SAP & EPC Calculations
Design & As Built Calculations for new SAP10 (Part L 2021 Edition)
  • Guaranteed maximum 5 day turnaround
  • Unlimited reviews to specification at design stage
  • Assessors will always be on hand
  • Low cost for multiple plots

The Standard Assessment Procedure (SAP) are calculations required at design stage for all planning applications in order to generate the final SAP reports and EPC (Energy Performance Certificate) to demonstrate compliance with current Part L building regulations for England & Wales. The report itself is designed to measure the energy performance of new build dwellings as well as refurbishment and conversions providing simple to read information on its energy usage to the occupant/s in the form of the EPC.

Sites registered with building control prior to the 15th June 2022 will be under previous 2013 Part L regulation see here.


Whats NEW ?

New Limiting Fabric U-Values & Notional Dwelling Specifications

New Carbon Factors (Big change to Electricity Electricity reducing from 0.519 to 0.136kgCO2/kWh)

ACDs (Accredited Construction Details) Archived

PV (Photovoltaic Solar) included in notional dwelling spec with gas boiler

Ability to include PV Battery Storage & Immersion Diverters

Standard Heating Pattern Changes

Chimneys and Flues

Dwelling Primary Energy Rating

H.U.Gs (Home User Guides) are back

New BREL (Building Regulations Part L) Report

Overheating now assessed under Approved Document O

New Part F 2021 Regulations


New Build

Change Of Use / Conversions

BREW Compliance - SAP Caluclations, SAP Assessments, EPC, Energy Performance Certificates, Design SAP, As Built SAP, Predicted EPC, Part L Compliance

Single Plot

Available From

SAP Reports undertaken at the design stage of your project, while offering advice on achieving Part L compliance for the project if necessary. 
Our price for a SAP assessment always 
includes the design stage SAP, predicted energy performance assessment PEA and the final As Built SAP and EPC.
With no extra hidden fees.
Unlimited reviews to the fabric should you consider alternative fabric, heating or renewable options throughout  the design phase. Available From £200

Wooden House - Multiple SAP Assessments,

Multi Plot

Available From

Multiple plots on one site can be a stressful job for those involved. We can take control of compliance from design stage SAP assessments down to managing the on site air tightness 
testing & schedule and producing the final As Built SAP & EPC following the air test.
From as little as £50
For larger projects of houses or flats please contact us for quotation.


BREW Compliance - SAP Caluclations, SAP Assessments, EPC, Energy Performance Certificates, Design SAP, As Built SAP, Predicted EPC, Part L Compliance



Please contact us for a quotation on commercial SBEM/BRUKL reports.


Roof lights and roof windows will now be classified separately in SAP assessments as to better show their differing thermal characteristics.

New definition

  • For a roof window in a pitched roof with a pitch of less than 70°. If the pitch is 70° or

    greater, treat as a vertical window.

  • Rooflights are assumed to be horizontal if less than 30°.

New Limiting Fabric U-Values & Notional Dwelling Specifications

For New Notional Dwelling Specifications 

Notional specifications provide being a guide to the basic fabric required to pass

See more at the following links;


New Carbon Factors

Carbon Factors.jpg

The implications of new factors in SAP 10

There are two main implications of adopting the reduced grid carbon factor for electricity published in SAP 10:

  • The first is that the carbon emissions from electric heating will now (almost) reflect the current reality, instead of being many years out of date.

  • The second is that technologies generating electricity, such as gas-engine CHP and PV, will only be credited with reducing carbon by the amount of current grid carbon electricity, instead of the historic figure used in SAP 2012 (which is 123% higher than the the figure from SAP 10).

Thermal Bridging - ACDs No Longer Available in SAP 10 - Defaults ONLY UNLESS SPECIFIED

ACDs are to be removed as they are deemed to be out of date and no longer work with fabric standards required to meet new regulations (accredited construction details have been archived)

There will be an increase in use of the details from other schemes; Constructive Details, CBA, BRE, LABC etc.

As an alternative bespoke thermal junction PSI Ψ modelling may be needed.

