SAP (Standard Assessment Procedure) is the government-approved method for measuring the energy performance of new and existing dwellings — and it sits at the heart of Part L building compliance. With energy efficiency requirements tightening year on year, navigating the regulations has never been more complex.
We provide full support and advice on Part L compliance from initial design through to building control sign-off — working with architects, developers, and homeowners to find the most practical route to a pass. Alongside standard SAP calculations, we also provide bespoke heat loss modelling at the junctions that exist in every building — where walls meet floors, roofs, windows, and corners. Rather than relying on conservative government defaults, these bespoke calculations use the actual detail of your building, which typically improves the overall energy performance result significantly. That improvement greatly increases the chances of achieving Part L compliance and can provide useful headroom — often meaning less spend on insulation, glazing, or renewables to get there.
We also support extensions and conversions, whether building control requires a full SAP assessment or a simpler Weighted Area Calculation. Whatever stage you're at, we'll advise on exactly what's needed — nothing more.
We don't just run calculations — we advise. Every project starts with a conversation about what you're trying to achieve, so the work we do is the right work for your specific situation.
Before we start any assessment, we take the time to understand your project — what building control has asked for, what your design looks like, and what the simplest compliant route is.
Every assessment uses verified inputs and documented evidence — designed to pass Elmhurst audits first time, with no need for revisits.
Fully current with Part L 2021, SAP 10.2, and the DPER / TFEE primary energy and fabric metrics — so you don't have to be.
We explain what the numbers mean for your project and what to do if something isn't passing — not just a report in your inbox.
Not sure what you need?
We'll tell you which route makes sense for your project — before you commit to anything.
Whether building control has asked for a full SAP, a weighted area calculation, or you're simply not sure, get in touch and we'll advise on the most straightforward path to compliance.
We advise on which services are actually needed for your situation — and won't recommend anything that isn't. All work is carried out by a qualified, regulated assessor.
Full SAP 10.2 compliance assessments for new build dwellings under Part L1A, meeting all three targets required by the 2021 regulations.
Where a dwelling has more glazing than the notional standard allows, a weighted area calculation demonstrates compliance by compensating with improved U-values elsewhere in the envelope.
Linear thermal transmittance (ψ — psi) values quantify heat loss at junctions. Accurate PSI values reduce the penalty applied in SAP for thermal bridging, often improving DER and DPER targets significantly.
A clear, standalone service for builders and homeowners navigating building regulations for extensions. We calculate the thermal transmittance (U-value) of your proposed construction — confirming it meets the minimum standards required by Part L before work begins.
We keep things simple and transparent — you'll always know where you are and what's coming next.
A quick conversation about what you're building and what building control has asked for. We'll advise on the right approach before any work begins.
We confirm exactly what's included, the timescale, and the fee upfront. No surprises, no scope creep.
We carry out the assessment and talk you through the results — flagging any compliance issues early and recommending practical solutions.
On as-built completion, we lodge with Elmhurst and issue the EPC — everything your building control officer needs.
SAP (Standard Assessment Procedure) is the UK government's approved methodology for assessing the energy performance of dwellings. Since October 2023, Part L 2021 introduced three compliance targets.
Failing any one target means the dwelling does not comply with building regulations — even if the others pass. Getting all three right from the design stage avoids costly late-stage revisions.
Dwelling Emission Rate vs Target Emission Rate
How much CO₂ the home will produce each year through heating, hot water, and lighting. The DER (your building's actual figure) must come in below the TER (the permitted maximum) — think of it as a carbon speed limit the design must stay under.
Dwelling Primary Energy Rate vs Target Primary Energy Rate
Looks beyond the home itself to account for the energy lost generating and delivering power to it — electricity, for example, requires more energy to produce at the power station than arrives at the socket. This metric encourages efficient heating systems and on-site renewables. Again, the dwelling's figure must beat the target.
Dwelling Fabric Energy Efficiency vs Target Fabric Energy Efficiency
Focuses purely on the building's insulation, windows, and airtightness — independent of what heating system is installed. A good fabric score means the home loses less heat in the first place, reducing running costs regardless of the energy source.
New build dwellings typically achieve Band B or A under Part L 2021. Energy Compass targets Band B minimum on all assessments.
Thermal bridging at junctions is a significant and often overlooked source of heat loss. Calculated PSI values replace SAP's conservative defaults — improving your assessment result and helping achieve compliance.
A Psi-Value (ψ-value) measures the rate of heat loss through a junction — the point where two thermal elements meet, such as an external wall and a ground floor. Heat loss at these junctions is referred to as non-repeating thermal bridging, which can account for up to 25% of the total fabric heat loss of a building.
The government has updated Building Regulations and the calculation methodology used to determine compliance. The introduction of strict new targets and the removal of Accredited Construction Details means it is increasingly difficult to comply using SAP default values alone. Calculated Psi-Values are more accurate — and under Part L 2021 they are often essential to achieve a pass.
Energy Compass are accredited members of the Elmhurst PSI-Value Competency Scheme, with the skills and knowledge to undertake 2D PSI calculations to BR 497 methodology. We can help you achieve compliance with Building Regulations and provide a report accepted by building control across England, Wales, and Scotland.
PSI modelling is priced at £50 per junction. A typical single new build dwelling has between 10 and 15 junctions, giving an indicative cost of £500–£750 — a small outlay that can be the difference between compliance and a costly redesign. Contact us for a fixed quote.
Illustrative impact of replacing SAP's default thermal bridging allowance with accredited 2D PSI calculations.
Common junctions we model
All calculations produced to BR 497 methodology by an Elmhurst PSI-Value Competency Scheme member, accepted by building control across England, Wales, and Scotland.
Get an instant indicative quote below — no contact details required. Simply enter the number of dwellings and we'll show you a price breakdown immediately.
Whether you have drawings ready or just need advice on what's required — even if you're not sure what to ask — get in touch and we'll point you in the right direction.
ℹ️ What to send us
Floor plans, elevations, site location, intended heating system type, and any U-value specifications you already have. The more detail at the design stage, the more accurately we can assess compliance from the outset.