Flat Roof Joist Construction

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.

Flat roof joist construction.

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. Joist spacing in this design mode incorporates different types of wood used in ceiling construction including 2 grades of southern pine douglas fir and hemlock fir types which are the most common. The most important thing to know about a flat roof says tom is that it s not flat to prevent water from pooling and eventually invading the home flat roofs are always built on a slight incline at least 1 8 inch per foot. The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls.

Flat roofing under construction plywood decking is then used to cover the joists with the width in between also determined by the weight being placed upon them. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. For additional stability you can also use steel joists that are built into one or both of the walls. The construction of the flat roof is similar to that of the timber upper floor.

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. Suitable for uk building regulation approval. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

1 enter joist details 1 1 span and joist spacing. This demo version is fixed at 1m. Getting the balance right here is crucial as too much weight will inevitably lead to an unstable roofing structure. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.

The standard construction of interior framing in a home uses 16 inch on center oc spacing for ceiling joists. This will give additional stability to the roof structure. Flat roof joist calculator.