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Part L · Design & As Built

SAP Calculations & EPCs
Fast, local, fully compliant.

Government-accredited SAP assessments and EPC certificates for new builds, extensions, and conversions across Birmingham, Bristol, Worcestershire, Gloucestershire, Oxfordshire, and the West Midlands. Most reports delivered within 3–5 working days — no hidden costs.

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What are SAP calculations?

The government-approved method for assessing the energy performance of homes.

EPC energy performance certificate rating

SAP (Standard Assessment Procedure) is the UK government's official method for assessing the energy efficiency of dwellings. Developed by the Building Research Establishment (BRE) and first published in 1993, SAP was formally adopted in 2007 as the method to produce Energy Performance Certificates (EPCs).

The assessment considers your building's construction materials, insulation levels, heating systems, ventilation, thermal bridging, and air tightness to produce a detailed energy performance model. The result is a SAP rating and an EPC — both of which are required for Building Control sign-off.

Beyond compliance, a good SAP rating reduces energy bills, improves comfort, and increases property value. In today's market, energy-efficient homes sell faster and at higher prices. The assessment is not just a regulatory hurdle — it's an opportunity to optimise your building's performance before construction locks in your choices.

When you need a SAP calculation

  • All new residential buildings in England and Wales require SAP to demonstrate Part L compliance
  • Major renovations and 'change of use' projects affecting energy performance
  • Extensions with more than 25% glazed area relative to floor area
  • Building Control requests for energy performance documentation
Part L 2021 changes: Accredited Construction Details (ACDs) are no longer available. You now need bespoke calculated Psi values or pre-calculated values from manufacturers. Default Psi values for heat-loss junctions often won't achieve compliance.
The SAP process

From initial consultation to EPC certificate.

The path to SAP certification is straightforward. We handle both the design stage assessment and the as-built calculation, keeping you compliant from planning through to handover.

01
Initial consultation & data gathering
We collect your architectural drawings, construction specs, and details on heating, ventilation, and insulation systems. Accurate data at this stage is critical for a reliable assessment.
02
Design stage SAP assessment
We model your building in SAP software, checking that the Dwelling Emission Rate (DER) and Fabric Energy Efficiency (DFEE) meet or exceed the targets set by Part L. You receive a Predicted Energy Assessment.
03
As-built verification
Once construction completes, we verify the as-built details — final boiler models, air tightness test results, and any specification changes. Updated data goes back into the SAP software for the final calculation.
04
EPC certificate issued
If everything complies, we issue an Energy Performance Certificate (EPC) for the finished property, confirming it meets current regulations. This is required for Building Control sign-off, sale, or rental.
What we need from you

Engaging early saves time and money.

Including SAP planning in the design stage is essential. Proactively modelling your SAP rating, identifying potential issues, and sticking to Part L requirements simplifies the building control process and avoids expensive changes later.

With the introduction of Part L 2021, water heating demand has become proportionately more significant as space heating decreases in well-insulated homes. Measures like Waste Water Heat Recovery (WWHR) systems can make a meaningful difference to your results.

Similarly, specifying DMEV (Decentralised Mechanical Extract Ventilation) allows product-specific fan powers to be used in calculations, improving efficiency and limiting over-specification.

Information required

Architectural drawings Floor plans, elevations, and sections showing dimensions and glazing areas.
Construction specification Wall, floor, and roof build-ups with insulation types and thicknesses.
Heating system details Boiler model, hot water cylinder, and any renewable technologies proposed.
Ventilation strategy Natural, MEV, MVHR, or DMEV — and the proposed system/model.
Window & door schedule U-values, solar transmittance (g-values), and frame types.
Design air permeability target Your assumed air tightness value for the SAP model.
Beyond compliance

Optimisation strategies for better SAP scores.

Getting a good score is more than meeting the minimum. It's about making your home energy-efficient — and an assessor can help you unlock value beyond a certificate.

Fabric first
Prioritise the Building Envelope
Use high-performance insulation, energy-efficient windows and doors, and sealed construction methods. A well-designed fabric reduces reliance on mechanical systems and locks in long-term savings.
Orientation
Optimise for Solar Gain
Angle your home to maximise sunlight in winter, reducing heating demand. Considered early in design, orientation adjustments cost nothing but can significantly improve your SAP score.
Renewables
Embrace Renewable Technologies
Install solar panels, heat pumps, or WWHR systems to reduce reliance on fossil fuels. SAP rewards renewable integration with higher scores, improving your EPC and reducing running costs.
Client feedback
"Build Envelope's local knowledge and speedy service helped us secure building control approval for our Cheltenham extension with zero hassle. Their SAP assessors knew exactly what was needed and delivered the report ahead of schedule."
SJ
Sarah J.
Homeowner, Gloucestershire
Government-accredited OCDEA assessors
Registered number EES/030713. Our SAP calculations and EPCs are legally valid for Building Control approval across the whole of England and Wales.
Fast turnaround — 3–5 working days
Avoid project holdups. Most reports are delivered within 3–5 working days of receiving complete information. Urgent turnarounds available on request.
Value engineering included
We don't just tell you pass or fail. We advise on practical ways to improve your SAP rating, reduce build costs, and lower future energy bills — all within the assessment process.
Proven track record across the UK
From single extensions to large multi-plot housing developments, we've helped homeowners and developers achieve compliance, optimal EPC ratings, and maximum property value.
SAP calculations near you

Local SAP assessors serving the Midlands, South West, and beyond.

We understand local planning and building control expectations across our core service areas. Our assessors work on-site and remotely to deliver fast, compliant results wherever your project is located.

