Should I add a garage conversion bonus room above my garage in Ottawa?

Building a bonus room over an existing garage is a space-efficient way to add living area. It uses a footprint you already have and doesn't eat into your yard. It can work as a home office, guest room, playroom or, with the right design, a separate unit.

The first question is whether the garage can support a room above it. Many attached garages have roof trusses designed only for the roof, not for living space. Turning that space into a habitable room usually means a structural engineer redesigns the framing, often replacing trusses with a floor system and new roof framing. If the garage has a flat or low-slope roof, building on top can be more straightforward, but the walls and foundation still need to be checked.

The foundation is the critical part. Garage footings are sometimes smaller than house footings, so an engineer needs to confirm whether they can carry a second storey or need to be widened or supplemented. Under the Ontario Building Code, footings in clay or soils that aren't clearly defined must be at least 1.2 m deep and not less than the depth of frost penetration, and on sensitive clay, including Leda clay, footing sizes must be engineered.

Living space over a garage needs proper separation from the garage to keep out fumes and slow a fire, and a bedroom needs an egress-sized window. Your designer will specify the floor-ceiling assembly, the window and other Code requirements. If the room will be a separate rental unit, the City always requires a permit for a secondary unit, and the drawings must show the fire-separation wall and floor-ceiling construction.

If you're creating a self-contained unit so a senior or an adult eligible for the disability tax credit can live with a relative, look at the federal Multigenerational Home Renovation Tax Credit. It applies to a self-contained unit with a private entrance, kitchen, bathroom and sleeping area, covers up to $50,000 of qualifying expenses at 14.5 per cent, for a maximum credit of $7,250. A room without a kitchen doesn't qualify.

As perspective only, not a quote, a complete over-garage room can range from roughly $80,000 to $160,000 or more depending on structure, mechanical work, a bathroom and finishes. Heating is worth special thought because the room sits over an unheated garage; ask your HVAC contractor for a heat-loss calculation and compare extending the existing system with a separate heat pump.

A building permit is required. Electrical work needs an ESA notification, and gas work is done by a TSSA-certified gas technician. You can browse addition contractors in the Ottawa Construction Network directory at justynrookcontracting.com and compare quotes.

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Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:

• Homeupgraders
• RenoMotion Inc.
• Home Front Services
• The Next Reno
• Renovo Construction