Flat Roof Rafters

Input the rafter span on the flat eave overhang and pitch of the roof.

Flat roof rafters.

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. 1 ft 0 3048 m. The roof rafters provide integral structural support to the roof. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no.

1 psf lb f ft 2 47 88 n m 2. Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2. They are nailed securely to exterior wall plates and to each other. A flat roof has a slope of 1 8 per foot to 2 12.

Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch. If you re framing a gable roof on a new house or building a shed or even a doghouse with a gable roof you ll need to cut a number of roof rafters. 2 are indicated below. You can use either 2 6 or 2 4 rafters for roofs with a 3 12 pitch or greater but it depends on the overall size of your shed.

Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. Rafter stock size calculator. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. Live load is weight of furniture wind snow and more.

Click the button to calculate the stock size needed for this job. Think of a flattened hip roof. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. If you have.

The boards creating the slope of the roof are wider than lumber used to build trusses 2x8s 2x10s and 2x12s are most common in rafters vs. It is not ideal for snow or heavy rain but modern materials and proper drainage have helped. The rafters in a flat roof serve as ceiling joists for the space below. Dead load weight of structure and fixed loads 15 lbs ft 2.

In finished space insulation is placed between the rafter boards and drywall or other material is fastened to the face. For roofs that will experience heavy snow or wind and will span the same distance use 2 6 rafters. Rafter boards are fastened to the ridge board at the peak and the top plate where they join the wall. If you build a flat roof try to have it slope in multiple directions to drains or gutters.

As a general rule roofs that have a high human occupancy rate should be framed with rafters every 16 structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes.