Start with the fabric, not the boiler
A high-output heating system in a leaky building is an expensive way to warm the outdoors. Loft insulation, wall insulation and draught-proofing reduce the heat demand that the heating system has to meet, and they improve the EPC rating directly. Do the fabric work first and a smaller, cheaper system will do the job.
Fix the cheap losses before the expensive ones
Draughty windows, unsealed doors, open chimneys and uninsulated pipework are low-cost to address and immediately improve comfort. They also stop the bigger measures from being undermined — insulation performs poorly in a building that is constantly flushed with cold air.
Treat airtightness and ventilation together
Making a building airtight without thinking about ventilation just moves the problem, usually onto the walls as condensation. Whatever you seal, plan how moisture-laden air leaves the building, whether that is background vents, extract fans or a proper ventilation strategy.
Get an assessment before you commit
An EPC assessment gives you a baseline and a ranked recommendation list. The value is not the certificate itself but knowing which measures your particular property rewards, and which ones are only worth doing if something else comes first.
Think about order of work, not just list of work
Internal wall insulation, replastering, redecorating and new heating all interact. Sequencing them properly means the plastering happens once and the decorating is not undone by the next trade through the door.
This guide explains how the work is normally approached. What your property needs depends on its construction, condition and existing systems — a survey is the only way to know for certain.