Construction Purlin Flat Roof

For example an 8 x 4 under purlin would support the center of a row of 6 x 2 rafters that in turn would support 3 x 2 roof purlins to which the roof cladding was fixed.

Construction purlin flat roof. Fasten the purlin with 16d common nails into each vertical rafter. A common arrangement is a rafter and purlin system which combines purlins and rafters. Cos of live load dead load x cos of the purlin spacing x purlin span squared 8 x sm section modulus of the member x duration of load 1 15 in areas with snowfall x cr repetitive member factor of 1 15 where members are 24 on center or less fb fiberstress required. Insert two equally spaced nails into the rafter.

Snap a chalk line horizontally across the roof two feet down from the top. Roof live load roof dead load x spacing x span of purlin 2. The roof support system is a ridgepole and either rafters which run perpendicular from the top of the walls to the ridge or purlins which run parallel to the ridge. In lightweight timber roof construction under purlins were used to support rafters over longer spans than the rafters alone could span.

Lay the first purlin at the ridge of the roof down to the chalk line beginning at either corner. Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. 8 x section modulus of a 4 2 of 1 3125 x fb fiberstress in bending x 1 15 duration of load x 1 15 cr repetitive member factor as the purlins are spaced 24 o c.