The message
from The Natural Philosopher contains these words:

It seems that the 'purlins' in this case ARE propped - at the gable ends.

Which was the nature of purlins in domestic house construction in this
country until very recently. (Although I don't accept that the
horizontal ties in truss roofs are purlins).

And the roof is not a trussed roof at all.

No idea why you should have thought it was in the first place. There is
nothing in Simons original post to suggest a loft stuffed full of
struts.

And nothing in your early posts to suggest you were confining your
remarks to a trussed roof either.

--
Roger Chapman