Flat Roof Joist Design

There are several methods and materials for the design of the exterior surface of a warm or cold flat roof.

Flat roof joist design.

This includes structural joists to hold up a roof deck usually of timber boarding a suitable membrane to reduce the risk of condensation and a layer of insulation to keep the warmth in. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Flat roof span tables allow for a maximum roof pitch of 5º.

Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2. The construction of the flat roof is similar to that of the timber upper floor. There are two types of flat roof system and they differ according to whether the insulation is above or below the structural roof deck. Let s consider a basic gable wood roof framing design.

Spantec has prepared these tables for use by people skilled in the design and specification of the. Flat roofs create long horizontal planes reminiscent of the broad horizon line seen often in nature. Flat roof with no permanent access and altitude not exceeding 100m 0 75 kn m udl 0 9 kn point load most areas exceeding 100m but not exceeding 200m excluding parts of scotland pennines north east england refer to bs 6399 3 1 kn m udl 0 9 kn point load. Continue reading below our video of the day.

Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. Floor beam span tables of residential structural design we will now look at roof rafter and beam design. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. 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.

In order to make this correctly you will have to work out exactly what you need to do with your truss in order to create a flat roof. Here we have a wood framed gable roof. Continuing on from part 3. They re simple in form and function and are a good example of the modernist principle of clean lines.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Use recommended minimum roof pitches as specified by roof sheet supplier. Posts these span tables are designed for a minimum post size of 50 x 50 x 2 5mm up to a maximum height of 3 0m.