Build Comply
SAP Calculation and Energy Performance Certificate
Part L SAP Calculation
New-build, Conversions, Extensions, Over-glazing and Retrofit.
Do you need a SAP Calculation?
Building Compliance Testing Limited can provide you with a fast and cost effective Elmhurst Certified SAP Calculations.
Learn more in the below sections as the requirements for a SAP Calculation are varied dependant on your project type.
SAP and HEM Assessments
SAP stands for ‘Standard Assessment Procedure’. This is soon to be replaced with HEM, which standards for ‘Home Energy Model’.
A SAP assessment involves using a calculation method to predict the energy performance of a building – this includes houses, flats and all other residential properties. However, it is not just required to have a SAP calculation carried out on a complete new build, it is also a requirement for certain extensions which exceed the threshold and any conversions.
This calculation works by assessing the level of energy which is likely to be used, taking into account the expected occupancy, and based on an average, comfortable way of living.
A SAP Assessor commences their work by utilising architectural plans and construction specifications in conjunction with a comprehensive HVAC (heating, ventilation, and air conditioning) specification. Consequently, the drawings must be meticulously scaled, accurate, and encompass all facets, including elevations, sections, floor plans, and site layouts.
The assessor then proceeds to create a model of the dwelling(s) within SAP software, working from these scaled plans, whether manually or electronically. This digital representation forms the foundation for SAP Calculations.
Within this model, the assessor integrates the heating, lighting, and ventilation systems, selecting specific products from manufacturer databases when applicable. Detailed thermal elements, encompassing walls, floors, roofs, and openings, are meticulously included, along with calculations for thermal junctions. Additionally, any renewable technologies and cooling systems are incorporated.
Upon finalisation, the SAP calculation generates an array of comprehensive reports, spanning site layout, heat losses, energy demands, seasonal variations, CO2 emissions, renewables contributions, and numerous other aspects.
The calculation is a desk based assessment and is typically split into two parts:
The first part is the design stage. At this stage, the assessor will work up a preliminary SAP assessment based upon the proposed/assumed design and specification to see if compliance is met. If the dwelling is falling short of compliance, we work with our clients to find a solution which meets their requirements in terms or practically and budget. This is known as Predicted Energy Assessment (PEA).
The second part is the as-built stage. This is where we check the dwelling as constructed against it’s design specification. Any material changes will be updated at this stage as long as completing a Photographic Evidence Report and Air Permeability Test.
All of this information is then lodged to generate your Energy Performance Certificate.
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SAP Calculation Considerations
SAP assessments are essential for demonstrating compliance with Part L of the Building Regulations and for achieving energy performance certification. Below are the key elements we evaluate to ensure accurate and compliant SAP calculations:
Building Materials
The thermal performance of walls, floors, roofs, windows, and doors is assessed based on their construction type and material properties. High-performance materials contribute to lower energy demand.
Insulation Values
U-values are calculated for all building elements to determine heat loss. The quality, thickness, and placement of insulation significantly affect the building’s energy efficiency rating.
Thermal Bridging
Linear thermal bridges at junctions (e.g., wall-to-floor, wall-to-roof) are assessed to account for additional heat loss. Accredited construction details or bespoke psi-values can be used to minimise impact.
Ventilation
The type of ventilation system—natural, mechanical extract, or MVHR—is evaluated for energy use and heat recovery efficiency. Proper ventilation also supports indoor air quality and moisture control.
Air Tightness
Air permeability testing is used to measure uncontrolled air leakage. Lower air leakage rates improve energy efficiency and are critical for achieving a good SAP score.
Space Heating, Hot Water & Controls
The efficiency of heating systems (e.g., boilers, heat pumps), hot water generation, and the presence of smart or zoned controls are key factors in reducing energy consumption.
Lighting
The proportion of low-energy lighting (e.g., LED and CFL) is assessed. Efficient lighting design reduces electricity demand and contributes to a better SAP rating.
Condensation & Overheating Risk
SAP includes checks for condensation risk in building fabric and evaluates the likelihood of summertime overheating, especially in airtight or highly glazed buildings.
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New-build SAP Calculation
A new build SAP calculation is a government-required assessment that evaluates the energy performance of newly constructed residential buildings. It involves calculating the Dwelling Emission Rate (DER) and Dwelling Fabric Energy Efficiency (DFEE), ensuring compliance with energy efficiency standards and producing an updated Energy Performance Certificate (EPC).
Extension SAP Calculation
A SAP calculation is a standardized method used in the United Kingdom to assess the energy performance of a building extension, whether it’s a new addition to an existing structure or a separate building attached to an existing one. It considers factors such as insulation, glazing, ventilation, heating and cooling systems, and location climate data. The results are crucial for ensuring compliance with UK building regulations and generating an energy performance certificate (EPC) for the entire building. Additionally, for overglazed extensions, a specific over-glazed SAP calculation is required to evaluate their impact on overall energy performance.
Change of Use SAP Calculation
A conversion SAP is required on a material change of use and is treated much like a new-build but some requirements do not have to be met. Examples including thermal bridging details and air tightness testing.
Over-glazed SAP Calculation
An over-glazed SAP calculation is specifically required when assessing the energy performance of extensions or conservatories with excessive glazing. Building Control typically requests SAP calculations if the total new glazing area in your extension or conservatory exceeds 25% of the extension floor area.