Flat Roof Joist Construction

1 enter joist details 1 1 span and joist spacing.

Flat roof joist construction.

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. Flat roofs with a slight slope can be achieved using trus joist tji joists and solid section products. 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. This will give additional stability to the roof structure.

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

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. Many slope in several directions like squashed hip roofs toward scupper holes that connect to downspouts. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. 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. 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. 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.

This demo version is fixed at 1m. For additional stability you can also use steel joists that are built into one or both of the walls. The standard construction of interior framing in a home uses 16 inch on center oc spacing for ceiling joists.