GHG Inventory Management Plan: What It Must Contain

The GHG Inventory Management Plan (IMP) is the foundational document for any organisation building a defensible GHG inventory. Under ISO 14064-3, it is the first document an assurance provider requests. Without it, or with one that does not match what you actually did, your assurance engagement will take longer and cost more.

This guide covers what your IMP must contain, the gaps that most commonly fail assurance review, and how long a credible IMP takes to build.

What Is a GHG Inventory Management Plan?

An IMP is a written policy document that governs how your organisation constructs, maintains, and improves its GHG inventory. It documents the decisions that you made — which entities are in scope, how you selected emissions factors, who owns which data — so that an auditor, or a future employee, can understand and reproduce your inventory without having to reconstruct it from interviews.

An IMP is required for any organisation seeking third-party assurance under ISO 14064-3 or ISAE 3410. It is also strongly recommended for companies reporting under CSRD/ESRS E1 (which requires limited assurance from year one), TCFD, SBTi, or CDP, where external scrutiny of your methodology is expected.

Who Needs a GHG Inventory Management Plan?

• Any organisation preparing for GHG assurance (ISO 14064-3 / ISAE 3410)
• Companies in scope for CSRD / ESRS E1 (mandatory limited assurance)
• SBTi-committed companies — Science Based Targets initiative expects methodology documentation
• CDP reporters where external verification is selected
• Organisations responding to customer or investor due diligence requests on emissions methodology

Even without a formal assurance requirement, an IMP is good practice for any company whose GHG emissions data is used in procurement decisions, financing conditions, or public reporting.

Required Contents of a GHG Inventory Management Plan

A defensible IMP covers eight core areas. Each maps to a specific line of auditor questioning.

1. Organisational boundary and consolidation approach

Define which legal entities, facilities, and operations are included in the inventory boundary, and which are excluded, with rationale. Specify your consolidation approach: equity share, operational control, or financial control. Auditors will test whether your reported boundary matches what is described here.

2. Emissions scope and source categories

List every Scope 1, 2, and 3 category you report, and every material category you have chosen to exclude. Exclusions must be accompanied by an estimated materiality percentage. The GHG Protocol requires that excluded sources account for less than 5% of total emissions — if you cannot justify that threshold, the source must be included. See our GHG Protocol guide for scope and category definitions.

3. Emissions factor selection rules

This is the most scrutinised section of any IMP. For every material emissions source, document: which factor database or source you used, the version or publication year, the geographic applicability, and why it was selected. An auditor applies the 'Valid' test: is the factor Relevant (correct activity type), Recent (latest available version), and Geographically Correct (matching the location of the activity)? Undocumented factor selection is the most common cause of audit findings. See our guide to emissions factors for database options.

4. Data collection procedures

For each emissions source, document: who owns the data (name or role), how it is collected (automated extraction, manual entry, supplier-provided), the collection frequency, the reporting cut-off date, and where the raw data is stored. This section enables auditors to trace a number from the reported total back to the source record. For example:

• Natural gas: operations team, extracted from utility billing system monthly, stored in [system name]
• Business travel: finance team, extracted from expense management system quarterly
• Scope 3 Category 1 (purchased goods): procurement team, spend data from ERP, annual cut-off December 31

5. Quality assurance and quality control

Describe your internal review process before data is submitted for reporting: who reviews calculations, what reasonableness checks are applied (e.g. year-on-year variance >20% triggers investigation), and what sign-off authority is required. Specify your materiality threshold (typically 5% of total emissions) and how you apply it to individual source corrections.

6. Base year selection and recalculation policy

State your base year and explain why it was chosen (data availability, representativeness, regulatory requirement). Then define the conditions that would trigger a base year recalculation: acquisitions or divestments exceeding a size threshold, methodology changes, discovery of a significant error, or structural changes to the business. Without a documented recalculation policy, your base year trajectory is unauditable.

7. Roles and responsibilities

Map accountability explicitly. An IMP should specify at minimum:

• Data owners: responsible for providing source data on time and in the required format
• Inventory compiler: responsible for running calculations and building the final inventory
• Internal reviewer: responsible for QA checks before submission
• Senior sign-off: executive or board-level approval of the final reported figures
• External assurer relationship: who manages the assurance engagement and provides document access

Ambiguity in roles is a leading cause of data arriving late or with errors. Auditors will ask who is accountable for each emissions source — if the answer is unclear in the IMP, it signals a weak control environment.

8. Document control

The IMP is a living document. It must include a version history, the date of last review, the author and approver of each version, and a log of material changes. Auditors will compare the current IMP version against the reporting year — if your IMP was updated after year-end to match what was actually done, that is a finding. Review and update the IMP at the start of each reporting cycle, not at the end.

Common IMP Gaps That Fail Assurance

Based on common GHG assurance findings, these are the most frequent IMP deficiencies:

• No emissions factor selection rationale: factors listed but not justified against the Valid test
• IMP describes a different process than what actually happened: written after the fact to match practice
• Missing data provenance: no record of where source data came from or who provided it
• No recalculation policy: base year adjustments made informally without documented criteria
• Roles listed by name rather than role: when staff change, accountability gaps emerge
• No version control: impossible to determine which IMP version applied to which reporting year

How Long Does It Take to Build a GHG Inventory Management Plan?

For organisations with existing emissions data and a reasonably organised data collection process:

• First-time IMP (data already collected): 3–6 weeks — primarily interviewing data owners, documenting methodology decisions already made, and writing up the boundary and EF rationale
• IMP where data collection is fragmented or manual: add 4–8 weeks to first establish repeatable collection procedures before they can be documented
• Annual IMP maintenance (subsequent years): 2–5 days — update for any methodology changes, new source categories, EF version updates, and personnel changes

A well-organised IMP materially reduces assurance cost. A first-time limited assurance engagement typically takes 8–14 weeks from kickoff to signed statement where the IMP and ESG data are well-organised. Documentation gaps — no EF rationale, incomplete boundary, missing data provenance — typically extend this by 4–6 weeks.

The GHG IMP and Your Assurance Engagement

Your assurance provider uses the IMP to design their testing programme. A strong IMP enables risk-based testing: the auditor identifies which sources are material, confirms the methodology is consistent with applicable criteria, and then samples the supporting data. Without an IMP, the auditor must reconstruct your methodology through interviews — which adds cost and creates a higher risk of findings. See our full guide to GHG assurance under ISO 14064-3 for what auditors test and how to prepare your data.