Traditional Purlin Roof Construction

Roofs and not for traditional purlin and rafter roof construction.

Traditional purlin roof construction.

The best way to transfer load is with a timber to timber joint a compression fixing. 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. 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. 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.

There are two basic methods of pitched roof construction. Building control guidance note purlin and rafter roofs timber sizes and construction details. Traditional roofs work by distributing loads from the rafters down through to the wall plate and then through to the walls below. It is a very common form of construction.

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. All the figures are based on roofing tiles or slates laid on. 3 lean to roofs less common.

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. In traditional construction spans of over 3 metres or so were often dealt with by adding a purlin. Sizes used in traditional roofing construction.