Date of Publication: June 9, 2026   [2023.25.V.02-C]

Subject: Insulation requirements for an existing building undergoing renovation 2024 OBC UPDATE

2024 Ontario Building Code [O.Reg. 163/24 Amended to 5/25] References: 

Articles 1.3.3.3B. and 1.3.3.3C. of Div. A.

Subsections 11.3.1.,11.3.2., and 11.3.3. of Div. B.

Article 11.4.2.3. of Div. B.

Section 11.5. of Div.B

Summary of changes: Updated code references

Incoming Request: 

An existing house is having the basement converted to living space. What are the insulation and vapour barrier requirements if the building is less than 5 years old vs more than 5 years old?

Executive Summary:

Existing basement insulation and vapour barrier that was code compliant at the time of construction may be left in place during basement finishing, even if it is not in compliance with today’s Code. If the existing insulation and vapour barrier is being completely removed and replaced, and it is being considered as a new building system, the new installation would have to meet today’s Code, subject to Compliance Alternative C207 if applicable. Municipalities may want to provide staff with a policy for consistent interpretation.

Considerations:

Article 1.3.3.3B. of Div A states that if a building has been in existence for more than five years, Part 11 is applicable. Article 1.1.3.3.3C. of Div. A further clarifies that the Code only applies to the design and construction of any material alterations or repairs. This means that if the existing insulation and vapour barrier on a basement wall are being left in place, no further upgrades are required, as the insulation is not being altered, repaired, or otherwise constructed. The only caveat is that the insulation and vapour barrier should be compliant with the Code at the time the basement was constructed.

In a case where insulation and vapour barrier are being partially left in place or being partially replaced for any reason it can be argued that Article 11.3.1.1. (Material Alteration or Repair of a Building System) would apply, i.e. performance after the repair shall be equal to or better than before.

In a case where new insulation is being proposed, construction is occurring and the provisions of Article 11.3.1.2. (New Building Systems and Extension of Existing Building Systems) will apply. New building systems are required to comply with other parts of the Code or Compliance Alternatives via Section 11.5. of Div B (see C194 and C207). In certain limited cases, where the work is considered a basic renovation, Article 11.3.3.1. of Div. B permits re-use of similar materials to “retain existing character, structural uniqueness, heritage value, or aesthetic appearance”. Note that this re-use is not permitted if it may create an unhealthy environment, nor to satisfy financial or convenience reasons.

For a building less than 5 years old, Part 11 would not apply, and any construction must be in compliance with the Code. Practically, this would only be a consideration if the proposed construction includes removing the existing insulation and vapour barrier and the Code requirements for basement insulation and vapour barriers have changed between the date on which the building came into existence (usually the occupancy date for a house) and the application date for the basement finishing permit.

It should be noted that the definition of building system in Article 11.1.1.2. of Div B does not explicitly include insulation and vapour barrier, but it can be argued that this does constitute a “complete major division of construction”. Large portions of the OBC are devoted to it, (Part 5, Section 9.25, SB-10 and SB-12), it is generally installed by a trade devoted to that system, and Construction Specifications International has a specific division (Division 7) devoted to thermal and moisture protection.

Risk/Benefit Analysis:

Application of Part 11 involves defining a building system as either “new or extension of existing” vs “materially altered or repaired” for application of either Subsections 11.3.1.1. or 11.3.1.2. The scope of work must also be defined as either an “extension of a building” (Subsection 11.3.2.) or a “renovation” (Subsection 11.3.3.) If it is a renovation, the construction must also be defined as a “basic renovation” vs “extensive renovation” to determine application of Articles 11.3.3.1. or 11.3.3.2.

Case 1:

Finishing of a previously unfinished basement space to create a recreation room could be considered a basic renovation, as it “is limited to a room or suite” and does not involve a reduction in the performance level of the building. Construction of new exterior walls with insulation and vapour barrier would be considered new construction. If new plumbing rough-in or fixtures are proposed, these would be subject to Part 7.

Case 2:

Finishing of a basement to create bedrooms may or may not be considered a basic renovation as it may increase the occupant load by more than 15%, triggering a reduction in performance level. If a portion of the basement were finished with framing and insulation less than today’s Code, it would be permissible to extend that existing level of insulation, vapour barrier and framing to the new area, by way of Compliance Alternative C207. 

Case 3:

Finishing of a basement to create a secondary suite would definitely be considered an extensive renovation as it is deemed a change in major occupancy by way of Sentence 11.4.2.3.(b) of div B, and results in a reduction in performance level. Insulation, vapour barrier and exterior wall framing could follow either of the above scenarios.

There is risk that an improperly installed vapour barrier or insulation may cause moisture damage or an unhealthy condition in the building. For this reason, it should be made clear on the approved plans or through inspection notes what is existing and what is to be replaced. There is also a risk to the municipality in how the public perceives the municipality’s practices, especially if they are inconsistent from project to project or between plans examination stage and inspections. For 

example, if an existing insulated and finished basement with stud walls is being repaired due to flood damage, with insulation and vapour barrier being removed but the studs left in place, the work might be considered “repair of an existing building system” for one building official, which would only require the work to meet previous performance levels. However, a different building official might view the work as “new or extension of existing building system” and the construction would have to meet today’s code requirements, subject to any applicable compliance alternatives found in Part 11.

Final Recommendation(s):

Municipalities may benefit from written guidelines to clarify the following:

• How to determine the date at which the building “came into existence” for application of Part 11.
• What is considered a building system for the purposes of Subsection 11.3.1.
• What is considered a “material alteration or repair to an existing building system” (Article 11.3.1.1.)
• What is considered a “new or extension of existing building system” (Article 11.3.1.2.)
• What is considered an extension of a building for the purposes of Subsection 11.3.2.
• What is considered an extensive renovation of a building vs a basic renovation of a building for application of Subsection 11.3.3.
• How to ensure frequent communication between plans examinations staff and inspection staff to confirm consistent application and provide ongoing feedback.

There are many possible scenarios, and no document will cover them all. Starting with guidelines for the most common scenarios will assist staff with consistent application of this complex part of the OBC. As more cases come up, guidelines can be expanded. Written guidelines can help mitigate the risks associated with application of Part 11 to insulation and vapour barrier requirements.

Recommendation to the Ministry of Municipal Affairs and Housing:

None at this time.

Referenced Documents:

2024 Ontario Building Code O.Reg. 163/24 Amended to 5/25

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.