SAP 2012 and Heating Systems
This article looks at the built in bias towards mains gas heating in the current SAP methodology, and the considers the likely impact of planned changes in SAP10 which should redress the balance in favour of greener electrical heating systems.
Standard Assessment Procedure (SAP) calculations on the energy and environmental performance of dwellings are currently based on SAP2012 methodology which uses out of date criteria to assess the impact of electric heating on building design. Significant changes to SAP are planned towards the end of 2021, which will update this methodology and ensure it reflects the greener nature of the electricity grid and which should help to promote the use of renewable energy.
What Is SAP?
The Standard Assessment Procedure (SAP) is a UK government approved methodology used to assess and compare the energy and environmental performance of dwellings. SAP was developed by the Building Research Establishment (BRE) based on their Building Research Establishment Domestic Energy Model (BREDEM) methodology.
SAP works by assessing how much energy a dwelling consumes when providing a defined level of comfort. The assessment is based on standardised assumptions for occupancy and behaviour. This enables a like-for-like comparison of dwelling performance. Related factors, such as fuel costs and CO2 emissions can be determined from the assessment
SAP quantifies a dwelling’s performance in terms of:
- energy use per unit floor area
- a fuel-cost-based energy efficiency rating (the SAP Rating) and emissions of CO2 (the Environmental Impact Rating)
- These indicators are based on estimates of annual energy consumption for the provision of space heating, domestic hot water, lighting and ventilation. Other SAP outputs include estimate of appliance energy use, the potential for overheating in summer and the resultant cooling load
- The SAP result is a measure of the actual DER (Dwelling Emissions Rate) against a TER (Target Emissions Rate) expressed as Kg of CO2 per m2 per annum.
SAP has been updated several times since its introduction, and the current standard is SAP2012. It’s a generally effective means of assessing energy and carbon performance of dwellings and enables like-for-like comparisons between properties, but is now out of date in several key areas. SAP2012 will therefore be replaced when the new versions of building regulations are introduced at the end of 2021.
When are SAP Assessments Needed?
All new dwellings require a SAP Assessment to meet Building Regulations. In addition, it is often the case that conversions, renovations and extensions require a SAP Assessment. UK Energy Assessors can advise when SAP Assessments are needed for different types of development. SAP Assessments are carried out by accredited assessors, who will work from architect’s plans and construction details, together with a full building services specification.
All domestic and commercial buildings in the UK available to buy or rent must also have an Energy Performance Certificate (EPC). An EPC can be produced by a domestic energy assessor, or by your SAP assessor. This applies an energy performance rating to the property ranked A-G, with A being the highest level. The EPC is calculated using RdSAP, which is a Reduced data SAP, rather than the full SAP used on new build projects. This is a light-tough assessment and as such, may not fully factor the energy efficiency measures you have undertaken.
Achieving a good SAP rating
The best advice is to engage a SAP assessor early on in the design stage, before submitting a Planning Application. This will help avoid possible issues as the project develops. UK Energy Assessors are advocates of the fabric-first approach to sound building design, and this is reinforced in SAP. Good building design focuses on:
• Lots of Insulation! U-values measure insulation effectiveness of building materials therefore approach U-value targets as the threshold to beat, not a minimum level to meet! Always maximise insulation of walls, floors and roofs.
• Heat is lost through windows and doors (even when not open) so aim for the best specification you can afford. Look for products with a U-value of 1.4W/m2 or less.
• Heating control is key: SAP rewards controlled heating systems, and penalises projects that overlook this key element of efficient heating design. It is relatively simple to control individual rooms, and individual heat sources within these rooms, to ensure heat is delivered when and where needed over time.
• Air-tightness: improved air-tightness reduces heat losses. Beyond good design, you should also ensure attention to detail during construction, so that your investment in good insulation isn’t compromised by poor construction finish and installation standards.
Changes to SAP and Heating
Heating is a significant element of SAP, alongside heating controls, so design decisions should be agreed early on in the project lifecycle to ensure compliance.
SAP works on a range of baseline measures, and in the case of heating, mains gas is used as the baseline. In real-terms, using mains gas for heating makes a SAP pass easier at present, because SAP2012 applies lower CO2 emissions from a gas central heating system (216g CO2/kWh) than electric (519g CO2/kWh). However, these emissions factors are out of date, no longer accurate, and are due to be updated in SAP10.
Changes to the electricity related CO2 emissions in SAP10 are significant – reducing from 519g CO2/kWh to 233g CO2/kWh, only slightly higher than mains gas (210g).
Currently SAP2012 assumes any electricity used in the dwelling produces 2.4 times the CO2 emissions of mains gas – this is because it uses an outdated carbon factor which does not reflect the energy mix of the UK grid.
In the UK, there are over 4m households without access to mains gas; over 2m households use electricity for heating. As the electricity grid becomes greener with increased use of renewables, it is inevitable that electric heating will become the cleanest heat source, enabling the move towards zero carbon.
SAP10 and the planned changes to Building Regulations Part L will be a game changer for electric heating. Because SAP2012 is weighted in favour of mains gas heating, and uses an outdated and inaccurate CO2 factor for grid-supplied electricity, electric heating is essentially penalised. The same project assessed under SAP10 will improve the rating of the dwelling and more accurately reflect the energy and carbon efficiency of your home. Ultimately, homes with a higher SAP rating cost less to live in and SAP10 is likely to elevate electric heating into the mainstream.