01 · Introduction
Why climate data sits on every permit set.
A house built for Windsor is not the same house built for Sudbury — the walls, the windows, the heating system, and the roof all change with the climate. The Ontario Building Code encodes those climate differences in two supplementary standards — SB-1 (the climate data itself) and SB-12 (the performance requirements that climate data triggers).
Every residential permit set in Ontario has to pick a climate zone for the project, and that zone determines the minimum R-values for every opaque assembly and the maximum U-values for every window. This is where heating costs, insulation specifications, and fenestration choices all get pinned down.
AD Polyline's OBC Climate & Thermal Tool pulls the full SB-1 climate table for any Ontario location, determines the SB-12 and SB-10 zone, and returns the required thermal values. This article explains what each of those numbers means and how they end up on a drawing.
What's in this guide
02 · Key Terms
The vocabulary behind SB-1 and SB-12.
Climate data has its own dialect. Most of the numbers you'll see on a permit cover page come from the definitions below — knowing what each one represents makes the rest of the conversation much easier.
HDD18
Heating degree days below 18 °C, summed over a year. It measures how much heating a location needs. Higher HDD18 = colder climate = more stringent thermal requirements.
Climate Zone (SB-12)
Zone 1 (HDD18 < 5 000) covers most of southern Ontario; Zone 2 (HDD18 ≥ 5 000) covers colder northern regions. SB-12 sets the minimum housing energy package.
Climate Zone (SB-10)
Three zones — 5, 6, and 7 — based on HDD18 thresholds of 4 000 and 5 000. SB-10 applies to larger buildings designed under ASHRAE 90.1.
Nominal R-value
The labelled thermal resistance of an insulation product — e.g. 'R-19 batt.' It reflects the insulation alone, not the full assembly.
Effective R-value
The real thermal resistance of the complete wall or roof assembly, accounting for framing and other thermal bridges. Always lower than the nominal R.
U-value
The inverse of R — how fast heat travels through an assembly. Used for windows and glazed doors. Lower U = better insulation. Units are W/(m²·K) or Btu/(h·ft²·°F).
ER (Energy Rating)
A composite rating for windows in Canada combining U-value, solar gain, and air leakage. Higher ER = better performance. SB-12 may require a minimum ER in lieu of a U-value.
Continuous Insulation (ci)
An unbroken layer of insulation on the exterior of the framing — e.g. 'R-5 ci' — that bypasses thermal bridging through studs and is increasingly required in Zone 1 code packages.
03 · The SB-1 card
What the climate data actually tells you.
SB-1 (Supplementary Standard SB-1: Climatic and Seismic Data) publishes a set of design values for every city in Ontario. The table that the tool returns is a digested version of the SB-1 row for your location. Not every value matters for every project — but each one is asked for somewhere in the Code.
Fig. 1 — A typical SB-1 climate card and the zone it resolves to. HDD18 drives both the SB-12 housing zone and the SB-10 zone for larger buildings.
Why each value shows up on a permit
January design temperatures size the heating system and inform window selection. Snow load (Ss, Sr) sizes rafters, trusses, and flat roofs. Wind pressure (hourly 1/10, 1/50) sizes cladding anchorage and controls required pressure ratings for exterior assemblies. Driving rain wind pressure drives water management details. Moisture index influences vapour-barrier and wall-cavity detailing. And HDD18 determines the climate zone — which in turn sets the entire thermal package.
04 · Climate zones
Two standards, two zone maps.
Ontario uses two different zone systems depending on which energy standard applies to your project. SB-12 governs houses and small residential buildings under Part 9. SB-10 governs larger and more complex buildings under Part 3 using ASHRAE 90.1. The same HDD18 number feeds both.
Fig. 2 — The same HDD18 value maps to two different zone systems. Use SB-12 zones for houses and SB-10 zones for larger buildings.
Which standard applies?
If your building falls under Part 9 of the OBC (most houses, small multi-unit residential, and many small commercial buildings), use SB-12. If it falls under Part 3 (larger or complex buildings), use SB-10. The tool reports both zones so you can pick the right one for your project classification.
Typical Ontario cities at a glance
| City | HDD18 | SB-12 Zone | SB-10 Zone |
|---|---|---|---|
| Windsor | ≈ 3 400 | Zone 1 | Zone 5 |
| Toronto | ≈ 4 050 | Zone 1 | Zone 6 |
| Ottawa | ≈ 4 500 | Zone 1 | Zone 6 |
| London | ≈ 4 050 | Zone 1 | Zone 6 |
| Ailsa Craig (example) | 3 840 | Zone 1 | Zone 5 |
| Sudbury | ≈ 5 550 | Zone 2 | Zone 7 |
| Thunder Bay | ≈ 5 650 | Zone 2 | Zone 7 |
Approximate HDD18 values for reference. Always look up the specific SB-1 value for your project address.
05 · Nominal vs. effective R
Why the numbers on the drawing are not the numbers on the bag.
A batt labelled "R-19" does not deliver R-19 through a framed wall. Studs, plates, and other framing members bridge heat around the insulation, reducing the actual thermal performance of the complete assembly. The Code recognizes this and usually asks for the effective R — the assembly value, not the product value.
