Garden Suites in Ontario: The Bill 23 Math

Most Ontario homeowners are sitting on a development project they haven't realized they have. Late 2022, the More Homes Built Faster Act (Bill 23) opened up garden suite zoning across nearly every municipality in the province. Under the new rules, building a secondary unit on a typical residential lot is now as-of-right in most cases, with significantly reduced or eliminated development charges. The regulatory unlock is real. The math has barely caught up. Here's how the numbers actually work, and why a garden suite often outperforms the alternatives most homeowners think they should compare against.

What Bill 23 actually changed

Before late 2022, building a garden suite in Ontario was a municipally-controlled approval process. Some cities allowed it, some didn't, and where they did, you usually needed a minor variance, a site plan, and several rounds with planning. Bill 23 flipped most of that. As-of-right zoning means you don't need a variance for a compliant garden suite. The act also eliminated most development charges on secondary units, removing one of the biggest cost drivers. There are still municipal building permit fees, setback rules, and lot coverage limits, but the framework is materially friendlier than it was three years ago.

The point isn't that the rules are gone. The point is that the rules now permit something most homeowners' lots can absorb, which means the question shifts from “can I build?” to “does it pencil?”

The build economics on a typical Ontario lot

A 1-bedroom detached garden suite in Ontario lands somewhere between $250,000 and $350,000 all-in, including foundation, full services (water, sewer, hydro, gas), interior finishing, and permits. Larger 2-bedroom units come in at $350,000 to $450,000. The cost variance is mostly site-specific: how far the unit sits from the main utilities, what the soil conditions are, and whether the lot needs any grading work. A serious builder gives you a tight number after a site visit, not before.

On the rent side, a finished 1-bedroom garden suite in Southern Georgian Bay or comparable Ontario markets rents in the $2,000 to $2,500 a month range. Tighter urban markets like Toronto or Ottawa run higher; smaller secondary markets a bit lower. Operating expenses (incremental property tax, insurance delta, utilities the landlord covers, maintenance) typically add up to $300 to $500 a month.

The cash flow picture on those numbers, before financing: roughly $1,500 to $2,000 a month of net operating income on a $250,000 to $350,000 build. That's a cap rate in the 5 to 8% range, solid for residential real estate, especially compared to the cap rates on existing investment properties that are already priced for scarcity.

The financing structure

Three real paths to fund the build, each with different math:

1. Refinance the primary mortgage. Lender reappraises the property (most lenders allow you to bake the projected post-build value into the appraisal), and you refinance up to their combined LTV ceiling, typically 80% on uninsured. The build cost gets rolled into the new mortgage. This is the cleanest path for most files.
2. HELOC draw + construction loan. Some lenders offer construction-draw mortgages where funds release at milestones. Useful when you don't want to refinance the primary's rate. More moving parts.
3. Sell an existing rental, redirect proceeds. If you already own a small rental that's underperforming, the sale proceeds (after capital gains tax + paying off that rental's mortgage) can fund the build with minimal or no refinancing on the primary. The lost rental cash flow is the opportunity cost. The Garden Suite calculator on this site models all three paths side by side.

Cash damming the suite

Here's where the structure gets interesting. The garden suite is a rental property. Its operating expenses are deductible on T776 like any other rental. But you can layer the cash-damming structure on top: route the suite's operating expenses through a HELOC instead of paying them directly, redirect the suite's rental income to the personal mortgage as additional principal, and generate deductible interest on the HELOC every year.

On a typical file with a $475,000 primary mortgage and a $300,000 garden suite generating $2,400 a month, the layered structure usually shaves an additional 3 to 6 years off the personal mortgage compared to building without the cash-dam. That's on top of the underlying advantage of having a rental unit on your property in the first place.

Where it goes wrong

Three failure modes show up most often:

Build-cost overruns. A $300,000 budget that ends at $370,000 is common when contractors aren't pinned down on scope before signing. The fix is fixed-price contracts where possible, and a 10 to 15% contingency on the financing side.

Lender LTV ceiling. If the post-build appraised value doesn't come in high enough, the refinance caps at 80% of the lower number, and the household has to bring cash to close the gap. The fix is to get a pre-construction appraisal opinion in writing from the lender before committing to the build.

Zoning surprises. Bill 23 simplified the zoning framework, but every municipality has its own implementation. Some still require minor variances for setbacks, lot coverage, or height. Check your specific municipality's zoning bylaw and site plan rules before falling in love with a build design.

Who this fits

Homeowners with a primary property valued $700,000 or higher (so the refinance LTV math works), a lot that physically permits a secondary unit (most Ontario lots do under Bill 23), a 10+ year horizon to capture the compounding benefits, and a marginal tax rate of 30%+ to make the cash-damming layer worthwhile. The clients who get this right treat it as a 2-year project and a 20-year wealth move, not a quick win.

The thing I keep coming back to is that this is one of the highest return-on-property moves Ontario homeowners can make right now, and it sits in a niche that almost nobody is modeling end-to-end. Bill 23 unlocked it. The math just needs to come out of the calculator.