SAP Calculations for Extensions

SAP Calculations for Extensions, also known as Overglazed SAP Reports or N & P SAP Calculations

By far, one of the most common questions we at Melin get asked is,

‘Will my extension need a SAP calculation’?

When it comes to extensions, there’s no denying that this is where it gets a little confusing…

In short, No, not all extensions will require a SAP, it all depends on the amount of glazing within the proposed project.

The easiest way to find out for sure, is to get in touch with our dedicated team of SAP specialists who will confirm whether an Extension SAP is required and guide you through the process.

So, what are the rules regarding SAP and Extensions?

Building Regulations require that, when proposing a new extension, areas of new glazing should account for no more than 25% of the new floor area (plus an allowance for any existing openings that are being removed).  This is to maximise the energy efficiency as glazing and openings lose more heat than walls and roofs.

But with all that lovely vitamin D that we look forward to shining through, recent trends in extending houses tend towards adding new, light, airy spaces with skylights and bifold doors. This means that the 25% allowance is easily quite quickly exceeded, and therefore the extension will not comply with this rule.  This is where SAP calculations are required.

How does a SAP Calculation help?

If you are planning a highly glazed extension, don’t panic, there is a solution – Part L allows for the ‘more flexible approach’ of the comparison of two reports. In other words, this is where the terms Notional & Proposed come in to play.

  • The Notional Report: A SAP calculation is made on the existing house with an extension attached to it, which is built to the exact specification of the Building Regulations, with exact U values (the thermal insulation level) and an area of glazing capped at the 25% allowance. This is called the Notional Extension or Report
  • The Proposed Report: A SAP calculation is then produced for the house and extension as they will actually be built – this can include upgrading of elements within the existing house or over compensating in other elements of the extension.
  • The comparison: The SAP calculations should prove that the CO2 from the house and the extension that will actually be built (Proposed Report) is no higher than the CO2 from the house and notional extension (Notional Report). 

What information do we need to complete a full SAP calculation on your extension project?

We only require the following;

  • A set of existing and proposed plans (to scale), including floor plans, elevations and cross sections.
  • Confirmation sheet including the intended construction and services specification.
  • <<<<insert conf sheet here to download>>>>>

The majority of our Extension SAP calculations can be carried out via desktop without the need for a site survey, however where existing plans of the property aren’t available, we’re more than happy to carry out a full site survey to gather the information required.

Get in touch

Sssshhh – We’ll let you in to a little secret;

Our founding director (Mel) absolutely loves getting her teeth into Notional & Proposed SAP calculations over and above her other (many) other responsibilities.
Mel and our specialist SAP team have been assisting architects, contractors and homeowners with these types of SAP calculations for nearly 20 years now and can proudly boast a 100% record in finding a compliant solution - at no extra cost and with no changes to your plans. We’ve even been known to speak directly to the building control officer, understand what they require and take care of everything for you.
Melin Energy Consultants

01554 571010

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