Birmingham & West Midlands
SAP calculations for new builds, extensions, and conversions across Birmingham, Solihull, Coventry, Wolverhampton, and the wider West Midlands. We work regularly with local building control teams and understand the region's planning requirements.
Bristol & South West
EPC certificates and SAP assessments for residential projects across Bristol, Bath, South Gloucestershire, and the surrounding South West region. Fast turnaround with local knowledge of authority-specific sustainability policies.
Worcestershire
Based in Worcester, we provide SAP calculations for projects across Worcestershire including Malvern, Droitwich, Evesham, Bromsgrove, and Redditch. Our home county — fastest response times and deepest local relationships.
Gloucestershire
SAP assessments and EPCs for new homes and extensions across Cheltenham, Gloucester, Stroud, Tewkesbury, and the Cotswolds. We've helped homeowners and developers navigate Gloucestershire's building control process with zero hassle.
Oxfordshire
Part L compliance and energy performance assessments for projects across Oxford, Banbury, Bicester, Witney, and the wider Oxfordshire area. Design stage and as-built SAP for residential developments of all sizes.
Wider England & Wales
As government-accredited OCDEA assessors (EES/030713), our SAP calculations and EPCs are legally valid across the whole of England and Wales. We regularly work with developers on projects outside our core regions — contact us wherever your site is located.

Looking for SAP calculations near you? Whether you're a homeowner with a single extension in Cheltenham, a developer with a multi-plot scheme in Birmingham, or an architect working on a conversion in Bristol — our qualified SAP assessors deliver accurate, compliant results with transparent pricing and no hidden fees. Call 01386 365145 or email us to get started.

FAQ

Common questions about SAP calculations.

For new-build homes, SAP calculations are carried out in two stages:

Design Stage: Your assessor reviews construction specifications — insulation levels, window types, and heating systems — and models the predicted energy performance. Key targets (TER, TFEE) are checked against your design's Dwelling Emission Rate (DER) and Fabric Energy Efficiency (DFEE). You receive a Predicted Energy Assessment.

As-Built Stage: Once construction completes, the assessor verifies the as-built details, including any changes from the original plans, air tightness test results, and final boiler models. If everything complies, an EPC is issued.

You need a SAP calculation by law when building a new home or making significant renovations that fall under Part L building regulations. Consider this from the very start of your design to meet all requirements and get the best value from the guidance.

With Part L 2021, Accredited Construction Details (ACDs) are no longer available, and generic Psi values are being phased out. You'll need bespoke or manufacturer-calculated Psi values. Relying on default values often won't achieve compliance.

Addressing energy efficiency early in design makes a significant difference:

  • Engage a SAP assessor early to identify efficient design choices that meet compliance and save costs
  • Share detailed plans upfront to highlight the most suitable solutions for your project
  • Clarify goals and constraints so your assessor can recommend options like improved insulation, smarter glazing, or renewables
  • Consider energy strategies before building — air tightness details and orientation for solar gain must be woven into initial design

Most design stage SAP reports are delivered within 3–5 working days of receiving complete information. The timeline can vary based on project complexity, how quickly information is provided, and building control responsiveness.

For larger developments or projects requiring value engineering analysis, allow slightly longer. We always confirm expected turnaround at the point of quoting.

As insulation has improved and space heating demand has dropped in modern homes, water heating now takes up a larger share of total energy use. This means reducing water heating demand is just as important as tackling space heating.

  • Install WWHR systems to capture warmth from shower and bath water
  • Optimise wet room layouts — positioning bathrooms near each other makes shared WWHR pipes easier
  • Choose efficient hot water appliances like high-performance cylinders and smart controls
  • Reduce hot water usage with aerated taps and low-flow showerheads

Default Psi values assume higher heat loss at critical junctions, which can force you to over-specify materials. Calculating values tailored to your construction details gives you:

  • Improved accuracy — your SAP results reflect actual performance, not worst-case assumptions
  • Cost efficiency — specify only what's required, avoiding unnecessary upgrades
  • Design flexibility — reuse bespoke values across multiple projects with consistent construction methods

SAP calculations are sometimes required for existing buildings — typically when major renovations occur or significant changes affect the property's energy efficiency. A simpler assessment called Reduced Data SAP (RdSAP) is used for existing properties not undergoing major work, providing useful insights and highlighting areas for improvement.

If you're unsure, we recommend talking with us or your local building control authority to determine what applies to your project.

Yes. We are based in Worcester and serve Birmingham, Bristol, Worcestershire, Gloucestershire, Oxfordshire, and the wider West Midlands as our core areas. We understand local planning and building control expectations in each region and work regularly with their teams.

As government-accredited OCDEA assessors (registered number EES/030713), our SAP calculations and EPCs are legally valid across the whole of England and Wales — so we also take on projects outside our core regions. Contact us wherever your site is located.

Decentralised Mechanical Extract Ventilation (DMEV) systems allow you to use specific fan power figures for the exact product installed, rather than generic values. If the fan is especially efficient, the lower power consumption directly improves your SAP assessment.

This helps you avoid over-specifying equipment and can reduce the overall energy demand of your property. Look for models with proven low power usage from reputable brands for the best results.

Related services

Services that work alongside SAP calculations.

Part O
Overheating Assessments
Required alongside SAP for new dwellings. We coordinate both to ensure your design meets Part L and Part O simultaneously.
Part L
Air Tightness Testing
Your air test result is a direct input into the as-built SAP. We coordinate both to avoid delays at completion.
Part L
SBEM Calculations
For non-domestic buildings. If your development includes commercial units alongside residential, we handle both SAP and SBEM.
Full Package
Value Engineered Compliance
SAP, overheating, air testing, and more — coordinated across your whole scheme with savings analysis included.
3–5 day turnaround

Ready to get your SAP calculation started?

Send us your drawings and specification — we'll provide a clear quote and timeline, and flag any compliance risks before you commit.

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