An EPC assessment is a look at the building, not at the people living in it. I measure every room and record the walls, roof, floors, windows, heating, hot water, ventilation and lighting. That information goes into the government’s method, which works out the rating. Your bills, your thermostat and your appliances play no part.
The visit, in order
- Outside first. How the walls are built matters a great deal, and the outside often gives it away: brickwork with every brick laid lengthways usually means a cavity wall, while a pattern with brick ends showing usually means a solid one. Extensions get the same look, as they may be built differently from the main house.
- Every room measured. I go room by room with a laser to work out the floor area of each part of the home.
- The loft. From the hatch I record the insulation and its depth. Rooms in the roof are measured too, gables included, and a flat with a shop or an unheated space above is recorded as such.
- Walls and floors. The construction and any insulation, including insulation added to floors later. Where there is paperwork, the actual thickness of wall insulation can be used.
- Windows and doors. Every window is measured, and the glazing, the frame and roughly when it was fitted are recorded.
- Heating and controls. The boiler or other main heating, and how it is controlled: room thermostat, timer and radiator valves all count.
- Hot water. Where it comes from, and for a cylinder its size and insulation.
- Ventilation. Open fireplaces, chimneys, flues and any mechanical ventilation.
- Lighting. The bulbs are counted and I note which are LEDs.
- Anything generating energy. Solar panels, and batteries or diverters fitted to them.
When something cannot be seen
The method used for existing homes, called RdSAP, works from a set of assumptions about the home, which keeps down how much an assessor has to collect. The catch is that anything which cannot be seen or proved is recorded as the worst reasonable case for the home’s age and construction. Insulation hidden in a cavity, under loft boards or beneath a floor is the usual example. Paperwork fixes it, which is why preparing for your EPC starts with finding documents.
What is not part of it
- How you live. The rating assumes a standard household, so how warm you keep the home and how many people live there make no difference.
- Appliances. Fridges, washing machines and televisions are not counted; the calculation covers heating, hot water, lighting, and the pumps and fans that serve them.
- The condition of the building. An EPC is not a survey of damp, cracks or the roof. That is what a buyer’s survey is for: EPC, floor plan or survey explains the difference.
After I leave
I enter everything into approved software, check it, and lodge the certificate on the government register, within 72 hours as standard. It is emailed to you as a PDF the moment it is on there, with the recommendations for improving the rating. From then on it is public: anyone can look it up by postcode, and it is valid for ten years. The method itself was updated in June 2025, so a new certificate can differ from an old one for reasons that have nothing to do with the home; RdSAP 10 explains what changed.
Common questions
How long does an EPC assessment take?
Usually 30 to 45 minutes for a flat or a typical house, when every room, the loft hatch, the boiler and the meters can be reached.
Does the assessor need to go into the loft?
I need to reach the loft hatch to see the insulation and its depth. If the hatch is blocked, the depth cannot be recorded and the method assumes the worst reasonable case.
Does an EPC assessment check my appliances?
No. It covers the building, its heating, hot water, lighting and the pumps and fans that serve them, not the appliances you plug in.
Is an EPC assessment a house survey?
No. An EPC rates energy efficiency. A survey reports on the condition of the building, such as damp and repairs, and is something a buyer arranges.
Can I be out during the assessment?
Yes, as long as someone can let me in and give me access to the whole home: a tenant, an agent with keys or anyone you trust.
Where to go next
Preparing for your EPC, what the rating means, and what to do if you think it is wrong.
Sources for this guide: GOV.UK, Standard Assessment Procedure (updated 8 June 2026); Elmhurst Energy, “SAP 10 analysis of changes” (13 May 2025); Energy Saving Trust, “Cavity wall insulation” (updated 8 May 2026); GOV.UK, reforms to the Energy Performance of Buildings regime: partial government response (January 2026, updated 9 March 2026); RICS, House surveys: the costs, types and benefits of an RICS Home Survey. Read 24 October 2026; GOV.UK and RICS checked again 4 November 2026.