When a tile or brick unit knows its limestone and dolomite tonnes, should it still use the 85 and 15 percent split?
No. The Intergovernmental Panel on Climate Change (IPCC) Tier 1 equation uses 85 percent limestone and 15 percent dolomite only when the split is unknown. Its Tier 2 says it is not good practice to use a default allocation. Its reporting section says that where the 85 and 15 default is used, it should be documented.
The two equations
Tier 1 (Equation 2.14): carbon dioxide (CO2) = tonnes of carbonate x (0.85 x limestone factor + 0.15 x dolomite factor). The blended factor is 0.85 x 0.43971 + 0.15 x 0.47732 = 0.44535 tonnes of CO2 per tonne of carbonate.
Tier 2 (Equation 2.15): CO2 = (tonnes of limestone x its factor) + (tonnes of dolomite x its factor). Under it the guide says: "It is not good practice to use a default for the allocation between these two primary carbonates."
What to keep
- Purchase and issue slips that name limestone and dolomite separately.
- Tonnes as pure carbonate. If you only know the weight of carbonate rock, the guide says a default purity of 95 percent can be assumed.
- A note wherever the 85 and 15 default is used: the guide says this should be documented.
How big the difference is
The default sits about 1.3 percent above an all-limestone answer and about 6.7 percent below an all-dolomite answer. The more dolomite you really use, the more the default understates.
Does a national tier apply to one unit
The guide writes Tiers 1 and 2 for national data. Applying the same rule to one unit's records is my reading: the equations are the same and the data are yours.
A unit that buys both
- Bought: 18.0 tonnes of limestone and 12.0 tonnes of dolomite, 30.0 tonnes in all
- Default split: 30.0 x 0.44535 = 13.361 tonnes of CO2
- Known split: 18.0 x 0.43971 = 7.915, and 12.0 x 0.47732 = 5.728, total 13.643 tonnes
- Difference: 0.282 tonnes, 2.1% of the default. To two significant figures the two read 13 and 14.
Tonnes are example numbers, taken as pure carbonate with full calcination.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records, so the fuel and power lines of a furnace or kiln are on file. In the self-serve product it does not read limestone or dolomite purchases as process emissions, so the split comes from your own purchase slips.
- Process CO2 for clay products without an assay
- Fraction calcined when not measured
- Which limestone uses release CO2
- Sanitaryware carbon footprint per piece
Sources: IPCC, 2006 Guidelines, Volume 3, Chapter 2: Mineral Industry Emissions
Last reviewed 2026-11-06. Quotes and figures are from the 2006 IPCC Guidelines, Volume 3, Chapter 2. The 2019 Refinement was not checked for this page; check it if a buyer names it.