Using regularised UK timber dimensions, it is possible to determine the maximum span of timber rafters subjected to different values of live loads according to BS 5268-7.5. Roof slope is the degree of change in height as a ratio of horizontal distance traveled, usually expressed as inches of rise per foot of horizontal run, or cm of rise per m of horizontal run. A jack rafter is one that has been shortened by falling on a hip rafter or being interrupted by a dormer window.Ī roof span is normally the same as the building width between the outer edges of the wall top plates. They extend up from the top of the wall plate at a right angle (90°) to abut into an existing hip rafter. Jack rafterĪ jack rafter is any rafter that is shorter than the whole length of the sloping roof, such as one that begins or ends at a hip or valley. To put it another way, it’s the main rafter at the bottom of a hip and valley roof. The valley rafter is the rafter in the valley line that joins the ridge to the wall plate along the meeting line of two sloped sides of a roof that are perpendicular to each other in a roof framing system. Traditional stick-framing techniques can be used to make these rafters, or they can be integrated in a pre-engineered steel or timber truss system.
A hip rafter connects to the ridge at a 45-degree angle, as opposed to ordinary roof rafters, which run perpendicular to the peak of the roof. These are rafters that runs diagonally between the roof ridge and the top of the wall plate, forming a hipped roof.
It could also be left as open space in an attic.įigure 8: The components of a hip and valley roof Hip rafter As a result, the area in the roof is left as a vaulted ceiling that may be finished with insulation and drywall. The rafters and external walls are then connected with ceiling joists. Hence, timber rafters are usually constructed in form of A-shape, consisting basically of the rafters, rafter ties, and ridge board/hips. Trussed rafters are generally employed for large scale timber roof construction, but direct timber rafters are more efficient for small scale constructions. Timber rafters rely on nails or screws for connection. The number of common rafter units needed for each project is mostly determined by the roof’s size and scope, as well as the distance each unit rafter must span. Many common, or general purpose, rafters make up each roof. The common rafters form the sloped sides of the triangle on a traditional gable roof, which has a triangular shape. Rafters are part of a basic wood framing system and are made of wood lumber. Timber rafters are popular options in timber/wooden roof structures. Figure 4: Steel portal frame consisting of stanchions and rafters Timber Rafters
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