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SAP Calculations for Extension from a leading Energy Consultancy

Our experienced team of engineers are well-versed in all aspects of energy efficiency, so you can rest assured that whatever the project – Part L1B  Extension – your home will meet the required standards and be highly efficient.

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SAP Calculations from £80+VAT.

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If you would prefer us to call you back today about your quote, please send us a short message using the form below or email

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Save up to 50% compared to architects

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Services available nationwide. Fast-Track available.

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Approved accredited assessors

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Client Portal System - manage your job on the go

How do SAP calculations for extensions work?

When it comes to glazing and openings, heat loss is higher compared to walls and roofs. Part L1b of the Building regulations requires that areas of new glazing should account for no more than 25% of new floor area.

Of course, many extension designs will propose more than this, and therefore will not comply with this rule. However, you can eliminate the negative effect of extra glazing in a highly glazed extension by upgrading other elements of the construction or showing additional solar gains from this extra glass.

We are here to provide you with various options that adhere to SAP regulations for extensions. Let us help keep your home energy efficient while maintaining its style!

Why you need a SAP calculation for an extension

If you’re planning an extension on your existing property, you will need to have a SAP calculation completed in order to comply with UK building regulations. A SAP test is required to establish the Energy Performance Certificate (EPC) rating of a building and accurately assess the energy efficiency of your proposed extension.

Focus 360 Energy offer this service as part of our range of New Build Services, ensuring that your extension meets all requirements, achieving compliance and providing peace of mind for you as the customer. Our knowledgeable and friendly team are on hand to answer any questions you may have about the process.

SAP Calculations for Extension:
Frequently combined with the following additional services:
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Energy Statement

water testing

Water Consumption Calculation (Part G)

part o

TM59 Overheating Assessment

air testing

Air Pressure Testing

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Sound Testing

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Energy Performance Certificate (EPC)

ventilation testing

Ventilation Testing


If you need assistance ...

Hi, I'm Will, the Customer Relationship Manager, and I oversee every aspect of your customer journey. If you need any further assistance, please get in touch.

Ready to get started?

SAP Calculations from £80+VAT.
Same day quotes available.

Ready to ensure your building project meets the highest standards of energy efficiency? Contact Focus 360 Energy today for a bespoke SAP Calculation quote. Let our accredited professionals guide you to compliance and beyond, with expert advice, efficient service, and competitive pricing. Start your journey to a greener, more efficient future now.

Download our Service Guide

Download our guide to the multiple services you may need for each stage of your project.

Services from Concept Doc V3

Our SAP Process makes it easy for you.

We want the whole process to be as easy as possible. On acceptance of a quote, you'll be emailed a simple checklist that can be completed online - no complicated PDFs or documents downloads that need to be completed and then returned!

To see the type of information required, view the example below.


Schedule your EPC

Schedule your appointment

Now that you’ve approved your quote in our online portal, you can schedule an appointment with the surveyor.


Schedule your EPC

Assess your plans and specifications

We will provide you with an online questionnaire to complete and are more than happy to coordinate directly with your architect and builder.


Schedule your EPC

SAP Design Stage Calculations

Our expert SAP Assessors will calculate and produce your Design Stage SAP Calculations.


Schedule your EPC

Guidance for pass (if applicable)

If required, we will provide guidance and advice to help you achieve an energy efficiency pass.


Schedule your EPC

Complete your SAP Calculations and EPCs

Our team will complete and publish your As-Built SAP Calculations and EPC Certificates.


Schedule your EPC

Supply your documents

We take care of everything and provide you with all the necessary documents.

SAP Calculations for all your building projects

If you are planning a New Build or Conversion, you may need additional services that our experts can assist with, for example Residential Air Testing, Sound Testing, Ventilation Testing, U-Value Calculations, Water Efficiency Calculations, Thermographic Surveys, Energy Performance Certificates, Part O Overheating Calculations, London Plan and Thermal Bridging Calculations.

Get started to day and speak to us about the additional services you may need.

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Part L1A
SAP Calculations for New Builds

All new dwellings must now have a SAP calculation performed at design stage in order to demonstrate compliance with Part L1A of the Building Regulations.

architects 1

Part L1B
SAP Calculations for Extensions

If you build an extension where the glazing is over 25% of the floor area, then we can undertake SAP Calculations to demonstrate Part L1B Building Regs compliance.

builders and developers

Part L1B
SAP Calculations for Conversion

If you renovate a building such that there has been a material change in use, then we can undertake SAP Calculations to demonstrate Part L1B Building Regs compliance.


SAP calculations for fully glazed extensions

While we all dream of having a bright and airy extension, the Building Regulations (and regional variations) Part L1b, unfortunately stipulate that the total area of any new glazing in an extension should not exceed 25% of its floor space.

