If you are planning a new build, finishing a basement, adding an addition, or upgrading your existing insulation in Ontario, there is one document that governs what you are legally required to install: the Ontario Building Code (OBC), specifically its energy efficiency section known as Supplementary Standard SB-12.
Getting this right is not optional. Inspectors across Hamilton, the GTA, and the rest of Ontario are trained to check insulation type, thickness, placement, and code compliance before they approve work. Homeowners who skip the details — or rely on advice from outdated sources — often face costly rework, failed inspections, or problems when it comes time to sell the property.
This guide covers the current OBC insulation requirements by building component, explains what climate zones mean for your project, breaks down the continuous insulation rules, and clarifies what the 2024 OBC update changed. Whether you are working with a contractor or simply want to understand what your permit requires, this is the reference you need.
What Is Supplementary Standard SB-12?
The Ontario Building Code is made up of the main code document and several supplementary standards that cover specific areas of construction. SB-12, titled “Energy Efficiency for Housing,” is the section that governs insulation and thermal performance requirements for residential buildings.
SB-12 works through a system of compliance packages. Each package is a combination of insulation levels, air sealing requirements, and mechanical system specifications that, together, meet the code’s energy efficiency targets. Builders and contractors can often choose between compliance packages — which means there is not always a single rigid answer to “what R-value do I need,” but rather a range of compliant assemblies depending on the heating system in the building and the climate zone it sits in.
The 2024 edition of the Ontario Building Code came into effect on January 1, 2025. For building permit applications submitted after March 31, 2025, only the 2024 OBC applies. That is the version this guide reflects.
Ontario’s Climate Zones and Why They Matter
SB-12 divides Ontario into climate zones based on Heating Degree Days (HDD) — a measure of how cold a location is over the course of a year. The colder the climate, the more insulation is required.
Zone 1 covers southern and eastern Ontario with fewer than 5,000 HDD. This includes the Greater Toronto Area, Hamilton, Oakville, Burlington, Mississauga, Brantford, and surrounding communities.
Zone 2 covers regions with 5,000 to 6,000 HDD, including Ottawa and parts of eastern Ontario.
Zone 3 covers regions above 6,000 HDD, primarily in northern Ontario.
For the communities that Samrai Spray Foam serves across Hamilton and the GTA, Zone 1 is the applicable standard. This guide focuses primarily on Zone 1 requirements, with Zone 2 references included where relevant for homeowners in those areas.
Attic Insulation: The R-60 Standard
The attic is where Ontario’s insulation code has seen the most significant change over the past decade. The minimum required R-value for attics in Ontario has risen steadily — from R-40 in earlier code editions, to R-50, and now to R-60 under the current standard.
Current OBC requirement: R-60 for ceilings with attic space above, in Climate Zone 1.
This applies to new construction and to additions or major renovations where a permit is issued. If your home was built before the R-60 standard took effect and you have not pulled a permit for attic work, you are not retroactively required to meet R-60 — but the gap between older and current standards is significant, and the energy savings from upgrading are real.
To understand what R-60 means in practical terms, consider how thick different insulation materials need to be to reach it. Blown-in fibreglass typically requires around 20 to 22 inches. Blown-in cellulose requires approximately 16 to 18 inches. Closed-cell spray foam, with its R-value of around R-6.5 per inch, can reach R-60 at roughly 9 inches of depth, though it is more commonly combined with other materials in a hybrid approach at this scale.
Above and beyond the minimum: Many building science professionals and insulation contractors recommend targeting R-70 or even R-80 in attics, particularly in older Ontario homes where heat loss through the ceiling accounts for a substantial portion of total energy use. The minimum is a legal floor, not a performance target.
Cathedral ceilings and unvented attics: Flat roofs, cathedral ceilings, and unvented attic assemblies operate under different design rules than a standard vented attic. In these situations, closed-cell spray foam is often the only practical solution because it can be applied directly to the underside of the roof deck, creating an unvented conditioned space without the depth limitations of a conventional attic. The code requirements for these assemblies are more complex and should be reviewed with a certified installer who understands unvented roof design in Ontario’s climate.
