Flat Roof Joist Construction Details

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

Flat roof joist construction details.

1 2 timber strength class and joist size. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Good installation begins with specification of the correct joist for the application. Many slope in several directions like squashed hip roofs toward scupper holes that connect to downspouts.

The construction of the flat roof is similar to that of the timber upper floor. Getting the balance right here is crucial as too much weight will inevitably lead to an unstable roofing structure. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. Other flat roof construction details often refer to the types of flat roof coverings.

I joists in floor and roof applications. Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size. In addition to floor and roof framing details this guide includes recommendations for cantilevers and placement of web holes. 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.

Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. A waterproof exterior layer is essential and there are a number of options including bitumen based felt or asphalt epdm rubber and pvc based systems as well as cold applied liquid systems bitumen coverings. 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. 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.

This will give additional stability to the roof structure. For additional stability you can also use steel joists that are built into one or both of the walls. I joist construction details.