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Additional Dwelling Units St Catharine's

If you’re interested in adding an Additional Dwelling Unit (ADU) to your property, we’d be happy to provide information and answer any questions you may have. An ADU can provide several benefits, such as extra living space for family members, a way to generate income through renting, or to increase the value of your property. We can guide you through the entire process, from design to construction. We can also provide insight into any regulatory requirements you’ll need to navigate. Contact us today to start exploring your options and taking steps towards your ADU goals.

What Are Additional Dwelling Units (A.D.U.'s)?

An additional dwelling unit, often referred to as an ADU, can be a solution to various housing challenges, providing affordable housing options, allowing homeowners to generate rental income, and making more efficient use of existing infrastructure.

An ADU, is a self-contained living space within a property that is designed to accommodate the needs of a separate household.

ADUs are commonly found on the same lot as a primary residential structure, such as a house, and they provide a separate and independent living space for another individual or household. 

The Building Code ensures comfortable living space in all dwellings, including basement apartments and in-law suites. The minimum size for rooms depends on whether they have walls or are part of an open concept layout. For instance, a separate dining room needs at least 7 square meters (75 square feet), while a bachelor unit with open concept living, sleeping, dining, and kitchen can be as small as 13.5 square meters (145 square feet).

Table 1: General minimum sizes for rooms and spaces
Room/SpaceMinimum required floor area
Living area13.5 m2 (145 ft2)
Dining aream2 (75 ft2)
Kitchen4.2 m2 (45.2 ft2)
Combined living, dining and kitchen areas in a one-bedroom unit11 m2 (118.4 ft2)
Master bedroom (without built-in closet)9.8 m2 (95 ft2)
Other bedrooms (without built-in closets)m2 (75 ft2)
BathroomSufficient space for sink, toilet and shower stall or bath
Combined sleeping, living and dining areas and kitchen space13.5 m2 (145 ft2)

Ceiling Heights

Don’t forget about ceiling heights! This can be tricky in existing homes, so choosing your second unit’s location is important. Here’s the breakdown:

  • Basements: Minimum ceiling height is 1.95 meters (6′ 4¾”) throughout the entire unit, including hallways leading to the exit.
  • Attics (with sloped ceilings): At least 50% of the usable floor area needs a minimum ceiling height of 2.03 meters (6′ 8″). Areas lower than 1.4 meters (4′ 7″) can’t be counted as usable space.

Remember: These are minimums. Aiming for a bit more height can make the space feel more comfortable.

Minimum Window Sizes

Room/Space:Minimum Required Window Area:
Living and dining rooms5% of the floor area
Bedrooms2.5% of the floor area
Laundry room, kitchen, bathroomWindows not required

Heating & Ventilation

Sharing the Heat (and Air): Good news! Your main house and the second unit can share a single furnace and air duct system, following Building Code guidelines. To keep things safe in case of fire, you’ll need a special smoke detector installed in the main supply or return air duct. This clever device acts like a fire alarm for the HVAC system. If smoke is detected, it automatically shuts down the furnace’s fuel supply and electrical power, preventing the spread of smoke through the air ducts and potentially between units.

Fire Separation

Creating a Safe Haven: Fire Separation Explained

Fire safety is a top priority when adding a second unit. Here’s where fire separation comes in. Imagine it as a built-in firewall, slowing the spread of flames between your main house and the new unit. This barrier needs to be continuous, with any openings (doors, vents) featuring special fire dampers. These smart devices automatically shut in case of fire, blocking smoke and flames from traveling through.

What exactly is a fire separation?

Think walls, floors, self-closing doors, or a combination of these. Regular building materials like wood studs and drywall can be used. For example, a typical 30-minute fire separation might involve 2×4 wood studs, ½-inch drywall on both sides, and fire-resistant insulation filling the gaps. Older homes with lath and plaster construction often have a 15-minute fire separation rating.

Building Code Requirements:

The Building Code mandates a 30-minute fire separation between your second unit and the main house, as well as any shared common areas. If your renovations involve altering existing floors or ceilings, these need to be upgraded to a 30-minute fire separation as well (see floor/ceiling diagram for details). There’s a potential exception: if your entire house has interconnected smoke alarms, the fire separation rating can be reduced to 15 minutes.

Remember: Consulting a professional is crucial to ensure your fire separation meets all safety regulations and building code requirements.