Attic air sealing as a prerequisite: A detail the code reinforces, and one that experienced installers will always address before adding insulation to an attic, is air sealing. Air leakage through attic bypasses — plumbing penetrations, electrical boxes, chimney chases, partition walls — can account for 30 to 40 percent of heat loss regardless of how much insulation sits on top of them. Sealing these gaps before or in combination with insulation installation is part of compliant practice.
Exterior Wall Insulation: R-22 to R-24
Above-grade exterior walls are where the code requirements become more nuanced, primarily because wall assembly compliance depends on your heating system’s efficiency rating and the compliance package being used.
Current OBC requirement: For new construction in Climate Zone 1 with a high-efficiency furnace (AFUE of 92% or higher, which is standard for any modern gas furnace installed in the past decade), the minimum wall insulation requirement under Table 3.1.1.2.A of SB-12 is R-22 in above-grade framed walls. This can be achieved using batt insulation in standard 5.5-inch (2×6) stud framing without the addition of continuous exterior rigid insulation.
For homes with lower-efficiency heating equipment or for certain addition and retrofit scenarios, other tables in SB-12 may apply and can require R-24 — which often means R-19 cavity insulation plus a continuous insulation layer on the exterior of the sheathing.
What is the practical difference between R-22 and R-24? It is less than the numbers suggest, for one specific reason: thermal bridging.
Thermal Bridging and Continuous Insulation
Thermal bridging is one of the most important building science concepts for understanding why OBC insulation requirements work the way they do — and why continuous insulation has become a larger part of the conversation.
Wood studs in a framed wall conduct heat. A stud in a wall cavity that is otherwise filled with R-20 fibreglass batts does not provide R-20 thermal resistance — it provides significantly less, because heat flows preferentially through the wood. When you calculate the actual, whole-wall thermal performance of a typical 2×6 framed wall with R-20 batts, the effective R-value is closer to R-16 or R-17 because of the thermal bridging effect of the framing members, which typically make up 20 to 25 percent of the wall area.
This is why continuous insulation matters. When a continuous layer of insulation — rigid foam board, exterior spray foam, or mineral wool board — is applied across the full face of the sheathing, it creates a thermal break that covers the studs. The studs no longer provide an uninterrupted path for heat to travel from the interior to the exterior. This improves the actual, real-world performance of the wall assembly regardless of what the nominal R-value of the cavity insulation says.
The OBC and continuous insulation: Under the 2024 OBC and SB-12, continuous insulation is required in certain compliance packages — but it is not universally required for every wall assembly. A ruling issued by the Ontario Building Officials Association in September 2025 clarified that if an assembly meets the minimum effective R-value or maximum U-value specified in SB-12, the continuous insulation layer is not independently required. The assembly just has to comply through one of the permitted performance metrics.
The practical effect: if you are using a high-efficiency furnace and your wall assembly achieves the required nominal or effective R-value under the applicable SB-12 table, you may not need continuous insulation. If you are adding onto a home with older, lower-efficiency mechanical systems, or if the applicable compliance package specifies continuous insulation, then it is required.
For builders and homeowners who want the best long-term thermal performance — not just minimum compliance — adding a continuous exterior layer of rigid foam or spray foam in addition to cavity insulation is the stronger approach. A common high-performance assembly in Ontario combines R-20 cavity insulation with R-5 to R-10 continuous exterior insulation. This reduces thermal bridging substantially and improves the actual, measured whole-wall R-value beyond what the nominal numbers alone indicate.
Basement Wall Insulation: R-20 for the GTA
Basement walls are governed by SB-12 in the same way as above-grade walls, with requirements that vary based on climate zone and heating system efficiency.
Current OBC requirement for Climate Zone 1 (GTA and Hamilton area): R-20 for basement walls, for homes with furnaces operating at 92% AFUE or higher.
This requirement applies from the underside of the subfloor down to the top of the concrete slab. The 2024 OBC reinforced the requirement for full-height coverage. Inspectors in Toronto, Mississauga, Brampton, Markham, and surrounding municipalities will expect to see insulation that runs the full height of the basement wall — not the partial-height installation that was common in older construction.
