Next select a the pitch the jack rafter is on. We use inches in this example. Tools needed to work out Roof Rafter lengths, Setting out Rafter Lengths with a Ready Reckoner, Adding the overhang onto the end of the rafters to fix the fascia boards to, Calculating rafter lengths with trigonometry, Grab the right tools for Cutting Roof Rafters to length, Marking out the roof rafter lengths onto the timber before cutting, Go old school & use a scientific calculator and trigonometry (complicated unless you are a maths wiz), When I pitch a small roof like a shed or dormer, I often just draw and set the rafter lengths out on a sheet of ply - no need for complicated calculations, just a straight edge and, For larger roofs though, I use a roofing ready reckoner. Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features. Rafters LONGER than 20 feet: Home improvement stores DO NOT sell pine boards longer than 20 feet. Create and Print Full Scale PDFs with diagrams on this page (templates), With a 45 bevel on the saw, cutting at the plumb cut angle of. 3. This article has been viewed 454,486 times. How to Calculate Rafter Lengths for gable, Hip and Valley rafters Your email address will not be published. Youll also need to purchase a copy of a roofing ready reckoner: a manual with rafter length tables. All we do now is use a calculator to multiply 1.610 by the measurement in the book: So, the rafter lengths 1.86m long - Easy! . Rafters Calculator - Estimate Rafter Length & Cost | RoofCalc.org The top of this calculator has three fields labeled Feet, Inches, and Fraction. The next 16 are the lengths of the jack rafters in inches and fractions. Tutorials, Calculators, and Building Codes. In retrofit applications, there are 100s of external factors that affect labor cost. laying out and cutting jack rafters - Fine Homebuilding There are 16 references cited in this article, which can be found at the bottom of the page. The formula we use to calculate total rafter length including the eaves is: To calculate where the rafter meets the wall plate, which is where you mark the birds mouth cut, use the line length formula: Bear in mind that these formulas call for the roof angle expressed in degrees not the pitch of the roof. Birdsmouth cuts go on top of the building's wall, and the tail cut goes at the bottom of the rafter. Most modern saws will adjust up to a 55. The calculator will automatically switch your board from PINE to LVL when you exceed 20 feet long threshold on rafter length. By Mike Guertin The valley between the north and east roofs is a common valley, with the intersecting roofs at the same 10-in-12 pitch. Always take safety precautions when working with any type of saw. Rake-Wall Key Findsthe stud sizes based onentered Right Triangle val-ues and the stored On-Center spacing. However, you still need to account for the thickness of the hip rafter so that the jack layout remains true. Determine the span, L, of the tributary load (1/2 of the jack rafter span) at the top of the rafter: L = 1/2 (13.71 ft)* = 6.86 ft *The clear span does not include the wall thickness of 3. . If there are not that many rafters then the results are displayed as negative numbers and should be simply ignored. Roof length the distance from one gable-end to the other. Select the following information by using the drop downs to enter values in feet and inches. C-clamps would work well for this. Hence, we did not even fathom to include cost of installation / demolition work it is completely outside the scope of this tool. Overhang from adjusted run (4 ft. 8-116-in). So from one Lover of wood and dimension s to another, i do applaud you, Thank You so much for my findings on your page. Fixr.com | The Rafter Length Calculator Formula: Determine Rafter Size Determine the hip rafter loading based on the tributary loads from each supported jack rafter (see figure above): Hip rafter horizontal span* = = 19.4 ft. {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/1\/13\/Cut-Roof-Rafters-Step-1.jpg\/v4-460px-Cut-Roof-Rafters-Step-1.jpg","bigUrl":"\/images\/thumb\/1\/13\/Cut-Roof-Rafters-Step-1.jpg\/aid9553763-v4-728px-Cut-Roof-Rafters-Step-1.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"