Weatherlawyer wrote
Mr Pounder Esquire wrote

Many years ago when I lived in Australia some houses had "tin" roofs.
Apparently when it rained the noise was awful.

Made up for, no doubt, by the fact it was raining.

Not necessarily, we have a wet winter at the moment.

The tin has several inches of insulation under it. The
major problem is preserving the weather seal at joints.

Not with metal decking which has no joints at all where
the water is, it is one continuous length with the joints
well up from the deck itself where there is no water.

Tin flexes in violent winds and expands
and contracts a lot more than stone or clay.

Yes.

Large sheets being both a blessing and a downfall.

Not when they are long and thin with the joint well up from
the deck. Which is why metal decking is done that way.

I imagine going around the finished product with
a soldering iron might be the only way to cure that.

You're wrong. The way to fix the problem is the way
metal decking does it, very long sheets that have no
joints at all where the water is with the joints between
the individual sheets of decking well up out of the water.
Works very well indeed and very easy to lift up a sheet
to get at the wiring etc and put it back again too.