Structural Timber Flat Roof Construction Details

A flat roof must be strong durable and stable throughout its lifetime.

Structural timber flat roof construction details.

Wherever possible joists should span the shortest distance of the roof plan. The construction of the flat roof is similar to that of the timber upper floor. That will help you remember certain factors and details to build the best possible flat roof. An example of each is shown in figure 2 1.

The rafters are not framed into the. So any timber joists that are used need to be strong enough to support this weight. Part b structure investigates the structural aspects of flat roofs. It must provide adequate protection against the elements keeping the buildings structure and interior dry.

The pitch is governed by the roof covering and the required rate of rainwater discharge. Sizes of joists needed for flat roof construction. The structural relationship between the rafters and the wall is the same in all types of roofs. When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off.

A roof is defined in bs 6229 as a flat roof if it has a pitch of 10 degrees or less. Modern timber roofs are mostly framed with pairs of common rafters or prefabricated wooden trusses fastened together with truss connector plates timber framed and historic buildings may be framed with principal rafters or timber roof trusses roofs are also designated as warm or cold roof depending on how they are designed and built with regard to thermal building insulation and ventilation. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc.

Having a manual for warm flat roof construction with details and a summary of rules to follow helps. Others would treat even steeper pitches as flat roofs. Old asbestos roofs are often replaced with flat roofs. The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls.

As part of the drive to deliver sustainable materials and energy efficient buildings the sta provides best practice guidance for its members. The definition of a flat roof according to bs 6229 is having a pitch less than 10 o to the horizontal however some in the industry would consider up to 15 o as their definition of a flat roof. The structural timber association sta is the membership body which promotes the use of structural timber and hybrid forms of timber construction such as structural insulated panels sip in buildings. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

Flat roof types. The most commonly used types of pitched roof construction are the gable the hip the intersecting and the shed or lean to.