Basement Apartments, Duplex, Triplex & Multiplex Conversions in Ontario

BASEMENT RENOVATIONS, TURN A SINGLE FAMILY HOME INTO DUPLEX, TRIPLEX OR MULTIPLEX

Start-to-Finish: Planning, Drawings & Construction.

At Suite Builders, we provide a complete design, drawings, and renovation service for finished basement apartments (granny flats), duplexes, triplexes, fourplexes and multiplex conversions, accessory dwelling units (ADUs or ARUs) and secondary suites across Southern Ontario. Our BCIN-certified team delivers building permit drawings and a seamless path from concept to completion, ensuring compliance with the Ontario Building Code and local zoning bylaws.

One team, one process, and one seamless path from idea to move-in.

Multiplex contractor Brantford Ontario, garage apartment conversionMultiplex contractor Brantford Ontario, garage apartment conversion

Proudly serving homeowners, developers and real estate investors across Southern Ontario, including: Hamilton, Niagara Falls, St. Catharines, Welland, Oakville, Burlington, Kitchener, Waterloo, Cambridge, Guelph, Wellington County, Brantford, Brant County, Woodstock, Oxford County, Norfolk County, Haldimand County, London, Middlesex, St. Thomas, Elgin County and surrounding areas.

Project Highlight: Turning A Single Family Home into a Triplex in Brantford, Ontario

Our team successfully designed & converted a single-family home into three separate, Ontario Building Code-compliant living spaces by utilizing the existing basement and garage for self-contained units. Basement renovations and garage apartment conversions are becoming increasingly popular choices for multigenerational living, investment properties, student housing and aging-in-place, by maximizing under-utilized space—without expanding a home’s footprint.

BCIN permit drawings and design-build construction for legal basement apartment in Ontario
Finished basement apartment with separate entrance created through secondary suite conversion
Ontario duplex conversion design-build project showing new self-contained rental unit
Triplex conversion layout for investment property with permit-ready architectural drawings
Fourplex multiplex renovation with code-compliant secondary suites and fire separation upgrades
Converted garage apartment used as additional residential unit (ARU) rental suite
ADU / ARU backyard home used to increase rental income on existing property in Ontario
Open-concept living space in legal secondary suite compliant with Ontario Building Code
Basement apartment kitchen and living area designed for legal rental unit approval
Before-and-after duplex conversion floor plan for Ontario investment property
Multiplex development feasibility review with permit drawings and construction planning
Design-build secondary suite project maximizing rental income for Ontario investor
BCIN permit drawings and design-build construction for legal basement apartment in Ontario
Finished basement apartment with separate entrance created through secondary suite conversion
Ontario duplex conversion design-build project showing new self-contained rental unit
Fourplex multiplex renovation with code-compliant secondary suites and fire separation upgrades
Loading the next set of gallery items...

The Market for Basement Apartments, ADUs & Multiplexes in Ontario

These compact residential living units are increasingly appealing to a wide variety of buyers and investors. Whether you’re looking to create a legal basement apartment, convert a home into a triplex or fourplex, or build an additional residential unit (ARU) for rental income, the demand for these types of units is growing fast across Ontario.

Today, many homeowners and investors are often asking:

  • “How to build a legal basement apartment in Ontario?”
  • “What are the costs to build a duplex, triplex or fourplex in Ontario?”
  • “What are the municipal zoning rules for multiplex conversions in Ontario?”
  • “Can I convert my detached garage into a rental suite or coach house?”

With strong rental demand, limited housing supply, and rising property values, finished basement apartments, duplex, triplex, multiplex conversions and secondary suites represent some of the most compelling investment property opportunities. These units offer added rental income, tax advantages, and a smart way to leverage existing real estate assets.

For a list of everything you need to know about adding a second living unit to your property in Ontario, click here.

