How to Prepare Your Property for an EPC Assessment

A domestic energy assessor walks into your property and scores it based on what they can see and verify. If they can't confirm that cavity wall insulation exists, they record "no insulation" — and your EPC rating drops accordingly. This isn't the assessor being difficult; they're legally prohibited from assuming unverified installations.

The result is that properties can receive lower scores when assessors cannot verify installed measures. For landlords near the Band E threshold, that can mean the difference between compliance and needing improvements or an exemption.

Why Worst-Case Defaults Hurt Your Rating

The Reduced Data Standard Assessment Procedure (RdSAP) requires assessors to use standardised assumptions when physical evidence isn't available. The assessment is non-invasive — assessors can't lift floorboards, drill into walls, or dismantle heating systems to check what's behind them.

So when documentation is missing:

• Wall insulation may be recorded using an age-based default if the assessor cannot verify an installation
• Loft insulation may be recorded using an age-based default if its depth cannot be verified
• Boiler efficiency defaults to a generic figure for the boiler type and age bracket
• Hot water cylinder insulation defaults to a thin factory-applied jacket

Each default can lower the SAP score. A property with 270mm of loft insulation that the assessor cannot verify may not receive full credit for that installation, which can affect a rating near a band boundary.

The Pre-Assessment Preparation Checklist

Building fabric evidence:

• Clear the loft hatch and make sure the assessor can safely access the loft space — they need to measure insulation depth directly
• If cavity wall insulation was installed, locate the installer's guarantee certificate (CIGA certificates are the standard for cavity wall insulation installed under guarantee)
• For solid wall insulation (internal or external), have building control completion certificates or installer invoices available
• If underfloor insulation exists, have the installer documentation ready — assessors can't see under floors

Heating system documentation:

• Find the boiler's model number and commissioning certificate — the assessor needs the exact make and model to look up the PCDB (Product Characteristics Database) efficiency figure instead of using a generic default
• If you've upgraded to a condensing boiler, the difference between the generic and PCDB figure can be significant
• Locate heating control documentation: programmable thermostat, TRVs (thermostatic radiator valves), and any zone controls should all be visible and operational during the visit
• For hot water, check whether the cylinder has a factory-applied foam jacket or an aftermarket one — the assessor records the type and thickness

Fixed lighting:

• Count your low-energy (LED or CFL) light fittings versus traditional ones — the assessor records the proportion of fixed low-energy lighting across the whole dwelling
• Replacing remaining halogen or incandescent fittings with LEDs before the visit is one of the cheapest rating improvements available

Windows and doors:

• If double glazing was installed, locate the FENSA or CERTASS certificate — without it, the assessor may record the glazing age as unknown and apply a default U-value
• For any replacement windows, check whether you have Building Regulations completion certificates

What Doesn't Affect Your EPC Rating

Assessors score the fixed building fabric and systems. These common items don't factor into the rating:

• Portable heaters, plug-in radiators, or freestanding appliances
• Smart thermostats that aren't hard-wired into the heating system
• Furniture, curtains, or soft furnishings
• Plug-in lighting (only fixed ceiling and wall fittings count)
• The property's current occupancy or energy bills

On Assessment Day

Make sure the assessor can access every room, including the loft space and any utility cupboards containing the boiler or hot water cylinder. Have your documentation folder ready — don't assume they'll come back for evidence later. The assessment is typically a single visit lasting 30–60 minutes for a standard property, and what they record on that visit is what gets lodged on the central register.

If the assessor identifies that your property is near a band boundary, ask which specific improvement would tip the rating. The recommendation report generated with every EPC lists suggested measures in order of cost-effectiveness, but the assessor can often tell you on the spot which one moves the needle.

Our EPC and MEES Compliance Guide includes a full pre-assessment preparation checklist and a breakdown of how each improvement type affects your SAP score.

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