Build, Maintain, or Buy: How to Choose the Right Carbon Accounting Approach

Carbon accounting has matured rapidly. What was once a niche reporting task is now a core business process tied to investor and client expectations, supply chain requirements, board-level commitments, and external scrutiny. As a result, the systems used to calculate and manage emissions need to be accurate, scalable, traceable, and aligned with the evolving guidance of the GHG Protocol and SBTi.

For some organisations, this leads to a critical strategic decision:

Do we build a tool for carbon accounting ourselves, maintain the one we already have, or buy a purpose-built platform?

This blog walks through the real considerations behind each path with a practical framework to help sustainability professionals and decision makers choose the route that delivers the most value.

Start With the Core Question: What Are We Trying to Achieve?

Before choosing whether to build, maintain, or buy a carbon accounting tool, you need to be clear on how the system will be used and who it will serve.

First, consider your users. Is the tool intended strictly for sustainability professionals within your organisation, or do non-technical users also need access? For example, will other departments need to submit data, or will senior leaders require high-level views that are simple to interpret?

Next, clarify the role of the system. Will it be used only for reporting or will it also be used to actively manage your carbon reduction initiatives? Think about how the results will flow. Will the outputs feed primarily into other tools, systems, or processes, or will this become your master system for carbon reporting and management?

Then consider the future requirements. As organisations mature in their carbon accounting journey, the types of data collected change. You may be using spend data for purchased goods and services today, but in the future, you may need functionality to collect actual emissions data directly from suppliers. You may also face increasing requirements for assurance. In that case, your tool must be auditable, clear, and transparent in the way calculations and data sources are handled.

This step is essential because carbon accounting has layers of complexity. Some organisations want a simple footprint. Others need a complete system covering data ingestion, classification, supplier engagement, forecasting, target tracking, and audit trails.

Path 1: Build From Scratch

Some organisations choose to build their own system, usually because they believe their needs are unique, they want full control, they have engineering resources available, or they see sustainability as core to their intellectual property.

Building can work, but only when the organisation understands the full lifecycle of what they are taking on.

1. Engineering Investment and Technical Complexity

A carbon accounting platform is not a dashboard. It requires:

• Data modelling for hundreds of emissions categories
• Automated data quality checks
• Full audit trails and evidence management
• Emissions factor databases managed and updated over time
• Calculation engines that support nuanced Scope 3 methodologies

These are not small engineering tasks. They require robust product design, data engineering capacity, ongoing development, and a long-term roadmap.

2. AI Readiness: A Quiet but Critical Question

Modern carbon accounting increasingly depends on AI.

• Automated classification of spend and activity data
• Intelligent gap filling
• Supplier document parsing and validation
• Anomaly detection and data cleaning

To build this internally, organisations need:

• Training datasets
• Specialist data science talent
• Domain-specific models
• Continuous retraining and improvement

This raises an important question:

Are you prepared to build not only a carbon accounting tool, but also the AI layer that is becoming essential for accuracy and efficiency?

For most companies, this is a major hurdle.

3. Keeping Up With Methodology Changes (SBTi and GHG Protocol)

Both SBTi and the GHG Protocol are evolving.

• SBTi guidance for FLAG sectors, supplier engagement, and category-specific targets
• Ongoing GHG Protocol revisions that will reshape Scope 2 and Scope 3 expectations

An internal build must continuously adjust to keep in sync with these updates, which requires sustainability expertise and engineering work to modify the calculation engine and workflows.

This is not a build once project. It is a permanent commitment.

4. Time to Value and Opportunity Cost

Even a basic internal carbon accounting tool usually takes 6+ months to develop.

During that time:

• You risk errors in calculations
• Reduction initiatives may be delayed
• Your sustainability team is maintaining spreadsheets rather than delivering impact

You are also pulling engineering talent away from your core product or business priorities.

Path 2: Maintain or Upgrade What You Already Built

Many organisations already have internal tools, often built as a temporary solution that gradually became a permanent system:

• Excel or Google Sheets
• PowerBI dashboards
• Custom databases or scripts
• Early stage internal web apps

This is not an afterthought. It is a common and important decision point.

