CutRoof: Rafter Calculator

About

A roof pitch and rafter calculator built for British carpenters and joiners. Millimetres and degrees, plumb and seat cuts, HAP and hip drop: the terms you actually use, with none of them translated from American. Free to download. Gable and lean-to roofs are free forever, full cut schedule and PDF included. Your first hipped roof is free as well, complete and uncrippled. After that it is one payment, once, and it is yours. Never a subscription. Enter the roof once. CutRoof gives you every rafter length and every cut angle, and shows the working behind each number so you can check it against your square. WHAT IT WORKS OUT Gable, hipped and lean-to roofs. • Common rafters: run, rise, true length, the tail for the overhang, and the overall length to order. • Hips: the shallower hip pitch, the plan run, the length to the apex, the shortening where the hip meets the crown rafter, and the cheek set-back, so you have the long point and the short point. • Jack rafters: the whole ladder, left hand and right hand, cut to the hip face rather than its centreline, with the common difference stated once above them and the side cut for each. • The ridge: board length, and a depth deep enough to take the rafters' plumb cuts, which is more than the rafter depth at every pitch. • Birdsmouths: notch depth, plumb-cut length and seat-cut length, which are three different numbers, plus the height above plate that keeps the roof planes true. • Dropped hips get the hip drop. Backed hips get the backing bevel. You say which, and it prints only the one you are actually cutting. IT SHOWS THE WORKING Tap any figure for the derivation, step by step, with your values already substituted. Deductions are always their own step, so you see the undeducted figure, the deduction, and the result. A length that quietly contains a ridge allowance is the thing this app is built against. IT ASKS RATHER THAN ASSUMES Where a carpenter makes a choice, you declare it instead of the app picking one behind your back. Where the run ends. Whether the hips are backed or dropped. How the birdsmouth is sized. Which reference the bevels are stated from. Where the first jack sits. Every schedule prints the settings that produced it, in words, so two people reading the same sheet cannot disagree about what the numbers mean. CHECKED AGAINST PUBLISHED TABLES The geometry is written twice, by two independent methods, and ten thousand random roofs go through both on every build. Thirteen worked examples from published sources are asserted figure by figure, four of them read straight from a standard UK roofing ready reckoner. ON THE ROOF • Works with no signal, because it never needs one. • A4 cut schedule to print, share or keep. • Saved jobs store what you typed, so a correction to the geometry fixes every job you have already saved. • Site rounding to 5 mm when you want it, which rounds lengths down, because timber can be trimmed and not stretched. • Full Dynamic Type and VoiceOver, with every figure spoken. • No account, no sign-in. Your roofs, jobs and schedules stay on your phone. CutRoof calculates geometry from your dimensions. Structural design and timber sizing are the responsibility of a competent person.