Shed Dormer vs Gable Dormer vs No Dormer: Attic Conversion Costs Compared
Attic conversion costs typically run {range:loft-conversion:mid} CAD; dormer type decides how much of that buys usable floor space.
The short answer
A Canadian attic conversion typically costs $55,000 CAD, with most jobs landing in the $42,900 – $71,600 range before GST/HST. But that range hides a big split by design: a no-dormer conversion (skylights and an egress window only) runs around $55,000, a shed dormer around $74,800, and a full gable dormer around $83,500. The gap between those three isn't decoration — it's the difference between a loft you can stand up in near the eaves and one you can't.
We calculate these figures from labour hours at local trade rates plus materials, then check the result against market quotes, so the comparison below reflects what contractors are actually charging for each configuration, not a rule-of-thumb markup.
Why the three options cost so differently
The driver isn't the window itself — it's how much the roof structure has to change to get there.
- No dormer keeps the existing roofline. You cut in one or two skylights and a code-compliant egress window, insulate the rafters, and finish the space. Framing work is minimal because nothing above the ceiling line moves.
- Shed dormer extends one roof plane upward and out, usually across most of the rear slope. That buys standing headroom over a much larger footprint and room for full-height windows, but it means new framing, new roof decking and flashing, and matching the existing roofing material at the junction.
- Gable dormer is a smaller, self-contained box with its own peaked roof, popped out from one section of the existing roof. It adds less overall floor space than a shed dormer but creates a distinct, finished-looking window bay — closer to a feature than a wholesale roof rebuild.
| Material | Typical | Usual range | Lifespan |
|---|---|---|---|
| No dormer: skylight and egress window | $55,000 | $42,900 – $71,600 | – |
| Shed dormer | $74,800 | $58,400 – $97,300 | – |
| Gable dormer | $83,500 | $65,100 – $108,600 | – |
Matching the dormer to the roof you have
A few situations point clearly one way or the other:
Steep or short roof, want the most usable square footage. A shed dormer is usually the only way to get full standing height across most of the attic. If the existing roof pitch is already shallow, there may not be enough height to make a no-dormer conversion worthwhile at all.
Modest budget, mainly want a legal bedroom or office. A no-dormer conversion with a properly sized egress window and skylights is the cheapest route to a code-compliant room, provided the existing ridge height clears minimum ceiling requirements over enough of the floor.
Want natural light and a view without reshaping the whole roof. A gable dormer adds a vertical window wall in one spot — good for a reading nook or a single bedroom's headboard wall — without the scale of work a shed dormer involves.
Heritage or strict municipal design rules. Some municipalities are more particular about how a dormer reads from the street than about the roofline itself; a smaller gable dormer is often an easier approval than a long shed dormer, though this varies by zoning and street, so check with your municipality before pricing the job.
Costs that don't show up in the headline number
Whichever dormer you pick, a few extras tend to catch people out:
- Roofing tie-in. New dormer walls need the surrounding roof reshingled or at least re-flashed to match, which is easier to price well when it's planned alongside a Roof replacement rather than patched in afterward.
- Heating and cooling. An attic room usually needs its ductwork, a baseboard circuit, or a small heat pump head extended up to it — ask your HVAC contractor to price this as part of the conversion, not as an afterthought once the room is framed.
- Windows. Skylights and dormer windows are priced into the attic conversion estimate itself, but if you're also replacing windows elsewhere in the house at the same time, it's worth getting one combined quote — see our Window replacement guide for what those run separately.
- Structural review. Any dormer, and even some no-dormer egress windows, can mean cutting into roof rafters or ceiling joists. A structural engineer's sign-off is often required by the building permit before work starts, and that review fee is on top of the construction cost above.
Getting a fair quote
Once you've picked a dormer type, ask contractors to break the quote into the same categories we use: framing and roofing tie-in, insulation and drywall, windows, and mechanical/electrical extension. That makes it much easier to see where one quote is higher than another — a shed dormer quote that's 30% above our typical figure, for instance, is worth a second opinion. If you already have a number in hand and want a quick sanity check against local rates, our "is my quote fair" tool will tell you where it sits.
For the full cost breakdown across all three dormer types, along with size and finish adjustments, see our Attic conversion guide.