Dormer Installation Cost Calculator
Estimate Canadian 2026 dormer addition cost by style (shed, gable, hipped, eyebrow), size, retrofit vs new-build, storey, and access — with window, drywall finish, permit, and crane line items.
Dormer Installation Cost Calculator
Estimate Canadian 2026 dormer addition cost by style (shed, gable, hipped, eyebrow), size, retrofit vs new-build, storey, and access — sized to NBC 2020 Part 9.23 framing and 9.26 roofing with optional window, drywall finish, building permit, and crane line items.
Estimated installed cost
$24,378
Range: $20,721 – $29,253
framing + window + interior + permit + crane
Framing + roofing
$15,133
Window unit
$1,300
Drywall finish
$7,425
Permit
$520
Crane
$0
What this calculator estimates
This calculator quotes the all-in installed price for a Canadian roof dormer addition in 2026 Canadian dollars. It covers the framing, exterior sheathing and roofing, weather-tight envelope, optional window, optional drywall interior finish, municipal building permit, and an optional crane day for large or eyebrow dormers.
Line items invoiced by real Canadian dormer specialists:
- Framing and roofing — cut existing roof, install engineered rafters and headers per NBC 9.23, sheathe and ice-and-water-membrane per NBC 9.26.5, install matching asphalt shingle or metal, clad cheek walls, and step-flash the intersection.
- Window unit — typically one per dormer. Triple-pane Low-E in zone 6 and above.
- Interior finish — drywall, mud, tape, prime, electrical first-fix (one circuit, two outlets, one switch, one fixture), and decoration.
- Building permit — municipal fee. Adds 30 to 60 percent on top of base permit in Toronto, Vancouver, Montreal, and Ottawa heritage districts.
- Crane day — for large or eyebrow dormers, or for jobs with restricted access.
A minimum job fee of C$3,800 applies in most Canadian metro markets.
Typical 2026 Canada dormer cost ranges
| Scope (single dormer, retrofit, two-storey, moderate access, window + drywall + permit) | 2026 installed price |
|---|---|
| Small shed (~3 ft x 4 ft) | C$8,500 – C$13,500 |
| Small gable | C$10,500 – C$16,500 |
| Medium shed | C$13,500 – C$22,000 |
| Medium gable | C$17,500 – C$28,500 |
| Medium hipped | C$21,500 – C$34,000 |
| Large gable (~8 ft x 10 ft) | C$30,000 – C$48,000 |
| Large hipped | C$36,000 – C$58,000 |
| Eyebrow (medium) | C$33,000 – C$54,000 |
| Three-storey adder | +25% |
| Difficult access adder | +30% |
| Climate zone 7A or higher framing adder | +5 to 10% |
Add 8 to 15 percent in coastal salt-spray regions for stainless flashings.
Cost drivers
Style. Shed dormers are the cheapest. Gable adds two pitched roof planes and end walls. Hipped adds four roof planes and more flashing. Eyebrow adds 60 to 110 percent over gable for custom-bent framing.
Size. Mobilisation, permit, weather-tight envelope, and engineering are roughly fixed. Cost per square foot falls as size increases.
Retrofit vs new-build. Retrofit adds 12 to 18 percent for tear-out, tarping, and shingle matching.
Climate zone. Zone 6+ requires triple-pane windows and higher R-value insulation, adding 5 to 10 percent.
Site access. Standard suburban lots are easy. Downtown rowhouse properties are difficult and add 25 to 40 percent.
Code references and standards (Canada)
- NBC 2020 Part 9.23 — Wood-frame construction.
- NBC 2020 Part 9.26.4 — Roof flashing (step-flashing at dormer intersections).
- NBC 2020 Part 9.26.5 — Ice and water shield membrane requirements.
- NBC 2020 Part 9.36 — Energy efficiency (effective R-value).
- NBC 2020 Part 9.19 — Ventilation of roof spaces.
- NBC 2020 Part 9.9.10 — Egress windows from sleeping rooms.
- CSA O86 — Engineering design in wood (structural calcs for cut rafters).
- CSA A123 / A220 — Asphalt shingle and metal roofing standards.
- Provincial OHS Regulations — Fall protection (Ontario O. Reg. 213/91 Part III, BC OHS Reg. 11.2, Quebec CNESST §29).
When to add a dormer versus when to expand differently
Add a dormer when:
- The attic has 7/12 (30 degrees) or steeper pitch and at least 2.1 m of ridge-to-joist height.
- You need 60 to 200 sqft of additional living area.
- The existing roof has 5+ years of remaining life.
- Local zoning and lot coverage permit the addition.
Expand differently when:
- The attic pitch is under 5/12 — usable head-height is minimal.
- The roof is engineered trusses without engineer’s sign-off.
- You need 300+ sqft of new space — a ground-floor addition or second-storey raise is cheaper per square foot.
- The existing roof is 15+ years old — re-roof first.
Related calculators
- Roof replacement cost calculator — bundle dormer with re-roof for shingle match.
- Skylight installation cost calculator — cheaper alternative when you only need light.
- Roof flashing cost calculator — flashing is critical at the dormer intersection.
