Flat Roof Joist Detail

In the warm flat roof construction there is insulation packed into every possible space where air can flow.

Flat roof joist detail.

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 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. The flange material is typically laminated veneer lumber lvl or solid sawn lumber and the web is made with plywood or osb. Cantilever nails may be used to attach backer block if length of nail is sufficient to allow clinching.

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. Nail to backer block and joist with 2 rows of 10d nails 6 o c. This demo version is fixed at 1m clear span. 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.

Downspout strap detail 1 4 dia. 1 enter joist details 1 1 span and joist spacing. 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. I joists are comprised of top and bottom flanges which resist bending united with webs which provide outstanding shear resistance.

Continuous ceiling joists or collar ties span from rafter to rafter. X 5 8 bolt brass alum. The full version allows any size. Detail for attachment to metal panel siding or fascia.

The construction of the flat roof is similar to that of the timber upper floor. Continuous insulation on top of sheathing exterior ci with fiber fill in joist cavity this is how to detail an unvented roof assembly for flat and low slope roofs. The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading.

This is the distance between joist centres. Minimum r value of exterior ci determined by total r value of insulated assembly see also. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. This detail for cmu installation only.

Flat roof joist calculator.