BCIN House 2024 Exam - Min. Glazing Requirements (OBC Part 9)

Minimum Window Areas for Residential Occupancy – Bathrooms, Bedrooms & More

Understanding Part 9 glazing requirements is essential for anyone preparing for the BCIN House Exam or working on residential permit drawings in Ontario.

One of the most commonly tested sections is OBC 9.7.2.3 – Minimum Window Areas, especially when questions involve bathrooms, basements, and second suites.

This blog breaks it down in plain language, ties it to real exam questions, and shows how it applies on actual projects.

Why OBC 9.7.2.3 Matters

The Ontario Building Code requires minimum natural light in residential rooms to support:

• Health & safety

• Habitability

• Code-compliant design

Understanding OBC 9.7.2.3: Ensuring Health, Safety, and Comfort with Adequate Natural Light in Residential Design.

However, artificial lighting changes the rules, and this is where many BCIN candidates get tripped up.

Key Code Reference

OBC 9.7.2.3 – Minimum Window Areas

Understanding Table 9.7.2.3

Table 9.7.2.3 provides two compliance paths:

Option 1 – No Electrical Lighting

A Larger window area is required to ensure adequate natural light.

Option 2 – With Electrical Lighting

Window requirements are reduced or eliminated because artificial light is provided.

Table 9.7.2.3: Comparing Compliance Paths for Lighting Requirements – Option 1 relies on natural light with specific window/area ratios, while Option 2 incorporates electrical lighting with specific fixture/wattage ratios.

👉 Most modern homes fall under “with electrical lighting.”

Bathroom Window Example (BCIN Exam Style)

Question

A bathroom window is located 900 mm above the finished floor and has an area of 1.2 m². What are the glazing requirements according to OBC 9.7.2.3?

Answer Choices

A) 5% of floor area

B) 0.37 m²

C) 5% of floor area

D) Not required due to artificial lighting

✅ Correct Answer

D) Not required due to artificial lighting

Why Answer D Is Correct

According to Table 9.7.2.3, for a water closet room (bathroom):

Condition	Requirement
No electrical lighting	0.37 m² minimum glazing
With electrical lighting	Windows not required

Since modern bathrooms are assumed to have electrical lighting, the Code does not require any minimum window area.

👉 The 900 mm sill height and 1.2 m² window size are irrelevant once electrical lighting is provided.

Extract from Table 9.7.2.3 (Simplified)

Room Type	No Electrical Lighting	With Electrical Lighting
Laundry / unfinished basement	4% of area	Windows not required
Water closet room (bathroom)	0.37 m²	Windows not required
Kitchen	10% of area	Windows not required
Living / dining rooms	10%	10%
Bedrooms	5%	5%

Why the Code Allows This

The intent of 9.7.2.3 is adequate illumination, not daylight at all costs.

• Artificial lighting provides consistent illumination

• Bathrooms are short-duration occupancy spaces

• Mechanical ventilation handles moisture (not windows)

Second Suite & Basement Bathroom Example

This is where many designers struggle 👇

Scenario

You’re designing a basement second suite with:

• A bathroom below grade

• Limited exterior wall exposure

• No practical window location

Modern bathroom featuring a glass-enclosed shower, sleek white vanity with a large mirror, and a minimalist design highlighted by warm, neutral tones.

Solution

✔ Provide electrical lighting

✔ Meet ventilation requirements under Part 9

✔ No glazing required under 9.7.2.3

This is perfectly code-compliant and commonly approved by municipalities.

Common BCIN Exam Mistakes

❌ Automatically choosing 0.37 m² for bathrooms

❌ Ignoring the “with electrical lighting” column

❌ Confusing habitable rooms with service rooms

❌ Overthinking window sill height (not relevant here)

💡 Exam Tip: If the question mentions electrical lighting, always check Column 3 first.

Important Notes from Table 9.7.2.3

• Doors & skylights count as windows

• Combined rooms follow the most restrictive requirement

• Bedrooms also trigger egress rules under 9.9.10

• Live/work units may fall under Part 3 requirements

Why This Knowledge Is Essential

For BCIN House candidates, this topic:

• Appears frequently on exams

• Affects permit approval

• Impacts the basement and second suite design

• Prevents unnecessary design changes and client costs

Part 11 Allowance for Existing Houses (C110) – 50% Glazing Reduction Explained

When working on older houses, designers often have more flexibility than they realize. The Ontario Building Code recognizes this through Part 11 – Renovations, specifically Compliance Alternative C110.

This provision is especially helpful for basement renovations and second suites, where meeting full Part 9 glazing requirements can be difficult due to tight property lines or spatial constraints that limit the amount of glazing that can be provided.

When Can Part 11 Be Used?

✔ The house is more than 5 years old

✔ The work is a renovation or change of use

✔ You are not creating new structural conditions requiring full Part 9 compliance

In these cases, a designer may apply Part 11 instead of the strict Part 9 rules.

A basement window well with a clear cover protects the window from debris while allowing natural light to illuminate the basement. Surrounded by a neatly maintained garden, the setup enhances both functionality and aesthetics.

Key Reference

Part 11 – Compliance Alternative C110 (Page 46)

Where windows are not used as a means of egress and where they do not conflict with ventilation requirements, the minimum glass area shown in Table 9.7.2.3 may be reduced by 50%.

