PAS 2035 is the British standard that governs domestic retrofit. If a property is being improved with public money — ECO4, or most council-run schemes — the work has to follow it. It is also the reason a retrofit assessment is a very different job from an EPC.

Why the standard exists

Because a decade of well-meant retrofit went wrong. Homes were insulated without regard to ventilation, and the result was condensation, mould and, in the worst cases, damaged fabric. PAS 2035 exists to stop measures being installed in isolation, by forcing someone to look at the whole building first.

That is the core idea worth understanding: a whole-house approach. You are not allowed to bolt insulation onto a damp, unventilated house and call it an improvement.

What the assessment covers

  • Occupancy assessment. How the household actually uses the home — heating patterns, hot water, how many people, whether anyone is home during the day, whether anyone is vulnerable to cold or to poor air quality.
  • Property condition survey. Structural condition, damp, mould, and existing defects. Anything that would make insulation a bad idea has to be found before, not after.
  • Ventilation assessment. Whether existing ventilation is adequate, and what it will need to be once the building is made more airtight. This is the part that was missing from the old approach.
  • Energy assessment (RdSAP). The baseline model the Retrofit Coordinator designs improvements against.

Who does what

PAS 2035 defines separate roles deliberately. The Retrofit Assessor gathers the evidence. The Retrofit Coordinator takes that evidence, applies a risk rating, and produces the improvement plan. A Retrofit Designer handles technical detail on complex measures, and the installer does the work. Separating assessment from installation is the point — the person specifying the work should not be the person selling it.

How long it takes

Two to three hours on site for a typical home, against 30 to 45 minutes for an EPC. That difference is the honest measure of how much more is involved.

Do you need one?

If you are applying for funded work, almost certainly yes — it is the gateway, not an optional extra. If you are paying privately and simply want to know what to do to your house in what order, it is still the most thorough answer available, and considerably more useful than an EPC recommendation list.

You can read more about what we cover on our PAS 2035 retrofit assessment page.