Hi
Just after some advice I've been asking to quote for cleaning a school. They want all windows inside and out cleaned which isn't to much of a problem just loads of windows 
The problem is that they want their skylites cleaned and there's about 50 of them only accessible by climbing on a flat roof I have a rule of not climbing on them.
So how do I find out how strong the roof is ?
I'm guessing it must be very strong as it is in a school and they don't want a roof falling in on a classroon full on kids.
Many Thanks
I'm sure anyone with building experience will back me up in saying that the weight of a single man could never be enough to cause the flat roof of any residential or commercial building to collapse (in this case I would class a school as 'commercial').
I would have no problem at all about walking on such a roof to clean skylights. I would be more concerned to be sure the ladder was properly set so that it couldn't slip or blow over sideways.
Having said that, the roof of the gymnasium of Camden School for Girls collapsed in the late 60's/early 70's - it was a job I used to clean regularly. Luckily it happened during the school holidays and also not while I was cleaning it!
It had been built with high-alumina cement which was widely used in the late 50's/early 60's but it corroded from the inside, meaning apparently sound concrete roof beams were actually disintegrating inside where no-one could see them. It caused a huge outcry at the time and many buildings had to be pulled down and rebuilt.