$200k–$400k+
All-in garden suite (typical market range)
450–900
Sq ft — Starlit ADU plan sizes
3 units
Now allowed per residential lot in Ontario
A garden suite in the London area typically costs somewhere between $200,000 and $400,000-plus all-in, depending mostly on size, site access, and how far the services have to run. A compact studio on an easy lot sits near the bottom of that range; a larger two-bedroom garden home with a tricky site lands near the top or beyond. Those are typical Southwestern Ontario market estimates for 2026, not a quote — the number for your backyard depends on your backyard.
The same building goes by a lot of names. An accessory dwelling unit, a garden suite, a granny flat, a secondary suite, a coach house — they all describe a self-contained second home on a property that already has one. Ontario has spent the last few years making them far easier to build, and for a lot of homeowners they've become the most practical way to add rental income, house a family member, or create a downsizing option without leaving the neighbourhood.
This is a builder's-eye view of what an ADU actually costs in the London region, what the new zoning rules allow, and how the rental-income math tends to work. The dollar figures are conservative market ranges that vary by site and spec — read them as a planning frame, not a price.
What Drives a Garden Suite's Cost
Size is the obvious driver, but it's not the only one. A 450 sq ft studio has one of everything — one bathroom, one compact kitchen, one mechanical system — and a 900 sq ft garden home isn't simply double the cost, because that fixed core of kitchen and bath gets spread over more floor area. Per square foot, smaller units often cost more, not less, which surprises people.
After size, the biggest swing factor is your site. A garden suite needs its own water, sewer or septic, and electrical service, and the cost of getting those across the yard depends entirely on how far they have to run and what's in the way. A unit that can tie in near the existing house is cheaper than one at the back of a deep lot. Access for equipment matters too — a tight urban backyard with no side-yard access drives up labour.
Size & Layout
The kitchen and bathroom are the most expensive rooms per square foot. A studio packs that cost into a small footprint; a larger unit spreads it out. Bedroom count and a full second bath add the most.
Servicing Runs
Water, sanitary, and electrical have to reach the unit. The farther from the existing house and the harder the dig, the more this line costs — often the single biggest variable between two otherwise identical suites.
Site Access
Can a small excavator and delivery truck reach the build location? Tight backyards with no side access mean more hand labour and higher cost.
Foundation Type
Slab-on-grade is typically the most economical. A full or crawlspace foundation, or a unit over a garage, costs more.
Finish Level
Like any home, finishes are the elastic line. A rental-grade interior costs less than a suite finished to match the main house.
Our ADU and garden suite plans come in three sizes — a 450 sq ft Studio, a 650 sq ft Suite, and a 900 sq ft Garden Home — and each is built to the same high-performance envelope standard as our houses. We don't attach a fixed price to those plans here, because the all-in cost depends on which one fits your lot and what your site requires. The plan size is one input; the site is the rest.
"A garden suite isn't a shed with a bathroom. It's a complete second home — its own services, its own envelope, its own permit — and that's where the real cost lives, not in the square footage."
The Zoning Rules Changed in Your Favour
The single biggest reason ADUs have taken off is that the rules got dramatically more permissive. Under recent provincial housing legislation, Ontario now allows up to three residential units on most urban residential lots "as of right" — meaning a property can have the main house plus two additional units (for example, a basement suite and a backyard garden suite) without a zoning amendment or minor variance in many cases.
That's a meaningful shift from the old world, where adding a second unit often meant a contested rezoning. The details still vary by municipality — setbacks, lot coverage, height limits, parking, and tree protection are all set locally, and London has its own specifics worth confirming for your address. But the default posture has flipped from "probably not" to "probably yes," and that's what's made garden suites pencil out for ordinary homeowners.
We handle the permit process as part of the build — the zoning review, the building permit, the inspections — so you're not the one untangling municipal requirements. Every secondary suite still has to meet the Ontario Building Code for a separate dwelling, including fire separation and egress, and that's exactly the kind of thing a builder who does this regularly handles without drama.
The Rental-Income Case
For a lot of owners, the garden suite math is really a rental-income question. A self-contained one- or two-bedroom unit in the London rental market commands a real monthly rent, and that income runs against the build cost to give you a payback period. The exact numbers depend on your rent, your build cost, and your financing, so we won't pretend to a single figure — but the structure is straightforward, and at current London-area rents the payback on a well-built suite is measured in years, not decades.
The non-financial cases are just as common. A garden suite is an in-law suite that keeps an aging parent close but independent, a landing spot for an adult kid, a downsizing option that lets you rent out the big house and live small on the same lot, or a home office that isn't in your spare bedroom. The flexibility is the asset — and because it's a permanent, code-built structure on your land, it adds to the property's value rather than depreciating like a temporary solution.
One thing we'd steer you away from: building the suite cheap. A poorly-insulated, leaky secondary unit costs more to heat than the rent comfortably covers, and an uncomfortable suite is a hard one to keep tenanted. Building it to the same envelope standard as a real house — tight, well-insulated, properly ventilated — keeps the operating cost low and the unit rentable, which is the whole point.
"The cheapest garden suite to build is often the most expensive one to own. A tight, well-insulated unit keeps its operating cost low — which is exactly what protects your rental margin."
Getting a Real Number for Your Lot
The ranges in this article are planning tools. The only way to know what your garden suite will cost is to look at your specific lot — its access, its servicing distances, its zoning — alongside the plan that fits it. That's a site visit and a spec conversation, not a number off a chart.
If you're weighing an ADU against a larger move, our breakdown of what it costs to build a full custom home in Ontario covers the same ground at house scale, and the FAQ answers the process questions we hear most. When you're ready, the next step is showing us the backyard.
Key Takeaways
Garden suites in the London area typically run ~$200k–$400k+ all-in — a market estimate that varies by size and site, not a quote.
Smaller units often cost more per square foot, because the kitchen and bath are a fixed cost spread over less floor area.
Servicing runs (water, sewer/septic, electrical) and site access are usually the biggest swing factors between two suites.
Ontario now allows up to three units on most urban residential lots as of right — the rules changed in your favour.
We handle the permit process; every suite still meets the Ontario Building Code as a separate dwelling.
Build it to a real envelope standard — a leaky cheap suite costs more to run and is harder to keep rented.
