Battery Energy Storage Systems and the OBC

Date of Publication:  November 26, 2025 [2025.08.V-01.C]

Subject:  Battery Energy Storage Systems (BESS) and the OBC

Ontario Building Code Reference(s):

Building Code Act, 1992 S.O. 1992, Chapter 23

Subsections 3.2.2, 3.2.5., 3.3.6, of Div.B.

Article 3.3.1.2 of Div. B

Volume 2 Appendix Note A-3

Incoming Request: 

An outdoor Energy Storage System (ESS) has been proposed, consisting of self-contained pre-manufactured shipping container-like units containing lithium batteries and associated wiring and controls. Some of the units are only serviceable from the exterior, while others have doors allowing a person to enter to service the unit. Should these be considered buildings for the purposes of the OBC?

Executive Summary:

The OBC definition of building is very broad and may include structures not typically considered as buildings. Structures need to be evaluated based on fire risk, occupancy patterns, and risk to adjacent properties or buildings. The Code is intended to be applied with discretion to maintain public safety. 

Discussion & Considerations:

The BCA defines a building in broad terms as “a structure occupying an area greater than ten square metres consisting of a wall, roof and floor or any of them or a structural system serving the function thereof.” Interpreted literally, this definition encompasses the structures in our example. Volume 2, Appendix Note A-3 further emphasizes the expansive nature of this definition, noting that it includes structures “that would not normally be considered as buildings in the layman’s sense.” (Importantly, whether a structure is designed for human occupancy or not, has no bearing on its consideration as a building under the BCA). Based on the above points, it is reasonable to conclude that the subject structures may be classified as buildings under the BCA.

While it may initially appear impractical to consider the structures as buildings (and apply the technical requirements of the Code), Appendix Note A-3 states that the technical requirements are intended to be applied “...with discretion to buildings of unusual configuration...” or where “...processes are carried out which make compliance with particular requirements ... impracticable”. This means that it is reasonable to take into account the building’s physical characteristics and occupancy patterns when applying Code requirements. 

Risk/Benefit Analysis:

For structures with limited floor space for trained personnel to enter for periodic maintenance, it may be impractical to apply code requirements of safety in floor areas and exits. However, other requirements, including but not limited to, structural, spatial separation, and exposure protection should still be considered, based on the fire load of the structure. It may also be useful to look at the definition of a confined space, keeping in mind that a confined space can only be entered by trained personnel following strict safety protocols.

Structures that are completely filled with equipment and where the structure is integral to the equipment (i.e. prefabricated, ground-based generators) would likely not be subject to the OBC, but may be subject to other legislation such as the Ontario Fire Code and municipal by-laws.

Where groups of prefabricated structures are proposed, it may be useful to look at them as a whole (similar to a group of portables) and use free-standing masonry walls or berms as a means to reduce the risk of fire spread between structures and to adjacent properties. Fire routes and hydrant placements should be based on the provisions of Subsection 3.2.5.. An Alternative Solution Proposal (ASP) may be warranted.

Further resources specifically for ESS installations can be found in the NFPA 855: Standard for the Installation of Stationary Energy Storage Systems, The Energy Storage Systems Book , published by the International Code Council, and the BESS Fire Protection Risk and Response Protection Standard produced by Hydro One Networks Inc.

Overall when evaluating industrial structures that do not cleanly fit into the definition of a building or into the OBC in general, the following considerations may be helpful:

• Case law on the definition of a building can be found in the Annotated Building Code Act by John Mascarin and Jeffrey Levitt.
• If it is considered a building, what is the fire load (to determine F classification)?
• Is the building or part of it subject to Article 3.2.2.2 Special and Unusual Structures, Subsection 3.3.6. Design of Hazardous Areas or Article 3.3.1.2. Hazardous Substances, Equipment and Processes?
• What is the occupancy pattern of the building?
• Is specific training required to enter? 
• Can the OBC be applied in a limited manner that ensures public safety but doesn’t place undue burden on the constructor/designer?
• Is public safety better addressed by a different legislation, i.e. Ontario Fire Code, The Electrical Safety Act, or the Occupational Health and Safety Act?
• Is there a relevant standard to consult, i.e. NFPA 885 for Energy Storage Systems?

Even if it is determined that a building permit is not required, the Building Department will still likely be asked to comment on the structure in relation to zoning or site plan application, so it is best practice to become informed on the structure. It is also highly recommended to consult and 

coordinate with the local Fire Department. As always, discretionary decisions such as these should be thoroughly documented and ideally formed into an internal policy.

Final Recommendation: 

The OBC defines buildings very broadly. However, the technical requirements are intended to be applied with discretion. In general terms, it is reasonable to consider the structures in this example as buildings, but then apply the Code with discretion to ensure public safety, taking into account the limited occupancy and unusual configuration of the building. 

Recommendation to Ministry of Municipal Affairs and Housing:

As energy storage systems become more common, building codes must make reference to them and any applicable standards or codes.

Referenced Documents:

2024 Ontario Building Code:

NFPA 855: Standard for the Installation of Stationary Energy Storage Systems

International Code Council Inc., Shawn Shaw, P.E. Energy Storage Systems: Based on the IBC®, IFC®, IRC® and NEC® 

Jeffrey L. Levitt and John Mascarin. Annotated Building Code Act, 2025 Edition

Hydro One Networks Inc. BESS Fire Protection Risk and Response Standard, Rev 1, Nov, 2023

Disclaimer:

This guidance document is intended to assist building officials by gathering relevant information to interpret the OBC Act and the prescriptive requirements of the Ontario Building Code, and is intended to be a best practice aid for building officials.

The views expressed within this guidance document should not be considered as the official interpretation of legislated requirements based on the Ontario Building Code, as the final responsibility for interpretation rests with the local Authority Having Jurisdiction. 

The views of this advisory committee should not be construed as legal advice.