Following the 2006 IPCC guidelines FoundationFootprint™ includes the ability to specify a "tier" to rate the reliability and methodological complexity of emission factors and activity data.

Three tiers are described for categorizing both emissions factors and for activity data. Tier 1 is the basic method, frequently utilizing IPCC-recommended country-level defaults, while Tiers 2 and 3 are each more demanding in terms of complexity and data requirements.

It is possible that a mixture of tiers will be needed to complete one emissions inventory, reflecting the availability of information in different parts of a country or organisation. In some cases calculation of the emissions from a single source will require use of different tiers of activity data or different tiers of activity data and emission factors especially when calculating supply chain or product emissions.

It is good practice to report tiers for all emission sources included in the inventory. In some cases where aggregate reporting is a significant goal, Country/Regional Supplements may make this a mandatory requirement. In any case organisations should strive to utilize the highest tier of data which is available.

I most cases FoundationFootprint™ assigns the tiers for you. For example, the default emission factors pre loaded for your location(s) are tiered. When adding your own emission factors you can set the tiers as you see fit. And activity data that comes into FoundationFootprint™ from invoices from your supplier are also automatically tiered.

Some standards and regional environmental programs recommend or insist on the use of tiers in inventories. Nevertheless, tiering gives an organisation and their stakeholders more confidence in the accuracy and validity of their GHG Inventory.