SAP vs SBEM vs Dynamic Thermal Modelling: Which Energy Assessment Does Your Project Need?

Whether you’re designing a new home, a commercial development or a complex mixed‑use scheme, understanding energy assessment methods is essential for meeting Part L compliance, securing planning approvals and achieving sustainability ambitions. These assessments are often a legal requirement for building projects to ensure compliance with building regulations and environmental standards.

It is crucial to conduct SAP, SBEM, and dynamic thermal modelling assessments at the design stage to optimize building performance and ensure regulatory compliance.

Many clients are unsure when to commission a SAP assessment, an SBEM calculation or a dynamic thermal model. This guide clarifies the differences, shows when each method is appropriate and highlights how they integrate with BREEAM, Whole‑Life Carbon Assessment (WLCA) and other services. If you’re looking for background on SAP and SBEM, see our What are SAP calculations? post and the service pages for SAP calculations and SBEM calculations.

Introduction to Energy Assessments

Energy assessments form the backbone of any smart construction approach, giving you and your design team the clarity you need to understand and optimize how your building performs. Whether you're developing new residential projects or working on commercial properties, getting a handle on energy use is essential for hitting efficiency targets and staying compliant with regulations. The Simplified Building Energy Model (SBEM) provides the government-approved framework for evaluating commercial building energy efficiency, while the Standard Assessment Procedure (SAP) handles the residential side of things. When your project demands deeper insight, Dynamic Simulation Modelling (DSM) delivers the detailed analysis you need to understand thermal performance, energy consumption, and broader environmental impacts. By putting these energy assessment tools to work, you can spot real opportunities to cut energy use, boost thermal performance, and demonstrate regulatory compliance – ultimately delivering buildings that are both more sustainable and more cost-effective for the long haul.

What is SAP?

Standard Assessment Procedure (SAP) is the UK government’s methodology for estimating the energy performance of dwellings. It serves two main purposes: demonstrating compliance with Part L of the Building Regulations and generating an energy performance certificate (EPC) for homes, which is a legal requirement for new dwellings. The energy rating shown on the certificate quantifies the building’s energy efficiency on a scale from A to G. SAP assessments model a home’s heating, hot water, lighting, ventilation, and fabric performance to evaluate overall energy efficiency. From this, several key metrics are produced:

• DER (Dwelling Emission Rate): carbon emissions performance.
• DFEE (Dwelling Fabric Energy Efficiency): how well the fabric reduces energy demand.
• DPER (Dwelling Primary Energy Rate): primary energy performance in line with Part L.

Together, these outputs determine whether a dwelling meets regulatory compliance and provide the foundation for its Energy Performance Certificate (EPC). The current version is SAP 10.2, though it will be replaced by the Home Energy Model for compliance with the future homes standards.

Key points:

• Use SAP for new build homes, new buildings up to ~450 m², or refurbished homes; it applies to houses, flats, care homes and some student accommodation. For very small dwellings (< 50 m²), SAP still applies but simplified modelling is often possible.
• SAP produces an EPC and demonstrates that the building complies with Part L, which is essential for achieving compliance at both design and as‑built stages, supported by photographic evidence (BREL/BRWL).
• SAP can interface with Whole‑Life Carbon Assessment: decisions about fabric, hot‑water systems and ventilation affect both operational and embodied carbon. Our WLCA team can model these interactions to meet net‑zero objectives.

What is SBEM (Simplified Building Energy Model)?

SBEM stands for Simplified Building Energy Model and is a government‑approved methodology developed by BRE for assessing the energy performance of non‑domestic buildings. It is a mandatory requirement for commercial buildings and commercial properties under new building regulations. SBEM models heating, cooling, ventilation, lighting and hot water in offices, schools, retail units and other commercial or public buildings. SBEM is required for building regulation compliance and is used to demonstrate that a commercial building complies with the latest standards. It generates a Building Emission Rate (BER) which is compared against a Target Emission Rate (TER) to show Part L compliance—a mandatory requirement to ensure the calculated CO2 emission rate does not exceed the TER. SBEM outputs BRUKL (Building Regulations UK Part L) or BRER reports, which are submitted to Building Control alongside design drawings. SBEM is required for both new builds and major refurbishments of commercial properties. SBEM also underpins non‑domestic EPCs.

Key points:

• SBEM (Simplified Building Energy Model) is required for new-build or refurbished non-domestic buildings with a floor area over 50 m². This includes offices, shops, warehouses, hospitals, hotels, and other commercial or public buildings.If you are working on an extension or a new-build non-domestic scheme above this threshold, SBEM calculations are mandatory to demonstrate compliance with Part L of the Building Regulations.
• SBEM is less detailed than dynamic modelling but sufficient for most straightforward commercial designs.
• For mixed‑use schemes, you may need both SAP and SBEM: for example, apartments assessed under SAP and ground‑floor retail assessed under SBEM. Coordination across interfaces is critical; our consultants can manage both assessments and ensure consistent inputs.

Qualified energy assessors are responsible for conducting SBEM calculations and ensuring energy compliance for all relevant builds.

What is Dynamic Thermal Modelling?

Dynamic thermal modelling (DTM) uses hourly simulation to predict temperature, energy use and comfort over time. Tools like IES VE and TAS build a 3‑D model of the building, capturing shading, occupancy patterns, thermal mass and HVAC control strategies. DTM can analyze annual energy consumption, lighting systems, HVAC systems, and air flow to optimize building performance. It is more computationally intensive than SAP or SBEM but provides deeper insight into overheating risk, natural ventilation performance and demand‑side response strategies.

