Roofing

What it's for

Takes off a shingle roof. From the roof area and pitch you get bundles, squares, underlayment rolls and nails. Enter the eave, rake, ridge, hip and valley lengths and it adds starter, drip edge, cap, valley flashing and a self-adhered ice-barrier membrane. You also get a roof plan drawing and a material list. It is an order takeoff. Its one code rule is the slope: under 2/12 it refuses asphalt shingles, and from 2/12 up to 4/12 it buys the underlayment the code wants there (see Low-slope roofs).

Step by step

The example is the screen as it opens: a 1000 sq ft footprint, gable roof, 6/12 pitch, architectural shingles, no edge lengths entered, 10% waste.

Roofing inputs at their defaults: AREA ENTRY Footprint × pitch (Measured area beside it), FOOTPRINT AREA 1000 sq ft with a stepper and the note measure to the ROOF EDGES (incl. overhangs), not the wall line, ROOF TYPE Gable, PITCH 6/12 with a stepper, WIND DESIGN AREA off, SHINGLE TYPE Architectural (3-Tab and Premium beside it), and EAVE LENGTH, RAKE LENGTH, RIDGE LENGTH and HIP LENGTH all 0". The answer bar reads 37 bundles, a green Ice barrier 6' 0" reaches 24" inside the wall (needs at least 3' 4-1/4") — IRC 2021 R905.1.2, and ≈ 11.18 squares · ≈ 1118 sq ft surface · order ≈ 1230. — Steps 1 to 5. The answer bar at the top keeps the bundle count and the ice-barrier line in view wherever you scroll.

Pick AREA ENTRY. Footprint × pitch works the roof surface out from the plan area and one pitch. Measured area takes the true surface you taped plane by plane. Use Measured area for a roof with more than one pitch.
In Footprint mode, enter FOOTPRINT AREA in square feet. Measure to the roof edges, overhangs included, not to the wall line. The screen says so under the row. Tap the number to type it, or nudge it 50 sq ft at a time with − and +. In Measured mode this row is replaced by MEASURED ROOF AREA.
Pick ROOF TYPE: Gable, Hip, Shed, Mansard or Gambrel. Then PITCH, from 0/12 to 24/12: tap it and type the rise, halves included, or use − and + to step by a half. In Measured mode the pitch row stays on screen with the note pitch is NOT applied in measured mode. Under 2/12 there is no shingle order, and under 4/12 one more row appears: see Low-slope roofs.
Pick SHINGLE TYPE: Architectural, 3-Tab or Premium. It sets the bundles per square.
Enter the edge lengths. Each one is the total for the whole roof, and each buys its own materials: EAVE LENGTH and RAKE LENGTH buy starter strip and drip edge; RIDGE LENGTH and HIP LENGTH buy cap; VALLEY LENGTH buys valley flashing. On a gable, the eave length is both eaves added together, and the rake length is all four rakes measured up the slope. Leave a length at 0" and that material is left off the list.
Leave ICE-BARRIER MEMBRANE on to buy it along the eaves. BARRIER WIDTH shows while it is on: how far up the roof from the eave edge the membrane runs. The rolls are figured from the eave length, so with no eave length there is no membrane on the list. EAVE OVERHANG shows with it: how far the roof edge sits out from the wall, level, 12" to start. IRC 2021 R905.1.2 wants the barrier to reach at least 24" inside the wall line, so the results card checks your width against (overhang + 24") up the slope — at least 36" on 8/12 and steeper. Green reads Ice barrier … reaches 24" inside the wall with the width it needs; red reads ICE BARRIER … STOPS SHORT OF 24" INSIDE THE WALL. A single 3' course is short at every pitch with a 12" overhang. Over a full-deck D1970 membrane there is no separate band and no line.
HIP LENGTH is the hip edge on the roof surface, out to the eave edge — the length the cap runs. It is longer than the framing hip Hip & Valley gives you; a note under the field says so. Hip & Valley's CAP AND LINE IT IN ROOFING fills it and sets PITCH to that roof's pitch.
Turn on WIND DESIGN AREA if your roof is where IRC Figure R301.2.1.1 requires wind design — hurricane coasts and special wind regions; your building department knows. There, Table R905.1.1(2) wants two layers of underlayment at every slope, so the list buys two layers (about 2.1 times the area) and says so. Left off, the one layer at 4/12 and steeper assumes wind design isn't required, and BASIS & WHAT WAS ASSUMED states that.
Set WASTE FACTOR. It is added to the order quantities only. The surface area and squares in the results stay true to the tape.

