Durham Region Second-Suite Specialists

Legal Basement Apartment
in Ajax

Ajax has some of the most homeowner-friendly second-suite rules in Ontario — up to four units on most properties, cash-back grants, and no extra parking required for your first unit. Here's exactly what the Town of Ajax requires, and how Cornerstone gets your suite approved, built, and inspected.

Start Your Basement Diagnostic Call 1-888-404-7383

The Two Rule Books

What Makes a Basement Apartment "Legal" in Ajax

In Ajax a second suite is an Additional Dwelling Unit (ADU). To be legal it has to satisfy both the Town of Ajax's zoning rules (how many units, parking, where a unit's allowed) and the Ontario Building Code (room sizes, ceiling height and safe exits). Ajax overhauled its ADU rules in 2025 — and they're now among the most permissive in the region.

Ajax Zoning

Sets the outside rules: up to four units, reduced parking and where a unit's allowed — modernized under By-law 23-2025.

Ontario Building Code

Sets the inside rules: minimum room dimensions, ceiling height, fire separation, smoke/CO alarms and a safe means of escape.

A legal second suite is fully self-contained, which means it needs its own complete kitchen and bathroom. We build both to the same standard as our kitchen renovations in Ajax and bathroom renovations in Ajax — including flood-tested, fully waterproofed wet areas.

Ajax Cash-Back Program

Get Money Back When You Build — "Build More, Get More"

The Town of Ajax is offering cash-back grants on new Additional Dwelling Units through its Build More, Get More program, funded by the federal Housing Accelerator Fund. The grant is a fixed amount per unit, scaling with the number of units you build. To qualify, the building permit application must be submitted on or after July 2, 2025 — grants are first-come, first-served while funds last, and paid out after construction is complete and the permit is closed. We'll confirm whether your project qualifies and time the application right.

See If Your Ajax Property Qualifies

Rule Book 1

Ajax Zoning Requirements

These are the property-level rules an Ajax home must satisfy to add a legal Additional Dwelling Unit — and 2025 made them notably easier.

Up to Four Units

  • Under By-law 23-2025, Ajax now permits up to four (4) dwelling units on most properties with a detached, semi-detached or townhouse dwelling.
  • That can mean a basement apartment, an upstairs unit, a unit in an existing garage, or a detached garden suite — or a combination.
  • Exact permissions depend on your property's zone, lot size and setbacks. Cornerstone confirms how many units your specific lot allows during planning.

Parking — No Extra Space for Your First Unit

  • No additional parking is required for the first ADU. For a typical detached home that already has its two required spaces, adding a basement apartment needs zero extra parking — removing the single biggest obstacle most homeowners worry about.
  • One additional space per unit is required for the third and fourth ADU, working out to roughly one space per unit overall.
  • Tandem parking is permitted — cars can sit one behind another in the driveway, so you rarely need to widen anything.

Check Your Property First

  • Ajax provides a free ADU Property Mapping Tool where you can type your address and see whether an ADU is permitted, plus your lot's zoning, setbacks, buildable area, height limits and parking — at map.resimate.build.
  • It's a quick first check, but it doesn't replace a real feasibility review. Cornerstone confirms what's actually buildable on your lot and handles the zoning and permit work.
  • If your property doesn't quite meet a rule, a minor variance may still make it possible.

Rule Book 2

Ontario Building Code: Inside the Suite

The interior of the suite is governed by the Ontario Building Code, which sets minimum areas room by room. These apply Province-wide, in Ajax the same as anywhere in Ontario.

Separate (Walled-Off) Rooms

RoomMinimum Floor Area
Living Room13.5 m² (145 ft²)May reduce to 11 m² if combined with other space in a one-bedroom unit.
Kitchen4.2 m² (45 ft²)May reduce to 3.7 m² in a one-bedroom unit.
Dining Room7.0 m² (75 ft²)May reduce to 3.25 m² if combined with another room.
Primary Bedroom9.8 m² without a closet, or 8.8 m² with a built-in closet.
Additional Bedrooms7.0 m² without a closet, or 6.0 m² with a closet.
BathroomNo set area — must fit a toilet, sink and tub/shower with proper clearance.

Open-Concept / Bachelor

For a studio or bachelor unit, the combined sleeping, living, dining and kitchen space must be at least 13.5 m² (145 ft²) total, designed for no more than two occupants.

Ceiling height rule: across living areas the ceiling must be at least 1.95 m (6 ft 5 in). It may drop to 1.85 m directly under beams or HVAC ducting. Low basement headroom is the most common reason a suite needs design work before it can be approved.