Multiplex development feasibility review with permit drawings and construction planning

Basement Apartments & Multiplexes: Affordable Housing & Added Income

Whether building a multifamily investment property, increasing property value, or creating a living space for multi-generational living or aging-in-place, finished basement apartments, garage apartments and multiplex conversions are becoming an increasingly popular solution to housing affordability and family wealth building.

1. Income Potential

Basement apartments are often more affordable for tenants compared to units on higher floors, making them an attractive option for individuals seeking cost-effective housing solutions. ​​ Additionally, factors such as the condition of the apartment, its accessibility, and the demand for rental properties in the area can influence the potential income that can be generated from a basement apartment.

2. Legal Basement Apartments in Ontario

Establishing a legal basement apartment involves proper egress windows for safety, sufficient ceiling height, separate entrances, and compliance with electrical, plumbing & fire safety standards. Some municipalities may also have occupancy and parking stipulations. Consult with a building professional to ensure the legal conversion of a basement into a rental unit.

3. Additional Dwelling Units

These apartments can be an affordable and cozy option, offering a cooler environment in summer and warmer in winter, thanks to their insulated position. They typically feature all the amenities of a standard apartment, including kitchenette, bathroom and living space. Cost to renovate your current basement depends on needs, but is often more affordable and can increase property value.

FREQUENTLY ASKED QUESTIONS

To build a legal basement apartment (also called a secondary suite, in-law suite, or granny flat), the unit must meet Ontario Building Code, fire separation, ventilation, egress (escape window), parking, and zoning requirements. Suite Builders handles zoning review, permit drawings, engineering, and the full design-build process — ensuring your secondary suite is approved and legal from day one.

Yes — in many municipalities, Ontario now permits Additional Residential Units (ARUs), meaning homeowners can convert to duplexes, triplexes, fourplexes or multiplexes. Feasibility depends on lot size, parking, zoning, and servicing capacity. We begin with a site feasibility assessment to confirm what’s permitted and provide accurate timelines and budget expectations.

Municipalities require BCIN-certified permit drawings, including architectural floor plans, building code compliance details, fire separation assemblies, HVAC details, and any engineering required. At Suite Builders, we produce permit-ready drawings and manage the entire submission process to avoid delays or rejections.

Costs depend on scope and existing conditions. On average:

  • Basement apartment / secondary suite: starting around $80,000–$160,000+
  • Duplex/Triplex conversion: starting around $180,000–$400,000+
  • Fourplex/multiplex conversion: highly variable depending on structural changes

However, rental income often offsets carrying costs, making these some of the strongest ROI property upgrades for Ontario homeowners and real estate investors.

Yes — garage conversions into garage apartments, coach houses, loft apartments, or ARUs are increasingly popular in Ontario. We design and build everything from converted garage apartments to backyard homes and tiny homes, handling zoning, design, drawings, and construction.

Why Choose Suite Builders TO BE YOUR Basement Apartment OR Duplex BUILDER?

When it comes to designing and building legal accessory dwelling units (ADUs), additional residential units (ARUs), secondary suites and complete multiplex conversions, Suite Builders offers what many firms cannot: a fully integrated design-build solution that removes the headaches, miscommunications and unnecessary delays that often plague these projects.

Our specialties include:

  • Finished basement apartments & legal in-law suites
  • Duplexes, triplexes, fourplexes & multiplex conversions
  • Garage conversion apartments & coach houses
  • Garden suites & tiny homes
  • Backyard homes & laneway suites
  • Home additions & multi-unit conversion of existing homes
  • Seasonal farm worker housing & bunkhouses

With a single accountable team managing everything—from initial site feasibility and building permit drawings to construction hand-over—you avoid the typical pitfalls of coordinating multiple contractors, dealing with permit rejections, scope creep, or code non-compliance.

If you’re a homeowner or investor in Ontario ready to build income-producing property, maximize value, or add flexible living space, contact Suite Builders today for a free discovery call and start your project the right way—on time, on budget, and code-compliant.