You have probably seen DER or TER mentioned within building regulations documentation (or even a planning condition), and are likely to be confused as to what it means... DER & TER relate to the target and actual carbon emissions of a new-build dwelling.
Energy assessors use the DER/TER emissions figures to guide the design team, establishing where a building may be underperforming against UK Part L compliance requirements.
The Dwelling Emission Rate (DER) and the Target Emission Rate (TER) are the primary CO2 factors that are measured by SAP Calculations. The DER/TER figures determine whether a new dwelling passes or fails on its carbon emissions targets set within Part L of the building regs.
The design-stage SAP Calculations provide a carbon target (TER) - this is the target CO2 emissions rate which must be achieved by the proposed dwelling (DER).
DER & TER CO2 emissions rates are measured in kgCO2/m² [i.e. kg of CO2 per m²]
The TER figure is derived from assumptions made for a notional dwelling of the same type & size, using the same heating fuel as the one proposed.
Although there are other compliance criteria which mean a pass or fail within SAP (fabric, design, controlled services, air tightness) if this primary target is not achieved the dwelling will not pass.
Fabric Energy Efficiency (FEE) also affects the SAP calcs, and is the secondary element in determining whether a dwelling passes or fails within the calculations.