The tributary area is the maximum distance between the rafters: 12-inches means 6” tributary area, 16-inches is an 8” tributary and 24-inches is 12”s of tributary area. Additionally, the greater the slope, the greater the impetus (gravity) for the roof to shed the snow. The closer the rafters are together, the thicker their depth, the use of collar ties, and the greater the slope, the better able to withstand snow load. If it has an overhang, that is added after calculating the rafter length.Ī roof can usually withstand more than its rated snow load based on the tributary area, duration, and inertia. Is the distance from the ridge beam to the wall, it is calculated using the total rise over the total run (Pythagorean Theorem). Is a cut notched into the rafter where it rests on the top plate of the supporting wall it helps transfer the roof force to the wall and makes it easier to securely toenail the rafter to the wall. Is a plank that supports the top end of the rafters, maintains spacing, and helps the roof structure to work as a connected system.Ī horizontal plank that helps hold two opposing rafters together, and thus the roof often located 1/3 to 1/2 down the rafter between the ridge and the ceiling. It can be under the rafters to support, or the rafters can tie into it for support. Transfers the roof load to the gable ends or a post and supports the rafter ends at the ridge. The upper edge where two roof slopes or decks meet. It is measured from the horizontal wall line to the sloped rafter using the rise over run: a 14° angle gives a 3/12 slope, 4/12 is an 18.2° angle, and 6/12 a 26.6° angle. Is used to cut the rafter where it meets the ridge beam, and to cut out the birds mouth at the wall. The span is the distance from one rafter supporting wall to the other rafter supporting wall. Is the height of the roof compared to the total span of the roof, usually expressed as a ratio of in feet (6-feet to 18-feet or 8:16). Measures the rise in inches for every foot of distance horizontally: 3” rise for a 12” run (3/12). It permits high storage on one wall and less on the other. The slope determines if it is a Skillion (greater than 6/12) or Shed roof. The Skillion or Shed roof provides a single slope roof deck running from a high wall to a lower wall. The Gable or Hip roof will give higher center storage or headroom. If you want headroom or storage on one side but not the other, the Saltbox is ideal. If you need a high usable attic/storage space, the Gambrel or barn roof is best. If you want a high side and a low side, the Saltbox, Skillion or shed roof is for you. If all walls are the same height, the Gable, Hip, and Gambrel roof works well. Hot, arid climates frequently have a low slope roof design with lots of ventilation and insulation.ĭifferent roof styles go with specific structures. The saltbox roof was designed for coastal winds. Damp shingles can lead to moss which will also rot the shingle.Ī strong prevailing wind or gusts usually means a lower slope windward to reduce wind force. Rain can pool on a low slope roof and rot cedar and asphalt shingles and find or enlarge gaps to cause leaks. The greater the snow load potential, the higher the slope should be (4/12 or better). Most roof designs can be made to work in most climates, just be aware that there may be higher costs involved to build them. Snow load, wind force, rain and heat all are climate factors that influence the roof. Where you’re building has an impact on roof slope and design. They may not be necessary on a shed, but they will help the roof last longer and help protect whatever you store in the shed. You’ve put a lot of sweat and money into building your shed, so protect your investment by using felt paper, ice guard, and drip edge. If the roof is less than 2/12, it should be either metal or have a rubber membrane covering it. There are special shingles available for 2/12, but you’re better off using other materials. Asphalt shingle can be installed on a pitch of 2 over 12 or greater. The pitch of the roof determines the roofing material you can use.

It must meet the local codes for thickness (at least 3/8”), which is also based on the rafter or truss spacing. Plywood or OSB is the most common materials used for the roof sheathing. Gable Shed Roof with Ridge Beam Framingįactors That Impact Your Shed Roof Design.Measure Rafter Length and Mark the Outside Edge of Building.Determine How Deep to Cut the Birdsmouth.Find the Length of Common Rafter on a Shed.Shed Roof Framing Process Explained – Step by Step Instructions.What is the Difference Between Pitch and Slope.Factors That Impact Your Shed Roof Design.

Shed roof rafter span calculator