Fig. 3 — A 2×6 wall with R-19 batt typically delivers R-15 to R-17 effective, depending on stud spacing and finishes. Adding continuous insulation recovers the gap.
Why continuous insulation matters
A layer of rigid foam or mineral-wool board on the exterior side of the framing — continuous insulation or "ci" — bypasses the studs entirely and adds almost its full labelled R to the effective value. This is why SB-12 Zone 1 wall packages now typically read R-19 + R-5 ci, or variants like R-24 effective. Both are code-compliant; which one you pick depends on cost, detailing, and available wall thickness.
06 · Reading a thermal performance table
SB-12 Table 3.1.1.11 for additions in Zone 1.
For additions to existing buildings in SB-12 Zone 1 (HDD18 < 5 000), the Code gives a typical performance package. This is the row you will see most often on southern-Ontario permit cover pages.
| Component | Min. Nominal R | Max. U-value | Min. Effective R | ER |
|---|---|---|---|---|
| Ceiling with attic | R-60 | 0.017 | R-59.2 | — |
| Ceiling without attic | R-31 | 0.036 | R-27.7 | — |
| Exposed floor | R-31 | 0.034 | R-29.8 | — |
| Walls above grade | R-19 + 5 ci | 0.049 | R-20.3 | — |
| Basement walls | R-20 ci | 0.047 | R-21.1 | — |
| Heated slab / slab ≤ 600 mm below grade | R-10 | 0.090 | R-11.1 | — |
| Windows & sliding glass doors | — | 0.28 | — | 25 |
Excerpt of SB-12 Table 3.1.1.11 — additions in Zone 1. Imperial units. U-values are Btu/(h·ft²·°F); nominal/effective R are (h·ft²·°F)/Btu.
Compliance options
Where the Code offers alternatives like R-19 + 5 ci ↔ R-24 (effective), you pick one — not both. The tool flags where these alternatives exist. For basement walls, common alternatives include R-12 + 10 ci, R-20 ci, R-15 ci, or R-12 + 5 ci depending on available wall section and budget.
Windows — U or ER, not both
SB-12 lets you comply for windows in one of two ways: meet the maximum U-value (in this case 0.28 Btu/h·ft²·°F, about 1.6 W/m²·K) or achieve the minimum Energy Rating of 25. Most manufacturers publish both numbers on their NAFS or ENERGY STAR label, and most modern double-glazed low-E windows with argon fill meet both requirements comfortably.
07 · When to use the tool
Where the climate tool earns its keep.
Permit cover page
Populating the climatic data box on the cover sheet with authoritative values from SB-1.
Wall specs
Selecting the SB-12 thermal package that drives wall, roof, and basement insulation choices.
Window selection
Checking the minimum U-value or ER for the project's zone before confirming a window schedule with a supplier.
Structural sizing
Pulling snow and wind values to size roof framing, cladding anchors, and girder beams.
Additions & renovations
Picking the right compliance path for partial retrofits where only the affected components are upgraded.
HVAC load
Providing the January design temperatures and HDD18 needed for a heating and cooling load calculation.
08 · Disclaimer & references
Using this guide responsibly.
IMPORTANT NOTICE
This article and the associated OBC Climate & Thermal Tool are provided for informational and preliminary design purposes only. They are not a substitute for the Ontario Building Code itself, for Supplementary Standards SB-1, SB-10 or SB-12, or for the judgement of a qualified designer, architect, or engineer of record. Final thermal specifications should be confirmed with the Authority Having Jurisdiction before committing a project to permit.
Climate data returned by the tool is derived from SB-1 values published with the 2024 edition of the Ontario Building Code. SB-1 is subject to periodic revision; always confirm current values against the in-force edition. Locations not listed in SB-1 may require interpolation or alternative sources, typically at the discretion of the local building official.
The thermal performance values summarized here reflect SB-12 Table 3.1.1.11 for additions in Zone 1. Other tables apply to new construction, to Zone 2, and to specific space-heating equipment types (electric vs. fuel-fired) or specific compliance paths. Consult the full standard for the applicable table.
U-values, R-values, and ERs shown are minimum code requirements. Many clients choose higher-performance assemblies for comfort, energy cost savings, or voluntary certifications (Net Zero Ready, Passive House, etc.). The tool does not evaluate voluntary programs.
AD Polyline makes no warranty, express or implied, regarding the accuracy, completeness, or fitness for a particular purpose of this content. Use at your own discretion and consult your designer for project-specific advice.
References. Ontario Building Code (O. Reg. 163/24); MMAH Supplementary Standard SB-1 — Climatic and Seismic Data; Supplementary Standard SB-12 — Energy Efficiency for Housing; Supplementary Standard SB-10 — Energy Efficiency Supplement.
Need the full thermal package on your permit set?
AD Polyline handles design, permits, and construction-ready documentation for residential and small-commercial projects across Ontario. Cover-sheet climate data, SB-12 compliance packages, and effective R calculations are part of what we do every day.
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