Ontario Building Code Bedroom & Basement ADU Guide 2026

11 min read

If you are finishing a basement bedroom, adding a garden suite, or converting space into a secondary unit in Brantford or anywhere in Ontario, the building code has a lot of opinions about your room. Ceiling heights, floor areas, window sizes, fire-rated walls, doorway widths. Every one of these rules shapes the physical space you sleep in. And every one of them affects which mattress actually fits.

We are a mattress store, not a building inspector's office. But customers walk into our showroom on West Street every week with the same story: they are renovating a basement, the contractor keeps talking about code, and nobody has explained how all those numbers translate to the bed they are trying to buy. A ceiling that barely meets the 1.95 m minimum means a platform bed, not a box spring. A narrow doorway means a bed-in-a-box, not a traditional innerspring. A fire separation wall changes where the bedroom can go in the first place.

This guide walks through the Ontario Building Code requirements that affect bedrooms, basements, and accessory dwelling units in 2026, and connects each one to a practical mattress decision. We pulled the code numbers straight from the OBC so you can bring them to your contractor or building department. Then we added the mattress part, because that is what we know.

Basement Ceiling Height: The 1.95 m Rule

The Ontario Building Code requires a minimum ceiling height of 1.95 metres (6 feet 5 inches) throughout a basement apartment. That includes hallways, the path to the exit, and every living space in the unit. Under beams, ducts, and stairs, the clearance can drop to 1.85 metres (6 feet 1 inch), but that is the absolute floor.

These are finished measurements. That means you subtract the thickness of your ceiling material (half-inch drywall at minimum) and your finished floor (typically 1 to 2 inches for subfloor, underlayment, and flooring). If your unfinished basement measures 6 feet 7 inches from concrete floor to bottom of joist, you might be right at the limit once everything is installed. Measure twice, and measure after you account for finishes.

What If You Are Short on Height?

If your basement does not meet 1.95 m after accounting for finishes, you have two options. One is underpinning: excavating below the existing foundation to lower the floor. The other is a bench footing, which creates a ledge around the perimeter and costs 20 to 40 percent less than full underpinning but reduces usable floor space. We cover costs for both later in this guide.

Homeowners have been known to frame, insulate, drywall, and furnish a basement, then discover at final inspection they are an inch and a half short on ceiling height. The fix at that point is tearing everything out. Measure before you start, not after.

Minimum Bedroom Floor Area and the Closet Exclusion

Under the Ontario Building Code (Article 9.5.1.3 in the 2012 code, renumbered to 9.5.1.1A in the 2024 code), the minimum floor areas for bedrooms do not include closets or built-in bedroom cabinets. This is a rule that catches a lot of people off guard.

Here is what the code actually requires:

• Regular bedrooms: 7 m2 (75 sq ft) minimum without built-in cabinets, or 6 m2 (65 sq ft) if built-in cabinets are provided
• Master bedrooms: 9.8 m2 (105 sq ft) minimum without built-in cabinets, or 8.8 m2 (95 sq ft) with built-in cabinets

The closet exclusion means the closet area does not count toward those minimums. If your basement bedroom measures 8 m2 total but 1.5 m2 of that is a built-in closet, your actual qualifying floor area is 6.5 m2, not 8 m2. That still meets the 6 m2 minimum for a bedroom with built-in cabinets. But if the closet were any bigger, you could fall below the threshold.

Egress Window Requirements for Bedrooms

Every floor level with a bedroom must have at least one window that can serve as an emergency escape. Under the Ontario Building Code (Section 9.9.10), that window must provide an unobstructed clear opening of at least 0.35 m2 (3.77 sq ft) with no dimension less than 380 mm (15 inches). It must open from the inside without tools. And for above-grade bedrooms, the sill cannot be higher than 1,000 mm (39 inches) above the floor.

The key word is "unobstructed." Only the actual opening counts, not the frame, not the sash, not the grilles. A window that looks big when closed might not provide 0.35 m2 of clear opening when you actually slide or crank it open.

Window Type Matters

Casement windows (side-hinged, crank open) give you the most unobstructed opening for their size. Sliding windows only open halfway, so they need to be roughly double the size of a casement to meet the same clear opening. Awning windows (top-hinged) are generally not accepted for egress by most building officials, regardless of size, because the opening geometry makes escape extremely difficult.

Window Well Requirements

If the egress window opens into a window well (which it will in a basement), there must be at least 550 mm (22 inches) of clearance in front of the window. If the sash swings toward the well, it cannot reduce the clearance in a way that blocks escape. These requirements add to the total cost of a basement bedroom: expect to pay $3,000 to $8,000 per egress window installed, including excavation, the window well, and drainage.