Permit & Approval

How a Legal Suite Gets Approved in Ajax

A legal ADU isn't just built — it's permitted, inspected and (for the grant) timed correctly. Here's the path.

Confirm Your Property

We check your zone, how many units your lot allows, parking, and whether the Build More, Get More grant applies before committing to a layout.

Design & Drawings

Scaled drawings showing existing and proposed floor plans, room areas, egress, fire separations and alarm locations — prepared to the Town's submission standards.

Building Permit

The application is submitted through Ajax's eApply portal. A permit applied for on or after July 2, 2025 may qualify for the cash-back grant.

Build & Inspections

We build to code and pass every required inspection — fire separation, egress, plumbing and electrical — through to final sign-off.

Permit Closed, Grant Paid

The grant is disbursed after construction is complete, all inspections pass, and the permit is closed. We carry the project cleanly to that finish line.

Timing matters with the grant. Funds are first-come, first-served while they last, and only released once the permit is closed. Getting the application in and the build done cleanly is how you protect the cash-back — exactly the kind of timeline discipline Cornerstone is built around.

Why Build It Legal

A Registered Suite Is Worth More

Real Rental Income

A legal, inspected unit can be rented with confidence — and with up to four units, an Ajax property can generate serious monthly income.

Resale Value

A permitted, code-built suite adds verified value and sells clean. An unpermitted one is a liability a buyer inherits — or walks away from.

Safety & Insurance

Code-built fire separation, egress and alarms protect your tenants and your home — and an undisclosed unit can void your insurance.

The Grant Requires It

The cash-back grant only pays out on a permitted, inspected, closed-out build. Doing it legally isn't just safer — it's how you get paid.

Common Questions

Ajax Basement Apartment FAQ

How many units can I really have on my Ajax property?
Under By-law 23-2025, Ajax permits up to four dwelling units on most properties with a detached, semi-detached or townhouse home. The exact number for your lot depends on its zone, size and setbacks — we confirm that during planning, and you can get a first read from the Town's mapping tool at map.resimate.build.
Do I need extra parking for a basement apartment in Ajax?
For your first ADU — no. Ajax requires no additional parking for the first additional unit, so a typical detached home that already has two spaces needs nothing extra. The third and fourth units each need one space, and tandem parking (one car behind another) is allowed.
Can I actually get cash back for building one?
Yes — the Town of Ajax's Build More, Get More grant pays a fixed amount per unit, funded by the Housing Accelerator Fund. The building permit application must be submitted on or after July 2, 2025, grants are first-come first-served while funds last, and the money is paid after the permit is closed. We confirm eligibility and time the application to protect it.
My basement ceiling feels low — is that a dealbreaker?
Not necessarily. The Code requires about 1.95 m (6 ft 5 in) across living areas, dropping to 1.85 m under beams and ducts. Many Ajax basements qualify; where they're tight, design choices (relocating ducts, adjusting the layout) often solve it. We assess this early so there are no surprises.
What affects the cost of a legal basement apartment?
Ceiling height and whether the floor needs lowering, a separate entrance, egress windows, the kitchen and bathroom layout, fire separation, and electrical/HVAC separation all drive cost. Ajax's no-extra-parking rule and the cash-back grant can reduce your net cost significantly. After a site visit we give you a clear, locked scope and price — not a guess.
What happens if I build a suite without permits?
You lose the grant entirely (it only pays on a closed, inspected permit), your home insurance can be voided, you can be held liable in a fire or injury, and the rental income may not count toward financing. Building it legal protects your home, your tenants and your money.
Bylaw and grant information last reviewed June 2026. Municipal requirements, grant funding and deadlines can change — Cornerstone confirms current Town of Ajax requirements with the Planning & Development Department on every project. Sources: Town of Ajax Housing & ADU pages (ajax.ca/housing), Zoning By-law 23-2025, Section 5 Parking consolidation; Ontario Building Code.
Part of Our Durham Legal Suites Guide
See requirements for every Durham town, plus the full second-suite overview
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Legal Basement Apartments Across Durham
We also build legal second suites in nearby Pickering, Whitby, and across Durham Region.

Thinking About a Legal Basement Apartment in Ajax?

Start with a basement diagnostic. We'll confirm how many units your property allows, whether the cash-back grant applies, and map out the path to a legal, inspected suite — built once, built right.

Start Your Basement Diagnostic Call 1-888-404-7383

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