Roof Rafter Layout

Calculating roof geometry was made much more simple for me after reading a different approach to rafter layout by john carroll.

Roof rafter layout.

Half building width minus 1 2 ridge thickness. A rafter or speed square will have marks for both of these angles. The crown will be the top edge of your rafter. Here we have a wood framed gable roof.

Check the rafter material and take note of the crown. The roof on this shed is a 4 in 12 slope which makes it a 18 and one half degree angle on the board ends. The roof rafters provide integral structural support to the roof. The article is in taunton s book framing roofs.

For standard shed roof rafter spacing see rafter span chart. We will mark the top of the rafter first. Rather than outside the wall to ridge the author made calculations from inside the wall for effective run of rafter at ridge. For every foot.

Laying out hip valley and jack rafters takes experience and skill but if you re building a simple gable or shed roof all you need is the common rafter the basic building block of roof framing. Allow for ridge thickness when determining rafter run to outer wall. To lay out a common rafter you need the pitch of the roof expressed in units of rise per foot of run in the gable roof example shown here a rafter with 6 in 12 pitch rises 6 in. Using this handy online tool you will have an easy way to determine and figure out the specific rafters needed for the unique slope and dimensions of your 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. Conclusions about the roof rafter length calculator. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. 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.

Let s consider a basic gable wood roof framing design. There is no standard spacing it depends on what size of rafters you want to use and the span of your shed. 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. Print full scale rafter cut templates and birdsmouth templates fold template over rafter to mark or cut through.

Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. If your lumber is this bad then i would suggest taking it back and finding a new supplier of materials for your roof layout. See rafter run to outer wall calculator below. The layout of your home or building will have a significant impact on the final design and slope of your roof.

Continuing on from part 3. Floor beam span tables of residential structural design we will now look at roof rafter and beam design.