Construction Flat Roof Joist Layout

If you re trying to reinforce a shed or gable roof use a simple king post truss design which has a single vertical joist running through the center of the triangular frame.

Construction flat roof joist layout. Structural calculations for timber joists timber beams glulam beams flitch beams using the latest design codes. Floor beam span tables of residential structural design we will now look at roof rafter and beam design. Surveyors and structural engineers utilise data from tables below to help calculate the correct size strength and centres of roof timbers for the required spans and loadings. Flat roof joist calculator.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc. Let s consider a basic gable wood roof framing design. Continuing on from part 3.

Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. For pitched roofs flat roofs and ceiling joists. Yet for historic modern style buildings like this old house s cambridge tv project flat roofs are at the core of the architecture meant to reflect the broad horizontal lines of the natural landscape. 1 enter joist details 1 1 span and joist spacing.

Sizes of joists needed for flat roof construction. Surveyors span tables for designing roof rafters. 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. Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size of roof joist 400mm 450mm 600mm 47 x 97 1 84 1 81 1 74 47 x 120 2 43 2 39 2 27 47 x 145 3 08 3 02 2 87 47 x 170 3 75 3 67 3 42.

Here we have a wood framed gable roof. Waterproof membrane to prevent water penetrating the structure and interior of the. For that reason cold flat roof construction needs to keep in mind the need for unblocked airflow. A roof is considered to be flat when it is of a slope of 1 5 o to the horizontal.

The 3 most common materials used for flat roof construction. For larger structures like floors roofs or decks try a fink truss design which has internal joists arranged in a w shape for extra support. Suitable for uk building regulation approval. A flat roof usually consists of the following.

Although flat roofs are cheaper to build than pitched roofs they have a shorter life span. Hot tar and gravel. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. So any timber joists that are used need to be strong enough to support this weight.

Of course you don t need to live in a modern house to deal with a flat roof. Old asbestos roofs are often replaced with flat roofs.