used screws and also adhesive to ensure the tiles were secure. But if you use adhesive you have to be sure to use a suitable type that is going to last – check with the supplier as they will have all the details for the various fixing systems.