What This Means in Simple Terms

If:

• A window is NOT required for egress, and

• Ventilation requirements are satisfied by mechanical ventilation,

👉 Then the minimum glazing area from Table 9.7.2.3 can be reduced by 50%.

This is a code-approved relaxation, not a workaround.

Simple Second Suite Example

Existing Condition

• House built in 2008 (older than 5 years)

• Basement converted into a second suite

• Bedroom floor area = 12 m²

Part 9 Requirement

• Bedroom glazing = 5% of floor area

• 12 m² × 5% = 0.60 m²

Using Part 11 (C110)

• Window not used for egress

• The bedroom has hard-wired electrical lighting

• Mechanical ventilation provided

✔ Allowed reduction = 50%

👉 Revised minimum glazing:0.60 m² × 50% = 0.30 m²

✅ Compliant under Part 11

Why This Is Critical for Basement Suites

Basement second suites often face:

• Shallow window wells

• Existing foundation limitations

• Property line setbacks

Part 11 C110 acknowledges reality and allows designers to work with existing conditions safely.

Important Limitations

❗ This reduction cannot be used if:

• The window is required for egress

• Ventilation requirements are not met

• Life safety is compromised

Always verify:

• Egress under 9.9.10

• Ventilation under Part 9

“May” vs “Shall” – BCIN Exam Gold

Understanding these two words is essential for the BCIN House exam.

Shall

• Mandatory

• No discretion

• Must be followed

Understanding the distinction between "may" and "shall": "May" indicates permission, offering optional actions without requirement, while "shall" signifies obligation, necessitating mandatory compliance.

Example:

Minimum window glass area shall conform to Table 9.7.2.3.

May

• Permitted

• Optional

• Designer discretion

Example from C110:

The minimum glass area may be reduced by 50%.

👉 This means:

• The designer is allowed to apply the reduction

• It is not mandatory

• The Authority Having Jurisdiction (AHJ) may still review applicability

Common Designer Mistakes

❌ Applying the 50% reduction to egress windows

❌ Using Part 11 for new construction

❌ Forgetting mechanical ventilation

❌ Assuming “may” means “must be accepted”.

BCIN Exam Tip

If a question says:

• Existing house

• Renovation

• Part 11 applies

👉 Always look for relaxations like C110.

Final Takeaway

OBC 9.7.2.3 – Minimum Window Areas is one of the most important glazing provisions under Part 9, and a frequent focus on the BCIN House Exam. The key to mastering this section is understanding that the Code is concerned with adequate illumination, not simply the presence of windows.

Designers who understand:

• when windows are required,

• when they are not required, and

• when reductions are permitted,

can design smarter, avoid unnecessary construction, and navigate both permit reviews and BCIN exam questions with confidence.

FAQ

Are windows required in bathrooms under the Ontario Building Code?

No. Under OBC 9.7.2.3, bathroom (water closet room) windows are not required when electrical lighting is provided. A minimum glazing area of 0.37 m² only applies when no electrical lighting is installed.

Does window height or sill elevation affect glazing requirements?

No. Sill height does not impact minimum glazing area under 9.7.2.3. Only the presence of electrical lighting and the room type determine the requirement.

Can a basement bathroom in a second suite have no window?

Yes. A basement bathroom may have no window provided:

• Electrical lighting is installed, and

• Ventilation requirements under Part 9 are met

This is fully code-compliant and commonly approved by municipalities.

When does the 0.37 m² bathroom window requirement apply?

The 0.37 m² minimum glazing applies only when a bathroom has no electrical lighting. This typically affects:

• Seasonal dwellings

• Off-grid buildings

• Older structures without permanent lighting

Do bedrooms always require windows?

Yes. Bedrooms must comply with:

• Minimum glazing area under 9.7.2.3, and

• Egress requirements under 9.9.10

Even when Part 11 applies, egress requirements cannot be reduced.

Can Part 11 reduce glazing requirements in older houses?

Yes. For houses older than 5 years, Part 11 – Compliance Alternative C110 allows the minimum glazing area from Table 9.7.2.3 to be reduced by 50%, provided:

• The window is not used for egress, and

• Ventilation requirements are met

Can doors or skylights count toward required glazing area?

Yes. Under the notes to Table 9.7.2.3, the unobstructed glass area of a door or skylight is considered equivalent to a window.

What is the most common BCIN House exam mistake related to glazing?

The most common mistakes include:

• Automatically selecting 0.37 m² for bathrooms

• Ignoring the “with electrical lighting” column

• Applying Part 11 reductions to new construction

• Assuming “may” means “must be accepted.”

How should I approach glazing questions on the BCIN House exam?

Follow this order:

1. Identify the room type

2. Check if electrical lighting is provided

3. Confirm if Part 9 or Part 11 applies

4. Verify egress and ventilation requirements (only if using part 11)

If you found this question helpful, we have hundreds of practice questions on our portal, including real exam-style scenarios, image-based questions, and challenging problems designed to help you pass the BCIN House 2024 Exam on your first attempt.

*Please note that the information shared in our blog is for educational purposes only, and we do not assume any liability for the actions or decisions made based on this information.