Often it won't. Plan as if the answer is no until you can show the lender a closed building permit for that unit. The money at stake is real, and a self-contained unit in Hamilton had a median asking rent of $1,800 a month in the twelve months to October 20, 2026, from Found Spaces' lease data. Under CMHC's two-unit rules, up to 100% of that gross rent can count toward qualifying, but only if the lender accepts that the unit exists.
That gap decides whether you can afford the house at all. The median up-and-down duplex in Hamilton was asking $749,000 over the last twelve months, per the Hamilton duplex, triplex and fourplex report. If the basement rent doesn't count, you're qualifying for a $749,000 house on your paycheque alone, and most first-time buyers can't.
I'm Steve LoPresti. I live in Ancaster and work with first-time buyers across Hamilton, Dundas, the Mountain and Stoney Creek, and house hacking is the path I spend the most time on. This is the conversation I wish every buyer had before they booked a showing.
The rent only helps you if the paper says the unit is real
House hacking works because the rent gets counted. You buy a home with two, three or four units, live in one, and let the tenant's rent carry a big share of the mortgage. CMHC lets a two-unit home be bought with the same minimum down payment as a regular house, which is 5% on the first $500,000. Then up to 100% of the gross rent can count as income when the lender works out what you qualify for.
In plain numbers, an $1,800 unit is $21,600 a year of extra qualifying income.
Now take the paper away. If the lender, or the appraiser the lender sends, decides the basement is a finished basement with a kitchen in it, then in their eyes it's a single-family house with no rental income attached, and you're back to qualifying on what you earn. The house that looked easy on the listing sheet suddenly sits out of reach, or it forces a much bigger down payment than you planned for.
That's the whole reason I care so much about legal status. It sits under the math, and the math decides everything else.
What "legal" actually looks like in a Hamilton file
Listing words are not proof. "In-law suite." "Basement apartment." "Great income potential." "Separate entrance." None of those tell you a permit was ever pulled, and even "legal duplex" is only as good as the document behind it.
A real second unit in Hamilton has a trail at the City. Someone applied for a building permit to create the unit. An inspector came out. The permit was closed after a final inspection. Along the way, the unit had to meet the Ontario Building Code and the fire rules for things like fire separation between the units, safe ways out, and smoke alarms. The zoning also has to allow the unit on that lot.
You can check this before you get attached. The City of Hamilton's building division keeps permit records by address. Ask the seller's agent for the permit number, then confirm it with the City yourself.
The tell I see most often is a house where the upstairs looks lived in and fresh, and the basement looks like it was finished on a weekend about fifteen years ago, with a kitchen dropped into what used to be the rec room. That's not always illegal. It's a reason to ask harder.
The one thing I ask for in writing
Before I write an offer on any house that's being sold as two units, I ask the listing agent, by email, for the building permit number for the second unit and whether it was closed. I want the answer written down, with a date on it, because "the sellers say it's legal" over the phone doesn't count.
If they can't give me a number, I still might write the offer. But I write it with a condition that gives my buyer time to check the City's records and talk to their lender with the real facts in hand.
On the showing itself, I go to the furnace room first. It tells me more about how the basement was built than the kitchen does.
A basement with a stove, and an offer that almost went wrong
Picture a young couple renting on the Mountain who find a house listed as a duplex near that $749,000 median, with a tenant downstairs already paying $1,800 a month. They love the backyard and the fresh upstairs kitchen, and they're ready to go in strong because the listing says the tenant covers a big piece of the mortgage. Then their lender asks for proof the basement is a legal unit, and there is no permit on file anywhere. Without the rent, the bank only approves them for a loan well below the asking price. Because they wrote the offer with a condition, they walk away clean, or they go back with a lower price that leaves room to legalize the unit after closing. The house didn't change. What changed was knowing what it really was before the money moved.
This is an illustration, not a client story. But every piece of it is a real risk on Hamilton listings right now.
Three and four units raise the bar
The rules get stricter once you go past two units. For a triplex or fourplex, CMHC wants at least 10% down, and only up to 50% of the gross rent (or the net rent) can count toward qualifying.
So the rent counts for less, and you need more cash. The median triplex in Hamilton was asking $799,900, or $266,633 per unit, over the last twelve months, and the median fourplex was asking $999,900, per the Hamilton multiplex report. On a building that size, one unit that turns out to have no permit can knock a hole in the lender's math, and it can also change how the building gets insured and appraised.
With three or four units, I want to see a permit for every unit, and I want to know which units the lender will actually count. Our underwriting standard shows how we work out the income side, including the operating costs that come off the rent before you call anything cash flow.
The market gives you time to check, so use it
This is a good moment to be careful. In September 2026, Hamilton had 333 home sales, down 27% from a year earlier, and homes took 44 days to sell on average, per the Hamilton market report for September 2026. There were 2,529 homes for sale.
That's a market where you can ask for a permit number, wait for the City to confirm it, and still be in the running. Buyers who skip those checks because they're scared of losing the house are often skipping them for no reason.
I also place the tenants in the units my house-hacking buyers don't live in. A legal unit is far easier to lease with a clear conscience, and a self-contained unit took a median of 14 days to lease in Hamilton over the twelve months to October 20, 2026. That's quick. A tenant who rents quickly and lives in a safe, legal space is the tenant you want carrying your mortgage.
What to do this month
If you're shopping for a house hack in Hamilton, do these before you fall for anything:
- Talk to your lender now and ask one direct question: what do you need to see before you count rent from a second unit?
- For every two-unit listing you like, ask for the permit number in writing.
- Look up the address with the City of Hamilton's building division and confirm the permit was closed.
- Price an unpermitted unit as a single-family house, then add a contractor's quote for making it legal.
The team's house hacking guide and starter kit walks through the full path, from picking a pocket of the city to placing the first tenant.
My take: a second unit without a closed permit is a single-family house with a kitchen in the basement. Price it that way, and you'll never overpay for rent the bank won't count.
Questions people ask
Can I buy a house with an illegal basement unit and make it legal after closing?
Yes, and sometimes it's the smartest buy on the street, because you're paying a single-family price. You'd apply to the City for a building permit and bring the unit up to the Building Code and fire rules. Get a contractor's quote before you firm up your offer, since fire separation and exits can cost more than buyers expect.
What happens to the tenant who already lives in the basement?
In Ontario, an existing tenancy carries on when the house is sold, so the tenant comes with the house. You can't simply ask them to leave because you've bought it. If the unit isn't legal, talk to a real estate lawyer before closing about your duties to that tenant.
Is a Hamilton house with an unpermitted second unit always a bad buy?
No. It's only a bad buy at a duplex price. For a sense of what single-family pricing looks like, the average freehold sale price in Hamilton was $659,430 in September 2026, down 10% from a year earlier, per the Hamilton market report. Compare the asking price to that kind of number, then decide what the legalizing work is worth to you.
Let's check the paper before you fall for the house
If you've found a listing that says "duplex" and you want a second set of eyes on whether the unit is real, send it to me. You can reach me through my page at Found Spaces, or book a plain conversation with our team. We'll look at the permit, the lender's rules and the rent together, before you write anything.