Traditional Purlin Roof Construction

All the figures are based on roofing tiles or slates laid on.

Traditional purlin roof construction.

In traditional construction spans of over 3 metres or so were often dealt with by adding a purlin. In architecture or structural engineering or building a purlin or purline is a horizontal structural member in a roof. Building control guidance note purlin and rafter roofs timber sizes and construction details. It is a very common form of construction.

3 lean to roofs less common. Nails bolts and screws create a mechanical fixing to stop uplift through wind etc. A truss roof using factory made trusses which are delivered to site complete and just erected. Common purlins in wood construction also called a major rafter minor purlin system.

Purlins support the loads from the roof deck or sheathing and are supported by the principal rafters and or the building walls steel beams etc. This is a large timber running at right angles to the rafters and usually positioned mid span. Common purlins are typically trenched through the top sides backs of principal rafters and carry vertical roof sheathing the key to identifying this type of roof system. Roofs and not for traditional purlin and rafter roof construction.

The best way to transfer load is with a timber to timber joint a compression fixing. 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 roofs work by distributing loads from the rafters down through to the wall plate and then through to the walls below.