Timber Joist Flat Roof

For timber floors between homes.

Timber joist flat roof.

Tables 1 and 2 in this chapter are derived from the trada technology ltd. Span tables for solid timber joists. On a basic level flat roof construction comes in the form of roofing timbers or joists as they are more commonly known or steels that are laid across two uprights walls in most cases. At least 40mm bearing on supports.

The construction of the flat roof is similar to that of the timber upper floor. Depth to width ratio should not be greater than 6. If insulation is placed on top of the flat roof joists and as such the joists are not fastened to the boarding above the depth to width ratio should not be greater than 4. The section sizes are based on regularised als or cls timber.

Joist breadth 47mm. 1 2 timber strength class and joist size. Eurocode 5 span tables for solid timber members in floors ceilings and roofs for dwellings 3rd edition. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Floor joists flat roof joists assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls.

Maximum slop3 10 deg. This will give additional stability to the roof structure. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. Span is clear span between supports.

All roof timbers including joists wall plates blocking strutting battens firings and noggings must be to be preservative treated unless the timber used is naturally durable. Supporting imposed load for access and repair only. Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support. For additional stability you can also use steel joists that are built into one or both of the walls.