Effective January 1, 2025, Ontario’s new Building Code takes effect, replacing a 2012 framework that has been amended more than two dozen times. On paper, the 2024 Ontario Building Code (OBC) is about harmonization with the National Building Code of Canada (NBC) and reducing red tape. In practice, it changes how homes, secondary suites, small buildings, farm structures, and complex developments are designed, reviewed, and approved.

For real estate investors, this isn’t a technical footnote for architects and engineers. The 2025 Code cycle will influence project costs, timelines, feasibility, and long-term risk—especially for investors who rely on renovations, secondary suites, rural properties, or more complex mixed-use projects.

Why the 2025 Code Matters for Investors

When the Ministry of Municipal Affairs and Housing filed the new Code in April 2024, it introduced roughly 2,400 changes relative to the 2012 OBC. The stated goals are:

• Increasing housing supply and innovation

• Protecting health and safety

• Managing cost

• Reducing red tape and construction barriers

• Delivering better-performing buildings

At the same time, Ontario is aligning more closely with national model codes and broader climate policy, including energy performance and greenhouse gas reduction targets. Even where energy-efficiency wording in the OBC appears relatively stable, the direction of travel is clear: buildings are expected to be safer, more accessible, and more environmentally robust.

For investors, that means two things:

1. Upfront complexity and cost may rise in certain project types.

2. Over the long term, compliant, well-built assets are likely to stand out in a more regulated, performance-focused market.

Part 9 vs. Part 4: Understanding the Compliance Paths

The Code continues to offer two main structural “paths,” and the 2025 revisions affect both:

• Part 9 – Prescriptive design This is the “recipe book” for standard houses and small buildings: span tables, footing sizes, wall assemblies, and simple structural layouts. It’s commonly used for typical low-rise residential projects, decks, and small accessory buildings.

  
  

• Part 4 – Engineered design This is the performance-based route. It applies when the building is larger, more complex, or outside the limits of Part 9—think wide open-concept spaces, tall walls, steel or concrete frames, or commercial and institutional occupancies.

The new OBC updates:

• Structural loads and climate data in Part 4: snow, wind, and seismic values are refined, with new provisions for roofs hosting solar panels and canopies, and more detailed wind requirements for parapets, balcony guards, and cladding.

• Importance categories and post-disaster standards, raising the bar for buildings that must remain functional after extreme events.

• Foundation design expectations, now clearly requiring a professional engineer and updated standards for wood foundations.

  
  

For most residential investors, these changes will show up indirectly—through engineers’ drawings and product specs rather than day-to-day decision-making. But if you’re pushing beyond “typical house” design, you should expect more rigorous structural assumptions and potentially higher engineering fees.

Secondary Suites and Small Buildings: The Basement Rules Are Evolving

For many small-scale and mid-size investors, Part 9 – Housing and Small Buildings is where the 2025 Code changes are most tangible.

Key revisions include:

• New terminology 

  The broad term “house” is replaced by more precise terms such as “secondary suite,” “a house with a secondary suite,” and “individual dwelling unit.” This reflects the reality that secondary suites are now a central piece of the housing strategy rather than an afterthought.

  
  

• Ceiling heights in secondary suites 

  The Code now allows reduced minimum ceiling heights in secondary suites, with slightly lower clearances under beams, ducts, and over stairs. This creates more flexibility in existing basements—but only if other safety, fire, and ventilation requirements are met.

  
  

• Stair and guard safety 

  A new article limits open stair risers in many Part 9 buildings and restricts triangular openings between treads, risers, and guards to block a 150 mm sphere. The goal is to reduce fall hazards, especially for children.

  
  

• Fire and smoke separation requirements are expanded for:

  • Fire separations between rooms and spaces, and

  • Smoke-tight barriers between dwelling units and their common spaces in a house with a secondary suite. In some configurations, a smoke-tight gypsum board assembly can substitute for a full 45-minute rated separation, but the bar for continuity and proper detailing is higher.

    
    

• Life safety and environmental health

  • Wireless technology is now permitted to interconnect smoke alarms in houses with secondary suites.

  • Radon rough-ins for subfloor depressurization are required in all new homes.

  • Basement and heated crawlspace foundation walls must now be insulated over their full height, eliminating previously accepted gaps.

    
    

The net effect for investors is mixed:

• There is more flexibility to legalize or build secondary suites in existing basements.

• But there is also less tolerance for marginal conditions: low ceilings, poor fire separations, inadequate ventilation, or missing radon provisions will increasingly stand out as code deficiencies.

  
  

If your strategy depends on adding or legalizing secondary suites, you should assume that permitting will probe deeper into fire, air, and moisture details than in prior cycles.

Health, Environmental Separation, and Mechanical Systems (Parts 5–8)

Beyond structural elements, the 2025 Code tightens expectations around how buildings deal with air, moisture, heat, water, and waste—all key drivers of operating risk and liability.

