Building Rafters

Introduction

Rafters are the part of the building used as a support frame or internal skeleton of the roof, holding the roof in place and giving it its shape. Though easily built for square or rectangular buildings, rafters can become complex and time consuming projects, depending on the specifications required. Building rafters requires the basic geometry knowledge of slopes, which is the height divided by the length.

The Purpose of Rafters

Building rafters correctly ensures that your building will be able to withstand the weight of its own roof, and ensures the roof's ability to withstand the elements. For small disposable buildings, some on-the-side carpenters decide to build roofs that slope only to one side, eliminating the need for rafters.

Types of Rafters

There are four basic rafter types: valley rafters, hip rafters, jack rafters and the common rafter. Each differentiates by the way in which it is set up. Determining which rafter type is suitable depends on the dimensions of the building or area being covered.

Valley rafters connect to the inner corners of the outer walls of the building.

Hip rafters connect in numerous spots, and resemble a symmetrical snowflake when viewed from above.

Jack rafters are similar to the common rafter, but do not extend the full distance between the ridge and the wall plate.

The common rafter is easily constructed and resembles an upside down v; roofs that cover such rafters are often left open on the ends, and later covered by siding.

Determining Lengths Needed For Rafters

Knowing how to calculate slope is needed to determine the specifications for building rafters. Assuming you are building common rafters, you need to find the slope length needed for the rafters, by calculating the desired roof pitch by the length or width of the building. Assume the building is 24 feet wide in the direction you will place the rafters and you've decided you want the roof's height to be 5 feet. Divide the length in half to determine the slope on each side of the roof's tip, or ridge. The length of one side of the roof is 12 feet. Five feet divided by 12 (the rise divided by the run) leaves approximately half-foot of slope, or a half foot of rise per foot of run.

Bear in mind that the example given is not exact. For exact specifications you can visit such sites as easyrafters.com or call or visit a local contractor or home improvement store and give them your building dimensions, and they'll be able to determine for you the length specifications for your rafters.

Cutting Rafters For Construction

After you've found the exact specification for your rafters, you will be ready to begin cutting the pieces of lumber that you'll nail together to form the rafters. A piece will be needed the length of the building that you will nail each individual rafter to. Use an L tool to cut your slope pieces according to the angle specifications. The slope pieces will be nailed to the center top piece as well as to the bottom supporting pieces cut the width of the building. When all rafters are in place, the roof can be constructed on top of the rafters.