Reading the results

Roofing scrolled to the results: RIDGE LENGTH, HIP LENGTH and VALLEY LENGTH all 0", ICE-BARRIER MEMBRANE on, BARRIER WIDTH 6' 0", EAVE OVERHANG 1' 0" and WASTE FACTOR 10%. RESULTS reads ≈ 11.18 squares · ≈ 1118 sq ft surface · order ≈ 1230; Pitch factor 1.118; and the green Ice barrier 6' 0" reaches 24" inside the wall (needs at least 3' 4-1/4") — IRC 2021 R905.1.2, then the BASIS & WHAT WAS ASSUMED row and the link Check before you cut · Measure twice. The answer bar keeps 37 bundles and the green line, cut off at wa…. — Steps 6, 7 and 9 (the last inputs), then the headline, the squares line, the pitch factor and the basis row.

The headline is shingle bundles to order. On the defaults it reads 37 bundles. It is figured from the order area, and Hip, Gambrel and Mansard roofs add a cut-waste allowance on top. The shingle row in the material list names the allowance when there is one.
Squares, surface, order. On the defaults: ≈ 11.18 squares · ≈ 1118 sq ft surface · order ≈ 1230. Surface is the real roof area with no waste. Order is the surface plus your waste factor — and on a Hip, Gambrel or Mansard roof it adds the cut allowance the bundles were bought on, as in order ≈ 1291 incl. +5% cut. Squares are figured from the surface, not the order. The ≈ means the figure is rounded to the places shown: 1000 × 1.118034 is 1118.03 sq ft.
Pitch factor is what the footprint was multiplied by to get the surface, here 1.118 for 6/12. In Measured mode this line reads Measured area — pitch factor not applied.
The drawing is a roof plan with an eave detail in the corner. Pinch to zoom, drag to pan, double-tap to reset, and use the expand button for full screen. See Drawings.
The notes under the drawing are where you check what was assumed. BASIS & WHAT WAS ASSUMED states the yields behind them: bundles per square, the extra cut waste for hips, gambrels and mansards, and the roll and bundle coverages for underlayment, ice-barrier membrane, cap, starter and flashing. The notes show the area sum, here 1000 SF ×1.118 = ≈1118 SF · ≈11.18 SQ, and the order line, ORDER ≈ 1230 SF · BUYS +10% WASTE. They also tell you what is missing: NO RIDGE/HIP ENTERED — NO CAP IN TAKEOFF and NO EAVE/RAKE ENTERED — NO EDGE MATERIALS. Enter those lengths in step 5 and the notes clear.
SCHEMATIC — NOT TO SHAPE means the outline on the plan is a stand-in. A footprint is an area, not a length and a width, so the drawing cannot know the roof's shape. Every number is still right. On a gable or shed roof, enter eave and rake lengths that agree with the footprint and the plan is drawn to shape and dimensioned. On a Mansard or Gambrel it reads 2 PITCHES: USE MEASURED AREA: switch AREA ENTRY to Measured area.
MATERIALS. On the defaults: shingles, underlayment in rolls, and nails in pounds. The shingle and underlayment rows carry their basis after the dash, such as 10-sq synthetic on the underlayment. Nails are counted at four a shingle (about 80 shingles a square, about 196 nails a pound) and the row names the nail IRC R905.2.5 wants: 12-gauge, 3/8" head, 3/4" into the deck. With edge lengths entered you also get hip and ridge cap, starter strip, drip edge, valley flashing and ice-barrier membrane, each with the length or coverage it was figured on. The valley row is an open W-valley, 24" wide at least in 26-gauge G90 steel (R905.2.8.2) — it is its own lining. Over 21/12 a line says to fasten and seal per the shingle maker (R905.2.6). The cap row tells you to verify the coverage against your cap product.

