Traditional Timber Roof With Purlins

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 timber roof with purlins.

Of course if there is intermediate support you can get away with a lighter and cheaper truss. It is a horizontal bar that used to support building at the roof structurally. Roof trusses can also span much greater distances without intermediate support than traditional beams purlins and joists. Video of traditional cut roof detail.

The collar ties and hangers are used to improve the overall strength and stability of the roof. The purlins are supported by struts which in turn are supported on an internal load bearing wall. The collar ties are used to connect the rafters preventing them from spreading outwards. 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.

A common arrangement is a rafter and purlin system which combines purlins and rafters. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. Is possible compared with about 5m. Purlins are installed horizontally under metal roofs.

In traditional construction spans of over 3 metres or so were often dealt with by adding a purlin. A truss roof using factory made trusses which are delivered to site complete and just erected. Building control guidance note purlin and rafter. Roofs and not for traditional purlin and rafter roof construction.

Purlin plate principal purlin and common purlin. In lightweight timber roof construction under purlins were used to support rafters over longer spans than the rafters alone could span. 3 lean to roofs less common. In traditional timber framing there are three basic types of purlin.

They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. Purlins are 2 by 4 feet and are installed much like metal roofing. Under purlins were typically propped off internal walls. 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.

All the figures are based on roofing tiles or slates laid on. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction. This is a large timber running at right angles to the rafters and usually positioned mid span. There are two basic methods of pitched roof construction.

It is a very common form of construction.