in answer to the preasure treated timber (and a couple of other things)
in the uk engineers, architects and building control officers almost always require strength graded and preasure treated timber to be used in joists and roofs.
my GUESS is that strength calculations are easier and the stamped grading guarantees that cowboys havent subtituted cheap low grade timber
preasure treatment of joists and roof timbers, makes sense to me
i fairly regularly have to replace floor joists that have suffered with dry or wet rot, i GUESS it is partly to do with our climate
second
for those who may not recognise C16 timber or C24 timber
they are strength grades, not visual grades, or batch grading
each individual piece of timber is put through a machine and stamped with its grade
anyway
the spec was for preasure treated C16 timber joists for this beam (32mm finished size, a non standard thickness)
so there are a couple of things that are slightly peculiar
first the strength grading is no longer valid, because the timber was graded at 47mm thick not at 32
however in practice timbers cut to length or ripped are still considered to be within grade
regardless of the preasure treatment, the engineer did not require the ripped faces to be re treated
