Energy Performance Certificates (EPCs) are not all the same. While most homeowners are familiar with a standard EPC for selling or letting, properties that are newly built or significantly converted may require a different assessment method.
The two main calculation methods used in the UK are SAP (Standard Assessment Procedure) and RdSAP (Reduced Data SAP). Understanding the difference is important if you are developing, converting or restructuring a property.
What Is RdSAP?
RdSAP is the methodology used for assessing existing dwellings. This applies to most properties that are already built and occupied.
An RdSAP EPC is typically required when:
- A home is sold
- A home is rented out
- An existing property’s EPC has expired
This is the standard type of EPC used in markets such as Bath, where historic housing stock is common, and in commuter cities like Cardiff, where a mix of traditional and modern homes exists.
What Is SAP?
SAP (Standard Assessment Procedure) is used for new builds and certain types of conversions. It is more detailed and is based on architectural plans, building specifications and construction data.
A SAP assessment is generally required when:
- A new dwelling is constructed
- An office or commercial building is converted into a residential unit
- A single dwelling is split into multiple new dwellings
This is because the property is effectively treated as a new dwelling for compliance purposes.
Do All Conversions Require SAP?
Not necessarily. The key factor is whether the conversion creates a new dwelling for building control purposes.
For example:
- Converting an office into a new flat typically requires a SAP EPC.
- Extending an existing house without creating a separate dwelling usually does not.
If building control approval was required for a change of use or new dwelling creation, SAP is often the correct route.
Why the Distinction Matters
Using the wrong assessment method can cause delays during sales or lettings. Lenders, solicitors and estate agents may query certificates if they do not align with the property’s planning or building control status.
This is particularly relevant in areas experiencing redevelopment or conversion activity, such as Stoke-on-Trent and Preston, where older commercial buildings are sometimes repurposed.
What If the Property Is Already Built?
If the dwelling already exists as a legally recognised residential unit and simply needs an updated certificate, RdSAP will normally apply.
If you are unsure, confirmation from building control documentation is usually the safest route.
How This Affects Property Sales
Confusion around EPC type can delay transactions. Buyers may question whether the certificate is valid, especially where recent conversions are involved.
For general guidance on how EPCs influence buyer perception and market behaviour, see our article on how EPC ratings affect house prices and demand.
Booking an EPC
If your property is an existing dwelling that requires a standard EPC for sale or letting, assessments can be arranged via the online booking page.
Where a SAP assessment is required, this will typically be arranged through a qualified On-Construction Domestic Energy Assessor during the build or conversion process.
Conclusion
The difference between SAP and RdSAP EPCs depends on whether a property is considered new or existing for regulatory purposes. Understanding this distinction helps prevent delays and ensures compliance when developing, converting or marketing a property.
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