Data Estimation Rules

Introduction

As a general rule, GRESB Participants must use actual data (i.e., non-estimated data) when reporting on aspects of Energy, GHG, Water, and Waste in the Performance Component.

However, when actual data is partially unavailable, participants may estimate, in accordance with GRESB estimation rules, to fill the gaps.

This page provides general estimation guidelines as well as guidance for borderline cases and practical examples of dos and don’ts.

Compliance with these guidelines is mandatory to ensure the accuracy and credibility of GRESB benchmarking data. GRESB reserves the right to contact participants to ensure full compliance with the Estimation Methodology below. Non-compliance with the GRESB reporting requirements may lead to a formal request from GRESB to adjust the entity’s reported data.

In 2026, GRESB clarified guidelines for data estimation to ensure consistent application and higher result integrity. For more details on the context of these clarifications, refer to the 2026 Standards Updates page.

Estimation Rules

General Estimation Guidelines

When data is partially unavailable, estimating asset-level data is allowed under two specific conditions:

1. The missing data does not exceed either of the following limits:

20% rule: Estimated data must not exceed 20% of the total period for which actual data is available. GRESB requires participants to report data for two consecutive reporting years. Estimations should be calculated for the longest continuous period for which actual data is available in cases where an asset has different coverage periods.

• Example: Do: If actual data for a reporting year is available for six months, estimated data for the missing months cannot exceed 1.2 months (20% of the six-month period). Alternatively, if an asset has data from January to March and from May to December, the estimation limit should be calculated based on the longest consecutive period in which data is available—May to December.

Three-month cap: This rule limits the amount of estimated data to a maximum of three months across both reporting years, even if the 20% rule would otherwise allow for more.

• Example: Do: If actual data is available for 10 months in Year 1 and 10 months in Year 2, the 20% rule allows estimating up to two months for each year (four months total). However, the total estimated data reported across both years must be limited to three months. Participants can decide how to allocate the allowable estimated data across the two years, as long as they comply with the 20% rule and do not exceed the three-month cap across both years.

• The three-month cap is used because of the frequency of quarterly reporting from tenants and/or utility companies. In practice, performance data from the final 3 months of the reporting year can be estimated if the prior 21 months have performance data.

1. The available data must be of the same type:

Estimation of asset-level data is only allowed when the available data covers the same performance aspect (Energy, GHG, Water, or Waste), area type (Base Building, Tenant Spaces, or Whole Building), and utility type (for energy, this means fuels, electricity, and district heating and cooling).

• Example: Do: If 10 consecutive months of electricity consumption data are available (from January 1st to October 31st) for all tenant spaces in an asset classified as Base Building and Tenant Spaces, participants can estimate the missing two months. However, the estimation must be based on the same utility type (electricity) and area type (Tenant Spaces). In this case, the data scope is 'electricity - Tenant Spaces.'

• Example: Don't: An asset has 12 months of fuel data but 0 months of electricity data; therefore, the entity cannot estimate electricity consumption from the fuel data.

Assets whose data availability does not cover the full year (> 355 days) for two consecutive reporting periods will be excluded from Like-For-Like calculations.

Estimation for Inconsistent Data Coverage Periods

Sometimes, when a single asset has multiple utility types and/or data sources, the coverage periods of the data can differ significantly. In these cases, the data availability period must be determined based on the overlapping timeframe during which actual data from all utility types (only applicable to energy) or meter readings (applicable to energy and water) is available.

Example of estimation for inconsistent utility types (i.e., fuel, district heating and cooling, and electricity)

• An asset has 12 months of electricity data but only six months of district heating and cooling data. The data availability period should reflect the overlapping six-month period across both utility types. Estimation for the remaining months should be done according to the general estimation rules mentioned above.

Example of estimation for inconsistent meter readings

• An asset has four meters, two of which have 12 months of data coverage, one has eight months of coverage from January to September, and another has five months from January to June. In this case, the data availability period should be based on the overlapping period across meters, which is five months. Estimation for the remaining months should be done according to the general estimation rules mentioned above.