Part 5 – Environmental Separation

Part 5 now more clearly addresses:

• Control of condensation, air and moisture movement, and heat transfer

• Requirements for materials separating different environments or exposed to exterior conditions

• Air barrier systems designed to minimize radon and soil gas ingress, especially where assemblies contact the ground

There is also a shift from trying to “prevent” surface water penetration to “minimizing” it—recognizing that some water entry is inevitable and must be managed rather than denied.

Part 6 – Heating, Ventilation, and Air-Conditioning

Changes include:

• Alignment with newer ANSI/ASHRAE ventilation standards for garages, crawlspaces, and heat recovery systems.

• Expanded requirements for smoke detectors and carbon monoxide alarms in care and residential occupancies.

• Lower maximum temperatures for exposed piping in areas where people may come into contact with it.

• New provisions for evaporative cooling towers and systems to limit Legionella risk.

Part 7 – Plumbing and Part 8 – Sewage Systems

Highlights:

• New acceptable plumbing materials (such as PE-RT and cellular core PVC).

• Clearer rules for non-potable water systems and rainwater harvesting, enabling more sustainable designs where appropriate.

• Lower maximum hot water temperatures in health care and seniors’ occupancies and additional safeguards in childcare settings.

• Updated standards for septic tanks, including secondary safety screens, clarified distribution bed layouts, and soil/percolation rules to support proper drainage.

For investors, these updates are less about day-to-day decision-making and more about ensuring your team is building to a standard that will age well under regulatory and environmental scrutiny. Good envelope, ventilation, and water system design reduces the risk of mold, radon, indoor air quality complaints, and costly remediation later.

Accessibility and Barrier-Free Design: More Requirements, Broader Market Appeal

The 2025 Code notably tightens barrier-free design and accessibility requirements, especially in Part 3 buildings:

• All pedestrian entrances to a barrier-free storey must be accessible.

• A direct, barrier-free path of travel is required between entrances, parking, loading zones, and public thoroughfares where these exist.

• Expanded and more detailed accessibility signage, including Braille and tactile characters.

• Wider exterior walkways and doors on barrier-free paths, plus mandatory power door operators for certain doors.

• Increased ramp widths and larger level landings.

• Requirements for assistive listening systems at service counters and at least one universal dressing/shower room where showers are provided.

  
  

These features carry a cost, but they also align assets with:

• A growing aging population

• Tenant and employer expectations around inclusivity

• Lender, insurer, and institutional investor preferences for accessible, future-ready buildings

In other words, while accessibility upgrades may feel like compliance today, they are increasingly part of asset quality tomorrow.

Farm Buildings and Rural Assets: New Clarity, New Thresholds

For investors with agricultural or agri-adjacent holdings, the introduction of a fully built-out Part 2 – Farm Buildings matters. It sets distinct rules for:

• Large farm buildings (over 600 m² or more than three storeys), and

• Smaller structures

  
  

with new Group G sub-classifications for high-hazard uses, general agricultural occupancies, greenhouses, and buildings with no human occupancy.

If your strategy includes agri-business, greenhouse operations, or rural diversification, you should expect:

• Clearer technical demands on large, complex farm structures

• More consistent expectations from building officials across municipalities

Timing and Transition

The new OBC is effective January 1, 2025, with a limited transition period:

• If construction documents are substantially complete on or before December 31, 2024, applications may be filed under the previous regime up to March 31, 2025.

• After that, new submissions are expected to comply with the 2024 OBC (effective 2025).

If you are mid-design on a development or major renovation, it’s critical to clarify which Code cycle your team is targeting and how that affects cost, design choices, and schedule.

What Investors Should Do Now

To navigate the 2025 revisions effectively:

• Audit your pipeline. Flag projects involving secondary suites, basement conversions, farm buildings, care occupancies, or rural sewage systems.

• Refresh your underwriting. Build in allowances for upgraded fire separations, ventilation, radon control, envelope performance, and accessibility.

• Engage professionals early. Ask architects and engineers explicitly how the 2025 Code affects your plans, and whether your design sits comfortably in Part 9 or requires a Part 4 engineered approach.

• Document performance. Radon rough-ins, air barrier details, insulation continuity, and ventilation strategies are easier to prove when they’re documented from the start—and that documentation can support both compliance and resale.

• Think long-term. Buildings that meet or exceed emerging structural, environmental, and accessibility standards are more likely to remain financeable, insurable, and attractive to tenants in a tightening regulatory environment.

Investor Takeaway

Ontario’s 2025 Building Code revisions are not a marginal technical update. They reflect a broader shift toward safer, more accessible, and more resilient buildings, in line with national harmonization and climate objectives.

In the near term, that means more detailed design, closer coordination with professionals, and potential increases in soft and hard costs for certain strategies—especially those involving secondary suites, complex structures, or rural systems. Over time, investors who understand and work with these rules are better positioned to own durable, compliant, and marketable assets in a province where building performance is under growing scrutiny.

The Code has changed. Smart investors will treat it not as a hurdle, but as a roadmap for building portfolios that can stand up to both regulation and time.