Montréal's building GHG disclosure and rating (By-law 21-042): what to report and how ratings work

Montréal was the first Canadian city to attach a public letter grade to a building's greenhouse gas performance. By-law 21-042 started as a disclosure rule: report your energy use and the City works out the emissions. Since the September 2025 ordinance fixed the rating methodology, it is also a rating rule, with the address and grade of every covered building published by the City.

That changes what the data means. A gap in a gas account or a missing tenant meter no longer just produces a wrong number in a spreadsheet; it moves a grade that a lender, a buyer or a tenant can look up. This article covers who is covered, what to disclose and when, how the rating works, what condo boards need to collect, and how to prepare for the 2027 cycle.

Who is covered

The City's page states that By-law 21-042, adopted September 27, 2021, applies to commercial, institutional and large multi-unit residential buildings of 2,000 square metres (21,528 square feet) or greater, or buildings with 25 dwellings or more. The page lists two exclusions: buildings whose predominant use on the assessment roll is industrial, and facilities already subject to the province's air contaminant reporting regulation. McMillan LLP's summary notes the by-law does not apply to the 14 other cities that make up the Montréal agglomeration.

Coverage was phased in. McMillan sets out the two private-building phases: a June 30, 2023 deadline for buildings of 5,000 to 14,999 m2 or 50 dwellings or more, reporting 2022 data, and a June 30, 2024 deadline for buildings of 2,000 m2 or more or 25 to 49 dwellings, reporting 2023 data. Journal Métro reported the first wave in 2022 as municipal buildings and commercial properties exceeding 15,000 m2, with roughly 6,400 buildings across the boroughs subject to the regulation overall.

What must be disclosed, and by when

Owners must submit monthly energy consumption data for the entire building, for all energy sources, covering January 1 to December 31 of the previous year, by June 30 of each year, through ENERGY STAR Portfolio Manager. Solution Condo's summary of Schedule A lists what that means: owner identification and a contact, address, construction year, total floor area, number of dwellings, use types and areas, monthly quantities and costs for electricity in kWh, natural gas in m3, district heating or cooling, and other fossil fuels, plus peak electrical demand per billing period in kW. Records must be kept five years and any breach is punishable by a fine; Journal Métro put the range at $700 to $4,000 for non-disclosure.

Note the phrase "entire building." A tower where tenants hold their own electricity accounts, or a condominium with separately metered units, still reports one whole-building figure per month per energy source. That is where most of the work sits. Ontario owners will recognize the pattern; our step-by-step EWRB guide covers the parallel requirement.

How the rating works

The rating is calculated by the City, not declared by the owner. BOMA Québec's release on the September 2025 ordinance quotes the City's division chief: the Bureau de la transition écologique et de la résilience calculates the rating from the disclosure data according to the adopted methodology, and the ordinance introduces no additional obligations for owners beyond continuing to disclose their annual energy data. Three mechanics matter for anyone reading their grade.

• Thresholds are fixed, not relative. The rating bands are based on the full dataset collected during the disclosure period ending June 30, 2025, defined once and not changed each year. A building's grade moves because its own emissions move, not because the neighbours improved.
• Comparison is by use type. The City describes the methodology as determining each building's GHG performance level by use type, relative to comparable buildings, with bands expressed as a range of GHG per square metre, so a hospital is not graded against an apartment block. Buildings with no comparables, such as the Olympic Stadium, fall into an "N" category for non-applicable.
• Publication is online, not on the door. The City states that only the building address and its rating will be published on its website, and that the by-law's requirement to post ratings at entrances has not come into effect.

On the scale itself, the City's own roadmap page describes a rating system ranging from A to F, with the A rating awarded to buildings that have achieved zero carbon and the least efficient buildings receiving F. Industry summaries since the ordinance describe the finalized scale with an extended top band above A and a separate mark for buildings that fail to report; we could not confirm those labels on a City page, so treat the published rating on your own building as the authority. The direction is not in doubt: the roadmap says large buildings must reach zero carbon, an A rating, by 2040, a target BOMA Québec notes was moved forward from 2050.

What drives a rating

Three inputs decide everything: the monthly quantity of each energy source, the emission factor applied to it, and the floor area in the denominator. The City applies the factors; the owner's job is the quantities and the area. Factors still matter for planning, because on a low-carbon grid moving load from combustion to electricity moves the numerator far more than efficiency on the gas side. We explain the choices in choosing electricity emission factors, and the path from bills to a Scope 1 and 2 inventory in from utility bills to a Scope 1 and 2 emissions inventory. Owners who also report under Canada's sustainability disclosure standards feed both from the same building-level data; see Canada's climate disclosure landscape.

What condo boards and multi-residential owners need to collect

Condominium syndicates are responsible parties under the by-law, and Solution Condo is candid about the difficulty: they possess no authority to compel co-owner energy data, and privacy law restricts disclosure of individual consumption. The same summary notes that the province's electricity and gas distributors now offer an aggregated data transfer to Portfolio Manager, operational since May 25, 2023, which requires co-owner authorization. The playbook for a board or a rental owner with tenant-held accounts:

1. Build the meter inventory: every common-area account, every unit or tenant account, every fuel, and the district energy supplier if there is one.
2. Collect authorizations early in the year so aggregated whole-building data can flow into Portfolio Manager without exposing individual consumption.
3. Where aggregation is not possible, collect bills and record what is missing, so the gap is documented rather than silently zero.
4. Reconcile floor area and use types once and keep the basis. The rating divides by area and compares by use.

Common data pitfalls

Disclosure feeds the rating, so the failures that break any benchmarking submission here change a public grade.

• A gas or fuel oil account left out because it is billed to a different entity than the electricity.
• Fuel oil and propane deliveries entered as monthly consumption, when a delivery is a fill, not a month's use.
• Estimated reads followed by true-ups, which put a false spike in one month and a false dip in the next.
• Units mixed across accounts: gas in cubic metres on one meter and gigajoules on another.
• Floor area changed by a renovation or re-measurement but not in the disclosure, which shifts the intensity and possibly the band.
• Tenant or unit data missing for part of the year, so the series is complete on paper and short in fact.

Preparing for the 2027 cycle

The 2027 disclosure covers calendar 2026, the first full year after the rating thresholds were fixed. A reasonable timeline: close 2026 with the meter inventory and authorizations in hand; load and check January through December in the first quarter of 2027; reconcile floor area and use types in April; run the data quality checks and share with the City in May; submit well before June 30. Then keep the data flowing monthly, so the intensity behind the grade is tracked all year rather than discovered in a published table. Our 2026 survey of building performance standards sets Montréal's regime alongside the others now in force in Canada.

How MartinAI fits

MartinAI does not submit to the City; the owner or the syndicate does, through Portfolio Manager. What it does is turn a year of electricity, gas, fuel oil and district energy bills into validated monthly whole-building quantities with the right units, test the series for gaps, overlaps and estimated reads, keep every figure tied to its bill, and show the resulting emissions intensity as the year unfolds. For a board that has to explain a grade to co-owners, that is the difference between a surprise and a plan.

By-law 21-042 asks for something simple, complete monthly energy data for the whole building, and does something consequential with it. Get the meter inventory, the authorizations and the 12 clean months right, and the rating becomes a number you manage rather than one you receive.