But don’t despair! If your plans do require more than this amount, you can still comply with regulations by introducing compensating measures or alternatively providing a calculation for approval from Building Control or a Verifier (Scotland). With our guidance, you can create an open, inviting addition to your existing house while staying within the guidelines that building regulations describe.

Involving an energy assessor early on in the project and having good coordination between all involved – such as architects and engineers – can lead to creating an even more efficient and comfortable home. When your SAP calculation figures have been calculated, they will form the basis for selecting a suitable system for each area.

How do we ensure compliance?

We leverage SAP technology to calculate the CO2 emissions for your current home with its existing structure and existing elements, as well as for a proposed extension. We also take into account the minimum standards outlined in the approved documents and technical booklets, which we refer to as ‘notional extension’. A notional extension means doing a SAP calculation on an entire house with an extension attached, which has been build adhering to exacting Building Standards and Regulations, with exact U values and the correct amount of glazing. As long as your proposed CO2 emissions are lower than those of the ‘notional extension’ category, you can rest assured that you will meet all requirements set forth by applicable laws and regulations.

Our process

Simply download and complete our checklist and supply all the required information to us and we are able to offer a fast and efficient 5 day turnaround for SAP calculations on extensions. If this isn’t soon enough for you, then our expert team can further accelerate the process for just £75 + VAT.

Helpful information you may need to supply?

  • Floor plans, sections & elevations
  • Orientation e.g. site plan of existing elements
  • Construction specification of existing walls, new structures, roofs and floors
  • Specification for all windows
  • Details on primary & secondary heating systems
  • Renewable technology (if any)

Please call 0333 772 2798 if you have any questions.

What is included?

  • All SAP calculation documentation required for compliance with the Building Regulations from Design (PEA) to On Construction 
  • Additional recommendations if required to ensure a pass is achieved every time
  • Advice and support throughout the whole process
  • Quick turnaround
  • We are happy to deal directly with your Builder, Architect or Building Control Officer during our site visit

Ready to get started?

SAP Calculations from £80+VAT. Same day quotes available.

Ready to ensure your building project meets the highest standards of energy efficiency? Contact Focus 360 Energy today for a bespoke SAP Calculation quote. Let our accredited professionals guide you to compliance and beyond, with expert advice, efficient service, and competitive pricing. Start your journey to a greener, more efficient future now.

Frequently Asked Questions

What are SAP Calculations?

SAP stands for ‘Standard Assessment Procedure’ and is the government’s method for calculating the energy performance of dwellings. These calculations are only necessary for residential properties. The calculations determine a Target Emissions Rate (TER) and a Target Fabric Energy Efficiency (TFEE) rate.

How much is a SAP Calculation?

Our fees are typically based upon the size and complexity of a dwelling. We do prefer to offer a bespoke quotation on a job-by-job basis to give you the best price – So get in contact and send us your plans today!

Can I do a SAP Calculation?

SAP Calculations must be carried out by an On Construction Domestic Energy Assessor or OCDEA, working with approved Government program. The Assessor must be certified under one of several accreditation schemes and is regularly audited to keep their certification.

What is required for a SAP Assessment?

Your Assessor would advise you of exactly what is needed. Typically you would need the following:

  • Floor plans, sections & elevations
  • Orientation e.g. site plan
  • Construction specification of walls, roofs and floors
  • Specification for all windows
  • Primary & secondary heating systems
  • Renewable technology (if any)
SAP Calculations for Extensions

Under the latest building regulations, the quantity of glazing must be a maximum of 25% of the floor area of the new extension. Therefore over compensations in the thermal elements in other areas within the property will need to be made to show the CO2 emissions coming from the current house along with the proposed extension is not any worse when compared to the existing house and an extension whose glazing is within the allowed amount judged against Part L1B of the building regulations. You need SAP calculations to find solutions and demonstrate compliance.

Will I need SAP Calculations

You will require SAP calculations whether you are extending, converting or changing the use of a property.  You will need to ensure that your specifications meet the requirements of building control.

  • Building a new property
  • Changing the use of an existing property (e.g, a barn conversion, commercial building to residential)
  • Extensions with more than 25% glazing
  • Opening up the main house to an existing conservatory
  • Extension where the extension is more than 50% of the original property wall area
  • Garage conversions
  • If requested by building control

This checklist is not exhaustive. If you’re unsure whether you need them contact us today for further information.

What happens if my design fails its SAP Assessment?

If your design fails its SAP Assessment, then you will need to revise the design to meet the requirements. Depending on the extent of the changes required, you may need to go through the assessment process again. In some cases, you may need to have additional testing done to verify the design’s performance. The SAP Assessor will provide guidance on the necessary steps to make your design meet the requirements.

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