Flat Roof Framing Detail

The steels or rsj s rolled steel joists are often built into one or both walls to give added stability to the roof structure.

Flat roof framing detail.

If you build a flat roof try to have it slope in multiple directions to drains or gutters. 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. The run or half the building span is the base of the triangle. You can do this with a foam layer that exactly fits your roof.

Some roofs actually slope in several directions ensuring optimal water runoff. From there the flat roof system you choose will determine the materials you apply. Here the rubber roof will need to run up the walls and glue to the sheathing. And the line length measurement from the roof peak to the building wall is the hypotenuse.

It is not ideal for snow or heavy rain but modern materials and proper drainage have helped. To keep water from pooling at these inside corners tom rips 2x4s lengthwise on a 45 degree bevel with a table saw. Flat roofs are always built at a slight incline at least 1 8 inch per foot. It can be framed like a floor system with horizontal framing members at 16 19 or 24 o c.

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. 2x framing wood joists timber framing laminated beams steel concrete or sips. The construction of the flat roof is similar to that of the timber upper floor. On two sides the roof abuts a parapet a short wall common around flat roofs as well as a wall for the third floor.

Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. The rise or height of the roof at its peak is the altitude of the triangle. Depending on the span many different materials can frame a flat roof.

Think of a flattened hip roof. The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle. This will help you create a flat roof framing plan.