Framing and roofing

Rafters — building width (outside of wall to outside of wall), pitch, the level overhang, rafter size, ridge thickness and plate width. You get the line length from the building line to the ridge (already shortened by half the ridge board), the tail, the overall length and the stock to buy, and the birdsmouth: the seat either takes the full plate width, or you set the height above plate (HAP) so rafters of different sizes or pitches line up. The checks keep 3½″ of rafter above the notch (IRC R802.7.1.1) and the ridge board at least as deep as the plumb cut (R802.3). The drawings show the whole rafter, the birdsmouth and the ridge cut; the steps say where to put the speed square. Choose Hip to get the hip/valley rafter (dropped by half its thickness × its slope, shortened by half the 45° thickness of the ridge, cheek cuts), and the jack rafters with their common difference; a gable roof gets its gable-end studs instead.

Pitch — type any one of rise per 12, angle or percent, or a measured rise and run, and the rest follow, with the framing-square rafter-table numbers for common pitches.

Spans — species, grade, spacing, roof load (20 psf live, or 30/50/70 psf ground snow) and dead load pick the column of IRC Tables R802.4.1(1)–(8); the smallest rafter that spans half the building is highlighted. Ceiling joists come from Tables R802.5.1(1)–(2). Raising the rafter ties above the plates reduces the spans by the factor in Table R802.4.1(9), interpolated between its rows.

Walls — list the walls with their length, corners, partitions meeting them and openings (rough width, height to the top of the rough opening, and sill height for windows). The take-off lays out studs on 16″ or 24″ centres, drops the ones that fall in openings, and adds king and jack studs, cripples, sills and headers. Headers come from IRC Table R602.7(1) (exterior: by building width 12–36 ft, interpolated as the table allows, and ground snow) or R602.7(2) (interior bearing), with the jack studs it lists and the king studs from Table R602.7.5; non-bearing openings get a flat 2x4 (R602.7.4). You get a cut list, plates, sheathing and 16d/8d nails per the fastening schedule (Table R602.3(1)), and an elevation of every wall.

Roofing — length, width, pitch, overhangs, gable or hip. The sloped area is the plan area including the overhangs times the slope factor, which holds for any roof whose planes share one pitch. It gives squares, bundles, sheathing, underlayment (doubled from 2/12 to 4/12, R905.2.2), drip edge (R905.2.8.5), starter strip, hip-and-ridge cap, nails (four per shingle, R905.2.6) and, if you need one, the ice barrier from the eave to 24″ inside the wall line (R905.1.2).

Rafter spans: IRC Tables R802.4.1(1)–(8); ceiling joists: Tables R802.5.1(1)–(2); raised-tie factors: Table R802.4.1(9); headers: Tables R602.7(1) and R602.7(2); king studs: Table R602.7.5; fasteners: Table R602.3(1); stud spacing: Table R602.3(5). The 2018, 2021 and 2024 editions print the same values in these tables. I transcribed them from two published copies, which agree; seven cells that were plainly mis-keyed in both (a span shorter at a closer spacing, 12-12, a missing row) are corrected from their neighbours and listed under the span table — check those against your printed code.

Hip, valley and jack rafters assume a regular hip: two roofs of the same pitch meeting at 90°.

Rules of thumb, flagged as such: a seat no deeper than a third of the rafter; 4×8 sheets with 10% waste; about 50 sheathing nails a sheet; shingle, cap and starter coverage (it varies by product).