Example of estimation when data availability has a gap in the middle

• An asset has six months of data from January to July and three months from October to December. If participants cannot bridge the data gaps through the advised data estimation above, it is required to pick the segment in the year for which more months of data available are known and report only that segment.

Estimation for Waste Data

Waste Tonnage

GRESB allows participants an exception to the general estimation guidelines noted above for waste data. The minimum missing data rules do not apply to waste in the context of the circumstances described here.

If a participant does not know an asset’s actual waste tonnage but can obtain the points below within the reporting period, the participant can convert this to a total waste tonnage for that period. The required data points are:

1. The number of waste bins per asset

2. The volume of waste bins

3. The filling level of the bins

4. The frequency at which the bins have been picked up (assuming the frequency remains constant throughout the year)

In cases where (3) is unknown, participants should apply a 'worst case' scenario, assuming waste bins were full at each collection.

Disposal Routes

Participants cannot use national or local waste disposal statistics, averages, or trends to estimate an asset’s waste disposal route split. Disposal route reporting must be based on asset-specific data (e.g., from waste contractors, haulers, or onsite measurements). If the actual proportion by disposal route is not known, report it as “Other/unknown."

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GRESB does not prescribe conversion factors. GRESB Participants are encouraged to refer to the US EPA guidelines for volume-to-weight conversion factors.

Alternatively, please consult one of GRESB's Partners for guidance and support.

Prohibited Practices

If the entity cannot adhere to the rules below, it must report 0% coverage for the relevant data type.

Full-Year Data Absence

The purpose of allowing estimations of asset-level data is to fill in small data gaps, not to replace missing data for the current reporting year entirely. Therefore, when data for the current reporting year is completely missing, it is not allowed to use data from the previous reporting year for estimation purposes.

• Example: Do: If no actual consumption data is available for an asset for the current reporting year, participants cannot use data from the previous year to estimate the missing data.

Prorating Consumption Data

1. Across time

It is not allowed to estimate beyond the overlapping period when assets have multiple data meters with varying data coverages.

• Example: If one meter has 12 months of data and another has six months, the estimation must be limited to the overlapping six-month period. An estimation for the remaining months should be done according to the general estimation rules mentioned above.

1. Across area

It is not allowed to base estimations on aggregated floor area or average across individual assets based on their area. All estimations must be based on actual metered data specific to each asset and area type. Aggregated data from different area types or other assets cannot be used to fill in missing or unmeasured data.

• Example 1: If consumption data is available for 10 months for all tenant spaces in an asset classified as ‘Base Building and Tenant Spaces’, participants cannot estimate the two missing months using data from areas outside the Tenant Spaces, such as Common Areas or Shared Services.

• Example 2: If consumption is available for multiple assets at an aggregate level, and not for each individual asset, it is not allowed to estimate the energy consumption of a specific asset by averaging or extrapolating from the total aggregated consumption of all assets. Each asset's consumption must be based on its own metered data.

1. Waste Specific

It is not allowed to divide waste data when more than one asset shares several bins, and it is unclear which bins are solely dedicated to a given asset. Dividing waste data proportionate to floor area or evenly is not acceptable because there is no certainty that assets with more floor area produce more waste (and vice versa), nor that each asset contributes equally to the total waste amount.

Using National Benchmarks or Other Sampling Methods

It is not allowed to use generic data sources for estimation purposes. All estimations must be based on the actual data available, subject to the applicable rules for estimation.

Additional Reporting Considerations

Disclose Estimation Use

Participants who use estimates are required to provide additional information in the open text box below each performance indicator table. Specifically, they must disclose the:

• Estimation methodology used

• Proportion of total reported data that is estimated (based on the time interval for which estimates are used, expressed as a percentage of the total actual data reported in that performance indicator); note that this percentage cannot exceed 20%

• Reason for using estimated values

This information will be used for reporting purposes only and will not impact scores.

If estimated consumption or emission values were reported in the previous GRESB reporting year, participants are required to replace it with actual data in subsequent GRESB submissions in order to use it as a basis for estimation.