A small exception exists: in basements with documented moisture or dampness concerns, the code allows a gap of no more than approximately 200 millimetres (about 8 inches) from the slab. However, the default expectation is full coverage from floor to ceiling.
Accepted assembly options for reaching R-20 in a basement: There is more than one way to achieve the required thermal value, and the code accommodates different material combinations.
A common approach is to apply R-12 continuous insulation directly against the concrete foundation wall (using closed-cell spray foam or rigid foam board), then frame a 2×4 stud wall in front of it and add R-8 or R-10 batt insulation in the cavities. This gives the assembly continuous thermal coverage on the concrete face while also providing cavity insulation in the framed wall.
Another accepted combination under SB-12 is R-12 continuous plus R-10 cavity insulation. The important distinction from current code guidance: R-12 continuous insulation on its own, with no cavity insulation, is no longer sufficient to meet the R-20 standard for a finished basement wall in most GTA permit applications.
Closed-cell spray foam in basements: Closed-cell spray foam applied at a thickness of 2 inches or greater has a vapour permeance low enough to function as its own vapour barrier. It also serves as an air barrier, eliminating the need for a separate polyethylene sheet against the concrete. This is one of the practical reasons spray foam has become widely used for basement foundation walls in Ontario — it does the work of two separate building envelope layers in a single application. For the rim joist area (where the floor joists meet the top of the foundation wall), closed-cell spray foam cut to fit and sealed is the most reliable solution, and inspectors across Ontario will look for this detail.
What the code does not require for basements: The OBC does not mandate insulation under a standard concrete slab for most residential basement renovations. However, installing R-10 rigid foam below the slab before it is poured is a common improvement in new construction and can make a measurable difference in comfort in basement living spaces.
Crawl Space Insulation Requirements
Crawl spaces are handled differently depending on whether they are vented or unvented (conditioned) spaces.
Vented crawl spaces: The conventional approach is to insulate the floor assembly above the crawl space — the underside of the first floor — rather than the crawl space walls. SB-12 specifies R-31 as the minimum for floor assemblies in Zone 1. Fibreglass batts or mineral wool supported between floor joists with netting or strapping are common materials for this application. Adequate cross-ventilation through the crawl space must be maintained, with the OBC requiring a ventilation ratio of approximately 1:300 between vent area and crawl space area.
Unvented (conditioned) crawl spaces: In this approach, the crawl space walls are insulated rather than the floor above, and the crawl space is treated as part of the conditioned building envelope. R-12 to R-15 continuous insulation on the crawl space walls, combined with a vapour barrier on the ground, is the standard assembly. This approach is increasingly preferred in building science practice because it eliminates the moisture and temperature problems common in vented crawl spaces, keeps plumbing within conditioned space, and removes the risk of freezing pipes.
Closed-cell spray foam is well suited to both approaches. For vented assemblies, it can be spray-applied between joists without the sagging issues associated with batt insulation. For unvented assemblies, it provides both thermal resistance and moisture control in the same application.
Spray Foam Certification Requirements Under the OBC
Beyond R-values and assembly requirements, the OBC has specific rules about what spray foam products and installers are permitted.
Product certification: Closed-cell spray foam products used in Ontario must meet the CAN/ULC S705.1 and S705.2 standards for medium-density foam. These are the Canadian standards for product formulation, testing, and performance. Products without this certification are not approved for permit work.
Installer certification: The OBC requires that spray foam be applied by certified professionals. In practice, this means installers trained under programs recognized by bodies such as the Canadian Urethane Foam Contractors Association (CUFCA). Using an uncertified installer on permitted work creates liability for both the contractor and the homeowner.
Thermal barrier requirement: Spray foam insulation exposed inside a living space must be protected by a thermal barrier — typically 12.7 millimetres (half-inch) of drywall. This is a fire code requirement that applies to basements, attic floors, and any other area where spray foam is within the habitable envelope. Crawl spaces, utility rooms, and garages have their own specific rules. Failure to cover spray foam before closing in a wall or ceiling is one of the more common causes of failed inspections on spray foam projects.
