Double materiality is where most sustainability reporting projects stall. It arrives sounding like a technical compliance exercise, somebody quotes a fee for running a workshop series, and the whole thing gets deferred another year.
It is not that complicated. It is two questions, asked of the same list of topics, from two directions.
The two questions
Impact materiality looks outward. How does our business affect people and the environment? This is assessed on the severity of the effect, meaning how bad, how widespread and how hard to reverse, and on how likely it is. Crucially it does not depend on whether the impact costs the company anything. A business can have a material impact on a local water supply while paying nothing for it.
Financial materiality looks inward. How could this topic affect our financial position, performance, cash flows, access to finance or cost of capital, over the short, medium and long term?
A topic is material if either answer is yes. That is the whole mechanism, and the reason the two cannot be merged into a single score: they measure different things and a topic can be severe on one and negligible on the other.
The two do connect over time. An impact that is free today becomes a cost when it is regulated, priced or litigated, which is why today’s impact-material topic is often tomorrow’s financially material one.
Running it yourself
Start from a list rather than a blank page. Take the topic list from whichever framework you report under and work through it. Inventing your own categories wastes a week and produces something nobody can benchmark.
Narrow by your value chain. Walk your business from inputs to end of life and ask which topics genuinely arise where. A professional services firm and a food manufacturer should produce visibly different shortlists. If yours looks generic, you have skipped this step.
Assess impact. For each topic, record the affected group, severity across scale, scope and remediability, and likelihood. Note whether the impact is actual or potential, and whether it comes from your own operations or your value chain.
Assess financial effect. For each topic, note the mechanism, not just a score. Carbon pricing, a customer requirement you would fail to meet, an insurance cost, a recruitment problem, a facility covenant. Then size it roughly and place it on a time horizon.
Talk to people who are affected. Proportionate, structured conversations with a few customers, your main suppliers, a lender and a group of employees will tell you more than a survey. Record who, when and what they said.
Set a threshold and apply it consistently. Then write down what fell below it and why. The exclusions get challenged more than the inclusions.
Document it as though it will be assured
This is the part that determines whether the exercise was worth doing. Assurance providers, and increasingly lenders and large customers, will ask how you reached your conclusions, not just what they were.
Keep, in one place: the topic list you started from and its source, the criteria and threshold you applied, the score or conclusion for each topic on both dimensions with the reasoning, who was consulted and when, who approved the result and at what level, and the date.
The reasoning column is the one that matters. A spreadsheet of scores with no explanation cannot be defended twelve months later by someone who was not in the room.
Getting it wrong in the usual ways
Collapsing both dimensions into one score, which quietly turns it back into single materiality and loses every impact-only topic.
Scoring everything medium, which is what happens when nobody wants to argue. If nothing is high and nothing is low, no decision has been made.
Running the assessment and then publishing a report covering different topics, which is the easiest inconsistency for a reviewer to spot and the hardest to explain.
Treating it as a one-off. Governance is part of the exercise: who owns it, who signs it off, when it gets revisited.
What it is for
The output is not a document. It is a decision about where to spend effort. A proper assessment tells you which four or five topics deserve real data collection, real targets and real disclosure, and gives you a defensible reason for saying the rest do not.
That focus is worth more than the report it feeds.