Roof Cost Estimator

Building & Roof

Quantities & Cost Breakdown

How this estimate works

Roof area = footprint (plus overhangs) × the slope factor for your pitch, with style factors for hip and gambrel geometry. Trusses = length ÷ 24" spacing + 1, priced per foot of span (hip sets ×1.15, gambrel ×1.25); attic trusses use their own rate (and see what room you get in the attic calculator); stick framing prices per square foot of roof surface. Sheathing = roof area ÷ 32 (+10% waste; metal over strapping may skip some sheathing — keep it for the conservative estimate). Covering = roof area × your material rate, defaults matching our roofing comparison. Result shown ±15%.

What drives the number

Roof area is not footprint area, and the gap grows fast with pitch. A 12/12 roof has over 40% more surface than the floor it covers. Every material priced per square — sheathing, underlayment, shingles or metal — scales with that larger number, not the footprint. This is the single most common error in DIY roof budgets, and it's why the slope factor exists in the calculation above.

Geometry costs more than area alone suggests. Hips and valleys mean angled cuts, more waste, more flashing, and slower work. A hip roof over the same footprint runs meaningfully more than a gable, and a gambrel more still — the truss factors above reflect it. Complexity compounds: dormers, intersecting roof lines, and changes in pitch each add labour and leak-risk detail well beyond their share of the area.

Covering material is the biggest single choice, and the honest comparison is cost per year rather than cost per square. Asphalt shingles are cheapest to install and shortest-lived; steel costs considerably more upfront and commonly outlasts two or three shingle roofs. On a garage you plan to keep, the arithmetic often favours metal despite the sticker. Our roofing materials comparison lays out lifespans against installed costs.

Trusses versus stick framing is a labour-versus-material trade. Engineered trusses arrive ready to set and go up in a day; stick framing costs less in material but far more in skilled hours, and is only sensible where the geometry is unusual or crane access is impossible. Attic trusses cost more again — worth it only if you'll actually use the room, which the Attic Space Calculator will show you before you order.

Pitch also affects what you're allowed to use. Most shingle products have a minimum slope below which they'll leak and the warranty won't apply. Low-slope roofs need different systems entirely. Check the material's minimum pitch before committing to a roof profile.

Snow load is a regional design input, not an optional upgrade. Truss design is governed by the ground snow load for your location, so identical spans in different regions aren't the same truss or the same price.

What this estimate does not include

• Tear-off and disposal on a re-roof — removing old layers and paying tipping fees. This tool assumes new construction.
• Flashing, drip edge, and penetration details — chimneys, vents, valleys, wall intersections. Individually small, collectively significant, and the source of most roof leaks.
• Eavestrough, downspouts, soffit and fascia. Where roof water goes matters as much as the roof itself — see Roof & Lot Drainage.
• Ventilation and insulation. Ridge and soffit venting, baffles, and attic insulation are a system; getting it wrong causes ice damming and condensation regardless of how good the covering is.
• Ice and water shield at eaves and valleys, which is required in most Canadian jurisdictions and is not a place to economize.
• Crane or lift rental to set trusses, and scaffolding or fall-protection equipment.
• Engineered truss design and delivery, which the supplier quotes separately and which has a lead time — often the long pole in a build schedule.
• Steep-slope labour premiums. Above roughly an 8/12, roofers work slower and charge accordingly.

For where the roof sits in the whole-building number, see the Garage Cost Calculator.