We price a full legal basement apartment in Ontario at $80,000 to $180,000 before HST in 2026, and legalising a basement that's already finished at $45,000 to $95,000. Your own price comes after James sees the basement, and the first estimate is free. In Durham Region, Ontario, the town's permit fee on a 700 sq ft unit adds $434 to $693 (our calculation), there are no development charges on the unit, and a federal tax credit can return up to $7,250 if the unit houses a senior or a disabled relative. All figures are as of October 2026.
Key takeaways
- Our 2026 range is $80,000 to $180,000 for a full legal basement apartment and $45,000 to $95,000 to legalise one that's already finished, before HST.
- A separate entrance is often the cost that surprises owners: we price a separate side entrance at $18,000 to $28,000, and underpinning the full perimeter at $60,000 to $120,000.
- The permit fee for a 700 sq ft unit, calculated from the 2026 schedules, ranges from $434 in Clarington to $693 in Whitby (Whitby's 2026 fee schedule).
- A second or third unit inside an existing house pays no development charges under section 2(3.2) of the Development Charges Act.
- The Multigenerational Home Renovation Tax Credit is 14.5% of up to $50,000 in costs, a maximum of $7,250, per the CRA's MHRTC page.
What does a legal basement apartment cost in Ontario in 2026?
Our ranges are wide, and the biggest jumps come from the entrance and from lowering the floor. They're our own 2026 prices, before 13% HST.
Here are our 2026 ranges for a basement unit and the work that often goes with it:
| Item | Our 2026 range |
|---|---|
| Full legal basement apartment | $80,000 to $180,000 |
| Legalise an already finished basement | $45,000 to $95,000 |
| Basement finishing, not a separate unit | $55 to $90 per sq ft |
| Basement bathroom | $25,000 to $50,000; the top end is when new plumbing has to go under the slab |
| Separate side entrance | $18,000 to $28,000 |
| Underpinning, full perimeter | $60,000 to $120,000 |
| Permit drawings for a basement apartment | $4,000 to $8,000, drawings only |
Note: these are our ranges, not a quote; your price comes after James sees the basement, and the first estimate is free. Drawing prices leave out permit fees, HVAC engineering, truss design, committee of adjustment applications and anything unforeseen.
What pushes a basement apartment to the top of the range?
Three things move the number most: the entrance, the ceiling height and the work behind the drywall. The entrance and the egress windows are what tend to surprise owners, especially where the foundation wall has to be cut.
On the entrance, we price a separate side entrance at $18,000 to $28,000. A walk-up costs more, because you're digging a stairwell, building retaining walls and adding a drain at the bottom.
The ceiling height comes next, because the 2024 Ontario Building Code sets 1.95 m for ceilings in a secondary suite and 1.85 m under beams and ducts (Div. B 9.5.3.1.). If your basement is lower, the floor has to come down. We price underpinning the full perimeter at $60,000 to $120,000.
Then the fire and life-safety work: Type X drywall on the ceiling and walls between the units, interconnected smoke alarms through the whole house, and an egress window in every bedroom level. None of it shows when you're done, and all of it gets inspected. Our requirements guide lists each rule with its Code article.
What do Durham towns charge in permit and registration fees?
Durham fees are small next to the build, but they vary by town and some towns add a deposit or a registration step. As of October 2026, here's the floor-area permit fee for a 700 sq ft (65.0 m²) unit, calculated from each town's 2026 schedule:
| Town | Permit fee, 700 sq ft unit (calculated) | Below-grade entrance fee | Registration |
|---|---|---|---|
| Whitby | $693 at $10.65/m², "Residential (ADU) Alterations" (Schedule N) | $305 flat | Required, $268 (Whitby ADU page) |
| Oshawa | No unit line; $507 at the $7.79/m² basement-finish rate (Oshawa fee by-law) | $160 walk-up stair | Two-unit house registration issued through the permit (Oshawa accessory apartments page) |
| Ajax | $630 at $9.68, "Residential Accessory Dwelling Unit" (Ajax 2026 fee schedule) | $329 | No current program found |
| Pickering | $479 at $7.37/m², plus a $1,000 refundable performance deposit (Pickering 2026 user fees) | $180 basement walkout | Mandatory under By-law 8040/23, fee not found (Pickering ADU page) |
| Clarington | $434 at $6.68/m², "Apartment In-House" (Clarington fee by-law) | Not found in the schedule | Not found |
Note: these are our calculations of the floor-area fee only; the town calculates the final permit fee, and Oshawa staff price a new unit case by case.
Whitby charges $534 to register a unit it finds through a complaint, instead of $268, so register on time. Whitby also reimburses the ADU permit fee, the registration inspection fee and the below-grade entrance fee through its Housing Accelerator Fund incentive, for complete applications made by 31 December 2026. Our Whitby ADU incentive guide covers the deadlines. For the basement permit itself, town by town, see basement permits in Durham Region.
Do you pay development charges on a basement apartment?
No. As of October 2026, a second or third unit inside an existing house, or one unit in a backyard building within the three-unit limit, pays no development charges under section 2(3.2) of the Development Charges Act. For scale, a new single detached house in Whitby pays $136,784 in Region, education and Town charges combined (our sum of the Durham Region July 2026 rates and the Town and school board rates).