Chimneys & Flues

Ventilation rates for chimneys, flues, fans and passive vents, flueless gas fires and passive stack ventilators are compared below;

Ventilation Rates.jpg

Heating Pattern Changes

Some people have their heating set to 25c all day every day, some people have their heating on for half an hour a day. To void this type of behaviour skewing EPC data, a standard heating pattern is used as reflected in the table below.

Heating Patterns.jpg


DPER – Dwelling Primary Energy Rating - The annual primary energy use of the building per unit floor area for space heating, water heating, ventilation and lighting, adjusted for any renewable primary energy generated on the site of the dwelling, expressed in kWh/m2/year.

DER/TER (Design & Target Energy Ratings)
DFEE/TFEE (Design & Target Fabric Energy Ratings)
Designs must meet all 3 target ratings.

Notional Dwelling - Gas Boiler Key Plant - Photovoltaic Solar

Full notional Specification is designed around a Gas Heating System (89.5%)

  • Photovoltaic –
         Houses - Kw peak requirement 40% of Ground Floor Area (including unheated spaces) / 6.5
         Flats & maisonettes - Kw peak 40% of dwelling floor area /(6.5 multiplied by number of storeys in block)

  • All showers to be equipped with Waste Water Heat Recovery

  • Heating system design for max temperature of 55C

BREL Reports & Home User Guides

BREL Reports - This is a new report that will be produced from the SAP10 software and provided by your assessor, however contractors and builders need to provide digital and of sufficient quality and high enough resolution to allow a qualitative audit of the subject detail. Close-up photographs may be needed where a long shot image provides insufficient detail.

Please click here to view required photographs. 

Home User Guides

The government have provided a template for a home user guide and a ventilation guide to inform homeowners how to operate and ventilate their dwelling in order to comply with the standard format.

Approved Document F - Changes to affect SAP Assessments

Increased whole dwelling ventilation requirements to improve indoor air quality

Background Ventilators

  • Use of intermittent extract fans and natural ventilation through background ventilators is only recommended for less airtight dwellings – aiming to have a design air permeability greater than 5m3 /(h·m2 ) at 50Pa

  • All newly designed dwellings will be classified as Highly airtight dwellings with an air permeability of less than 5m3

NOTE: As defined in Appendix A, less airtight dwellings are dwellings which have one of the following.

       a. A design air permeability higher than 5m3 /(h·m2 ) at 50Pa

       b. An as-built air permeability higher than 3m3 /(h·m2 ) at 50Pa.

Essentially anything with a design below 5m3 /(h·m2 ) at 50Pa will need to incorporate mechanical ventilation. 

Purge Ventilation

“A system for purge ventilation should be provided in each habitable room” and “should be capable of extracting at least four air changes per hour per room.”

Approved Document O - Changes to affect project design

Simplified or Dynamic

•The simplified approach is more suited for standard house designs. This will be assessed through SAP10. 

•The dynamic approach uses (CIBSE) TM59 and thermal modelling, suited for City developments or heavily glazed dwellings.

Simplified Method 


Assessing whether ‘cross-ventilation’ is possible

Cross-ventilation requires openings on opposite facades (having opening on facades that are not opposite will not meet the criteria, eg a corner flat.

The openable free area of all the windows (panes –suggested terminology)

• Height and width of the openable pane

Limiting Solar Gains

High Risk Area Requirement

High risk area – Most of Greater London and advised for central Manchester (but not a requirement)

Residential buildings in the high risk location should, in addition to following the maximum glazing areas in Table 1.1 and Table 1.2, provide shading for glazed areas between compass points north-east and north-west via the south. Shading should be provided by one of the following means.