DTM is typically required when:

• Complex designs or mixed‑use buildings have irregular shapes, atria, large glazing ratios or multiple HVAC zones. SAP and SBEM cannot adequately model these nuances.
• Planning conditions demand overheating assessments, such as CIBSE TM52 (non‑residential) or TM59 (residential), which require dynamic simulation. DTM can assess solar gain, air temperature, and the risk of overheating during the summer months to ensure occupant comfort and regulatory compliance.
• Passivhaus, Net‑Zero and BREEAM Outstanding projects seek to optimise comfort and energy use; DTM enables detailed optimisation and can produce data for BREEAM credits (e.g., Ene 02 prediction of operational energy).
• Acoustic studies or daylight simulations are needed. Many software suites integrate energy, daylight and acoustics modelling, supporting an integrated design approach. DTM can also be used to calculate psi values for thermal bridging analysis.

Building Regulations and Compliance

Building regulations ensure that all new and existing buildings meet minimum standards for energy efficiency and environmental performance, and we help you navigate these requirements with confidence. For your commercial buildings, you'll need a mandatory SBEM calculation to demonstrate compliance with Part L of the building regulations, ensuring your building hits the targets for energy consumption and thermal performance that matter. When you're developing residential buildings, including new homes and apartment blocks, you'll require a SAP calculation to show that your project meets the required standards. We use Dynamic Simulation Modelling (DSM) to give you a more accurate prediction of your building's energy consumption and thermal performance, allowing your design team to fine-tune the approach and ensure you achieve compliance with building regulations seamlessly. With the introduction of Approved Document O in 2022, all your new residential buildings must be designed to mitigate the risk of overheating—a requirement that DSM is particularly well-suited to address, and we're here to guide you through it. By working with us on dynamic simulation modelling, you can ensure your buildings not only comply with current regulations but also deliver the improved comfort and energy efficiency that your occupants deserve.

Benefits of Energy Assessments

Energy assessments offer practical, comprehensive benefits that we help building owners, designers, and developers realize throughout their projects. By evaluating your building's energy performance, efficiency, and thermal characteristics, these assessments guide you toward meaningful improvements that reduce energy consumption and cut operational costs where it matters most. We work with you to ensure compliance with building regulations, minimizing risks and avoiding potential penalties that can derail projects. Through detailed analysis using proven tools like SBEM, SAP, and DSM, our team helps design teams optimize building performance, reduce carbon emissions, and enhance the real-world sustainability of their developments. Better energy ratings make your buildings more attractive to buyers and tenants while increasing property value—outcomes that align with your project goals from the start. Ultimately, energy assessments provide a practical pathway to energy conservation, regulation compliance, and buildings that are comfortable, efficient, and future-ready throughout construction and beyond, and we're here to guide you through every step of that process.

When to use SAP, SBEM or DTM – a quick decision guide

Our energy consultants can provide advice on achieving emission targets, integrating renewable technologies, and maximizing energy savings to meet the targets set by planning authorities or sustainability frameworks. This includes guidance on compliance strategies, system selection, and optimizing building performance to support your sustainability goals.

Integration with BREEAM, WLCA and other services

BREEAM Version 7 encourages projects to move beyond prescriptive metrics and adopt performance outcomes. Recent updates to BREEAM and other standards place greater emphasis on building design strategies that enhance energy savings and sustainability. Dynamic modelling feeds into BREEAM’s Ene 02 – prediction of operational energy credit and helps demonstrate compliance with overheating and thermal comfort requirements. DTM outputs can also support Whole‑Life Carbon Assessments, where accurate operational energy predictions feed into lifecycle carbon modelling and optimize building design for compliance and performance. Conversely, SAP and SBEM results feed into LCA by informing operational carbon assumptions.

When you work with Darren Evans, we can provide:

• SAP and SBEM assessments across all project stages, ensuring consistent assumptions and integrated outputs.
• Dynamic thermal modelling to satisfy TM52/TM59, Passivhaus, overheating and demand‑response requirements.
• BREEAM assessments and WLCA services, using energy modelling data to secure credits and quantify embodied carbon.

Practical steps to choose the right method

1. Define your building type and size – Is it domestic, non‑domestic or mixed‑use? How large is it? This determines whether SAP or SBEM applies, and whether dynamic modelling is beneficial.
2. Check planning and regulatory requirements – Some local authorities require TM52/TM59 overheating assessments or BREEAM credits that necessitate DTM. Part L compliance always requires SAP or SBEM.
3. Consider design complexity and performance targets – Unusual geometry, high glazing ratios, low‑carbon technologies and Passivhaus standards all point towards dynamic modelling.
4. Engage experts early – Involving qualified energy assessors and energy modellers at the design stage is crucial for achieving compliance. Their expertise ensures that whichever method you use, the outputs can inform both compliance and sustainability strategies.
5. Plan for integration – Coordinate SAP, SBEM and DTM models so that inputs align, and use results to inform whole‑life carbon and BREEAM submissions.

Ready to choose the right energy assessment?

Selecting the appropriate methodology doesn’t have to be complicated. Our team at Darren Evans can review your project brief, recommend the correct assessment (SAP, SBEM or DTM), and integrate it with BREEAM and WLCA services to meet your net‑zero goals.

If you have any questions, contact us for a consultation. We can also provide a quick quote via our SAP calculations or SBEM calculations pages, or help you explore dynamic thermal modelling as part of a BREEAM assessment.