Detail Flat Roof Joist Construction

What is the process of building a flat roof.

Detail flat roof joist construction.

In addition to floor and roof framing details this guide includes recommendations for cantilevers and placement of web holes. The definition of a flat roof according to bs 6229 is having a pitch less than 10 o to the horizontal however some in the industry would consider up to 15 o as their definition of a flat roof. Some observers suggest it s harder to replace a flat roof than a traditional pitched shingle roof because of the labor required to remove its layers especially on older flat roofs. 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.

Old asbestos roofs are often replaced with flat roofs. Others would treat even steeper pitches as flat roofs. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. I joist construction details.

This could mean flat roofs may not raise the same red flags they used to. Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc. Of course you don t need to live in a modern house to deal with a flat roof.

Good installation begins with specification of the correct joist for the application. I joists in floor and roof applications. So any timber joists that are used need to be strong enough to support this weight. The starting point involves laying roofing joists across the two upright items which in most cases will be the walls of the structure.

The construction of the flat roof is similar to that of the timber upper floor. Flat roof detail masonry cavity wall flat roof insulation above and between. In the warm flat roof construction there is insulation packed into every possible space where air can flow. 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.

When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off. Flat roofs are hard to replace. There are key differences between constructing a flat roof compared to a pitched roof and it s important to understand the basic criteria. Important note for cold roof construction a 50mm airspace is required for ventilation purposes over the insulation the minimum depth of joist required is usually taken as 175mm even if a lesser depth would be acceptable from a purely structural point of view ventilation details for flat roofs.

Masonry cavity wall flat roof insulation above and between joists.