Fire Separation and Type X Drywall

If you are creating a secondary suite in your basement, the walls and ceiling between the units need to resist fire for at least 30 minutes. Under the Ontario Building Code, a 30-minute fire separation can be achieved with a single layer of 15.9 mm (5/8-inch) Type X drywall. This is the membrane-only solution outlined in Supplementary Standard SB-3: one layer equals a 30-minute rating (designated M1), two layers equal a 60-minute rating (M2).

For most residential secondary suites, the full fire-resistance rating required is 45 minutes. That typically means one layer of 5/8-inch Type X drywall on each side of the wall assembly, with all penetrations fire-stopped (electrical boxes, pipes, ducts) and mineral wool insulation in the cavity.

Why Type X Drywall and Not Standard?

Type X drywall contains glass fibres mixed into the gypsum core. Those fibres hold the panel together longer during a fire, roughly quadrupling the protection time compared to standard half-inch drywall. Standard drywall provides about 15 minutes of fire resistance. A single layer of 5/8-inch Type X provides approximately 60 minutes per layer. The cost difference at the hardware store is modest, maybe $0.35 to $0.55 per square foot for materials, but the labour, fire-stopping, and inspection process add up to $3,000 to $8,000 for a typical separation wall in a Brantford secondary suite conversion.

The Smoke-Tight Barrier Exception (Article 9.10.9.16)

Here is a provision that can save you thousands if your home qualifies. Article 9.10.9.16 of the Ontario Building Code waives the full fire separation requirement between suites in a house with a secondary unit, provided you install a continuous smoke-tight barrier of not less than 15.9 mm Type X gypsum board on the underside of floors and on both sides of walls between units.

This is not the same as a full 45-minute fire-rated assembly. A smoke-tight barrier requires the 15.9 mm Type X drywall, but the joints and penetrations need to be sealed for smoke-tightness rather than meeting the full fire test standard. It is a meaningful cost reduction for homeowners in existing houses (more than 5 years old) adding a secondary suite, especially when combined with interconnected smoke alarms throughout both units.

Who Qualifies?

The 2024 OBC update expanded this exception. If your home is more than 5 years old and you are adding a secondary suite, you may qualify for the smoke-tight barrier approach instead of a full fire-rated separation. You still need the 15.9 mm Type X drywall. You still need all joints sealed to CSA A82.31-M standards. You still need interconnected smoke alarms (wireless interconnection is now permitted). But the overall cost and complexity are lower than a full fire-rated assembly.

Talk to your local building department about whether your project qualifies. The savings can be significant enough to redirect some of your renovation budget toward a better mattress for the suite, which is a choice we have seen more than a few Brantford landlords make.

Mezzanine Bedrooms and the 2100 mm Clearance

Mezzanine bedrooms, sometimes called sleeping lofts, are popular in tiny homes, laneway houses, and certain garden suite designs. The Ontario Building Code (Section 9.5.3.2) requires a minimum ceiling height of 2,100 mm (approximately 6 feet 11 inches) both above and below the mezzanine floor assembly.

That means the room hosting a mezzanine bedroom needs a total floor-to-ceiling height of at least 4,200 mm (about 13 feet 9 inches) plus the thickness of the mezzanine floor assembly itself (typically 8 to 12 inches of structure). In practical terms, you need a room with at least 14 to 15 feet of ceiling height to make a mezzanine bedroom work legally.

Doorway Width and Accessibility

Standard interior doorways in Ontario homes are 30 to 32 inches wide (762 to 813 mm clear opening). That is fine for most people walking through, but it presents two challenges: mattress delivery and wheelchair accessibility.

Mattress Delivery Through Narrow Doorways

A queen mattress is 60 inches wide. Even turned on its side, it is about 10 to 14 inches deep depending on the model. Getting a traditional innerspring queen through a 30-inch doorway usually works, but it is tight, and thick pillow-top models sometimes will not bend enough.

A king mattress (76 inches wide) on its side is the same 10 to 14 inches deep but heavier and harder to manoeuvre. If your basement has a 30-inch doorway at the top of the stairs and a 90-degree turn at the bottom, a bed-in-a-box (compressed and rolled) is often the only practical option for a queen or king.

