The Chancery Lane Project, a collaborative effort of UK lawyers to develop new contracts and model laws to help fight climate change, has published model clauses for Design and Build Contracts to make energy efficiency part of Practical Completion. If the required standards are not achieved, then the contractor would have to retrofit the building until they are satisfied as there are no liquidated damages in lieu.
The model clause is available in the attached volume at page 56 (“Mary’s Clause”).