The codes
Woodland Carbon Code (woodland creation), Peatland Code (peatland restoration), and forthcoming BSI Flex Standards for hedgerow and grassland carbon. Each code carries an additionality test that the BNG units must clear separately to stack.[S15]
The IPGN principle
Investing in Planet, Nature and the Green economy (IPGN) work led by IEMA and the BSI sets out the principle that stacked revenue is permitted where each unit is genuinely additional; the principle is settled, the implementation detail still developing through code-by-code consultation.
Market discount
Secondary market evidence suggests stacked Woodland Carbon Code + BNG parcels clear at 10% to 20% discount per standalone BU compared to single-revenue BU; the woodland carbon premium offsets part of the discount.