  1. External shutters with means of ventilation.

  2. Glazing with a maximum g-value of 0.4 and a minimum light transmittance of 0.7.

  3. Overhangs with 50 degrees altitude cut-off on due south-facing façades only.

Dynamic Thermal modelling

When do we consider the CIBSE TM59 route –
􏰀If the dwelling fails the simplified calculations
􏰀The Architect would like to Overglaze the dwelling
􏰀External factors, night time noise &/or pollution levels means that bedroom windows can not be opened at night.
􏰀Security issues stopping bedroom windows from being opened at night

Change Of Use / Conversions

New Limiting Fabric U-Values For New and Retained Elements

Whole Dwelling Vent Rate.jpg
Types Of Ventilation.jpg
Purge Ventilation.jpg
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What is a SAP and EPC assessment?

A SAP assessment calculates various parameters but the most important being the TER (Target Co2 Emission Rate) and DER (Dwelling Co2 Emission Rate), TFEE (Target Fabric Energy Efficiency) and DFEE (Dwelling Fabric Energy Efficiency). The designed dwelling must match or better these targets generated by the SAP software or in some cases the DER must exceed the TER by a 25% reduction for example. 

The SAP assessment also calculates a figure ranging from 1 – 100+ with energy bands A-G assigned and reflected on the EPC (Energy Performance Certificate) as seen in the example rating graph here. The rating provided by the SAP assessment denotes the energy efficiency of the building that has been assessed; the higher the rating, the more energy efficient the building is according to the SAP. The assessment must be provided by an appropriately qualified and accredited OCDEA professional, who will use the latest approved SAP software to calculate various energy expenditure elements of the building or development.

L1A SAP Assessment?

Part of the SAP assessment also involves calculating the U-values and ensuring these also meet the minimum standards outlined in Part L1A & L1B regulations. New build projects must conform to the minimum U-values in L1A, however it's now pretty much become standard practice that designs exceed these u-values substantially in order to achieve compliance for both the DER (Dwelling Co2 Emission Rate) and DFEE (Dwelling Fabric Energy Efficiency) within the SAP compliance report. Other parameters such as overheating, glazing, water cylinders and more must also meet minimum requirements and show as compliant as illustrated in an example here. This is what makes design stage SAPs so important in order to ensure compliance at the final stage of completion. Any changes to fabric or heating plans must be re-run in the SAP software to ensure compliance will be achieved. 

L1B SAP Assessment?

For L1B regulations. Conversion and renovation projects must conform to the minimum U-values outlined in L1B, however these values need not be exceeded to achieve compliance for the DER (Dwelling Co2 Emission Rate) and DFEE (Dwelling Fabric Energy Efficiency) within the SAP compliance report and only all other parameters must pass from section 2 onward as illustrated in an example here. 

We can help advise you on the most cost effective solutions to bring your existing elements in-line with L1B regulations by modelling any retained elements such as a solid brick wall within a U-value calculator. While there are no strict pass or fail criteria for conversions other than minimum

u-values it's worth bearing in mind that if you plan on renting the property then you must meet a minimum rating of E on the Energy Performance Certificate (EPC). 

Over Glazed Extension SAP (Glazing greater than 25% of floor area)

Building Regulations require that the glazing in a new extension does not exceed 25% of the floor area so a SAP Calc will usually be required by Building Control if you are proposing to build an extension with a large amount of glazing to demonstrate compliance with Part L1B.

The work required for over glazed extensions is double that of a new build or conversion, as two SAP calculations are required.

Existing Dwelling plus a 'Notional' extension - This will show the dwelling as it stands plus an extension that has a glazing area that is only 25% of the floor area. The External Walls, Floor and Roof will show the minimum requirements to meet building regulations.

Existing Dwelling (with any necessary improvements) plus the 'proposed' extension - This will show the existing dwelling with any improvements plus the extension based on the proposed specifications. The external walls, floor, and roof, glazing and heating system are likely to be an improvement on that of the assumptions in the 'Notional' extension. 


The idea of carrying out the notional and proposed calculations is to show that the Primary Energy rate, CO2 emissions and fabric efficiency of the Dwelling plus the 'actual' extension are no higher than the C02 emissions of the dwelling plus the 'notional' extension. If this isn't the case for your proposed extension one of our experienced SAP assessors will be on hand to guide and work with you through possible solutions. 

Please enquire via our quotation form.