On 22/08/2016 12:51, fred wrote:
I wish to span 3.0m or thereabouts with galvanised corrugated
sheeting. (Sheet size 3.0m x 0.6m) Three purlins, one top and bottom
and one mid span. Pitch of about 5 degrees. What size rafter would I
need and what spaceing ? (It's for a lean-to type shed Im
comtemplating)

sounds like you have no more than 750mm between purlins, so the length
of unsupported rafter is small. 3x2 would me more than adequate, and you
could go for 600 centres. (in reality many a shed will have a larger
span, wider spacing, and a heavier felt roof, or 2x2 or even thinner!)



--
Cheers,

John.

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