Ontario Building Code for Detached Garages and Sheds: Auto Repair Shop Requirements Explained

Why the Ontario Building Code Matters for Shop Owners

Many independent auto repair shop owners start small. A detached garage or backyard shed feels like a natural first location. It is affordable. You already own the space. But the moment you use that structure for business, the rules change. The Ontario Building Code (OBC) draws a firm line between residential and commercial use. Crossing that line without the right permits can result in stop-work orders, fines, or forced closure. Understanding the OBC before you build or convert is not optional. It is the foundation of a legally operating shop.

Residential vs. Commercial: Two Very Different Standards

The OBC does not treat all buildings the same. A garage detached from a home is classified as a residential accessory structure. It is built to house vehicles and store personal items. A commercial repair garage is a workplace. It must meet higher standards for fire safety, structural load, ventilation, and occupant protection. When you start using a residential accessory building for auto repair, diagnostics, or parts sales, that building no longer qualifies as a residential structure under the code. It becomes a commercial building in function, and the law requires it to meet commercial standards in form.

Understanding Occupancy Classifications Under the OBC

The Ontario Building Code assigns every building an occupancy classification based on how it is used. This classification drives every other code requirement. For auto repair shops, the relevant classifications are Group F, Division 2 (F2) for general repair garages and Group F, Division 1 (F1) for operations involving spray painting or flammable materials. If your shop does oil changes, tire swaps, and diagnostics, you are likely F2. If you do spray finishing or bodywork with flammable coatings, you move into the more restrictive F1 category. Misidentifying your occupancy class is one of the most common and costly mistakes new shop owners make. A qualified designer or building official can help you confirm the right classification.

Ontario Building Code Occupancy Groups Relevant to Auto Repair

• Group F, Division 1 (F1): High-hazard industrial use, including spray painting with flammable finishes and operations involving explosive or highly combustible materials
• Group F, Division 2 (F2): Medium-hazard industrial use, including auto repair, service garages, and diagnostic work
• Group F, Division 3 (F3): Low-hazard industrial use such as storage or light fabrication with minimal fire risk
• Residential Accessory under Part 9 of the OBC: Detached garages and sheds serving a single dwelling; not permitted for commercial business activity without formal reclassification

When Do You Need a Building Permit in Ontario?

In Ontario, a building permit is required for any new construction or change of use that affects a building's classification. For sheds and detached garages, the threshold for a permit on new residential construction is 15 square metres, which is approximately 161 square feet. Any accessory structure over 15 square metres requires a building permit. Detached garages always require a building permit regardless of size. But size thresholds apply only to residential construction. If you intend to use any structure for commercial purposes, a permit is required regardless of size. You will also need a Change of Use permit if you are converting an existing residential accessory building into a commercial workspace. This applies even if you make no physical changes to the structure.

What Is a Change of Use Permit and Do You Need One?

A Change of Use permit is issued when an existing building is proposed for a different occupancy classification. You do not need to renovate to trigger this requirement. Simply changing how you use the building is enough. If you convert a garage previously used for personal vehicle storage into a space where you repair customer vehicles, you are changing the occupancy from residential accessory to Group F. Your local building department must be notified. They will assess whether the existing structure meets the requirements for the new use. In most cases, upgrades to fire separation, ventilation, electrical systems, and exits will be required before the permit is granted.

Common Building Code Upgrades Required When Converting to a Commercial Repair Shop

• Fire separation between the shop and any adjacent residential structure
• Mechanical ventilation to remove vehicle exhaust and combustible fumes
• Proper floor drainage for oil, water, and chemical runoff
• Upgraded electrical service and grounding to handle shop equipment loads
• Accessible exit doors with compliant hardware and required clearance
• Signage for fire exits and hazard areas
• Appropriate fire extinguisher type and placement per the Ontario Fire Code
• Spill containment for oil and fluid storage areas
• Carbon monoxide detection where vehicles operate indoors

Zoning By-Laws Work Alongside the Building Code

The Ontario Building Code sets construction and safety standards. Zoning by-laws determine what uses are permitted on a given property. These are two separate but linked systems. Even if your building meets OBC requirements for an F2 repair garage, your local zoning by-law may prohibit commercial auto repair in a residential zone. Many Ontario municipalities do not allow auto repair shops in residential areas at all. Some permit limited home-based businesses but explicitly exclude automotive repair, vehicle storage, and heavy equipment use. You must check with your local planning department before investing in upgrades. Building code compliance does not override zoning restrictions.

How to Read the Ontario Building Code: A Practical Starting Point

The Ontario Building Code is organized into Divisions and Parts. Division A covers application and objectives. Division B contains technical requirements, which is where most shop owners need to focus. Part 9 covers housing and small residential buildings, including residential accessory structures. For commercial repair garages, you will primarily work within Part 3, which governs occupancy, fire safety, and structural requirements for buildings beyond residential scope. The OBC is available free through Ontario.ca. Reading it directly is challenging. Most shop owners work with a BCIN-registered designer who interprets and applies the code on their behalf. This professional prepares permit drawings showing how your building meets each applicable requirement.

Key Steps to Legally Open an Auto Repair Shop in a Detached Structure in Ontario

• Confirm your intended use and occupancy classification with a BCIN-registered designer or your local building official
• Contact your local planning department to verify the property zoning permits auto repair use
• Apply for a Change of Use permit if converting an existing residential accessory structure
• Apply for a Building Permit if constructing a new structure or making structural changes
• Complete required upgrades including fire separation, ventilation, drainage, and electrical systems
• Schedule all required inspections through your local building department
• Obtain your occupancy certificate before opening to customers
• Register your business and apply for any additional trade licences required by your municipality

Fire Safety Requirements for Auto Repair Occupancies

Fire safety is one of the most demanding areas of the OBC for repair garages. Motor vehicles carry flammable fuel, oil, and other combustible materials. The code requires fire separations between an F2 occupancy and any adjacent dwelling or different occupancy type. Sprinkler systems may be required depending on building size and location. Ventilation systems must be capable of diluting and removing combustible vapours. Fire extinguisher types and placement are governed by the Ontario Fire Code, which operates alongside the Building Code. Both apply to your shop. Non-compliance with fire code requirements is one of the leading causes of forced closures among new independent garages.

Electrical and Mechanical Systems: Not a DIY Area

Commercial electrical work in Ontario requires a licensed electrical contractor. The Electrical Safety Authority (ESA) must inspect and approve all commercial electrical installations. For a repair shop, your electrical demands are significant. Hoists, compressors, welders, diagnostic equipment, and lighting all require dedicated circuits and proper grounding. Your incoming service must be sized for commercial loads. Mechanical ventilation must meet the standards referenced by the OBC. Both systems must be designed, installed, and inspected by qualified professionals. Attempting to self-install these systems is illegal in Ontario and will fail inspection.

Environmental Compliance: The OBC Is Just the Start

Auto repair shops generate waste oil, coolant, solvents, and contaminated water. The Ontario Building Code governs the physical structure, but environmental compliance falls under the Ontario Environmental Protection Act and municipal sewer use by-laws. Your floor drain cannot discharge to a storm sewer without treatment. Waste oil must be stored in approved containers and removed by a licensed collector. Some municipalities require a Stormwater Management Plan or environmental site assessment for commercial properties. Understanding the full regulatory picture before you open protects you from orders, fines, and liability that no building permit alone can shield you from.

Frequently Asked Questions