Lot coverage in Ottawa is the share of a lot covered by buildings, sheds and detached garages included, written as a percentage of the lot area. Every building permit application deemed complete since 2026-03-11 has to satisfy two zoning by-laws, the new Zoning By-law 2026-50 and the old By-law 2008-250, and the more restrictive provision of the two applies.
The new by-law sets no lot coverage maximum in its N1 to N6 Neighbourhood zones.
It limits sheds and detached garages to half of the yard they stand in and 55 square metres in total, and among its Neighbourhood zones the only overall coverage cap is in the Neighbourhood Unserviced (NU) zone: 25% where the lot has city water, 15% where it does not.
A homeowner in Riverside South wanted a 6m by 8m rear addition. Drawings done. Quote signed. We were two weeks from breaking ground when the zoning report came back: the addition put the lot at 38% coverage in an R1 zone capped at 35%.
The 3% gap on a 460 m² lot was 14 m². The homeowner had two options: shrink the addition by about 1.8m on one side, or file a minor variance and add roughly 10 weeks plus application and consultant costs to the project.
Lot coverage is the single most-overlooked zoning rule in Ottawa. Setbacks get all the attention, but coverage kills more projects at the design stage. Here is how it actually works.
What Lot Coverage Means
Section 64 of Zoning By-law 2008-250 defines lot coverage as "the combined area of all buildings on a lot, expressed as a percentage of the lot area, measured at grade."
The math is straightforward. Take the footprint of every building on your lot at ground level. Add them up. Divide by the lot area. Multiply by 100. That percentage cannot exceed the cap for your zone.
The City always uses the largest horizontal projection. A second-storey overhang counts at its widest dimension, even if it does not touch the ground. A cantilevered bay window counts. A covered porch with a roof counts. An attached garage counts.
The Ottawa Caps by Zone
By-law 2008-250 sets coverage caps that vary by zone and lot size. The most common residential caps:
- R1 (single-detached): 35% on standard lots, may be 40% on smaller suburban lots, sometimes 45% on infill lots in older neighbourhoods
- R2 (semi-detached and duplex): 40% typical, sometimes 45% in older zones
- R3 (row house, three-unit): 45% to 50% typical
- R4 (low-rise apartment, multi-unit): 50% to 55%, varies more by sub-zone
- Rural Residential (RR, RU): 25% to 30%, much larger lots
- Village zones (V1, V2): 30% to 40% depending on lot size
To find your exact cap, look up your zone code in the City's zoning map (geoOttawa or maps.ottawa.ca), then read the corresponding zone section in By-law 2008-250. R1 alone has subzones R1A through R1HH with different rules.
Lot Coverage Under Zoning By-law 2026-50
Ottawa City Council approved the new zoning by-law on 2026-01-28, and the City enacted it as By-law 2026-50 on 2026-03-11. On 2026-07-02 the Ontario Land Tribunal ordered the parts that are not under appeal into force, which is most of it. The City still applies the more restrictive provision of the old and new by-laws, so a coverage cap from By-law 2008-250 can still decide a project.
The R1 to R5 zones are gone from the new by-law. A residential lot now carries an N1 to N6 zone for height and density, plus a subzone letter that sets lot width and yards, A for the most urban lot pattern through F for the most suburban (Section 801).
Neither table that holds those numbers, Table 801A or Table 801B, has a lot coverage row. The house's footprint is held in by the envelope the yards leave instead:
- Rear yard: 25% of the lot depth, never less than 6 metres and never required to be more than 7.5 metres. In subzones A to C this rule is still under appeal at the Ontario Land Tribunal.
- Interior side yards: a combined minimum set by the subzone letter, listed with the front yards in our guide to Ottawa setbacks.
- Building depth: 20 metres at most for a building with six units or fewer, a provision the City's online text also marks as under appeal.
- Rear yard soft landscaping: at least 25% of the rear yard outside the Downtown Core and Inner Urban areas. Inside them it is 35 square metres, 50 square metres or half the rear yard, depending on lot size.
Section 199 of the new by-law defines lot coverage as the part of a lot covered by buildings, accessory and ancillary buildings included. It leaves out eaves, eavestroughs and other features at or above the first-storey ceiling, plus the projections Section 204 allows into yards.
A worked example: a 15 by 30 metre lot in N1D
Take a 15 by 30 metre lot, 450 square metres, zoned N1 with subzone D. Fifteen metres is the narrowest lot subzone D allows. Table 801B sets a 6 metre front yard and side yards that add up to 3 metres, each at least 1.2 metres. The rear yard is 25% of the 30 metre depth: 7.5 metres.
