Traditional Cut Purlin Roof

A cut roof this is the traditional method of cutting the timber on site and building up the roof using rafters ridge boards joists and purlins etc the exact details being determined by the size of roof size of timbers etc.

Traditional cut purlin roof.

A common arrangement is a rafter and purlin system which combines purlins and rafters. 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. 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 traditional timber truss construction purlins rest on the principal rafters of the truss.

In the left hand image you can see the overall layout of the roof. They span from the wallplate to the ridge board providing a platform for the underlay battens and tiles. It has a timber purlin on each slope built into the gable ends. This roof shown on a previous page is a good example of a traditional cut roof with dormers.

From the 1970s onwards most low rise domestic pitched roofs have been formed with trussed rafters. A truss roof using factory made trusses which are delivered to site complete and just erected.