Traditional Purlin Roof Construction

3 lean to roofs less common.

Traditional purlin roof construction.

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. 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. Building control guidance note purlin and rafter roofs timber sizes and construction details. A truss roof using factory made trusses which are delivered to site complete and just erected.

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. In architecture or structural engineering or building a purlin or purline is a horizontal structural member in a roof. Traditional roofs work by distributing loads from the rafters down through to the wall plate and then through to the walls below. Roofs and not for traditional purlin and rafter roof construction.

The use of purlins as opposed to closely spaced rafters is common in pre engineered metal building systems and both the ancient post and beam and newer pole building timber frame construction methodologies. In traditional construction spans of over 3 metres or so were often dealt with by adding a purlin. All the figures are based on roofing tiles or slates laid on. There are two basic methods of pitched roof construction.

Nails bolts and screws create a mechanical fixing to stop uplift through wind etc. Common purlins in wood construction also called a major rafter minor purlin system. The best way to transfer load is with a timber to timber joint a compression fixing.