harry wrote:

Thomas Prufer wrote:

Onduline is still crap!

Mine's seven years old, and I can get maybe three more years out of it. It's
been repainted once with bituminous glop: The red color came off after a few
years, and after pressure-washing the algae and moss off

Yes, you're right about sagging.
It's largely caused by the interior of the building getting hot. (Black roofs don't help).

Mine (actually I think it's the thinner coruline), is on a sturdy T&G
roof, with cross-battens spaced as recommended, nailed using the proper
fixings. Part of it is under a tree but after 4 years it hasn't needed
pressure washing or glop, the rain seems to keep it clear, maybe it's
down to the angle?