Diagram of typical floor/ceiling that would generally achieve a 30-minute fire separation

Smoke & Carbon Monoxide Alarms

Double Down on Safety: Smoke and Carbon Monoxide Alarms

Your second unit needs reliable smoke alarms to meet the CAN/ULC-S531 standard. Look for this label on the alarm to ensure it meets safety regulations. These alarms should also have a flashing light to grab attention during emergencies. Smoke alarms are readily available at hardware and home improvement stores.

Where to Put Your Smoke Alarms?

Placement is key! Here’s a breakdown:

  • Every floor of your house, including the basement and attic (if applicable)
  • Outside all sleeping areas, potentially serving as the level’s primary alarm
  • Inside each bedroom of the second unit
  • Common areas shared by both units, like entrances and laundry rooms

Carbon Monoxide Alarms: Not Always Required, But Always a Good Idea

While not mandated in every situation, carbon monoxide (CO) alarms are highly recommended, especially if your house has a fuel-burning furnace (natural gas, propane, etc.) or an attached garage. These alarms come in battery-operated or electrical models, and should be placed in these key locations:

  • Near bedrooms and sleeping areas in the second unit
  • Inside the furnace room, if it’s separate from the living spaces

Remember: Regular testing of both smoke and CO alarms is crucial. Make sure they’re functioning properly to keep everyone safe.


Two Ways Out: Ensuring Safe Exits for Your Second Unit

Having safe and accessible exits is vital for your second unit. The specific requirements depend on the unit’s location within your house. Here’s a breakdown:

  • Separate Exit Preferred: Whenever possible, aim for a dedicated exit for the second unit. This offers the greatest safety and convenience for all occupants.
  • Sharing an Exit: If a separate exit isn’t feasible, a common exit for both units can be allowed. However, there are strict safety measures in place:
    • The shared exit area must have a 30-minute fire separation wall/door for added protection.
    • Smoke alarms throughout this common area need to be interconnected, ensuring both units are alerted in case of fire.
  • Windows as Escape Routes: In some situations, an exit from one unit might lead through another unit. Here, an additional escape route, typically a window, is mandatory.
    • These escape windows need to be large enough for a person to climb through easily.
    • They must also be operational without any tools, ensuring quick and hassle-free escape during emergencies.
    • Diagrams (not shown here) outline specific requirements for escape window size and placement depending on whether they’re in the basement or upper floors.

Remember: Always prioritize clear and unobstructed access to all exits and escape windows.

Escape window for upper floors

Ground floor or basement escape window

Window wells for basement escape windows (sectional view)

ADUs can come in various forms, including:

  1. Secondary Suites or Basement Apartments: These are living spaces located within the primary residential structure, often in the basement or as a separate wing. They usually have their own entrance, kitchen, bathroom, and sleeping areas.

  2. In-law Suites: Similar to secondary suites, in-law suites are designed to provide a separate living space for extended family members while allowing them to remain close to the main household.

  3. Detached ADUs: These are separate structures on the same property as the main house, such as converted garages, guest houses, or stand-alone units. They are fully self-contained and have all the necessary facilities for independent living.

Thinking of adding a separate living space to your house? You’ve got options! Second units can be built anywhere, on a single floor or spread across multiple levels. Basements and attics are popular choices, but building code requirements can vary depending on the location.

What Are The Benefits of A.D.U.'s ?

Secondary units, familial suites, basement lodgings, and interior domicile quarters within a residence, or situated in an auxiliary edifice like a garage. These supplementary living spaces are essentially autonomous, featuring a private kitchen, bathroom, and sleeping area.

Renting out the ADU can provide a steady source of passive income, helping with mortgage payments and other expenses.

ADUs offer separate living quarters for family members, fostering both privacy and close proximity.

ADUs create more affordable housing options, as they are often more cost-effective than standalone homes.


ADUs address housing shortages by using existing infrastructure, supporting sustainable growth in established communities.

ADUs can serve as rental units, guesthouses, home offices, studios, or short-term rentals, adding versatility to the property.

Renting out an ADU to local workers can potentially reduce commuting distances and associated traffic congestion.

When you choose The Innovative Group as your general contractor, you're choosing a partner dedicated to delivering quality, innovation, and value. We're fueled by a passion for pushing boundaries and turning your ideas into reality.

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