A new energy assessment methodology for residential construction is on the horizon. Harry Hinchliffe, Energy Consultant and BREEAM Assessor at C80 Solutions, outlines the changes and their impact on planning and design.

Like every other industry, construction has been preoccupied with unprecedented circumstances over the past year. As we still come to terms with the impact of covid, it’s easy 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. Following a consultation launched by the Department for Business, Energy & Industrial Strategy (BEIS), SAP 10 was formulated to replace the increasingly outdated SAP 2012 methodology.  SAP 2012 has been criticised for various shortcomings, including its poor representation of how well a design is built. Under SAP 10, assessments will incorporate a detailed audit trail relating to the assessment and verification of design and construction across a project timeline. Current estimates expect SAP 10 to come into play in June 2022, but the timetable is not set in stone. The official arrival could be delayed, but it’s also entirely possible that it could be brought forward.

A greener grid brings electric heating to the fore

Probably the most significant change between SAP 10 and its predecessor is a reduction in the CO₂ emission factor for electricity. The new methodology has adjusted the prices, CO₂ and primary energy factors of various fuel types recognised in SAP. Electricity’s CO₂ emission factor has decreased from 0.519 kgCO2/kWh to 0.233 kgCO2/kWh, reflecting a much greener national grid which increasingly benefits from electricity produced by renewable energy technologies.

As a result, SAP 10 makes it easier to achieve compliance with electric heating. As electricity becomes the most environmentally friendly and best performing heating method for EPC ratings, a move from gas to electric heating will become more viable, causing a significant impact on the way new homes in the UK will be heated. 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.

A new formula for photovoltaic energy

Designers of apartment developments should be aware of the effect of SAP 10 on calculations for photovoltaic (PV) panels. It will demand much more thought in the design and installation of systems. For example, electricity generated by PV systems is factored into SAP 2012’s calculations for a flat even when there is no direct connection to the property. That often causes a misrepresentation in the many apartment buildings where only one connection exists, to a landlord’s supply.

SAP 10 addresses that issue with a new formula which only factors in PV supply if the apartment is directly connected. This change has clear implications for developments which need to meet carbon reduction requirements as a planning condition. SAP 10 provides the option to account for battery storage technology when calculating electricity generated by PV. The methodology can also account for cases where PV is directly feeding an immersion coil in a cylinder.

More accurate heating patterns

SAP 2012 has also been criticised for an inaccurate representation of energy use in domestic properties. Its calculations are based on different standard heating patterns attributed to weekdays and weekends, but further studies demonstrate that this distinction in assumed patterns does not necessarily bear out in real life. Those conclusions were made pre-pandemic, so the probability of any difference is even less likely now that working from home has become much more widespread.

SAP 10 provides more detailed calculations and applies the same standard heating pattern for every day of the week. Heating will now be defaulted to being used less at the weekends. In practice, this assessment will result in a reduction in energy use and energy costs.

New calculations for hot water use

SAP 10 will introduce a more precise estimate of hot water demand, accounting for factors such as the number of showers and baths within a dwelling as well as shower types and flow rates (for example, electricity use from instantaneous electric showers will now form part of assessments). These new calculations will in most cases result in higher energy use in assessments.

Greater detail in lighting assessment

Lighting is another factor that will see a significant overhaul. Under SAP 2012 the lighting assessment is extremely basic, only accounting for the number of low energy fittings being installed, but SAP10 will recognise the use of new lighting types which provide higher efficiency. The assessment of fixed lighting design will involve a level of detail more in line with the non-domestic methodology known as SBEM.

Its calculation of lighting energy use will be based on the quantity and efficiency of the fixed lighting whilst taking into account the contribution of natural light, bringing window design into the assessment mix. This will make it important to know more detail at the design stage regarding the specification of windows and lighting.   SAP 10 will calculate a ‘reference lighting capacity’ based on the property’s 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.

Changes to thermal mass and ventilation

Thermal mass of building materials – their ability to absorb and store heat – is another aspect of energy performance that will be subject to more detail under SAP 10. In building design and construction, thermal mass provides a buffer against rapid fluctuations in temperature.

SAP 2012 used indicative options of low, medium and high to assess Thermal Mass Parameter (TMP). SAP 10 has removed these ratings and instead all dwellings 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 change the way designers address the risk of overheating, reducing the amount of ventilation that they can assume is being gained from open windows, with factors such as outside noise and security taken into consideration. As a result, designers will be encouraged to reduce heat gains in other areas.

New methods to record thermal bridging

Greater precision will also be applied to the recording of thermal bridging. Under SAP 2012, heat losses through junctions in the construction have been offset by using the ACD (Accredited Construction Details) scheme. However, ACD is no longer considered to be sufficiently accurate in the context of current building and the scheme has been removed under SAP 10. Assessment will therefore need to be based on other established sets of construction details. Construction professionals may have to re-think many of their design practices and standard details. Assessors should encourage the modelling of more junction details to enable accurate calculation of psi values which measure the rate of heat loss through a junction.

SAP 10 has altered many of the default psi values: rooms within the roof constructions will be penalised by an increase in R1-R9 junctions (a new R10 Junction has also been added for any other roof or room in roof junction not covered by R1-R9). 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. This will entail a stiffer penalty for developers who fail to consider heat loss through building junctions.

Time to embrace the change

As an energy consultancy, C80 Solutions has examined the proposed changes of SAP 10 and we consider them a welcome addition to the calculation 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 the energy grid continues to become greener, SAP 10 gives developers the opportunity to be more flexible in their design whilst still working towards the government’s carbon reduction targets.

Although SAP 10’s details were published some time ago, getting to grips with the implications dropped down the list of priorities in the wake of the pandemic. 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.

C80 Solutions has teamed up with electric heating manufacturer, ThermoSphere, to launch TalkSAP10, an initiative helping the construction sector to understand and embrace the changes. Construction professionals can join the conversation and register for TalkSAP10 by visiting www.thermosphere.com/talk-sap-10