Part L: Extension SAP Calculations

Building Compliance Testing Limited can provide you with a fast and cost effective Elmhurst Certified SAP Calculations.


green tick BCTExtension SAP Calculations


A SAP (Standard Assessment Procedure) calculation for an extension 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 that’s attached to an existing one. The purpose of the SAP calculation is to determine the energy efficiency of the extension and its impact on the overall energy performance of the entire building. Here are the key components and considerations of a SAP calculation for an extension:

Building Information: Detailed information about the extension’s design, construction, and intended use, including floor area, orientation, heating and cooling systems, and lighting.

Insulation: Data on the insulation materials and thickness used in the walls, roof, and floor of the extension. This includes U-values, which represent the thermal performance of building elements.

Glazing: Information about the type and specifications of glazing, such as windows and doors. This includes details on the glazing’s U-values and any solar heat gain characteristics.

Ventilation: Details about the ventilation system in the extension, including its type, efficiency, and controls. Proper ventilation is essential for indoor air quality and energy efficiency.

Heating and Cooling: Information about the heating and cooling systems in the extension, including their energy efficiency, fuel sources, and controls.

Thermal Bridging: Consideration of thermal bridging, which is the heat loss that can occur at junctions or connections between different building elements. Reducing thermal bridging helps improve energy efficiency.

Air Permeability: Results of an air permeability test, which measures how airtight the extension is. Lower air permeability values indicate better energy efficiency.

Solar Heat Gain: Assessment of the solar heat gain from glazed areas in the extension. This accounts for the impact of sunlight on the heating and cooling requirements of the space.

Occupancy and Usage: Information on how the extension will be used and the expected occupancy patterns. This data includes internal heat gains from occupants and appliances.

Location and Climate Data: The location of the building and local climate data are considered in the calculation, as different regions have varying energy demands for heating and cooling.

SAP Rating: The SAP calculation generates a rating on a scale from A (most energy-efficient) to G (least energy-efficient) for the extension, based on its energy performance.

SAP calculations for extensions are crucial to ensure that the extended building complies with UK building regulations and achieves a minimum level of energy efficiency. The results of the calculation are typically used to generate an energy performance certificate (EPC) for the entire building, which provides information on the energy efficiency of both the existing structure and the extension. Compliance with these regulations and achieving a satisfactory EPC rating is essential for obtaining necessary approvals and demonstrating sustainability and energy efficiency.


To learn more about what are SAP Calculations click here.


The SAP Calculation Process


A SAP Assessor commences their work by utilizing 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 finalization, 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.


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Other Services

We can also offer a variety of other specialist services through our Partners, including:

Water Efficiency Calculations

Air Permeability Testing

Overheating Assessments

– U-value Modelling

– SBEM Calculations

– Energy Statements

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Find below a list of common frequently asked questions about Air Permeability Testing.