Construction Purlin Flat Roof

Insert two equally spaced nails into the rafter.

Construction purlin flat roof. Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member. Snap a chalk line horizontally across the roof two feet down from the top. Fasten the purlin with 16d common nails into each vertical rafter. Under purlins were typically propped off internal walls.

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. A common arrangement is a rafter and purlin system which combines purlins and rafters. Here is the formula for calculation of a roof purlin. Roof live load roof dead load x spacing x span of purlin 2.

In lightweight timber roof construction under purlins were used to support rafters over longer spans than the rafters alone could span. 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. The rafters are generally spaced every 16 inches on center.