You let it out
Compliance drives you, the tenant gets the saving, and you fund the work. We say that plainly rather than pretending otherwise.
You can act on the fabric, the roof and the plant you own, and on anything that falls to you between lettings. What the tenant controls day to day is theirs, and access usually needs arranging around them.
The tenant pays the bill, so the tenant sees the saving. What you get is a building that stays lettable as the minimum rating rises, and a rent and void position that reflects it. Every measure in the report is marked with who pays and who saves so the split is visible before you commit.
The ones this building type tends to suit. Each is still read against your building before anything is proposed, and a measure that does not suit yours will say so.
Ratings that lapse between lettings, and service charge recoverable work treated as though it were all yours to fund. Where a tenant would carry part of the cost or part of the benefit, that belongs in the case before it goes to committee.
Time the work to a void or a lease event where you can, because that is when access is easiest and the rating change is worth most. Check the rating and its expiry date first, since that is what governs whether you can let at all.
Read your own buildings
Add a building and its energy data, and every measure is read against it. It costs nothing and nobody contacts you unless you ask.