Construction Flat Roof Joist Layout

The construction of the flat roof is similar to that of the timber upper floor.

Construction flat roof joist layout.

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. 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. Typically the roof beam is made by nailing together a few pieces of dimensional lumber. Of course you don t need to live in a modern house to deal with a flat roof.

Build a fink truss to bolster a floor roof or deck. Flat roof joist calculator. The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls. Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof.

For additional stability you can also use steel joists that are built into one or both of the walls. Timber floor joists shall be adequate for the spans and loads and be correctly installed. Solid timber joist sizes are provided in the bs 8103 3 span tables. On a basic level flat roof construction comes in the form of roofing timbers or joists as they are more commonly known or steels that are laid across two uprights walls in most cases.

Fink trusses were originally invented for the purpose of beefing up bridges but many contractors now use them to increase the strength of interior structures. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. From there the flat roof system you choose will determine the materials you apply. Where the tables do not apply or where there are concentrated loads floor joists should be designed by an engineer in accordance with technical requirement r5.

Underneath the basics flat roofs are usually constructed with a ceiling nailed to joists which support a deck usually wood in residential construction a vapor barrier insulation and a roof board. This will give additional stability to the roof structure. Once again you will need to look at your local charts and use your local snow load factor to determine the maximum span for a given wood rafter size. Structural calculations for timber joists timber beams glulam beams flitch beams using the latest design codes.

Surveyors span tables for designing roof rafters. Built up roof beams you will need a roof beam as a nailing surface to support the rafters. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. In a fink truss the internal joists are arranged in a w shape ensuring even weight distribution from one end to the other.

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.