Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
Both ridge and purlins only serve to stop the rafters moving sideways.
(Euler buckling etc,). They have very little structural effect beyond
that.

Perhaps you'd explain why my loft conversion involved the fitting of steel
purlins if they have so little work to do?


No idea. Possibly because whoever did it didn't do the sums, and just
decided to play safe in an ignorant sort of way. Its pretty common. I
have yet to meet a builder that really understood engineering
mathematics. The guys that did my house didn;t even understand triogonmetry.

They had to lay out the rafters at the right angle (52 degrees for
thatch) on the ground and measure across the span to get them cut to the
right length. Using a large protractor,...