1. The two levels of requirement
They correspond to the two kinds of reconstruction. Full and partial routes require different classes.
| Kind | Requirement |
|---|---|
| Full reconstruction | reach at least energy performance value class C |
| Partial reconstruction | at least a one-class gain, for instance from class D to class C |
The two routes are covered by the article on comparing full and partial. The requirements are cumulative with other conditions, concerning building services for instance, and must be taken from the regulation as a whole.
2. What class C is as a number
Here is the detail a designer needs and which communication rarely states. It concerns the basis of the calculation.
In the support regulation class C is expressed as an energy performance value of up to 150 kilowatt-hours per square metre per year. The class is therefore a threshold rather than a judgment, and in design the number has to be calculated, with the letter following from it.
The general methodology of the energy performance value and the class scale are covered in a separate guide on building energy performance. One observation calls for care here: the general energy performance class scale and the threshold named in the support conditions are not necessarily the same version, so the applicable number must be taken from the support regulation in force rather than from the general energy performance regulation.
3. Which buildings are exempt
One exempt group is named in the conditions. The exemption has to be read from the text.
According to professional sources the class C requirement does not apply to buildings of cultural value. There have been separate application rounds for heritage-protected apartment buildings and those in conservation areas, which shows that they are treated as a distinct target group.
The precise extent of the exemption and the conditions applying to it must be checked in the regulation in force, since they have differed between rounds. The exemption does not mean that energy performance is not improved, but that the required level is adjusted to the extent of the protection.
4. What a gain means in practice
Three observations affect the volume of work, and the last two go together. They concern the baseline class and the package.
| Observation | Consequence |
|---|---|
| The class bands are not of equal width | the same gain requires different volumes of work in different buildings |
| A building near a class boundary | may move up with a small measure |
| A building in the middle of a class | needs considerably more for the same gain |
The baseline class alone therefore does not say how much work is needed: what is needed is the baseline number rather than the baseline letter. Two buildings in class D may be very different distances from class C, and that is a practical reason to commission a proper calculation before deciding.
5. What to check before design
Four things, and the fourth is the decision point. The current energy performance value as a number rather than a class. The applicable threshold from the support regulation in force. The gap between the two. And whether that gap can be closed with a realistic volume of work.
Where the gap is too large, either a larger package or a renovation without support has to be considered. The choice belongs at the start of the design.
Summary and four practical rules
Full reconstruction requires at least class C, expressed in the support regulation as a threshold of an energy performance value of up to 150 kilowatt-hours per square metre per year, and partial reconstruction at least a one-class gain. The class bands are not of equal width, so the same gain requires different volumes of work in different buildings, and two buildings in class D may be very different distances from class C. The class C requirement does not apply to buildings of cultural value, but the extent of that exemption has differed between rounds.
Four rules: work with numbers rather than class letters. Take the threshold from the support regulation in force, not from the general energy performance regulation. Check the extent of the exemption for buildings of cultural value separately. Measure the gap before choosing the works, since the gap determines the package.
This article offers professional orientation as at the date of verification. It does not replace the support regulation.