That leaves a box 12 metres wide and 16.5 metres deep for the house, 198 square metres or 44% of the lot. A detached garage or shed in the rear yard adds to that within its own limits. Where no older coverage cap applies, the 7.5 metre rear yard decides how far back a home addition in Ottawa can reach on this lot.
If the lot's old R zone carried a lower coverage cap under By-law 2008-250, the lower number governs while both by-laws apply.
Sheds, garages and coach houses
Section 202 allows two accessory buildings per lot in the N zones. Together they cannot cover more than half of the yard they sit in, or exceed 55 square metres of floor area. Our guide to Ottawa height restrictions has their height limits, and the setback guide has their distances from the lot lines.
A coach house is not an accessory building under the new by-law, but under Section 701 the building that holds it shares one cap with any sheds or garages in the same yard: half the yard, and no more than 95 square metres of footprint.
Sources: City of Ottawa, Zoning By-law 2026-50, Part 8, Neighbourhood Zones, Part 2, General Provisions, Part 7, Housing Provisions and Section 199, Definitions, and its memo to Council on the appeals (2026-07-07); Engage Ottawa, New Zoning By-law. All read 2026-10-05.
What Counts in the Coverage Calculation
This is where most homeowners go wrong. The City counts:
- Main building footprint at grade (entire ground floor outline)
- Attached garage footprint
- Attached deck or porch with a roof (the roofed portion counts)
- Cantilevered upper floors and bay windows (counted at maximum projection)
- Detached garage on most lots (this is the most argued one)
- Detached coach house footprint
- Pool house, garden shed over a certain size (typically 10 m² threshold)
- Permanent gazebos with a roof
What Does Not Count
The City excludes from coverage:
- Open uncovered decks at any height (often the design solution to a coverage problem)
- Driveways and walkways (these affect Permeable Surface calculations, not coverage)
- Patios at grade with no walls or roof
- Sheds under 10 m² (usually exempt; verify in your zone)
- Open balconies cantilevered from upper floors (the support structure may count if it touches grade)
- Cornices, eaves, and roof overhangs projecting up to 0.6m (these are not counted at grade)
- Bay windows that do not project beyond a defined limit (typically 0.6m)
- Window wells (ingress/egress wells dug into the ground)
- Heat pumps and AC condensers (mechanical equipment is not building coverage)
The detached garage exemption that often does not apply
Some Ottawa subzones exempt detached structures up to 60 m² from the principal lot coverage cap, treating them as "accessory" with their own separate cap. Others count every roofed structure equally. Always check your specific subzone before assuming a 50 m² detached garage is "free." The wrong assumption has burned more projects than any other coverage mistake we see.
Working the Math: A Real Example
A typical Barrhaven lot, R1HH zone, 14m wide x 33m deep. Lot area: 462 m². Coverage cap: 35%. Maximum buildable footprint: 462 x 0.35 = 161.7 m².
The existing house is a 1990s two-storey with:
- Main house footprint (excluding garage): 88 m²
- Attached garage: 38 m²
- Existing covered front porch: 6 m²
- Total existing: 132 m² (28.6% coverage)
Headroom for additions: 161.7 minus 132 equals 29.7 m².
The owner wants:
- Rear sunroom addition (covered, heated): 24 m²
- New uncovered rear deck: 22 m²
- New 8 m² garden shed
The math:
- Sunroom: counts (covered): adds 24 m² to coverage
- Deck: does not count (uncovered): adds 0
- Shed under 10 m²: typically exempt: adds 0
- New total: 132 + 24 = 156 m² (33.8% coverage)
Within the cap. Project proceeds. If they had wanted a 28 m² covered sunroom (4 m² more), they would be at 35.7% and need a minor variance.
How Bill 23 Did Not Change This
A common confusion. Bill 23 permits up to three units as-of-right on most residential lots in Ontario. It did not change the building envelope. Setbacks, height, and lot coverage still apply.
So if your R1 lot caps coverage at 35%, you can fit three units inside that 35% envelope (basement suite, main floor, second floor) without a variance. But you cannot add a coach house in the back yard and exceed 35% just because Bill 23 allows three units. Coverage is coverage.
This is why the practical Bill 23 path on most older single-family lots in Ottawa is interior conversion (basement + main + upper) rather than adding a detached unit; the detached unit usually pushes coverage over.