CCMC approval: All spray foam products used on permitted projects in Ontario should carry Canada Construction Materials Centre (CCMC) approval. This documents that the product has been independently evaluated against Canadian building code standards. Reputable installers carry product documentation and can provide it on request.
What the 2024 OBC Update Changed
The 2024 Ontario Building Code came into effect on January 1, 2025. For insulation, the update did not change the R-value floors for attics, walls, and basements in Zone 1 — those thresholds were established in earlier code revisions. What the 2024 update reinforced and expanded includes:
Airtightness testing requirements: The 2024 OBC places stronger emphasis on airtightness testing and, for larger projects, whole-building energy modelling as part of the compliance pathway. This reflects the growing recognition that insulation R-value alone does not determine building performance — air leakage can undermine even a well-insulated assembly.
Full-height basement insulation: The requirement for basement wall insulation to run from the underside of the subfloor to the concrete slab was reinforced in the 2024 edition. Partial-height insulation on basement walls — common in pre-2009 construction — has not been acceptable practice for over 15 years, but the 2024 update made this expectation more explicit.
Alignment with national standards: The 2024 OBC brings Ontario’s code into closer alignment with the National Building Code of Canada, which makes compliance expectations more consistent for builders and designers who work across multiple jurisdictions.
Renovation triggers: If you are renovating a home built under an older edition of the code, the general rule is that the current code applies to the scope of permitted work. If you are pulling a permit to frame and insulate your basement, your inspector applies the 2024 OBC requirements to that work — even if the rest of the house was built under 1990s standards. This is why understanding current requirements before starting a project matters: unexpected code requirements discovered mid-project are expensive.
Building Permit for Insulation Work
Not all insulation upgrades require a building permit in Ontario. Topping up attic insulation in an existing home — adding blown-in material on top of what is already there — typically does not trigger permit requirements if no structural changes are involved.
A permit is required when you are:
Framing new walls in a basement and adding insulation as part of a basement finishing project. Adding an addition to your home that includes new insulated walls, roof, or foundation assemblies. Performing a major renovation that changes the building envelope in a way that affects structural elements or that crosses the threshold for “major alteration” under the OBC. Converting a crawl space or garage to conditioned space.
When a permit is required, insulation, vapour barriers, and air barriers must be inspected before they are covered by drywall or other finishes. Scheduling this inspection correctly — not closing in walls before the inspector has reviewed the work — is a basic permit compliance requirement that saves homeowners from potentially tearing out finished walls.
The Case for Going Further
The numbers in SB-12 are minimums. They represent the baseline below which the province has determined a building is too inefficient to permit. They are not recommendations for optimal performance.
In Ontario’s climate, where heating season runs from October through April across much of the province, the long-term cost difference between building to the minimum and building to a higher standard is significant. An attic insulated to R-70 rather than R-60 will perform measurably better. A basement wall with R-25 effective insulation will be noticeably warmer and drier than one that barely clears R-20.
For homeowners who want to maximize energy efficiency, qualify for rebate programs like the Enbridge Home Efficiency Rebate Plus (HER+), or simply build a home that performs well for decades without ongoing discomfort, working with a contractor who thinks beyond the minimum is the practical approach.
Working with Samrai Spray Foam on OBC-Compliant Projects
At Samrai Spray Foam, every project we work on across Hamilton, Oakville, Brantford, Mississauga, Toronto, and the surrounding GTA is completed using certified products that meet CAN/ULC and CCMC standards, by trained installers who understand SB-12 compliance requirements for each application type.
We work with spray foam, blown-in insulation, fibreglass batts, and mineral wool — which means we can recommend the assembly that makes the most sense for your specific project, not just the one we happen to carry. If your project requires a building permit, we can discuss the inspection timeline and make sure the installation is documented and ready for review before anything gets covered.
If you are planning a new build, renovation, basement finish, or attic upgrade in Hamilton or the surrounding area, contact our team for a free estimate and an honest conversation about what your project actually requires.
