SAP vs RdSAP: What’s the Difference and Which One Do You Need?

Energy Performance Certificates (EPCs) are a legal requirement for selling, letting, or building homes in the UK. But when it comes to getting one, there's often confusion between two key methods of assessment: SAP and RdSAP.

At Harpr Surveyors, we provide both types of EPCs - but which one applies to your property depends on how and when it was built. This post will help you understand the distinction, explain what each method involves, and outline how we can help, whether you're based in Cornwall or elsewhere in the UK.

What Is SAP?

SAP stands for Standard Assessment Procedure, and it's the official methodology used to assess the energy performance of newly built homes, conversions, and in some cases, extensions.

If you're constructing a property from scratch or converting a non-domestic building (like a barn) into a home, you'll need a SAP assessment to show that the building meets energy efficiency standards under Building Regulations.

This process happens in two stages:

• Design Stage: A provisional calculation is made before building begins, using architectural drawings and specifications.
• As-Built Stage: Once construction is complete, the assessment is updated with finalised details to produce the official SAP EPC and a Building Regulation Compliance Report.

SAP assessments involve detailed calculations and input from architectural plans. Because of this, they can't be based on visual inspections alone.

At Harpr Surveyors, we provide SAP assessments for any suitable property across the UK, whether you're building a single house or managing a multi-unit development.

What Is RdSAP?

RdSAP, or Reduced Data SAP, is the method used for assessing the energy efficiency of existing homes. It was introduced as a simplified version of SAP that can be carried out through a site visit, without requiring full architectural plans.

If your property was built and signed off by Building Control before:

• 6 April 2008 in England and Wales
• 30 April 2008 in Northern Ireland
• 7 January 2013 in Scotland

…it's considered an existing dwelling, and RdSAP is the appropriate method for your EPC.

This type of assessment is typically required when a home is being sold or rented. It involves a trained Domestic Energy Assessor inspecting features such as insulation, heating systems, and glazing. Assumptions are applied where data isn't visible, based on national conventions.

We offer RdSAP EPCs exclusively across Cornwall, including St Austell, Truro, Newquay, Falmouth, and surrounding areas. It's also worth noting that in order to get a better energy rating, you may want to explore our MEES Reports or our post about them.

SAP vs RdSAP: Key Differences

Although both methods result in an EPC, their processes and purposes differ significantly. Here's how they compare:

Which One Do You Need?

As a general rule:

If your home is already built and you're selling or letting in Cornwall, you'll need an RdSAP EPC.

If you're building, converting, or extending a property anywhere in the UK, you'll need a SAP EPC.

If you're unsure whether your property qualifies as new or existing - especially in cases where work has recently been completed - we can help you clarify that before booking.

How Harpr Surveyors Can Help

At Harpr, we're accredited to deliver both SAP and RdSAP EPCs, with a clear service area split:

RdSAP EPCs for existing homes: Available throughout Cornwall, with flexible appointments and fast turnaround.

SAP EPCs for new builds and conversions: Available across the UK, supported by detailed plan-based assessments and Building Regulation compliance reports.

We're happy to guide homeowners, landlords, architects and developers through the process to make sure you get exactly the right type of assessment.

Frequently Asked Questions

Can I get an RdSAP EPC for a new build?

No. Only a full SAP EPC is valid for new dwellings. However, if a home is newly completed and officially signed off, an RdSAP EPC may be lodged for non-compliance purposes - such as sale or rental - provided this is made clear.

Is an EPC required when selling a home?

Yes. Homes being sold or let require a valid EPC. In Cornwall, we offer RdSAP EPCs for this purpose.

How long does an EPC last?

EPCs are valid for 10 years, unless you've made major changes to the property that affect energy performance.

What happens if I get the wrong type of EPC?

An incorrect EPC could delay sign-off or invalidate compliance. If in doubt, we're happy to advise before booking.

What is the lead time for a SAP or RdSAP EPC?

99% of all RdSAP EPCs are delivered as soon as the site visit has been completed - that last 1% relates to properties we request additional information for such as insulation or glazing verification. SAP calculations are delivered within 7 days of instruction.

What happens if my SAP calculation doesn't pass building regulations?

We strongly encourage that a preliminary calculation is performed in the form of an "As Designed" prior to laying a brick. This will allow you to understand where the property may not be up to standard. If you've already completed the build and the SAP Calcs don't pass, we can recommend measures to install in order for it to be signed off.

Final Thoughts

Choosing the right type of EPC matters - whether you're applying for planning, trying to sell your home, or simply staying compliant with energy efficiency regulations.

At Harpr Surveyors, we provide:

• Local RdSAP EPCs in Cornwall for existing properties
• UK-wide SAP EPCs for new builds, conversions, and extensions

Need help deciding? Contact us today for guidance - or book the right assessment with one of our accredited surveyors.