SAP vs SBEM: Which Energy Assessment Do You Need?

If you’re dealing with Building Regulations Part L compliance, you’ll encounter two main calculation methods: SAP and SBEM. Using the wrong one means a rejection from Building Control, wasted time, and delayed projects.

The difference is usually straightforward: SAP is for new build homes, SBEM is for commercial buildings. But the grey areas cause confusion. Mixed use buildings, live-work units, care homes, and student accommodation often leave people guessing.

This guide explains exactly which calculation you need, why it matters, and what happens if you get it wrong.

The Basic Rule: Domestic vs Non-Domestic

SAP (Standard Assessment Procedure) Calculations covers new dwellings. All new dwellings in the UK need a SAP Calculation to prove they meet Approved Document (Part) L1A of the building regulations. This is relevant for:

• Houses and bungalows
• Flats and apartments
• Holiday homes
• Student accommodation (self-contained units)
• Care homes (self-contained units)

SBEM (Simplified Building Energy Model) Calculations cover commercial and non domestic buildings. Compliance with Approved Document L2A is shown via a BRUKL report. These are the types of commercial buildings covered by SBEM:

• Offices
• Retail units
• Warehouses
• Schools
• Hotels
• Restaurants
• Industrial buildings

It seems pretty straight forward, but real world projects are not always this clear cut.

The Grey Areas That Cause Problems

Mixed-Use Buildings

Shop with flat above? Office with caretaker flat? In these cases, both are usually required. The commercial element of the building will need SBEM where the domestic part will need a SAP Calculation.

Each part is assessed separately against its relevant Part L requirements. The shop must meet Part L2 targets using SBEM. The flat must meet Part L1 targets using SAP.

Live-Work Units

Quite rare, but we do see these from time to time. It is possible that these buildings could need both SBEM and SAP Calculations. Usually though, Building Control apply a little discretion and and pick the majority usage. Live/work classified units would need SAP, work/live units need an SBEM. Building Control will clarify for you as part of the planning application.

Student Accommodation, Care Homes & Supported Living

This is another example where both could be required. If the unit has its own front door, kitchen and bathroom that unit would need a SAP Calculation. But any shared areas, like communal kitchens, lounges and bathrooms would likely need an SBEM Calculation. This is particularly true in where the accommodation contains only a bedroom, with most / all other living facilities being shared between rooms, like a hotel.

Hotels

Standard hotel rooms need SBEM. Serviced apartments with kitchen facilities that could work as permanent dwellings might need SAP. The length of typical stay and facilities provided determine which applies.

If you are unsure which energy assessment you need to fulfil Part L compliance, check your planning documents, it should be on there. Your building control officer / approved inspector will also be able to help. We’re happy to provide guidance too, give us a call on 0333 567 9010 and we can check the technical documents.

Why Using the Right Calculation Matters

The wrong energy assessment will be rejected by building control. Commercial buildings and dwellings are assessed using different criteria, specific to their use.

• Different targets apply to each assessment.
  • SAP Calculations are passed when a building hits the DER (emissions), DPER (energy) & DFEE (fabric). All three need to pass.
  • With SBEM, two different metrics are used, the BER (emissions) and BPER (energy). They are similar, but calculated in completely different ways.
• Although both domestic and commercial EPCs use the A-G scale with A being the most energy efficient, how these scores are calculated is very different. Commercial EPCs classify an A Band as between 0-25 points (less is better) where domestic properties are classified as a Band A with a score above 92 (more is better). There is not a way to convert between the two assessments.
• Different software is used for each assessment. We use Design SAP 10 (by Elmhurst Energy) for dwellings and for non domestic, iSBEM (government maintained) or DesignBuilder is used.
• The costs vary for each assessment too. SAP calculations tend to be cheaper than an SBEM Calculation. Non domestic buildings and the assessment are more complicated. There are also few qualified assessors.

Key Differences in the Calculations

Both SAP and SBEM assess the predicted energy performance of the building, but behind the scenes, they work differently.

Within SAP, the heating, hot water and lighting demand is based on fixed occupancies and patterns for the size of the building. The types of building services that can be modelled is on the basic end too.

Whereas in SBEM, complex HVAC systems can be modelled with a different system assigned to each room if required. There is much more freedom with lighting with some specific commercial only adjustments like process gains / losses and display windows / lighting can be modelled too.

SBEM handles the complexity of commercial buildings where every zone might have different requirements. A restaurant kitchen, dining area, and toilets all have different energy profiles. SAP generalises lots of information based on some standard assumptions.

Common Conversion Projects

Conversions often require a new energy assessment too. Let’s look at some of the common projects that we handle.

Commercial to Residential

You would need SAP Calculations for this. Even if the old property has a valid SBEM, each new dwelling within the building will need a SAP Calculation.

Residential to Commercial

Converting a house to offices or a nursery? Previous SAP calculations (if they exist) are irrelevant. You need new SBEM calculations for the commercial use.

Barn to Holiday Let

Agricultural buildings don’t have energy calculations. Converting to holiday accommodation that works as a dwelling needs SAP. If it’s more like hotel accommodation (no kitchen facilities), you might need SBEM.

House to Flats

If the number of dwellings within a building changes, whether that is up or down, each of the new dwellings needs a SAP Calculation.

What Building Control Actually Wants

Building Control needs the right calculation type at both stages:

Design stage: Submit the appropriate calculation (Design SAP or SBEM) showing the design meets Part L targets.

Completion: Provide as-built calculations and the correct EPC type. Domestic EPC for SAP projects, commercial EPC for SBEM projects.

Using the wrong calculation type means starting over. Building Control won’t accept SBEM calculations for a dwelling, regardless of how detailed they are.

Quick Decision Guide

Ask these questions:

1. Could someone live here permanently?
Yes, with kitchen and bathroom = SAP
No = SBEM

2. Does each unit have its own front door?
Yes = probably SAP
No, shared entrance = probably SBEM

3. What does the planning permission say?
C3 use class = SAP
Other use classes = usually SBEM

4. Is there a commercial element?
Mixed use = both calculations needed
Pure residential = SAP only
Pure commercial = SBEM only

Costs and Timescales

SBEM calculations typically cost more than SAP:

• SAP calculations: £180-500 for most dwellings
• SBEM calculations: £500-2000+ depending on building complexity
• Mixed-use buildings: Need both, so budget accordingly

Timescales are similar (3-5 days typically), but complex commercial buildings take longer to model. Finding SBEM assessors can be harder than SAP assessors, especially for urgent projects.

The Bottom Line

Getting this right matters. The wrong calculation means project delays, additional costs, and Building Control rejection. When in doubt, describe your project to an assessor before commissioning work.

For mixed-use or unusual buildings, clarify with Building Control which calculations they expect. They’d rather answer questions upfront than reject incorrect submissions later.

Remember: SAP for homes, SBEM for commercial. The edge cases need careful consideration, but that basic rule covers 90% of projects.