Timber Joist Flat Roof

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

Timber joist flat roof. At least 40mm bearing on supports. Eurocode 5 span tables for solid timber members in floors ceilings and roofs for dwellings 3rd edition. Tables 1 and 2 in this chapter are derived from the trada technology ltd. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. For timber floors between homes. Supporting imposed load for access and repair only. 1 2 timber strength class and joist size.

The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls. The joists should be sized using either the trada span tables or bs en 1995. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. Maximum slop3 10 deg.

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. Should refer to trada document span tables for solid timber members in floors ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. This will give additional stability to the roof structure. Floor joists flat roof joists assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2.

Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. The section sizes are based on regularised als or cls timber. The construction of the flat roof is similar to that of the timber upper floor. 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.

Joist breadth 47mm. 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. Depth to width ratio should not be greater than 6. Span tables for solid timber joists.