Traditional Purlin Roof Construction

Building control guidance note purlin and rafter roofs timber sizes and construction details.

Traditional purlin roof construction.

Traditional or cut roof. They span from the wallplate to the ridge board providing a platform for the underlay battens and tiles. It s an l shaped house with two very different roofs one is a collar roof the other a purlin roof with rsjs forming the purlins see photos below. This house s roof construction used prefabricated trusses from turner timber.

The traditional option is steeply pitched rarely less than 35. Parts of a traditional queen post roof truss. The overall construction of a traditional cut roof is to ensure that the load of the roof is evenly transmitted to the walls below. At the eaves and halfway between the two where they are known as purlins.

Pitched roof construction. Roofs and not for traditional purlin and rafter roof construction. All the figures are based on roofing tiles or slates laid on. In traditional timber framing there are three basic types of purlin.

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. Purlin plate principal purlin and common purlin. The rafters are the main load bearing elements of the roof. Sizes used in traditional roofing construction.

There are two basic methods of pitched roof construction. There are three types of purlins in wood construction. Nowadays finding a traditional roof being constructed on a new building is quite difficult. They also provide a speedy construction reduce onsite labour and costs and are most importantly versatile and provide a form of flexibility as they tend to have the capacity for a wide range of roof coverings.

The longitudinal horizontal beam that is sitting on a post or the principal rafter of a truss and used to support common rafters. Once the purlins are in place the panels can be craned in in a matter of minutes. Since warm moist air is able to meet cold timber care must be taken to ventilate the roof void to minimise condensation and the possibility of rot. 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.

Here insulation is usually placed between the roof joists i e. The alternative construction is the traditional cold deck. By chance we came across this roof a few miles outside bristol. Purlin roofs and prefabricated roofs are the two common forms of roof structures.