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Two king post trusses linked to support a roof. Key:1: ridge beam, 2: purlins, 3: common rafters. This is an example of a "double roof" with principal rafters and common rafters. A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof.
This is accomplished by using metal ties fastened to each rafter or truss. This is not normally a problem in areas not prone to high wind or extreme weather conditions. In the UK, a concrete tiled roof would normally have rafters at 600 mm (24 in) centers, roof battens at 300 mm (12 in) centers and ceiling joists at 400 mm (16 in) centers.
Rafter ties are designed to tie together the bottoms of opposing rafters on a roof, to resist the outward thrust where the roof meets the house ceiling and walls. This helps keep walls from spreading due to the weight of the roof and anything on it, notably wet snow. In many or most homes, the ceiling joists also serve as the rafter ties. When ...
Compass rafter: A rafter curved or bowed on the top (the top surface of a rafter is called its "back") or both the top and bottom surfaces. Curb rafter: The upper rafters in a curb (kerb, gambrel, Mansard roof) roof. Hip rafter (angle rafter): The rafter in the corners of a hip roof. The foot of a hip rafter lands on a dragon beam.
The gable roof [2] is so common because of the simple design of the roof timbers and the rectangular shape of the roof sections. This avoids details which require a great deal of work or cost and which are prone to damage. If the pitch or the rafter lengths of the two roof sections are different, it is described as an 'asymmetrical gable roof'.
Roof shingles, like other building materials on vernacular buildings, are typically of a material locally available. The type of shingle is taken into account before construction because the material affects the roof pitch and construction method: Some shingles can be installed on lath where others need solid sheathing (sheeting) on the roof deck .
In steel construction, the term purlin typically refers to roof framing members that span parallel to the building eave, [5] and support the roof decking or sheeting. The purlins are in turn supported by rafters or walls. Purlins are most commonly used in Steel Framed Building Systems, where Z-shapes are utilized in a manner that allows ...
If built using dimensioned timber, each rafter is usually jointed into the previous one. More commonly, these roofs are constructed with roundwood poles where each rafter is laid upon the previous one. In both of these approaches, the roof is assembled by installing a temporary central support that holds the first rafter at the correct height.