L1A New Build SAP Calculations
Design-stage and as-built SAP calculations for new homes, helping demonstrate compliance with Building Regulations, optimise the proposed specification and obtain the final Energy Performance Certificate.
SAP Calculations for New-Build Homes
SAP calculations assess the predicted energy performance of a new dwelling. They consider the building fabric, heating, hot water, ventilation, lighting, airtightness and renewable technologies to determine whether the proposed home satisfies the relevant Part L requirements.
New-build dwellings normally require both a design-stage assessment before work begins and an as-built assessment after construction. The design-stage SAP helps establish a compliant specification, while the final assessment reflects the dwelling as actually built.
One Stop Consult coordinates accredited energy assessors who can complete the calculations, identify areas of non-compliance and recommend practical improvements to the proposed design.
When Are L1A SAP Calculations Required?
SAP calculations are generally required for newly constructed self-contained dwellings and certain residential developments.
New-Build Houses
Detached, semi-detached and terraced homes constructed as new residential dwellings.
New Apartments
Individual flats within apartment buildings, including larger multi-unit developments.
Replacement Dwellings
New homes constructed following demolition of an existing property.
Housing Developments
Multi-plot schemes where house types may be assessed individually or through an agreed development strategy.
New Residential Units
Certain newly created self-contained dwellings where the applicable Building Regulations route requires new-build SAP assessment.
Building Control Submissions
Projects where design-stage calculations are required before work starts and final evidence is needed at completion.
Design-Stage and As-Built SAP Calculations
New-build SAP compliance is normally completed in two connected stages.
Design-Stage SAP
The proposed drawings and specification are modelled before construction to demonstrate that the dwelling is capable of achieving the required energy and carbon targets.
Predicted Energy Assessment
The design-stage results can support production of the Predicted Energy Assessment, showing the expected energy rating before the dwelling is completed.
As-Built SAP
The model is updated at completion using the final construction, systems, airtightness result and evidence of any design changes.
Final EPC
Once the as-built information is complete and compliance is confirmed, the final Energy Performance Certificate can be lodged.
What Is Assessed in a SAP Calculation?
The assessment models the dwelling as a complete energy system. The outcome is affected by the size and shape of the property, the construction specification and the efficiency of its building services.
Accurate drawings and technical information are therefore essential to avoid assumptions and reduce the risk of changes being required later.
How New-Build SAP Compliance Is Demonstrated
The calculated dwelling is compared against target performance values produced by the approved methodology.
Dwelling Emission Rate
The calculated carbon emissions of the proposed dwelling are compared with the applicable Target Emission Rate.
Fabric Energy Efficiency
The dwelling's predicted fabric energy demand is compared with the relevant target for the notional dwelling.
Primary Energy
The assessment considers the primary energy associated with the fuels and systems used by the proposed home.
Minimum Standards
Individual building elements and services must also satisfy the applicable limiting standards and specification requirements.
Solar Gains and Overheating
The design is reviewed for excessive solar gains, although a separate Part O or overheating assessment may also be required.
Evidence and Consistency
The calculations should reflect the drawings, specification and products that will actually be installed on site.
Building Fabric and Thermal Performance
The thermal performance of the walls, floors, roofs, windows and doors has a major effect on the SAP result. The assessment uses U-values to model heat loss through each element of the building.
A strong fabric-first design can reduce heating demand, improve comfort and limit reliance on additional renewable technology to achieve compliance.
Thermal Bridging and Construction Junctions
Heat is also lost through junctions such as wall-to-floor, wall-to-roof and window-to-wall connections. These junction losses are represented within SAP through thermal-bridging values.
Using suitable accredited or calculated details can significantly improve the result compared with default assumptions. The selected junction strategy should be coordinated with the construction drawings and site workmanship.
Heating, Hot Water, Ventilation and Renewables
Building-service choices can substantially affect carbon, primary energy and overall SAP performance.
Heating Systems
Boilers, heat pumps, direct electric systems, underfloor heating and controls are modelled according to their efficiency and setup.
Hot-Water Provision
Cylinder performance, distribution losses, heating source and controls all influence the calculated result.
Ventilation
Natural ventilation, decentralised extract, MEV and MVHR systems are assessed using their relevant characteristics.
Heating Controls
Zoning, thermostats, weather compensation and time controls can improve system efficiency within the model.
Solar Photovoltaics
Solar PV can offset electricity demand and support compliance where suitable roof area and orientation are available.
Other Low-Carbon Measures
Additional technologies can be considered where appropriate to the dwelling, site and wider energy strategy.
What Happens If the Design Does Not Comply?
