Secondary Suite vs Rooming House: Understanding the Difference

The Simple Definitions

Secondary Dwelling Unit (SDU): A self-contained living space within your home - typically a basement apartment. It's "secondary" to your "primary" dwelling (the main house).

Accessory Dwelling Unit (ADU): A broader term that includes SDUs PLUS detached units like garden suites or laneway houses. SDU is a type of ADU.

Additional Dwelling Unit: The official City of Ottawa term for any secondary housing on a residential lot. This is what shows up on permits.

Rental Unit / Basement Apartment: Everyday terms for an SDU that you rent out. Same thing, less technical.

Botton line: If you're finishing your basement as a separate apartment, you're building an SDU. That's the term that matters for permits.

Basement SDU vs Garden Suite ADU

Both create rental income, but they're very different projects:

Basement SDU (Internal) - Uses existing space in your home - Lower cost: $70,000 - $120,000 - Faster: 8-12 weeks - Limited by basement conditions (ceiling height, moisture) - Tenant is in your home (less privacy) - Better ROI due to lower cost

Garden Suite ADU (Detached) - New building in your backyard - Higher cost: $150,000 - $300,000+ - Slower: 4-8 months - No ceiling height issues - Complete privacy for both parties - Uses backyard space - Lower ROI but higher rent potential

For most Ottawa homeowners, the basement SDU makes more financial sense. You're using space you already have.

Requirements Are Similar But Not Identical

Both need: - Building permit - Separate entrance - Full kitchen and bathroom - Smoke and CO alarms

Basement SDU specifically needs: - 1.95m (6'5") minimum ceiling height - 45-minute fire separation from main unit - Egress windows for bedrooms - Ground-level entrance (can't require tenant to go through main unit)

Garden Suite specifically needs: - Maximum 1,200 sq ft (Ottawa limit) - Proper setbacks from property lines - Often needs separate utility connections - May need site plan approval

The basement SDU requirements focus on safety within a shared structure. Garden suite requirements are more about zoning and property impact.

The Financial Comparison

Let's compare real numbers for Ottawa:

Basement SDU Construction cost: $90,000 average Monthly rent: $1,800 - $2,200 Annual income: $21,600 - $26,400 Payback: 3.5 - 4 years ROI after payback: 24-29% annually

Garden Suite Construction cost: $220,000 average Monthly rent: $2,200 - $2,800 Annual income: $26,400 - $33,600 Payback: 6.5 - 8 years ROI after payback: 12-15% annually

The basement SDU wins on ROI because the cost difference is larger than the rent difference. But garden suites make sense if your basement isn't suitable (low ceilings, moisture issues) or you want maximum privacy.

Which One Is Right for You?

Choose basement SDU if: - Your basement has 6'5"+ ceilings - You want the best return on investment - You need rental income sooner (faster build) - Budget is a primary concern - You're okay with tenant in your home

Choose garden suite if: - Your basement isn't suitable (low ceilings, wet) - Privacy is very important to you - You have a good-sized backyard - Budget is less of a concern - You may want to house family (in-law suite)

Consider both if: - You want to maximize rental income - Your property can support 3 units - You're building long-term wealth