Flat Roof Rafts And Joists

Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size.

Flat roof rafts and joists.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. The rafters in a flat roof serve as ceiling joists for the space below. Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground. Roofs come in various sizes and shapes such as shed hip flat gable gambrel to name a few.

It is always better to have a large rafter rather than be concerned with a sagging roof. Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. 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. They are nailed securely to exterior wall plates and to each other.

However with advanced technology new construction techniques have started using trusses shown on the right image above. Structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. Overwhelmingly popular roof rafters shown on the left image above were used in most houses in the past. 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.

In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. Span calculator for wood joists and rafters also available for the android os. 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. 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.

Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. 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.