1. The Sunk Cost Fallacy

One of the biggest blockers to moving forward is psychological.

Many teams feel that because money or time was invested in building the current tool, they must continue using it.

But sunk cost does not equal future value. The question is not what have we spent. It is what will continuing to maintain this system cost us in accuracy, time, risk, and credibility.

2. Hidden Maintenance Burden

Internal tools often require:

• Manual updates to emissions factors
• Rework when SBTi or the GHG Protocol changes
• Fixes every time the business adds a category or business unit
• Review of fragile formulas
• One or two people who are the only ones who understand how it works

This becomes a growing operational risk as the organisation scales.

3. Structural Limitations

Internally built tools often struggle with:

• Supplier engagement workflows
• AI-supported classification
• Audit trails
• Integrations
• Multiple user roles and approval processes
• Scenario modelling and forecasting

They rarely keep pace with organisational growth or complexity.

4. When Maintaining Still Makes Sense

Keeping your internal tool is viable when:

• Your needs are simple and stable
• Your tool acts as an ingestion or pre-processing layer
• You use a dedicated platform for the heavy lifting such as calculations, audit, and reporting

For many mature organisations, the internal tool becomes a complementary component rather than the source of truth.

Path 3: Buy a Purpose Built Carbon Accounting Platform

Buying is not the automatic choice, but it is often the optimal choice for organisations that need:

• Supplier engagement at scale
• Rapid deployment
• AI-driven workflows
• Continuous alignment with SBTi and GHG Protocol
• Lower long-term ownership cost

1. Faster Time to Value

Most platforms can be implemented in weeks rather than months.

This means:

• You start reporting sooner
• You unlock insights earlier
• Your sustainability team spends time on reduction planning rather than tool building

2. Lower Total Cost of Ownership

A subscription typically includes:

• Engineering improvements
• AI model updates
• Emissions factor management
• Methodology updates
• Data security and certifications
• Support and onboarding

These are all costs you avoid carrying internally.

3. Built In AI Capabilities

Vendors have training datasets, domain knowledge, and specialised models that most organisations cannot replicate internally.

This results in:

• Faster and more accurate classification
• Automated data validation
• Supplier document parsing
• Fewer manual processes

The performance gap between internal tools and specialist AI is widening every year.

4. Alignment With SBTi and GHG Protocol

Dedicated carbon accounting platforms monitor changes and continuously update methodologies so clients remain aligned.

This removes the burden of:

• Monitoring changes
• Reworking calculation engines
• Communicating implications internally
• Ensuring defensibility during audits

Methodology alignment becomes an automatic part of the subscription.

A Practical Decision Framework: 12 Questions to Guide You

Use these questions to pressure test your direction.

1. What problem are we really solving
2. Are our needs stable or evolving
3. Do we need SBTi alignment now or in the future
4. Can we keep up with GHG Protocol updates internally
5. Do we have dedicated sustainability methodology expertise
6. Do we have engineering capacity for ongoing development
7. How essential is AI to our efficiency
8. How quickly do we need actionable results
9. Will our internal tool scale across business units and suppliers
10. Do we need audit-grade traceability and governance
11. What integrations must be supported
12. What is the long-term total cost of each option

Conclusion: Choose the Path That Delivers Real Impact

Build
Ideal for organisations with highly specific needs, deep internal engineering resources, and stable methodologies, but rare.

Maintain or Upgrade
Useful when your internal tool still serves a purpose, but recognise when it is becoming a bottleneck or a risk.

Buy
Delivers the fastest and most reliable route to accurate, audit ready carbon accounting, especially for teams that need AI capabilities, supplier engagement, and ongoing alignment with SBTi and the GHG Protocol.

Choosing to buy is not a concession. It is a strategic decision to focus your internal talent on what matters most: delivering meaningful carbon reductions rather than maintaining software.

For any questions or to learn more about our solutions, please contact us at: [email protected]