Whitby's ADU page adds one wrinkle: education development charges still apply to a detached ADU in the backyard, and to a unit in a new house occupied for less than 12 months. A basement unit in a house you've lived in longer doesn't trigger them. Our Bill 23 guide explains how many units each town allows.
Is there a tax credit for a basement apartment for a parent?
Yes, if the unit is for a senior or a disabled adult relative. The federal Multigenerational Home Renovation Tax Credit is 14.5% of up to $50,000 in qualifying costs, so a maximum of $7,250. It's refundable, per the CRA's MHRTC page (updated 20 January 2026), which sets out the rules for the 2025 tax year.
The CRA's eligibility page sets the conditions. The unit has to be self-contained, with a private entrance, kitchen, bathroom and sleeping area. It has to satisfy local permits, codes and by-laws, which is one more reason to build it legally. The person it's for must be 65 or older, or 18 to 64 and eligible for the disability tax credit. Only one renovation can be claimed for that person in their lifetime.
The CRA's expenses page excludes appliances, financing costs and work done by a relative who isn't registered for GST/HST. Permits and building plans count. Check the rules for the year you'll finish with the CRA before you count on the credit.
How do you protect the money once you've signed?
Pay in stages and hold back what the law lets you hold back. Ontario recommends a deposit of no more than 10%, and the Construction Act requires you to hold back 10% of the value of work as it's supplied until lien rights expire. This matters for basements in particular: in July 2026 CP24 reported a Brampton owner who'd paid $33,000, about 90% of the contract, for a basement apartment left unfinished. Our guide to HCRA and Tarion explains why renovators aren't licensed like new home builders.
How we work on basement apartments
We're Jarvis Contracting, a family design-build firm based in Ajax. James Jarvis runs construction and his wife, Ceara Jarvis, runs design through her studio Juliette Interiors. We draw permit drawings in-house and build basements and additional units, so the entrance, the ceiling height and the fire separation are priced by the team that draws them for the town and builds them. Our contracts are fixed price, and any change goes through a change order you sign.
The ranges above are ours, but we don't quote a basement from a range, because the two biggest variables, the floor-to-joist height and where an entrance can go, can only be measured on site. Your price comes after James sees the basement, and the first estimate is free. Our one published project, Greenwood, is in east Toronto, roughly 40 km west of Whitby. It's an addition with an enlarged basement, not a second unit. See our basement renovations page for how we run a basement job.
Questions
Is it cheaper to legalise a finished basement than to build a new basement apartment?
Legalising a finished basement is usually the cheaper route. We price legalising an already finished basement at $45,000 to $95,000 before HST in 2026, against $80,000 to $180,000 for a full legal basement apartment. The saving shrinks fast if the existing finish has to be opened up for fire separation, egress windows or a ceiling that's under the 1.95 m the Building Code sets for a secondary suite.
How much does a separate entrance for a basement apartment cost?
We price a separate side entrance for a basement apartment at $18,000 to $28,000 before HST in 2026. A walk-up costs more, because it means digging a stairwell, building retaining walls and adding a drain at the bottom. Cutting the foundation wall is what makes any entrance expensive.
Do I pay development charges on a basement apartment in Durham Region?
No. As of October 2026, the Development Charges Act exempts a second or third unit inside an existing house from development charges anywhere in Ontario, including Durham Region. Whitby still charges education development charges on a detached backyard unit, and on a unit in a house occupied for less than 12 months, but not on a basement apartment in an established house.
Can I claim the Multigenerational Home Renovation Tax Credit for a basement apartment?
You can if the basement apartment is for a relative who is 65 or older, or an adult eligible for the disability tax credit. The credit is 14.5% of up to $50,000 in costs, a maximum of $7,250. The unit needs its own private entrance, kitchen, bathroom and sleeping area. The CRA allows one claim per qualifying person in their lifetime.
How much is the building permit for a basement apartment in Whitby?
The Whitby building permit for a 700 sq ft basement apartment works out to about $693 at the 2026 rate of $10.65 per m², by our calculation from Schedule N. A below-grade entrance adds a $305 flat fee and registration costs $268. Whitby's Housing Accelerator Fund incentive reimburses the permit and entrance fees for complete applications made by 31 December 2026.
Sources
- Whitby's 2026 fee schedule media-003-ca.cdn.govstack.com
- Development Charges Act ontario.ca
- CRA's MHRTC page canada.ca
- 2024 Ontario Building Code publications.gov.on.ca
- Whitby ADU page whitby.ca
- Oshawa fee by-law media-002-ca.cdn.govstack.com
- Oshawa accessory apartments page oshawa.ca
- Ajax 2026 fee schedule ajax.ca
- Pickering 2026 user fees corporate.pickering.ca
- Pickering ADU page pickering.ca
- Clarington fee by-law weblink.clarington.net
- Durham Region July 2026 rates media-003-ca.cdn.govstack.com
- eligibility page canada.ca
- CRA's expenses page canada.ca
- recommends ontario.ca
- Construction Act ontario.ca
- CP24 reported cp24.com