Roof Rafter Centres

Maximum clear span of rafters in metres for roof pitches of between 15 and 45 degrees.

Roof rafter centres.

With rafter spacing of. Provides guaranteed actual ventilation opening of 25 000mm m. The spacing between rafters in a given building is part of the engineering calculations that determine the required structure of the roof. Wane as allowed in bs 4978 2007 a2 2017 is permitted in all sections included in these span tables.

Depending upon the roof covering material the rafters are spaced 30 to 45 cm centre to centre. Other relevant factors include the type of wood being used for the rafters the size of the rafters and the load that the rafters need to support. At eaves level vertical straps 1m long should be fixed as shown in the diagram opposite at a maximum of 2m centres. Holes drilled at the neutral axis centre line are not to exceed 0 25 of the depth of a joist and are not to be less than three diameters centre to centre apart and are to be located between 0 25 and 0 4 of the span from the support.

Note that these are normally only required to trussed rafter roofs and not for traditional purlin and rafter roof construction. Battens should be fixed to rafters set at centres not more than 600 mm apart and should span at least 3 rafters. Gable walls need to be strapped to the roof at mild steel straps. Universal rafter trays which adjust to the correct roof pitch and can be used in new build or in refurbishment without disturbing the roof covering.

Maximum 2m centres using 30 x 5mm galvanised. Surveyors span tables for designing roof rafters. Pole barn roof truss spacing generally tens to operate according to similar spacing principles though there are some proponents of having higher pole barn roof truss spacing. They transfer the load coming from the roof to the beam and wall.

Surveyors and structural engineers utilise data from tables below to help calculate the correct size strength and centres of roof timbers for the required spans and loadings. Rafter is a inclined member of roof which support the batten and roofing material above it. Rafter ventilators are designed to ensure a clear air path between roof underlay and insulation at all types of eaves. These member runs from the ridge to the eaves.

Size of rafters in mm. Span tables for purlin supporting rafters to bs 5268 7 6 imposed loads of 0 75 kn m snow load are applicable to most areas where the altitude does not exceed 100 metres refer to bs 6399 3 imposed loads of 1 kn m snow load are applicable to most areas where the altitude exceeds 100 metres but does not exceed 200 metres but excluding parts of scotland pennines north east england. Roof pitch between 15 and 22 5 degrees. Especially when steel roof truss spacing is concerned some engineers would argue that it is possible to only have a roof truss spacing of four feet off center even eight feet has been suggested.

For pitched roofs flat roofs and ceiling joists.