OBC 2024 Guide: Mezzanine Height Exemptions and Fire-Rated Membrane Regulations
Sarah's Expert Insight
OBC Compliance Specialist
"The 40% mezzanine rule is a frequent point of confusion for developers in London and Oakville looking to maximize square footage without triggering 'storey' classifications. At empcontracting.ca Inc. your construction contractor in London, Ontario, we meticulously plan electrical box offsets and partition heights to ensure your fire separations pass inspection the first time, preventing delays in high-stakes Muskoka cottage or London commercial builds."
Understanding the nuances of the 2024 Ontario Building Code (OBC) is essential for any successful build. At empcontracting.ca Inc. your construction contractor in London, Ontario, we specialize in navigating these complex requirements to ensure your project is both compliant and efficiently designed.
Mezzanine Calculations and Building Height (OBC 9.10.4.1)
According to Section 9.10.4.1, a mezzanine is not always counted as a storey when calculating building height. To qualify for this exclusion, the aggregate area of the mezzanine must not exceed 40% of the open area of the room. Furthermore, the space must remain open without partitions higher than 1,070 mm, though a small enclosed space (up to 10% of the room area) is permitted if visual communication is maintained.
Multiple Mezzanines and Industrial Platforms
If your design includes more than one level of mezzanine within a single storey, the OBC requires each additional level to be counted as a separate storey (9.10.4.2). For industrial applications in areas like London or Oakville, platforms and catwalks used strictly for maintenance are exempt from these floor assembly calculations, provided they are noncombustible.
Basement Garages and Rooftop Enclosures
Section 9.10.4.3 allows basement storage garages to be treated as separate buildings for fire safety purposes, provided there is a 2-hour fire-resistance rating in the masonry or concrete separations. Similarly, rooftop enclosures for elevator machinery or stairways are excluded from storey calculations under Section 9.10.4.4.
Fire-Resistance Ratings and Permitted Openings (OBC 9.10.5.1)
Maintaining the integrity of a fire-rated assembly is a top priority for empcontracting.ca Inc. your construction contractor in London, Ontario. Section 9.10.5.1 prohibits piercing the membrane of a fire-rated assembly unless it has been specifically tested. An exception exists for electrical service boxes, provided they are offset to prevent the transfer of fire through the wall or ceiling cavity.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.