Timber Flat Roof Construction Details

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

Timber flat roof construction details.

Others would treat even steeper pitches as flat roofs. The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls. When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off. It must provide adequate protection against the elements keeping the buildings structure and interior dry.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. 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 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.

A flat roof must be strong durable and stable throughout its lifetime. Applying a liquid waterproofing agent will often add a few more years to the roof. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. A popular method involves a cold application bitumen emulsion which is applied onto the surface.

Having a manual for warm flat roof construction with details and a summary of rules to follow helps.