Sap Calculations Explained


What are they?

Sap stands for Standard Assessment Procedure and is the methodology used by government in the UK to rate the energy efficiency in domestic buildings.

Why are they needed?

Sap calculations are used to demonstrate compliance with building regulations. Part L1A is the document by which new dwellings are assessed and Part L1B, which is less stringent, is used for existing dwellings.

You will normally be asked by building control to get a qualified assessor to produce these calculations to prove your building meets the energy efficiency requirements.

How to get them done?

Sap calculations are carried out by a qualified and accredited On Construction Domestic Energy Assessor or OCDEA for short. A site visit is not normally required as it is normally done from the building plans. If you require sap calculations, get in touch and we would be happy to provide a quotation.

SAP For Extensions & Overglazing

  • Reports for Part L1B compliance
  • Free Advice

SAP For Conversions

  • Carbon Emissions Reports
  • Heat Loss Calculations
  • Free Advice

SAP For New Build

  • Reports for Part L1A Compliance
  • Free Advice

Get A Quote For Your Project

Sap calculations throughout the UK, get a FREE No Obligation quote within 24 hours.

Sap Calculations For Extensions – Part L1B

You will need Sap Calculations if your extension has more than the permitted amount of glazing. Part L1B of the building regulations states that the amount of glazing must be no more than 25% of the floor area.

If you change a conservatory roof to a fully insulated roof, which is common these days, then it effectively becomes an overglazed extension and will require a sap calculation.

Modern extensions with roof lights and bi-fold doors have lots of glazing but the heat losses are often too high, so Sap calculations are used to demonstrate compliance by one of the following methods:

1. Area Weighed Uvalue / Heat Loss Calculations.

This method can be used by improving the thermal value of other elements of the extension, such as the walls, roof, floors or glazing so that the area weighted Uvalue/ heat losses on the proposed overglazed extension are no worse than an extension the same size with the permitted amount of glazing.

This method can only be used if the extension is still at design stage and if the amount of overglazing is only slightly over the permitted amount, as there is only so far that you can sometimes go with improving the thermal elements.

The second and most commonly used method is called:


2. The Whole House Method

With this method compliance can be demonstrated if the CO2 emissions from the proposed overglazed extension and the main house are no worse than an extension with the permitted amount of glazing and the main house. This means that energy saving improvements already made to the main house or that have to be made to the main house will go towards compensating the additional heat losses of the overglazing.

Typical improvements that can be made to the main house can include things such as improving the insulation of the walls, or roof, or upgrading a boiler. Sap calculations are used to calculate the CO2 emissions. We provide expert advice and will help you achieve compliance regardless of what stage you are with your project.

Sap calculations for extensions cost

The cost of a sap assessment for an extension starts from as low as £120. Let us know about your project for a fixed price quotation and free advice. We’ll get your extension compliant so you can start to enjoy that additional space you’ve always wanted. 

Sap Calculations For Conversions

Under Part L1B, sap calculations are required for;

  • Dwelling change of use – e.g changing a commercial building to residential accommodation.
  • Increasing or decreasing the amount or dwellings – e.g changing a single property to self-contained flats.

When converting a property the building regs sees this as a perfect time to improve the thermal elements of the property such as the walls, roof, floors, glazing and heating. Therefore certain targets need to be achieved depending on what the Uvalue of the element is to start with and whether it is an existing element or whether it is a new addition.

There are a whole lot of regulations that need to be complied with. We’ll take the stress out of trying to keep planning happy so you can get your project moving fast. The earlier we work with you on your project, the easier it is to achieve compliance.

Sap Calculation Cost

The cost of Sap calculations can vary depending on many factors but the cost can be as low as £120 to £330 depending on the size, quantity and complexity of your project. Contact us today to get a quote.

Here are some simple guidelines that will speed up your approval.

  1. Get your SAP calculations completed at the design stage.
  2. Fabric first – invest in good building fabric.
  3. Consider ways to lower the thermal mass.
  4. Don’t shy away from renewables.
  5. Insulate party walls.
  6. Enhance your heating controls.
  7. Use low energy light bulbs.

Sap Calculations For New Build

All new build properties require SAP calculations to demonstrate compliance with Part L1A of the building regulations. To be compliant the completed building must achieve the following:

The Dwelling Fabric Energy Efficiency (DFEE) must be no higher the Target Fabric Energy Efficiency (TFEE) and the Dwelling Emission Rate (DER) must be no higher than the Target Emission Rate (TER).

The target rates are calculated in the software and are based on a property the same size and shape that complies with the building regulations.

Because you’re starting with a blank slate, gaining compliance with a newly built property can either be a relatively straight forward process, or it could be a stressful nightmare. Which experience will you have?

You should be getting your Sap calculations done at design stage so you’re guaranteed to be building a property that will pass. The earlier you get in touch the easier your journey will be.

However, if you’ve left it until the building is completely built – there’s still hope. Although the options are less at this stage, your Assessor will have solutions that will help your building pass. Contact us for a quotation.

To be able to produce your sap report, your Assessor will need the following information:

  • Floor Plans to include sections and elevations drawings.
  • A written specification which must provide:
  • Details of the construction specification of walls, roof and floors.
  • Details of the insulation present for walls, roof and floors .
  • Details of the specification for all doors and windows.
  • Details of primary and secondary heating and provision for hot water.
  • Details of type of heating controls.
  • Details of how hot water is provided.
  • Details of any renewable technology (ie solar, heat pumps etc).

Energy Statement

We can produce an Energy Statement if required. An Energy Statement is required by some Local Authorities where they require the proposed building to achieve a CO2 emission reduction of typically anywhere between 20 and 30% above that of the building regulations.

These are challenging targets and will probably require implementation of renewables such as heat pumps or solar. It is important that we do the calculations at the earliest possible stage as any shortfall in obtaining the target may mean a carbon levy being paid to the Local Authority for every tonne of CO2 produced annually that is under the set target.

Other Services

Air tightness testing a house

Air Tightness Test

For most new buildings to achieve the Target Emission Rate, it’s going to need an air leakage test. We can arrange this for you and ensure you meet the targets required to achieve a pass.

Sound Insulation Testing

Building Sound Insulation Testing

Sound testing is required where walls or floors adjoin between dwellings. We’ll get you to achieve the targets required by Part E of the building regulations.

Water Calculations

Water Calculations

Part G of the building regs require a new dwelling to use no more than 125 ltrs per person per day. We’ll help you get it sorted.

Young woman looking at property energy rating

Energy Performance Certificates

All new builds, properties for sale or rental, by law must have an Energy Performance Certificate.

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