A failing result does not always require a complete redesign. The model can be reviewed to identify the most effective improvements.
Improve Insulation
Increase thermal performance within selected walls, floors or roof elements where practical.
Upgrade Glazing
Improve window and door U-values, glazing performance or frame specifications.
Review Thermal Bridging
Replace conservative defaults with suitable accredited or calculated construction-junction values.
Improve Airtightness
Adopt a realistic but improved design air-permeability target, coordinated with the ventilation strategy.
Upgrade Heating Systems
Consider more efficient heating, hot-water and control systems.
Add Renewable Technology
Introduce or increase solar PV or other suitable low-carbon measures where required.
How the L1A SAP Process Works
The most efficient process starts before construction, while the design specification can still be adjusted without disrupting work on site.
Design Review
Obtain the drawings, dimensions, construction build-ups and proposed building services.
Design-Stage Calculation
Model the proposed dwelling and assess it against the applicable compliance targets.
Specification Advice
Recommend suitable changes where the initial design does not achieve compliance.
As-Built Update
Confirm the final specification, airtightness result, installed systems and any construction changes.
Final Documentation
Issue the as-built compliance information and lodge the final Energy Performance Certificate where included.
Information Required for a Quotation
Provide the full project address, number of dwellings, current project stage and the latest proposed architectural drawings.
Please also send any available construction specification, insulation details, window information, heating and ventilation proposals, thermal-bridging details and renewable-energy designs.
Information Needed for the As-Built SAP
The final assessment must reflect the dwelling as actually constructed, not simply the original design.
Final Construction Build-Ups
Confirmation of the insulation, materials and thicknesses installed within the walls, floors and roofs.
Air-Test Result
The measured air-permeability result for the completed dwelling, where testing is required.
Installed Heating and Hot Water
Manufacturer and model information for the systems and controls actually fitted.
Ventilation Information
Final details for fans, MEV or MVHR equipment and associated commissioning evidence where applicable.
Renewable-Energy Details
Final PV capacity, orientation, inclination and system information where renewable technology has been installed.
Changes From the Design
Details of any substituted products, altered layouts or changed specifications introduced during construction.
L1A SAP Calculations for a Range of New Homes
Assessments can be coordinated for individual properties, repeated house types and larger residential developments.
Nationwide New-Build SAP Calculation Service
One Stop Consult coordinates design-stage and as-built SAP calculations for new residential developments throughout mainland UK. Assessments can be provided for single dwellings, repeated house types, apartment schemes and larger multi-plot projects.
Other Services Your New-Build Project May Require
SAP calculations are commonly coordinated alongside testing, certification and wider Building Regulations services.
Important SAP Calculation Information
SAP compliance depends on the applicable Building Regulations, dwelling design, construction specification, installed systems and evidence provided. The design-stage assessment should be completed before construction so that any required changes can be incorporated early. The as-built result may change where products, systems or construction details differ from the approved design. One Stop Consult provides consultancy and coordination support through its specialist accredited energy-assessor network.
L1A New Build SAP Calculation FAQs
What is an L1A SAP calculation?
It is an energy-performance assessment used to demonstrate compliance for a new-build dwelling under the relevant domestic Part L requirements.
When should the design-stage SAP be completed?
It should be completed before construction starts so that the proposed fabric and building services can be checked and any necessary changes made early.
What is the difference between design-stage and as-built SAP?
The design-stage assessment models the proposed dwelling. The as-built assessment is updated using the final construction, installed systems, airtightness result and any changes made on site.
Do I need SAP calculations for every dwelling?
Each dwelling must be appropriately assessed, although repeated house types and development layouts can sometimes be coordinated efficiently within one project instruction.
What happens if the dwelling fails the SAP calculation?
The assessor can review the model and recommend practical improvements such as better insulation, glazing, thermal bridging, heating efficiency, airtightness or renewable energy.
Is an air test required for the final SAP?
New dwellings commonly require airtightness testing, and the measured result is used within the as-built SAP calculation where applicable.
Does SAP include the final EPC?
The final EPC can normally be produced after the as-built SAP has been completed and all required evidence has been received.
Can you help choose a compliant specification?
Yes. The calculation can be used to compare different fabric, heating, ventilation and renewable-energy options and identify a practical route to compliance.
Do you provide new-build SAP calculations nationwide?
Yes. We coordinate suitable accredited assessors for eligible new-build projects throughout mainland UK.
Request Your Free L1A SAP Calculation Quote
Complete the form below with the project address, number of dwellings and current design stage. Upload the latest floor plans, elevations, sections and available construction specification so our team can review the project and coordinate an appropriate quotation.