Construction Flat Roof Joist Layout

Floor beam span tables of residential structural design we will now look at roof rafter and beam design.

Construction flat roof joist layout.

A roof is considered to be flat when it is of a slope of 1 5 o to the horizontal. Flat roof construction for residential. Hot tar and gravel. The 3 most common materials used for flat roof construction.

Although flat roofs are cheaper to build than pitched roofs they have a shorter life span. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Of course you don t need to live in a modern house to deal with a flat roof. 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.

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. Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. Let s consider a basic gable wood roof framing design.

Waterproof membrane to prevent water penetrating the structure and interior of the. So any timber joists that are used need to be strong enough to support this weight. There are several methods and materials for the design of the exterior surface of a warm or cold flat roof. 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.

Here we have a wood framed gable roof. 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. A flat roof usually consists of the following. Structural calculations for timber joists timber beams glulam beams flitch beams using the latest design codes.

For that reason cold flat roof construction needs to keep in mind the need for unblocked airflow. Continuing on from part 3. 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. Old asbestos roofs are often replaced with flat roofs.

Suitable for uk building regulation approval. 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. Flat roof joist calculator. 1 enter joist details 1 1 span and joist spacing.

Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc.