The Background to SAP/NHER Ratings

Since 1995 energy ratings have been used to set standards for Building Regulations and for Housing Association and Local Authority properties. The European Performance of Buildings Directive (EPBD) made it compulsory for energy ratings to be provided when a home changes hands, in order to provide independent information on the energy efficiency and likely fuel running costs of the property. As a consequence, energy ratings have become an essential part of the house buying process since 2007; these ratings and costs are shown on an Energy Performance Certificate (EPC), which is produced from the SAP calculations. Since October 2008 prospective tenants of rented homes also have to be given an EPC.

Energy efficiency is clearly a good thing–everyone wins with energy efficiency. The householder is better off and so is the environment. The government has promoted improvements in energy efficiency for more than 20 years – and the minimum standards required by the Building Regulations have increased significantly over this period. However, since it is much more expensive to retrofit energy efficiency improvement measures to homes than to incorporate them when the property is first built, it is important that new homes are built to be as energy efficient as possible. To this end, and towards the achievement of the government’s target of zero carbon homes by 2016, successive issues of the Building Regulations have included reduced CO2 emissions targets (the Target CO2 Emission Rate, or TER) – the current regulations (2010) has a target 25% less than the previous issue (2006).

The requirements of Part L1A (new dwellings) of the Building Regulations (2010) include an assessment of the carbon dioxide emissions (the Dwelling CO2 Emission Rate, or DER) at an early stage in the home‘s design. This can only be undertaken using the SAP 2009 procedure. Having an energy rating assessment for the design of new homes during an early stage encourages the incorporation of energy efficiency measures into the design. The developer has to demonstrate that their dwelling, once constructed, is built in accordance with a design that does not exceed a specific carbon dioxide target. The prospective buyer will be informed of the final energy rating, which may help inform their purchase decision.

The NHER Rating

The NHER is calculated by estimating the total annual fuel costs for the property, divided by the floor area and adjusted to fit on a 0 to 20 scale. At an NHER of 20 the total running costs for the dwelling is calculated to be zero. The running costs are calculated using a standard (average) heating pattern.

The fuel costs used for the NHER calculation are based on a rolling average of the fuel prices over the last three years, deflated using the retail price index for fuels. This reduces the impact of changes in fuel prices over time.

The SAP Rating

The use of the NHER in the early 1990s led to the development of a slightly simpler energy rating known as SAP (Standard Assessment Procedure). The Standard Assessment Procedure is a government calculation method used to determine the energy rating and carbon dioxide emissions for a residential dwelling.

The SAP calculates a rating for the energy cost due to the built structure of the home and its heating system, internal lighting and any renewable energy technologies used in the home. It does not include energy used for cooking or appliances. Also unlike the NHER, which is based on regions of the UK, the SAP uses a standard - middle of England - location for calculating the level of heating required throughout the year, regardless of where the property is located (however, in properties with mechanical cooling, the assessment of cooling load in SAP is sensitive to region).

SAP ratings for new dwellings are produced by an On Construction Domestic Energy Assessor (OCDEA), using approved computer software. Building Regulations Part L1A includes legal requirements which developers and designers must be aware of, which include:

• The DER must be less than or equal to the TER
• An EPC must be given to the building owner at the latest five days after completion and the RRN (EPC Report Reference Number) given to Building Control
• Reasonable provision must be made for conserving fuel and power (refer to Approved Document L1A)

The OCDEA should assist the client to achieve compliance with the legal requirements.

Assessment Procedures

The SAP rating is produced in two stages of assessment:

• Design Stage
• As Built

Design Stage

An assessment is made of the construction specification and plans, with the main factors (there are others) contributing towards the SAP rating being:

• Site factors (e.g. exposure to wind) and orientation of the dwelling
• Materials used in the building fabric
• Thermal insulation materials
• Thermal efficiency of the windows and doors

The above three factors determine the U-value (heat loss characteristics) and Thermal Mass of the building fabric elements.

• Ventilation characteristics (including air-tightness of the building envelope)
• Heating and hot water system type, efficiency and controls
• Renewable (low and zero carbon) energy technologies
• Low energy lighting
• Cold bridging details (Thermal Bridging in SAP 2009)

Prior to the current Building Regulations, design submissions were recommended practice, but not mandatory. In the current Part L1A 2010 this is now a legal requirement; Regulation 20D states

“Not later than a day before the work starts the person carrying out the work shall give the local authority a notice which specifies:

• The Target CO2 emission rate (TER) for the building
• The calculated CO2 emission rate (DER) for the building as designed
• A list of the specifications to which the building is to be constructed”

The role of the OCDEA in this is to:

• Gather the data required to assess the dwelling, and the documentary evidence
• Carry out the SAP based assessment in accordance with the quality assurance standards
• Point out to their client anything that might lead to the design and as built submissions being rejected
• Provide the documentation required by Building Control

The documentation required by the Building Control Body (BCB) at the Design Stage as a minimum would be:

• Building Regulations Compliance report
• A copy of the Predicted Energy Assessment (PEA)
• The SAP Data Input Sheet

The SAP software is able to produce a number of different reports and the BCB may require some or all of these, and possibly additional supporting information.

As Built

The As Built assessment is intended to confirm the design rating if there are no changes, or to reassess and re-rate the dwelling if any changes to the design have been made.

The As Built SAP rating provides the basis for the Energy Performance Certificate (EPC) required by the EPBD, which places the SAP rating on an A-G scale (similar to that used for the energy labels on white goods); the A to G relates to a scale from 1 to 100, with A being 92 or better and G being 1 to 20.

All EPCs must include:

• ‘Benchmark‘ standards with which consumers may compare performance
• Recommendations for cost effective improvement of energy performance

Certification of the performance of an apartment in a single block may be based on:

• A common certificate for the whole building (if there is a common heating system)
• Assessment of another representative apartment in the same block

The documentation required by the Building Control Body (BCB) at the As Built Stage as a minimum would be:

• Building Regulations Compliance report
• A copy of the EPC
• The SAP Data Input Sheet

The BCB may require additional supporting information.

Front Page of an Energy Perfomance Certificate