- Rule #1: fix moisture before insulating. A damp basement should not be insulated from the inside.
- Permit: not needed for a simple finish, required if you add plumbing, change the structure, dig down or create a unit.
- Toronto budget: about $35 to $75 per sq ft for a standard finish, $90 to $140+ for a secondary suite.
In a city where every square foot is expensive, the basement is often the most affordable way to gain space: family room, office, guest room, gym or rental unit. But it is also the room most exposed to water and cold. Well prepared, a basement becomes as comfortable as the rest of the house.
Step 1: fix moisture
First, make sure the basement is dry. Natural Resources Canada is clear: a damp basement should not be insulated from the inside until the problem is fixed.
- Check the outside: downspouts discharging away from the foundation, ground sloping water away from the house.
- Look for signs: white marks (efflorescence) on concrete, musty smell, stains at the bottom of walls.
- Protect against sewer backup: backwater valve and sump pump. In Toronto, the City covers up to 80% of this work (see our rebates article).
- Waterproofing if needed: about $3,000 to $10,000 from the inside, $10,000 to $35,000 from the outside.
Step 2: insulate properly
The basement can account for about 25% of a home's heat loss. Good practices recommended by Natural Resources Canada:
- Air-seal first, especially at the sill plate and rim joist.
- Use rigid foam insulation, medium to high density and moisture-resistant, directly against the concrete.
- Aim for at least R-12 with foam alone, or R-10 of foam combined with an insulated framed wall.
- Do not add polyethylene over foam insulation; set the wall's bottom plate on a sill gasket.
For the floor, waterproof luxury vinyl plank is the safest choice in a basement: it handles moisture and stays pleasant underfoot.
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Step 3: know whether you need a permit
| No permit | Permit required |
|---|---|
| Finishing with no structural change: framing, insulation, drywall, flooring, paint | Adding or moving plumbing (bathroom, wet bar) |
| Waterproofing repairs | Structural changes, new openings |
| Installing a sump pump | Excavation, lowering the floor (underpinning) |
| New exterior entrance, backwater valve | |
| Creating a secondary suite |
In every case, electrical work must be reported to the Electrical Safety Authority (ESA) before work starts, and must not be covered before inspection. In Toronto, some small residential projects can use the express permit service.
Secondary suites
A basement rental unit can help pay your mortgage, but the requirements are stricter. The Ontario Building Code includes, among other things:
- a minimum ceiling height (around 1.95 m, and lower under beams and ducts);
- an egress window in each bedroom;
- interconnected smoke and carbon monoxide alarms;
- a fire separation between the two units.
The exact requirements depend on your house: they are confirmed during the permit application with Toronto Building.
What budget should you plan?
| Project | What is included | Typical budget |
|---|---|---|
| Basic finish | Framing, insulation, drywall, basic electrical, flooring, paint | $35 – $55 / sq ft |
| Full finish | Adds a three-piece bathroom, defined rooms, better finishes | $55 – $75 / sq ft |
| High-end or secondary suite | Kitchen, separate entrance, Code requirements for a unit | $90 – $140+ / sq ft |
A basement bathroom alone costs about $15,000 to $25,000. Lowering the floor (underpinning) is a separate project, often $30,000 to $60,000 or more.
A real example: our Etobicoke basement, with a soundproofed home theatre, wet bar and three-piece bathroom, was completed in 9 weeks.
Frequently asked questions
How long does a basement finish take?
Usually 6 to 10 weeks for a full finish with a bathroom, not counting the time to get a permit if one is needed.
Can a basement with a low ceiling be finished?
Yes for a family room or office, by optimizing duct routing. For a secondary suite, the Code's minimum height applies, which may require lowering the floor.
Which flooring is best for a basement?
Waterproof luxury vinyl is the safest. Solid hardwood is not recommended; engineered wood is possible if the basement is perfectly dry.