Technical Booklet D Structure·Page 49·4B.14
Flat roof joist span and spacing definitions and minimum bearing
Clear span is measured horizontally between supports, joist spacing is centre-to-centre dimension, roof slope must not exceed 10 degrees, and minimum bearing length is 35 mm.
Tables 4B.35 to 4B.40 are for a slope of up to 10° from the horizontal. Clear roof joist span is the clear dimension measured horizontally between supports. Take the roof joist spacing as the dimension between their centre lines. The minimum bearing of roof joists should be 35 mm.
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