Flat Roof Rafter Detail

A roof dormer may be gabled as in our sketch above or it may be a low slope or flat roof.

Flat roof rafter detail.

Definition of hip rafter. A rafter that runs diagonally between the roof ridge and the top of the wall plate forming a hipped roof. That will help you remember certain factors and details to build the best possible flat roof. The pitch of the roof determines the roofing material you can use.

It must meet the local codes for thickness at least 3 8 which is also based on the rafter or truss spacing. The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls. Asphalt shingle can be installed on a pitch of 2 over 12 or greater. Notice that the hip rafter forms what amounts to a descending ridge a single line that starts at the top of the roof and descends to the wall top plate at a wall corner.

In our rafter type sketch above the hip rafters are drawn in blue. The rafters in a flat roof serve as ceiling joists for the space below. The size of rafters for a flat roof depends on the horizontal span of the building the type and grade of timber used and the load on the roof. The flat roof design detail can go up against different style that when nitty gritty right can ooze a cutting edge feel.

Plywood or osb is the most common materials used for the roof sheathing.