Flat Roof Rafters

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2.

Flat roof rafters.

This calculator is to be used as an estimating tool only. The rafters in a flat roof serve as ceiling joists for the space below. Rafter boards are fastened to the ridge board at the peak and the top plate where they join the wall. They are nailed securely to exterior wall plates and to each other.

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. Think of a flattened hip roof. 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. 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.

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. If you have. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. Rafter stock size calculator.

Input the rafter span on the flat eave overhang and pitch of the roof. Dead load weight of structure and fixed loads 15 lbs ft 2. 1 psf lb f ft 2 47 88 n m 2. 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.

For roofs that won t experience heavy snow loads a gable roof can span up to 22 with 2 4 rafters. In finished space insulation is placed between the rafter boards and drywall or other material is fastened to the face. It is not ideal for snow or heavy rain but modern materials and proper drainage have helped. 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.

Click the button to calculate the stock size needed for this job. 2 are indicated below. A flat roof has a slope of 1 8 per foot to 2 12. 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.

If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. 1 ft 0 3048 m. Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. If you build a flat roof try to have it slope in multiple directions to drains or gutters.

Live load is weight of furniture wind snow and more.