Guides
Plain-English background to the formulas behind the calculators — from roof pitch and squares to shingle quantities, gutter sizing, siding, window egress and attic insulation.
How to measure roof pitch (from the ground, the attic, or a photo)Three safe ways to measure roof pitch — with a level in the attic, on the roof, or from a photo — plus how to read the x/12 result and turn it into degrees.Roof pitch multipliers: from footprint to true roof areaWhat the roof pitch multiplier is, where the formula M = sqrt(1 + (rise/12)^2) comes from, and how to use it to turn a flat footprint into real roof area.How many squares is my roof? Squares, waste and orderingWhat a roofing square is, how to work out how many squares your roof is from footprint and pitch, and how much waste to add before you order material.How many bundles of shingles do I need?How to work out shingle bundles from roof size and waste, why there are 3 bundles per square, and how to order the right amount without running short.Roofing underlayment: felt vs synthetic, and how many rollsFelt vs synthetic roofing underlayment compared, how roll coverage differs, and how to work out how many rolls your roof needs from squares and waste.How to read a roofing quote: price per square, tear-off, line itemsHow roofing quotes are built — price per square, tear-off and line items — and how to convert any quote format so you can compare bids fairly.Asphalt vs metal roof: comparing YOUR quotes per year of serviceHow to compare asphalt and metal roofing on cost per year of service using your own quotes and realistic lifespans — not a generic price table.What size gutters do I need? 5-inch vs 6-inch K-styleHow to size gutters from roof drainage area, pitch and local rainfall intensity, and when to step up from 5-inch to 6-inch K-style to avoid overflow.How many downspouts do I need, and where to put themHow to work out downspout count from gutter length and from drainage area, what capacity 2x3 and 3x4 downspouts have, and where to place them.Gutter slope: getting the fall rightHow much slope a gutter needs, the 1/4-inch-per-10-feet rule, how to work out the total drop, and how to pitch long runs from a high center.How much siding do I need? Measuring walls, gables and openingsHow to measure a house for siding — wall area, gables and openings — convert to squares with waste, and turn squares into vinyl panels and cartons.Window egress requirements explained (2021 IRC R310)The 2021 IRC R310 egress window minimums — clear opening, width, height and sill — explained, and why the 20x24 inch minimums do not equal 5.7 sq ft.Attic insulation: how deep for R-38, R-49 and R-60How deep attic insulation must be to reach R-38, R-49 or R-60 by material, using R-per-inch, plus how to work out blown-in bags from your bag label.Attic ventilation math: the 1:150 rule, soffit and ridgeHow to size attic ventilation with the 1:150 and 1:300 net-free-area rules, split intake and exhaust 50/50, and count vents from per-vent NFA.