Flat Roof Joist Layout

They are important load bearing structural elements.

Flat roof joist layout.

Waterproof membrane to prevent water penetrating the structure and interior of the. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Continuing on from part 3. Sizes of joists needed for flat roof construction.

The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof. Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size. Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall. 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.

As you may imagine there is a fair amount of weight involved here in terms of boards felt etc. A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space. Let s consider a basic gable wood roof framing design. Although flat roofs are cheaper to build than pitched roofs they have a shorter life span.

So any timber joists that are used need to be strong enough to support this weight. Roof rafter span use this table to determine the maximum lengths of roof rafters based on species and grade of lumber spacing dimensions load and slope. Ceiling joists can be on both low sloped roofs and high sloped roofs and help to prevent racking and spreading of your rafters or walls which could lead to sagging. A roof is considered to be flat when it is of a slope of 1 5 o to the horizontal.

Floor beam span tables of residential structural design we will now look at roof rafter and beam design. Old asbestos roofs are often replaced with flat roofs. Similarly ceiling joists are the planks of wood that create the flat surface of your attic floor or top story ceiling. Here we have a wood framed gable roof.

A flat roof usually consists of the following. Joists are the repeated structural members that are used to build a deck. There are design differences for each type.