The amount of PTZ given also depends on the ratio of energy expertise and energy class housing (classes A to G). It is effectively equal to a percentage of the overall cost ceiling.
| Zone A | Zone B1 | Zone B2 | Zone C | |
| New BBC 2005 | 40% | 35% | 30% 25% | |
| Nine non-BBC | 27% 22% | 17% 15% | ||
| Former A to D | 20% 20% | 20% 20% | ||
| Old E and F | 10 | % 10% | 10% | 10% |
| Former G | 5% 5% | 5% 5% |