New energy assessment methodology is on the horizon. Harry Hinchliffe, Energy Consultant and BREEAM Assessor at Leeds-based C80 Solutions, outlines the changes and their impact on design.

Having faced unprecedented challenges over the past year, it has been easy for the construction industry to overlook other issues which were on the sector’s radar before the pandemic hit. One such issue is an expected (and many say overdue) overhaul of the Standard Assessment Procedure (SAP) for assessing dwellings for their energy efficiency credentials, with SAP 10 replacing the increasingly outdated SAP 2012 methodology. Current estimates expect SAP 10 to come into play in June 2022. The official arrival could be delayed, but it’s also entirely possible that it could be brought forward.

The most significant change is a reduction in electricity’s CO2 emission factor, decreasing from 0.519 kgCO2/kWh to 0.233 kgCO2/kWh, reflecting a much greener national grid which increasingly benefits from renewable energy technologies. This will make it easier to achieve compliance with electric heating. With plans also in place to prohibit gas boilers in new build homes by 2025, many developers are likely to turn to heat pumps, electric panel heaters and electric underfloor heating as their primary heat sources. There could also be an increase in the use of electric boilers with an indirect cylinder for hot water.

Electricity generated by photovoltaic (PV) panels is factored into SAP 2012’s calculations for a flat even when there is no direct connection to the property, causing a misrepresentation in the many apartment buildings where only one connection exists, to a landlord’s supply. SAP 10’s formula only factors in PV supply if the apartment is directly connected, with clear implications for developments that need to meet carbon reduction requirements as a planning condition.

SAP 2012’s representation of energy use in domestic properties is based on different standard heating patterns for weekdays and weekends, but further studies demonstrate that this distinction does not necessarily bear out in real life. The probability of any difference is even less likely now that working from home has become much more widespread.  In contrast, SAP 10 applies the same standard heating pattern for every day of the week. It will also introduce a more precise estimate of hot water demand, accounting for the number of showers and baths as well as shower types and flow rates (for example, electricity use from instantaneous electric showers will now form part of assessments).
SAP 2012’s extremely basic lighting assessment only accounts for the number of low energy fittings. SAP10 will involve more detail in line with the non-domestic methodology known as SBEM and will recognise the use of new lighting types which provide higher efficiency. It will account for the contribution of natural light, bringing window design into the assessment mix.   A ‘reference lighting capacity’ calculation will be based on floor area and solar gains. If the lighting design falls outside of this reference lighting range (either above or below), the predicted lighting energy will be increased to account for ‘poor’ lighting or ‘surplus’ lighting.

SAP 10 will remove SAP 2012’s indicative options of low, medium and high to assess Thermal Mass Parameter (TMP) and instead will include a detailed calculation of a building’s actual TMP based on build material, construction, and kappa values which are referenced in BS EN ISO 13786. SAP 10 will also reduce the assumed amount of ventilation gained from open windows, with factors such as outside noise and security taken into consideration.

In SAP 10’s thermal bridging provisions, the Accredited Construction Details (ACD) scheme used under SAP 2012 is no longer considered to be sufficiently accurate. Assessment will be based on other established sets of construction details, prompting a re-think of many design practices and encouraging more junction details to enable accurate calculation of psi values. Where no details of thermal bridging are provided, the default y-value used in assessments has been raised from 0.15 w/m2k to 0.2 w/m2k, entailing a stiffer penalty for developers who fail to consider heat loss through building junctions.

SAP 10 is a welcome update to the methodology, more accurately representing how buildings perform. Its role in encouraging more precision and detail in energy assessment will prove to be a very positive influence across residential construction.

As we tentatively approach a return to normality, SAP 10 is likely to return to the forefront of the industry’s thoughts. The need to understand and embrace its principles is now a much more pressing matter.