New shed roof

9 Jun 2014
Reaction score
United Kingdom
I don't need regs for my new shed/workshop.

My span for the roof joist will be 3.6m and the actual open span will be 3.35m.

Looking at the tables for flat roofs i really need to use a 170mm joist as this covers a 3.75m span.

Do you think i will be ok with the 145mm joist at 400mm centres ? This covers up to 3.08m

The roof will have insulation between the joists and osb sheets on top, finished with fibre glass.
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The restriction is just for deflection really, primarily under snow load as most roofs aren't designed for foot traffic. Maybe the odd cat. So in short it's fine, but you might have a bit of sag.

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