Sources: 2026 CRCA, HomeStars, Renomii installed-quote data; NBC 2020 Parts 9.19, 9.23, 9.26.4, 9.26.5, 9.36, 9.9.10; CSA O86, A123, A220; provincial OHS regulations; Toronto, Vancouver, Montreal, Calgary, Ottawa dormer-specialist contractor benchmarks.
Frequently asked questions
How much does a dormer cost to install in Canada in 2026?
A typical 5x6 ft gable retrofit dormer with one window, drywall finish, and a municipal building permit runs C$17,500 to C$28,500 installed in 2026. A small shed dormer (~3 ft x 4 ft) starts around C$8,500 to C$13,500. A large hipped dormer (~8 ft x 10 ft) can reach C$38,000 to C$62,000. Eyebrow dormers cost 2 to 3 times a gable of equivalent footprint. Source: 2026 CRCA (Canadian Roofing Contractors Association), HomeStars, Renomii, and Toronto / Vancouver / Montreal / Calgary dormer-specialist installed-quote data.
Do I need a building permit for a dormer in Canada?
Yes — every Canadian municipality requires a building permit for a new dormer. The framing must comply with NBC 2020 Part 9.23 (wood-frame construction) and Part 9.26 (roofing and flashing). The window must meet NBC 9.9.10 egress requirements if the dormer creates a sleeping room. Energy code compliance under NBC 9.36 (Ontario SB-12, BC Step Code, Quebec novoclimat) requires a minimum effective roof R-value (typically R-40 in zone 5, R-50 in zone 6, R-60 in zone 7A). Permit fees in 2026 range from C$420 in rural municipalities to C$1,400 in Toronto and Vancouver. Skipping the permit voids homeowner insurance on any future claim.
What is the snow load impact on dormer framing in Canada?
Significant. NBC 2020 Table C-2 ground snow loads vary from 0.8 kPa in southern coastal BC to 6.5 kPa in Iqaluit and northern Quebec. Dormer rafters and headers must be sized for the unbalanced snow load on the leeward side of the dormer, which can be 30 to 60 percent higher than a flat roof of the same area due to snow drifting against the dormer cheek walls. Always require a structural engineer's stamped drawing if the dormer is in zones 5 and above (most of Canada outside coastal BC). The calculator's framing line includes typical engineering for southern Ontario and Quebec — add 5 to 10 percent in Manitoba, Saskatchewan, and northern climate zones.
Is a shed dormer cheaper than a gable dormer in Canada?
Yes, by 20 to 30 percent for the same footprint. A shed dormer has a single sloping roof and two side walls. A gable dormer has a two-pitch roof, vertical end walls, and a more complex valley intersection with the main roof. Shed dormers are common across the back of bungalows and 1.5-storey houses in Ontario, Quebec, and Atlantic Canada because they maximize headroom for the lowest cost. Gable dormers are usually chosen on street-facing elevations for curb appeal. Hipped and eyebrow dormers cost 30 to 90 percent more than gable.
How long does dormer construction take in Canada?
A typical retrofit dormer takes 6 to 12 working days from tear-out to weather-tight, plus another 5 to 10 days for interior drywall, electrical, and paint. Critical path is the weather-tight envelope — once the existing roof is cut, the dormer must be framed, sheathed, ice-and-water-membraned, and windowed before the next precipitation. Reputable contractors will schedule tear-out for the dry summer months (mid-June through mid-September in most of Canada) and avoid shoulder-season starts that risk freeze-up before completion. Winter dormer construction is possible but adds 15 to 25 percent in heated-enclosure costs.
Does adding a dormer add value to my Canadian home?
Yes — a properly designed dormer with finished attic room typically returns 65 to 80 percent of its cost in resale uplift across major Canadian markets. The CMHC and Royal LePage 2026 renovation ROI surveys consistently rank attic conversions with dormers in the top quartile of residential renovations. The bigger win is qualitative: a finished attic with proper head-height, egress window, and NBC-compliant insulation turns into a functional bedroom that is far more valuable to buyers than the same square footage as unfinished attic. Always retain the building permit closing inspection certificate — buyers and lawyers ask for it.
What about ice dams near a dormer?
Dormers are a frequent location for ice dam formation in Canadian climates because the dormer cheek walls and valley flashing interrupt the natural eaves-to-ridge airflow on that section of roof. Without proper detailing, the dormer roof becomes a heat-leak that melts snow, which then refreezes at the cold eave, building an ice dam that backs water under the shingles. Insist on: (1) NBC 9.26.5 ice-and-water shield membrane from eave to at least 600 mm inside the warm-side wall plane, (2) NBC 9.19 ventilation restored by adding soffit vents to the dormer cheeks, and (3) a cold-roof assembly with vented airspace under the sheathing wherever practical. See our ice dam risk calculator for more.
What can go wrong with cheap dormer builds in Canada?
Three common failure modes: (1) the weather-tight envelope opens too long during a shoulder-season storm and ruins ceilings below; (2) flashing at the dormer-to-main-roof intersection is improperly installed — step-flashing must be woven into each shingle course per NBC 9.26.4, not surface-applied; (3) ventilation is forgotten and ice dams form within the first winter. Always insist on a written weather-tight plan, NBC-compliant flashing, and a ventilation calc that restores eaves-to-ridge airflow.