I acquired an ordinary national certificate in mechanical engineering
some 40+ years ago, unused since.

Can some kind person direct me to a source for understandable formulae
for working out approximate purlin loading on a simple pitched roof? I
assume the existing trusses will be adequate.

I am replacing a time expired corrugated steel roof and am considering
using composite roof panels which are much heavier:-)

The original building is Victorian/agricultural but I can't see any
evidence of an earlier slate covering and the truss/purlin spacing is
only suitable for rigid sheeting.

Having just glanced at a chapter on theory of structures (Mitchell,
building construction) I fear I may be heading for deep water:-)

regards
--
Tim Lamb