Flat Roof Framing Detail

If you build a flat roof try to have it slope in multiple directions to drains or gutters.

Flat roof framing detail.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. And the line length measurement from the roof peak to the building wall is the hypotenuse. You can do this with a foam layer that exactly fits your roof. Here the rubber roof will need to run up the walls and glue to the sheathing.

The rise or height of the roof at its peak is the altitude of the triangle. It can be framed like a floor system with horizontal framing members at 16 19 or 24 o c. Some roofs actually slope in several directions ensuring optimal water runoff. When framing a flat roof you will need to create a slight incline.

The construction of the flat roof is similar to that of the timber upper floor. Think of a flattened hip roof. From there the flat roof system you choose will determine the materials you apply. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls.

It is not ideal for snow or heavy rain but modern materials and proper drainage have helped. On two sides the roof abuts a parapet a short wall common around flat roofs as well as a wall for the third floor. 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. Cad details document name pdf dwg download all cad construction details 37 1 mb 3 4 mb mc01 identification of roof areas 694 kb 167 kb mc01a single layer underlayment 678 kb 302 kb mc01b double layer underlayment 711 kb 322 kb mc02 vent pipe flashing 626 kb 349 kb mc03 valley.

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure. A flat roof has a slope of 1 8 per foot to 2 12. Flat roofs are always built at a slight incline at least 1 8 inch per foot. 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.

The run or half the building span is the base of the triangle. To keep water from pooling at these inside corners tom rips 2x4s lengthwise on a 45 degree bevel with a table saw. The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle.