Ottawa basement renovations, finished properly.
Without the surprises.

Turn your basement into a revenue asset

Ottawa's 2024 zoning by-law allows secondary suites on most residential lots, including R1 single-family homes. If your lot qualifies, a legal basement suite is the highest-ROI renovation available to Ottawa homeowners.

• Works on most R1, R2 & R3 Ottawa lots
• City permit managed entirely by our team
• Minimum 6'5" ceiling height required
• Separate entrance required (we design & build it)
• ESA electrical inspection included in scope
• Fire separation & egress windows, all included

Making a basement apartment legal in Ottawa

The City of Ottawa now calls a legal basement apartment an additional dwelling unit (its older pages said secondary dwelling unit), and its additional dwelling unit page sets the zoning side under Section 133 of the Zoning By-law. A detached, linked-detached, semi-detached, duplex or townhouse lot on city water and sewer can hold up to two additional units, for three dwelling units in total.

On a septic system or a well, the limit is one. The unit needs its own access at ground level unless the building or fire code allows another route. No extra parking space is required, and a new one cannot go in the front yard.

You need a building permit even if nothing gets built. The City reviews the change of use against the Ontario Building Code, so an apartment a previous owner finished without a permit is not legal until it passes that review.

Units that existed before 2005 in the former municipalities that already allowed them (Cumberland-Urban, Gloucester, Nepean-Urban, Osgoode, Goulbourn and West Carleton) still have to meet the Building Code and the Fire Code.

Adding two units inside the house takes drawings from a designer registered under a Building Code Identification Number (BCIN). The City lets a homeowner take design responsibility only for a single unit where none exists yet. Our permit drawings page covers that step, and a coach house is the other way to use a lot's second unit.

The Ontario Building Code numbers for a basement unit

Ontario's 2024 Building Code (O. Reg. 163/24) came into force on January 1, 2025. The Ministry of Municipal Affairs and Housing's August 2024 briefing on the Part 9 changes and the City's own advisory give the figures a basement suite is inspected against:

• Ceiling height of at least 1.95 m (about 6 ft 4¾ in) across the suite, and 1.85 m (about 6 ft 1 in) under beams and ducting, under Article 9.5.3.1.
• Article 9.10.9.16 accepts a continuous smoke-tight barrier of at least 15.9 mm (5/8 in) Type X gypsum board on the walls and on the underside of the floor framing between the units, in place of a rated fire separation. The ministry's guide Add a second unit in your house describes the rated route: a 30-minute fire separation between the units.
• Smoke alarms interconnected between the two units. Sentence 9.10.19.5.(2) now allows that link to be wireless, which helps when each unit has its own electrical service.
• City of Ottawa Building Code Services' egress window advisory (August 2025, Article 9.9.10.1) covers the floor level that holds a bedroom: a window that opens from inside without tools, an unobstructed opening of at least 0.35 m² with no dimension under 380 mm, held open without props, and 550 mm of clear space in front of it if it opens into a window well. A well deeper than 1,000 mm needs a way to help the occupant climb out.

What a basement renovation costs in Ottawa

Our price comes as a fixed-price contract after the in-home visit, because what moves an Ottawa basement budget has to be measured on site: how wet the foundation is now, how much clear height is left under the ducts and beams, and how many bathrooms or other wet rooms you want. Our basement finishing cost guide walks through what each scope includes.

Does a basement renovation add value?

HomeStars' 2026 Basement Renovation Cost Guide for Ottawa says Ottawa homeowners typically recover 60 to 75% of a basement renovation's cost at resale.

A legal secondary unit adds rent on top of that, and the City of Ottawa's additional dwelling unit page lists what changes with it: MPAC may reassess your property taxes, rent counts as income under the Income Tax Act, and your insurer or broker should hear about the plan before work starts.

Permits, inspections and how long a basement takes

Do I need a permit to finish my basement in Ontario?

Yes. The City of Ottawa's finishing a basement page grounds the rule in Ontario's Building Code Act, which requires a permit to alter a building, and the City lists basement finishing among the projects that need one. Wiring runs on a separate track: the Electrical Safety Authority (ESA) permits and inspects electrical work across Ontario.

The permit fee comes from the City's Comprehensive Building Code Fee Schedule (January 1, 2026). A renovation that adds no new floor area pays $12.75 per $1,000 of construction value, with a $117 minimum, and construction value counts materials, labour, overhead and professional fees. We file the application through My ServiceOttawa as part of the job; our building permits page covers the rest of the process.

How long does it take to finish a 1,000 sq ft basement?

HomeStars' Ottawa cost guide puts a standard mid-range basement renovation at 6 to 12 weeks of on-site work, plus 2 to 6 weeks of permit review beforehand. The City's own target for a first review of a basement finishing permit is 5 business days under its Council-approved enhanced service level. An additional dwelling unit gets 15.

Once work starts, inspections set the pace. For a finished basement the City lists seven: excavation where pier footings or underpinning are involved, underground plumbing, plumbing rough-in, framing, insulation and vapour barrier, plumbing final, and a final inspection.

Each one is booked 48 hours ahead, and if one is missed the City can order the work opened up so the inspector can see it. That is why drywall waits until framing and insulation have passed.

Test an Ottawa basement for radon before you finish it

Radon is a radioactive gas released from the soil, and the basement is where it gets into a house. Health Canada lists the entry points: cracks in foundation walls and floor slabs, construction joints, openings around water pipes and support posts, and floor drains and sumps.

Its guideline is 200 becquerels per cubic metre (Bq/m³) as a yearly average. Ottawa Public Health notes that levels vary a great deal within the City of Ottawa, and in Health Canada's cross-Canada survey, 6.2% of the 64 Ottawa homes tested came in above 200 Bq/m³.

The time to test is before the drywall goes up. Health Canada's guide for radon measurements in homes says to test in the lowest lived-in level, and it counts a basement being renovated to add a bedroom as lived-in space. A long-term test runs at least 3 months, with at least 91 days in the heating season, so a detector placed in October stays out until about January.

Health Canada also recommends testing again after a renovation that changes the structure or ventilation of the house, and renovating a basement is one of its own examples.

If the result is over the guideline, Ottawa Public Health advises hiring a professional certified under the Canadian National Radon Proficiency Program (C-NRPP), and fixing it within two years for 200 to 600 Bq/m³ and within one year above 600. The usual fix is sub-slab depressurization: a pipe through the floor slab and a fan that sends the soil gas outside.

In an unfinished basement that pipe has an open route to an outside wall. Once the walls and ceiling are finished, the installer may have to cut through them, so have the test result in hand before the framing plan is final.