Flat roof... strength?

[Westyfield2]

I've always been paranoid when up on a flat roof. Walk really gently, and keep to the edges.

When the garage roof was being re-tarmaced, the builders were walking right down the middle of it, with a few of them up there at a time. Plus they each weighed a good bit more than me . Neighbours are having some work done today, and their builders are walking around all over their garage's flat roof too.


So... are flat roofs stronger than I thought? Or do the builders like living on the edge and they're going to fall through any minute now?

 

[Westyfield2]

Thanks. Had a look in the Garage, and 50+ years later you can still read the stamp of the Canadian woodmill on the underside! Says they're 3/4", so that's 19mm .

Our plumber fell through our flat roof when installing the condensate drain for a new boiler. To reach it he'd put a ladder on top of the flat roof! The point load was too much and he and the ladder came crashing through the roof, squeezing between the joists.

Muppet! I know the square root of nothing about building, but even I would think to spread the load out rather than a point!