Flat Roof Rafter And Joists

Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure.

Flat roof rafter and joists.

When placing rafters for a tin roof also frequently referred to as corrugated metal or steel it is common to set the distance between rafters based on the size of the roofing panels. The boards creating the slope of the roof are wider than lumber used to build trusses 2x8s 2x10s and 2x12s are most common in rafters vs. In a typical roof framed with dimension lumber the rafters rest on the exterior wall top plate at the lower end and bear against a ridge board at the top. 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.

In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. Also available for the android os. Span calculator for wood joists and rafters also available for the android os. Similarly ceiling joists are the planks of wood that create the flat surface of your attic floor or top story ceiling.

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. 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. Ceiling joists can be on both low sloped roofs and high sloped roofs and help to prevent racking and spreading of your rafters or walls which could lead to sagging. Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 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. In finished space insulation is placed between the rafter boards and drywall or other material is fastened to the face. Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size.

Conventional framing the first thing to understand is how a roof framed with wood i joists differs structurally from a traditional stick framed roof. They are nailed securely to exterior wall plates and to each other. The rafters in a flat roof serve as ceiling joists for the space below.