An Extension Energy Assessment forms part of 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 existing structure and the proposed conversion, including the size of the building, orientation, layout, and any modifications to be made.
Insulation
Data on the insulation materials and thickness used in the conversion, including U-values for walls, roofs, and floors. The U-value represents the thermal performance of building elements.
Glazing
Information about the type and specifications of glazing, such as windows and doors, including details on the glazing’s U-values and solar heat gain characteristics.
Ventilation
Details about the ventilation system in the conversion, 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 conversion, 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 converted building is. Lower air permeability values indicate better energy efficiency.
Solar Heat Gain
Assessment of the solar heat gain from glazed areas in the conversion. This accounts for the impact of sunlight on the heating and cooling requirements of the space.
Occupancy and Usage
Information on how the conversion will be used and the expected occupancy patterns. This data includes internal heat gains from occupants and appliances.
Location and Climate
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.
U Value Targets for Extensions
U-Value Targets for Extensions:
U-value targets for extensions can vary based on the specific building type, the materials used, and local building regulations. However, in general, the U-value targets for conversions aim to achieve the minimum required standards for insulation. The UK building regulations set specific U-value targets for different building elements, such as walls, roofs, and floors. For example:
External walls: The U-value target for external walls in conversions may be around 0.28 W/m²K, but this can vary depending on factors like insulation thickness and the type of wall.
Roof: The U-value target for roofs in conversions may be around 0.18 W/m²K, although this can also vary depending on the specific circumstances.
Floors: U-value targets for floors in conversions can be around 0.25 W/m²K, but, again, it depends on various factors.
It’s essential to consult with a qualified energy assessor or consultant to determine the specific U-value targets and requirements for your conversion project, as they can vary based on the building’s location and the local authority’s regulations.
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.