Flat Roof Joist Detail

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

Flat roof joist detail. Minimum r value of exterior ci determined by total r value of insulated assembly see also. Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall. Of course you don t need to live in a modern house to deal with a flat roof. Downspout strap detail 1 4 dia.

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. Cantilever nails may be used to attach backer block if length of nail is sufficient to allow clinching. The construction of the flat roof is similar to that of the timber upper floor. Detail for attachment to metal panel siding or fascia.

Continuous ceiling joists or collar ties span from rafter to rafter. A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space. In a typical roof framed with dimension lumber the rafters rest on the exterior wall top plate at the lower end and bear against a ridge board at the top. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure.

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. 1 enter joist details 1 1 span and joist spacing. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. Flat roof joist calculator.

Flat roofs aren t architecturally logical as rain and snow will shed much more quickly off a sloped roof. In the warm flat roof construction there is insulation packed into every possible space where air can flow. This demo version is fixed at 1m clear span. X 5 8 bolt brass alum.

This is the distance between joist centres. This detail for cmu installation only. There is no need for bearing posts under the ridge board which is nonstructural. Figure 3 i joist cantilever detail for balconies 1 1 2 x l4 minimum 4 maximum where l is length l of cantilever 2 x 8 min.

The full version allows any size. 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.