Why Does a SAP EPC Often Score Higher Than an RdSAP EPC?

I’m occasionally asked why a property’s original SAP EPC has a higher rating than a more recent RdSAP EPC. It can be confusing, particularly when the property hasn’t changed much since the first certificate was produced. However, SAP and RdSAP assessments use different types of information, and this can affect the final score.

A SAP EPC doesn’t automatically receive a better rating. The difference is usually caused by the amount of detailed information available, the assumptions the assessment has to make and the fact that SAP is generally used for newer properties.

What Is a SAP EPC?

SAP stands for Standard Assessment Procedure.

It is the methodology used to assess new-build homes, conversions and some properties undergoing a change of use. The assessment is normally completed using detailed information supplied during the design and construction process.

This can include:

• Architectural drawings

• Exact wall, floor and roof specifications

• Calculated U-values

• Insulation products and thicknesses

• Window specifications

• Heating-system details

• Ventilation information

• Airtightness test results

• Thermal-bridging calculations

• Details of solar panels and other renewable technology

Because this information is available, the SAP calculation can use values specifically relating to the property rather than relying on standard assumptions.

What Is an RdSAP EPC?

RdSAP stands for Reduced Data Standard Assessment Procedure.

It is the methodology used for most existing homes. Rather than working from a complete set of construction plans and calculations, a Domestic Energy Assessor visits the property and records the information that can be established during a non-invasive assessment.

This includes features such as:

• The property’s age and construction

• Its dimensions and layout

• Heating and hot-water systems

• Windows and glazing

• Loft insulation

• Heating controls

• Fixed lighting

• Renewable technology

An RdSAP assessment is not designed to involve opening walls, lifting floors or drilling into the building. If something cannot be seen, measured or supported by acceptable evidence, the assessor may have to use an assumption based on the property’s age and construction.

Why Can the RdSAP Rating Be Lower?

Less detailed construction information

A SAP assessment may have access to the exact U-value of a wall, floor or roof.

During an RdSAP assessment, those calculations may no longer be available. If the construction cannot be fully identified and there is no suitable supporting evidence, the assessment must use the relevant RdSAP assumption.

That assumption may not give the property as much credit as its original SAP calculation.

Insulation cannot always be confirmed

A property might have insulation inside its walls or floor, but an assessor cannot simply record it based on what an owner believes was installed.

If the insulation isn’t visible and suitable documentation isn’t available, it may not be possible to include it in the assessment. This can reduce the rating compared with an original SAP EPC that had access to the full construction specification.

SAP uses more precise information

SAP can include detailed information about thermal bridging, airtightness and ventilation.

RdSAP uses a reduced set of information suitable for assessing an existing property without carrying out destructive investigations. This makes it practical for existing homes, but some of the precise information used in the original SAP calculation may not be available.

The property may have changed

The home may also have changed since its original EPC was produced.

A boiler may have been replaced, heating controls altered or renewable technology removed. Even relatively small changes can affect the result.

The assessment methodology, fuel prices and underlying calculations can also change over time, so two certificates produced years apart should not always be expected to return exactly the same score.

New properties are usually more efficient

There is another important point: SAP EPCs are generally produced for new dwellings.

Modern properties are normally built to more recent energy-efficiency standards, with better insulation, more efficient heating, improved glazing and greater airtightness. They would therefore generally be expected to achieve a higher rating than an older property assessed using RdSAP.

This doesn’t mean SAP simply awards additional points. The property itself is often more energy efficient.

Does a Lower RdSAP Rating Mean the Assessment Is Wrong?

Not necessarily.

A difference between a SAP EPC and an RdSAP EPC does not automatically mean that either assessment is incorrect. They may have been produced at different times, using different versions of the methodology and different amounts of available evidence.

An assessor must record what can be established at the property and follow the approved RdSAP methodology. They cannot assume that insulation or another improvement is present without the evidence required to support it.

This is why paperwork can be important.

What Evidence Can Help?

If you’re arranging an EPC for a newer property, extension or converted building, it’s helpful to have any relevant documents available.

These could include:

• Building Regulations completion documents

• Approved plans

• Insulation specifications

• U-value calculations

• Window installation information

• Boiler and heating-control details

• Solar panel documentation

• Previous SAP reports or EPC information

Having the original SAP EPC on its own does not necessarily prove that every feature remains present. However, supporting construction documents may help the assessor record improvements that cannot be confirmed visually.

SAP and RdSAP Are Used for Different Situations

SAP and RdSAP are both approved energy-assessment methodologies, but they are designed for different circumstances.

SAP uses detailed design and construction information, usually for a new dwelling. RdSAP provides a consistent and practical way of assessing an existing home based on an on-site assessment and the evidence available.

A SAP EPC can therefore score higher, but it isn’t guaranteed. The result will always depend on the individual property, its energy-related features and the information available at the time.

If you need an EPC for an existing property across York, Selby, Tadcaster, Castleford, Pontefract, Knottingley or Sherburn in Elmet, contact me for a quotation.

Domestic EPCs start from £85, with certificates usually issued within 24 hours of the assessment.