Coverage and Existing Non-Conforming Buildings
Many older Ottawa homes (1920s to 1960s) sit at coverage percentages above the current cap because they were built under earlier rules. The Planning Act allows these to remain as legal non-conforming. You can:
- Maintain and repair the building, including reroofing, repointing, and window replacement
- Replace the building like-for-like if it is destroyed by fire
- Sell the property without losing the non-conforming status
You cannot:
- Expand the footprint to make the non-conformity worse
- Demolish and rebuild larger without a minor variance
- Add a second-storey or detached structure that pushes coverage further over
"Existing non-conforming protects what's already there. It does not let you do new work that makes the issue worse."
Coverage and Decks: The Workaround Everyone Uses
Most clients we work with hit the coverage cap on additions. The classic workaround: design the rear extension as a covered enclosed sunroom up to the cap, then a generous open uncovered deck off the back.
The uncovered deck:
- Does not count toward coverage (no roof)
- Does need a building permit if over 600mm (24") above grade
- Does need to respect rear yard setback (7.5m typical R1 measured to deck edge)
- Does need to respect side yard setback if attached to the house
A 22 m² deck off a 24 m² addition is functionally a 46 m² rear extension to the house, but only 24 m² counts against coverage. This is the single biggest design move on coverage-tight lots.
Coverage and Heritage
For Part IV designated properties or those inside Heritage Conservation Districts, coverage is governed by both the zoning by-law and the heritage rules. Even if your zone permits up to 50% coverage, the HCD Plan may cap your specific lot at 35% to preserve the streetscape.
Always cross-reference both before designing.
What to Do Before You Sign a Contract
- Find your zone code on the City's zoning map (geoOttawa or maps.ottawa.ca)
- Look up the coverage cap for that zone in By-law 2008-250
- Check the lot against Zoning By-law 2026-50 as well; while both by-laws apply, the stricter provision wins
- Get a survey or measure your existing buildings to calculate current coverage
- Subtract from the cap to find your buildable headroom
- Design within the headroom, or budget for a minor variance application (8 to 12 weeks plus application and consultant costs)
If this sounds like math you do not want to do alone, we run it as part of our free 48-hour lot feasibility review. We pull the zoning report, measure the buildings, and tell you within 48 hours how much addition your lot will accept before triggering a variance. Our permits service handles the variance side if your project needs one.
Call 613-862-4555 for a coverage check before you spend a dollar on drawings.
Frequently asked questions
How is lot coverage calculated for a house?
Lot coverage is the combined footprint of all buildings on a lot at ground level, divided by the lot area and multiplied by 100. The City uses the largest horizontal projection, so a second-storey overhang, a cantilevered bay window, a roofed porch and an attached garage all count.
On a 462 square metre lot with a 35% cap, the maximum buildable footprint is 161.7 square metres. Subtract the existing buildings to find the headroom left for an addition.
Can I expand an older house that already exceeds the lot coverage cap?
An older house that already exceeds the current lot coverage cap can remain as legal non-conforming under the Planning Act, but it cannot be expanded in a way that makes the non-conformity worse. The owner can maintain and repair the house, replace it like-for-like after a fire, and sell it without losing the status.
Expanding the footprint, demolishing and rebuilding larger, or adding a structure that pushes coverage further over needs a minor variance.
Do decks count toward lot coverage in Ottawa?
Open uncovered decks do not count toward lot coverage at any height, which makes them the usual design answer on a coverage-tight lot. A roofed deck or porch does count for its roofed portion. An uncovered deck still needs a building permit if it sits over 600mm above grade, and it must respect the rear yard setback, typically 7.5m in R1, plus side yard setbacks if attached.
A 22 square metre deck off a 24 square metre addition adds only 24 to coverage.
Which structures are left out of the lot coverage calculation?
Lot coverage leaves out open uncovered decks, driveways and walkways, patios at grade with no walls or roof, and sheds under 10 square metres in most zones. Eaves, cornices and roof overhangs projecting up to 0.6m are not counted, and neither are bay windows within a defined limit, typically 0.6m.
Window wells, heat pumps and AC condensers are also excluded. Detached garages count on most lots, so check the specific subzone before assuming one is exempt.
Did Bill 23 change lot coverage limits in Ontario?
Bill 23 did not change lot coverage limits. Bill 23 allows up to three units as-of-right on most residential lots in Ontario, but setbacks, height and lot coverage still apply. On a lot capped at 35%, three units can fit inside that envelope as a basement suite, main floor and second floor without a variance.
A coach house that pushes coverage past the cap still needs one, which is why interior conversion is the practical path on most older lots.