Flat Roof Rafts And Joists

Overwhelmingly popular roof rafters shown on the left image above were used in most houses in the past.

Flat roof rafts and joists.

The rafters in a flat roof serve as ceiling joists for the space below. In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. It is always better to have a large rafter rather than be concerned with a sagging roof. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center.

Span tables for flat roof joists to bs 5268 7 2 imposed loads of 0 75 kn m for maintenance and snow load are applicable where there is no permanent access no fixed ladder or staircase and most areas where the altitude does not exceed 100 metres refer to bs 6399 3. Span calculator for wood joists and rafters also available for the android os. Roof rafter span use this table to determine the maximum lengths of roof rafters based on species and grade of lumber spacing dimensions load and slope. They are nailed securely to exterior wall plates and to each other.

Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. The size of rafters for a flat roof depends on the horizontal span of the building the type and grade of timber used and the load on the roof. However with advanced technology new construction techniques have started using trusses shown on the right image above. If you have a low sloped roof or flat roof of less than 2 in 12 these evenly spaced planks will be called roofing joists.

Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground. Structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size of roof joist 400mm 450mm 600mm 47 x 97 1 84 1 81 1 74 47 x 120 2 43 2 39 2 27 47 x 145 3 08 3 02 2 87 47 x 170 3 75 3 67 3 42. Also available for the android os.