Flat Roof Joist Design

They re simple in form and function and are a good example of the modernist principle of clean lines.

Flat roof joist design.

Continue reading below our video of the day. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. A flat roof truss is also known simply as a flat truss and is not completely flat but rather slightly sloped in order to allow water to run off of the roof. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial.

Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. The construction of the flat roof is similar to that of the timber upper floor. 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. There are two types of flat roof system and they differ according to whether the insulation is above or below the structural roof deck.

Flat roofs can cantilever into daring overhangs for shade protection and solar gain control. 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. 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. Let s consider a basic gable wood roof framing design.

Use recommended minimum roof pitches as specified by roof sheet supplier. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. 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. Spantec has prepared these tables for use by people skilled in the design and specification of the.

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. Flat roofs create long horizontal planes reminiscent of the broad horizon line seen often in nature. Floor beam span tables of residential structural design we will now look at roof rafter and beam design. Here we have a wood framed gable roof.

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. Continuing on from part 3. There are several methods and materials for the design of the exterior surface of a warm or cold flat roof.