The short answer
In London, Ontario, most houses can still have up to four units on the property, with up to three additional residential units on the lot. What changed is size. Under the City's interim rules, each new additional unit is limited to two bedrooms, can be no more than 80 percent of the main home's floor area, and the property is capped at five bedrooms across its additional units. Permanent rules adopted in March 2026 are under appeal, so the interim rules apply for now. Confirm what is allowed on a specific lot with the City before you buy or price a home around a unit.
Basement apartments and backyard units come up in a lot of conversations I have with buyers, investors and homeowners in London. The rules on how big those units can be have changed, and many people are still working from the older ones. Here is what applies right now, what is still being decided, and why it matters if you are buying, selling or planning a unit.
What is an additional residential unit?
An additional residential unit, often called an ARU, is a self-contained unit on the same property as a main home. In practice that usually means a basement apartment, a unit added inside the house, or a separate building in the backyard such as a garden suite or coach house.
What has not changed?
Most houses in London can still have up to four units on the property where zoning allows: the main home plus up to three additional residential units. Up to two of those additional units can be in a detached building on the lot.
What has changed in 2026?
An interim control by-law (CP-1600-300) now limits the size of new additional units. According to the City of London:
| Rule | What applies right now |
|---|---|
| Bedrooms per additional unit | Up to 2 |
| Size of each additional unit | No more than 80 percent of the main home's gross floor area |
| Bedrooms across all additional units | Up to 5 on the property |
| Number of additional units | Up to 3 per lot (up to 2 in a detached building), up to 4 units including the main home where zoning allows |
Source: City of London, Additional Residential Units page and file Z-25159, checked October 20, 2026.
Are the permanent rules in effect?
Not yet. Council adopted amendments to the additional residential unit permissions on March 3, 2026 (file Z-25159), but they have been appealed. Until the appeals are resolved, the interim control by-law stays in effect. If the appeal is decided, the rules could change again, which is one more reason to check the current position before you commit to a plan.
Why does this matter if you are buying?
If you are buying a house with a plan to add a unit, the plan you made last year may not fit the current rules. A three-bedroom basement apartment you pencilled in may now have to be a two-bedroom unit, and that changes the numbers you were working from. Run your plan against the current limits before you firm up an offer.
Any new unit also needs a building permit, and a rental licence before someone moves in. Build those steps into your timeline.
Why does this matter if you are selling?
If you are selling a home that could suit a unit, buyers will ask what is allowed. If you already have a unit, buyers will want to know about its permits and licence. Being ready with accurate information, and pointing buyers to the City for lot-specific answers, keeps the conversation on solid ground.
What should you check before you buy or price around a unit?
- Confirm the zoning and what is allowed on that specific lot with the City of London.
- Check the current bedroom and size limits against the unit you have in mind.
- For an existing unit, ask about the building permit and rental licence.
- Recheck the status of the Z-25159 appeal close to your decision date.
- Run your numbers at two bedrooms per unit, not the layout you hoped for.
Frequently asked questions
How many units can I have on a house lot in London, Ontario?
Where zoning allows, up to four units: the main home plus up to three additional residential units, with up to two of those in a detached building. Confirm what applies to your specific lot with the City of London.
How many bedrooms can a basement apartment have in London right now?
Under the City's interim control by-law, each new additional residential unit can have up to two bedrooms, and the property is limited to five bedrooms across all of its additional units.
How big can an additional residential unit be in London?
Under the interim rules, an additional unit can be no more than 80 percent of the main home's gross floor area.
Are London's new ARU rules final?
No. Council adopted permanent amendments in March 2026, but they are under appeal. The interim control by-law stays in effect until the appeals are resolved.
Running the numbers on a property with a unit?
If you are looking at a home in London where a basement or backyard unit is part of the plan, I am glad to be a second set of eyes on it.
Call 519-870-8104 or visit shaneharrison.ca.
Video transcript
Hey everyone, Shane Harrison here with The Realty Firm. This week I want to talk to you about ARUs. If you're thinking about adding a basement apartment or a backyard unit in London, the rules on how big that unit can be have changed, and a lot of people are still working from the old ones. Here's what hasn't changed. Most houses in London can still have up to four units on the property, with up to three additional units on the lot. Here's what has. Right now, an interim bylaw limits each new additional unit to two bedrooms. The unit can't be more than 80 percent of the size of the main house, and the whole property is capped at five bedrooms. Council approved permanent rules in March, but they've been appealed. So for now, the interim rules are the ones that apply. Why does this matter? If you're buying a house planning to add a unit, the rent you pencilled in last year might not work at two bedrooms. And any new unit still needs a building permit and a residential licence before someone moves in. So before you buy around a unit, or price a home around one, confirm what is allowed on a specific lot with the City. If you're running the numbers on a property in London and want a second set of eyes, call me, 519-870-8104. I'm Shane Harrison with The Realty Firm. Hope to talk to you soon. Take care. Bye.
