Flat Roof Joist Construction

The starting point involves laying roofing joists across the two upright items which in most cases will be the walls of the structure.

Flat roof joist construction.

This demo version is fixed at 1m. 1 enter joist details 1 1 span and joist spacing. Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall. Rolled steel joists or rsj s are used to support joists in flat roofs.

Strutting is fixed between the joists to. Having a manual for warm flat roof construction with details and a summary of rules to follow helps. Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. The construction of the flat roof is similar to that of the timber upper floor.

There are key differences between constructing a flat roof compared to a pitched roof and it s important to understand the basic criteria. 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. A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space. For additional stability you can also use steel joists that are built into one or both of the walls.

The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls. Flat roof joists. Flat roof joist calculator. 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.

It is the responsibility of the designer of record to address items like ponding snow drift loads lateral loads wind loads bracing ventilation and insulation when adding a slope to roofs. Suitable for uk building regulation approval. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. If you have a low sloped roof or flat roof of less than 2 in 12 these evenly spaced planks will be called roofing joists.

Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. Flat roofs with a slight slope can be achieved using trus joist tji joists and solid section products. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Of course you don t need to live in a modern house to deal with a flat roof.