Wheelchair Accessible Master Suites

The Ontario Building Code's barrier-free path of travel requires a minimum unobstructed width of 1,100 mm (about 43 inches). A standard 32-inch doorway does not meet barrier-free requirements. If you are building or renovating a master suite for wheelchair accessibility, the doorway needs to be significantly wider than standard. Many builders in Brantford now offer 36-inch (914 mm) doorways as a standard upgrade, and fully accessible suites use 42-inch or wider openings.

Radon Protection for New Construction

As of January 1, 2025, the 2024 Ontario Building Code mandates a radon rough-in for all new residential construction in Ontario, including in Brantford. This is not optional. Every new house, including additions to existing houses, must include a sub-floor depressurization rough-in that allows a radon mitigation system to be connected later if testing shows elevated levels.

Previously, radon mitigation was only required in designated high-risk areas. The new rule applies province-wide because radon levels can be elevated anywhere, and the cost of installing the rough-in during construction is minimal compared to retrofitting later.

What the Rough-In Looks Like

A radon rough-in typically includes a sub-slab gas collection layer (usually a bed of gravel), sealed slab penetrations, and a vent pipe pathway from below the slab to the roof. During construction, this costs a few hundred dollars. After the house is finished, retrofitting the same system can cost $2,000 to $5,000 or more, because you are cutting through finished floors and walls.

The relevant OBC sections are 9.13.4, 9.25.3, and Supplementary Standard SB-9. After occupancy, homeowners should test for radon and install an active mitigation system (fan-driven) if levels exceed Health Canada's guideline of 200 Bq/m3. A properly installed Level 3 active system reduces radon levels by approximately 90 percent.

Basement Temperature Design: The 18C Change

The 2024 Ontario Building Code lowered the basement temperature design from 22 degrees Celsius to 18 degrees Celsius. This affects insulation requirements and heating system sizing for basement apartments. At the same time, the code now requires full-height insulation for basement walls, replacing the older allowance for partial-height insulation.

What does this mean for sleeping? An 18 C (64 F) room is cooler than most people prefer for sleeping, though sleep researchers generally recommend bedroom temperatures between 15 and 19 degrees Celsius for optimal rest. The change means your heating system needs to be designed to maintain at least 18 C in the basement, and full-height wall insulation helps achieve that efficiently. If you prefer a warmer bedroom, the system can still heat above 18 C, but the design standard sets the baseline.

For mattress selection, a cooler room means your mattress does not need to work as hard on temperature regulation. Memory foam, which tends to sleep warmer, is actually a reasonable choice in a cooler basement. Conversely, if you prefer a warm bedroom and crank the thermostat past 22 C, a gel-infused foam or innerspring hybrid will help dissipate heat and keep you comfortable.

What Underpinning Costs in Ontario

If your basement does not meet the 1.95 m ceiling height requirement after accounting for finished floor and ceiling, underpinning is the most common solution. Here is what to expect in terms of cost:

The return on investment can be strong. At $2,400 per month in rent (realistic for a legal one-bedroom in Brantford in 2026), that is $28,800 per year. Many homeowners recover their full investment in 3 to 5 years while building long-term equity in the property. Just make sure the bedroom is set up properly, starting with a quality mattress that fits the space you have built.

Where Building Code Meets Your Mattress Decision

We are not trying to make you memorize OBC section numbers. But when you walk into our showroom and say "I am finishing a basement bedroom," these are the questions we are going to ask:

• How tall is your ceiling after finishes? (This tells us whether you need a low-profile base or can use a box spring.)
• How wide are the doorways and staircases? (This tells us whether a traditional mattress will fit or whether you need a bed-in-a-box.)
• What are the room dimensions excluding the closet? (This tells us whether a queen fits or whether you should go with a double or twin XL.)
• Is it a secondary suite with a tenant? (This tells us whether durability matters more than luxury, and we will recommend accordingly.)

Every code requirement we covered in this guide translates to a practical mattress decision. Low ceilings mean platform beds. Narrow doorways mean compressed mattresses. Small rooms mean smaller sizes. Good bedroom design starts with the room's constraints and works inward to the sleep surface.

If you are partway through a renovation and not sure what mattress will work in the finished room, come talk to us before the drywall goes up. We can help you plan the mattress and bed frame around the room you are actually building, not the room you wish you had.

Related Reading

• 2026 Ontario Fire Code Bedroom Safety Guide
• 2026 Bedroom Design Trends That Actually Help You Sleep
• Mattress Materials and Engineering Durability Guide
• Hospital Discharge Home Bed Setup Guide for Ontario
• Paris Ontario New Home Mattress Delivery Guide 2026