DEV Community

Cover image for I Reverse-Engineered NYC Local Law 97. Here's What 40% of Buildings Are Getting Wrong.
Tinashe Nedi
Tinashe Nedi

Posted on • Originally published at linkedin.com

I Reverse-Engineered NYC Local Law 97. Here's What 40% of Buildings Are Getting Wrong.

#climatetech #nycbuildings #proptech #smartbuildings

LL97 Penalties Aren’t What Most Calculators Show

The $268/Tonne Problem

NYC Local Law 97 is one of the most aggressive building performance standards in the United States. Buildings larger than 25,000 square feet can be fined $268 per metric tonne of CO₂e above their annual emissions limit.

After reviewing hundreds of LL97 estimates, I noticed the same issue repeatedly appearing in reports and calculators: the carbon math is often wrong.

Most tools use the EPA eGRID electricity emissions factor for NYISO (0.000371 tCO₂e/kWh).

LL97 does not use EPA eGRID values.

That difference alone can completely change a building’s projected penalties.

What LL97 Actually Uses

According to 1 RCNY §103-14 Table 1, the official LL97 emissions coefficients are:

Fuel Source LL97 Coefficient EPA eGRID (NYISO) Difference
Electricity 0.000288962 tCO₂e/kWh 0.000371 tCO₂e/kWh -22%
Natural Gas 0.00005311 tCO₂e/kBtu 0.0000531 tCO₂e/kBtu ≈0%
#2 Fuel Oil 0.00007421 tCO₂e/kBtu 0.0000749 tCO₂e/kBtu -1%

The biggest discrepancy is electricity. LL97’s electricity coefficient is roughly 22% lower than the EPA value most calculators rely on.

Why the Numbers Are Different

LL97 was written using New York City’s 2018 grid baseline.

EPA eGRID values are updated regularly to reflect the current generation mix. Since 2018, NYC’s electricity supply has shifted, with greater reliance on natural gas and fewer hydroelectric imports. As a result, EPA values now show higher emissions.

LL97 intentionally locked in the earlier baseline so building owners would not be penalized for grid changes outside of their control.

Real Example: 75,000 SF Office Building

Building Information

  • Annual electricity usage: 1,250,000 kWh
  • Annual natural gas usage: 8,500 therms
  • Building occupancy: Office (Group B)
  • Building size: 75,000 SF

2024–2029 LL97 Limit 

0.00536 tCO₂e/sf
Enter fullscreen mode Exit fullscreen mode

Incorrect Calculation Using EPA eGRID 

elec_co2 = 1_250_000 * 0.000371
gas_co2 = 850_000 * 0.00005311

total_co2 = elec_co2 + gas_co2  # 508.6 tCO₂e

intensity = total_co2 / 75_000  # 0.00678 tCO₂e/sf

limit = 0.00536

excess = (intensity - limit) * 75_000  # 106.5 tCO₂e

penalty = excess * 268  # $28,542/year
Enter fullscreen mode Exit fullscreen mode

Using EPA coefficients produces a projected penalty of:

$28,542 per year
Enter fullscreen mode Exit fullscreen mode

Correct Calculation Using Official LL97 Coefficients 

elec_co2 = 1_250_000 * 0.000288962
gas_co2 = 850_000 * 0.00005311

total_co2 = elec_co2 + gas_co2  # 406.3 tCO₂e

intensity = total_co2 / 75_000  # 0.00542 tCO₂e/sf

limit = 0.00536

excess = (intensity - limit) * 75_000  # 4.5 tCO₂e

penalty = excess * 268  # $1,206/year
Enter fullscreen mode Exit fullscreen mode

Using the actual LL97 coefficients changes the result dramatically:

$1,206 per year
Enter fullscreen mode Exit fullscreen mode

That is a difference of more than:

$27,000 annually
Enter fullscreen mode Exit fullscreen mode

from the exact same building data.

The 2030 Compliance Cliff

LL97 has two major compliance periods:

  • 2024–2029
  • 2030–2034

The second period is where the law becomes significantly more aggressive, with emissions limits dropping by roughly 40–50% depending on occupancy type.

For this same office building:

Compliance Period Estimated Penalty
2024–2029 $1,206/year
2030–2034 $41,832/year

Many calculators fail to model this transition correctly.

Getting LL97 Calculations Right

1. Use Official LL97 Coefficients 

LL97_COEFFICIENTS = {
    "electricity": 0.000288962,
    "natural_gas_kbtu": 0.00005311,
    "fuel_oil_2": 0.00007421,
    "fuel_oil_4": 0.00007753,
    "district_steam": 0.00004489
}
Enter fullscreen mode Exit fullscreen mode

These values come directly from 1 RCNY §103-14 Table 1.

2. Identify the Correct Occupancy Group

LL97 emissions limits are occupancy-specific.

An office building, multifamily property, hospital, hotel, or retail space will all have different allowable emissions intensities under Table 2.

Incorrect occupancy classification can invalidate the entire calculation.

3. Include DER (Distributed Energy Resource) Deductions

LL97 allows buildings to deduct qualifying renewable generation from their reported emissions.

For example:

der_deduction_tco2e = annual_solar_kwh * 0.000288962
Enter fullscreen mode Exit fullscreen mode

A 50 kW rooftop solar installation generating 65,000 kWh/year would reduce emissions by:

deduction = 65_000 * 0.000288962  # 18.8 tCO₂e/year

penalty_saved = 18.8 * 268  # $5,038/year
Enter fullscreen mode Exit fullscreen mode

Over 25 years, that becomes:

$125,950 in avoided LL97 penalties
Enter fullscreen mode Exit fullscreen mode

before even considering utility savings.

API Example

The Energy Audit Automation API handles LL97 calculations automatically using the correct coefficients and occupancy rules.

Request 

curl -X POST https://energy-audit-api.p.rapidapi.com/audit/full \
  -H "X-RapidAPI-Key: YOUR_KEY" \
  -d '{
    "property_type": "office",
    "sq_ft": 75000,
    "annual_kwh": 1250000,
    "annual_therms": 8500,
    "city": "nyc",
    "grid_region": "NYISO"
  }'
Enter fullscreen mode Exit fullscreen mode

Response 

{
  "ll97": {
    "emissions_limit_2024": 0.00536,
    "your_emissions": 0.00542,
    "excess_tco2e": 4.5,
    "penalty_2024_usd": 1206,
    "penalty_2030_usd": 41832,
    "compliant_now": false,
    "compliant_2030": false,
    "source": "1 RCNY §103-14 Table 1 & 2"
  }
}
Enter fullscreen mode Exit fullscreen mode

Red Flags in LL97 Proposals

Watch for these signs when reviewing vendor reports or compliance tools:

  • “EPA emission factor” referenced without LL97 citations
  • No source documentation for penalty calculations
  • Identical penalties shown for both 2024 and 2030 periods
  • No occupancy group classification included
  • No explanation of DER deductions or renewable offsets

Further Reading

Final Takeaway

A surprising number of LL97 estimates are based on the wrong carbon coefficients.

If a calculator or proposal does not explicitly reference 1 RCNY §103-14, there is a good chance the penalty estimate is inaccurate.

Under LL97, the difference between using EPA values and the actual legal coefficients can mean the difference between compliance and tens of thousands of dollars in annual penalties.

Top comments (0)