Flat Roof Rafter Layout

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.

Flat roof rafter layout.

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. The layout of your home or building will have a significant impact on the final design and slope of your roof. Conclusions about the roof rafter length calculator. If you look at the rafter span chart you ll notice that 2x4s can be used for rafters on spans up to 11.

Discover the pros and cons to multiple roof designs. 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. This article will discuss a gable roof without valleys or dormers because it s the most common and the easiest for a first time builder to tackle. Learn the 1 rafter design that will guarantee your roof that is safe and strong for years to come.

Check the rafter material and take note of the crown. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. We will mark the top of the rafter first. If your lumber is this bad then i would suggest taking it back and finding a new supplier of materials for your roof layout.

There are design differences for each type. 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. 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. The major difference between the warm flat roof and the cold flat roof has to do with the air flow between the roofing timbers known as joists that help to hold up the roof.

The crown will be the top edge of your rafter. Half building width minus 1 2 ridge thickness. Allow for ridge thickness when determining rafter run to outer wall. After you determine the rise span run line length and pitch the next step is to lay out the rafters or mark the cuts on a pattern rafter to create the roof.

See rafter run to outer wall calculator below. 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 every foot. This illustration shows an exaggerated crown to get my point across.