Roofing scrolled to the end: the BASIS & WHAT WAS ASSUMED row and the link Check before you cut · Measure twice, then the roof plan drawing with an eave detail (1ST, UNDERLAY), a 6/12 → ×1.118 pitch triangle, the notes NO RIDGE/HIP ENTERED — NO CAP IN TAKEOFF, NO EAVE/RAKE ENTERED — NO EDGE MATERIALS, 6/12 · 26.6° · 1000 SF ×1.118 = ≈1118 SF · ≈11.18 SQ, ORDER ≈ 1230 SF · BUYS +10% WASTE, and SCHEMATIC — NOT TO SHAPE (FOOTPRINT IS AN AREA), over the title strip ROOF PLAN — GABLE, 6/12 · 37 BDL, NOT TO SCALE. MATERIALS lists Shingles (architectural) — Gable roof 37 bundles; Underlayment — 10-sq synthetic — 12 sq roof 2 rolls; Roofing Nails — 4 per shingle; 12-ga, 3/8" head, 3/4" into the deck (IRC R905.2.5, R905.2.6) 21 lbs. SHARE PDF and SAVE start at the bottom edge. — The drawing, its notes, the schematic note and the material list. The basis row is just above the drawing.

Roofing is a Pro calculator. SHARE PDF and SAVE are Pro as well, a one-time purchase. SHARE PDF and the list icon at its right end stay dim until you have entered your own measurements. SAVE stays lit, but until then a tap only answers Enter your job's numbers first and saves nothing.

Low-slope roofs

Asphalt shingles are allowed only at 2/12 or steeper, and from 2/12 up to 4/12 they need double underlayment (IRC 2021 R905.2.2).

Under 2/12 the results read Asphalt shingles need 2/12 or steeper (IRC R905.2.2) — use roll roofing or a low-slope membrane. There is no drawing, no material list and nothing to share or save until the pitch is 2/12 or more.
From 2/12 up to 4/12 a LOW-SLOPE UNDERLAYMENT row appears under SHINGLE TYPE, with two choices.
- Two layers, the default and the code's own method (Table R905.1.1(2)): a 19" strip along the eave, then 36" sheets each lapping the one below by 19". Only 17" of each sheet shows, so two layers take 36/17, about 2.12 times, the underlayment of one. The underlayment row reads 2 layers, 19" laps (IRC R905.2.2). A 1000 sq ft footprint at 3/12 buys 3 rolls, where one layer would buy 2.
- D1970 membrane: self-adhered ice-barrier membrane over the whole deck instead of underlayment (R905.1.1 Exception 1). The list buys it by area at 200 sq ft a roll, in a row named Self-adhered membrane (ASTM D1970). The underlayment row and the separate eave ice-barrier membrane row drop off, because the membrane already covers the eave.
The choice shows in the results as a line such as 2/12 to under 4/12: two layers of underlayment (IRC R905.2.2), with a basis line saying how the order was worked. The eave detail on the drawing labels the band 2 LAYERS or D1970; with the ice barrier on, the band reads BARRIER and 2 LAYERS labels the underlayment lapped over it. The cut sheet and a saved result carry a Low-Slope Underlayment row.
At 4/12 and steeper the row is hidden and nothing changes: one layer, as before.

Common mistakes

Ordering one layer of underlayment for a 2/12 to 3-1/2/12 porch or addition roof. The code wants two layers, or a full self-adhered membrane. The list now buys one or the other, so check which you picked.
Measuring the footprint to the wall line. The overhangs are roof too. The screen's own note under FOOTPRINT AREA says to measure to the roof edges.
Ordering off the list with the edge lengths still at 0". You get shingles, underlayment and nails and nothing else: no cap, no starter, no drip edge, no ice-barrier membrane. Read the notes under the drawing before you order.
Entering one eave or one rake. The lengths are totals for the whole roof.
Using Footprint × pitch on a mansard or gambrel. One pitch cannot describe two. Tape the planes and use Measured area.
Adding waste twice. The order area and every material row already carry WASTE FACTOR. The surface and squares do not, on purpose.