Construction Flat Roof Joist Layout

Sizes of joists needed for flat roof construction.

Construction flat roof joist layout.

As you may imagine there is a fair amount of weight involved here in terms of boards felt etc. Hot tar and gravel. Of course you don t need to live in a modern house to deal with a flat roof. Surveyors span tables for designing roof rafters.

Let s consider a basic gable wood roof framing design. 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. Continuing on from part 3. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.

Here we have a wood framed gable roof. So any timber joists that are used need to be strong enough to support this weight. 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. Floor beam span tables of residential structural design we will now look at roof rafter and beam design.

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. Structural calculations for timber joists timber beams glulam beams flitch beams using the latest design codes. Suitable for uk building regulation approval.

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. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. There are several methods and materials for the design of the exterior surface of a warm or cold flat roof. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2.

Old asbestos roofs are often replaced with flat roofs. A flat roof usually consists of the following. Waterproof membrane to prevent water penetrating the structure and interior of the. 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.

Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. Flat roof joist calculator. For pitched roofs flat roofs and ceiling joists. 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.

Although flat roofs are cheaper to build than pitched roofs they have a shorter life span. For that reason cold flat roof construction needs to keep in mind the need for unblocked airflow.