Flat Roof Joists

This demo version is fixed at 1m clear span.

Flat roof joists.

Flat the most economical flat truss for a roof is provided when the depth of the truss in inches is approximately equal to 7 of the span in inches. These triangulated structures with a high degree of strength and stability due to the geometry used form both the joist and rafter components of a building. Usually 400 450 or 600mm but any value can be used up to 610mm max. The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof.

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 47 x 195 4 41 4 31 3 92 47 x 220 5 04 4 85 4 41 75 x 170 4 50 4 38 3 99. In the warm flat roof construction there is insulation packed into every possible space where air can flow. Roof truss span chart. 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.

Spaced sheathing or 1x boards may be reduced slightly. Roof trusses in many modern construction projects prefabricated roof trusses are used. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. 1 enter joist details 1 1 span and joist spacing.

2 by 4 inch lumber. They are important load bearing structural elements. These structures are typically manufactured offsite to a detailed plan and delivered complete. Our floor joist span tables are based on loadings given in the newer amended version of bs 6399 1.

The full version allows any size. To build a roof joist for a flat roof you need some carpentry skills and a few basic tools. 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. Spans for 2x4 top chord trusses using sheathing other than plywood e g.

Similarly ceiling joists are the planks of wood that create the flat surface of your attic floor or top story ceiling. Flat roof joist calculator. Flat roof joists rafters purlin span tables for domestic floor joists to bs 5268 7 1 note. This is the distance between joist centres.