SAP calculations are a requirement of Part L of the Building Regulations, and are required for all newbuild dwellings in the UK.
A SAP Rating has been required for all new homes to satisfy Part L (Part L1A or L1B) of the building regulations since 1995, making them an important part of the building process.
However, many first time self-builders and developers will be new to what is an often challenging aspect of the planning and building control process.
The purpose of a SAP Calculation:
SAP is short for ‘Standard Assessment Procedure’. It is the UK government approved system for assessing the energy performance of new homes. SAP assessors must be accredited and registered with an offical certification body. At Energycount we are accredited with Elmurst Energy Systems.
A SAP Rating is a way of comparing the energy performance of new homes – the number varies between 1 and 100+ and is split into bands representing the letters from A to G. The higher the SAP rating, the lower the fuel costs to run the home will be (and the lower the associated CO2 emissions).
A SAP Calculation shows the 'regulated' energy cost and CO2 emissions based on the insulation levels of the dwelling, the heating & hot water systems, ventilation, lighting and any renewable technologies installed. SAP calculations do not however include energy used for cooking or appliances, as these are deemed 'unregulated'.
In order to meet current building regulations, home builders & developers must gain a ‘pass’ in their SAP Calculations, or building control will not sign off the development and the house cannot be let or marketed for sale.
There are of course other reasons to care about SAP. A SAP assessor will assist the house designer/ developer/ architect in shaping the energy strategy of their new dwelling in order to minimise its energy use and CO2 emissions. We do this by advising on construction types, heating systems , technologies and other, more subtle aspects in making project work in SAP. These are all be accurately measured in our SAP software to give real-time guidance to show the performance of the building.
A SAP calculation is also where the Energy Performance Certificate (EPC) for a new dwelling comes from. NB. the EPC is the document required for every house that is sold or let.
A SAP ‘pass’ is obtained by meeting various compliance targets, including:
In SAP, the primary CO2 emissions are shown as a comparison of 'DER/TER' figures. CO2 emissions are measured by comparing a Target Emission Rate (TER) against the predicted Dwelling Emission Rate (DER).
The Target Emission Rate (TER) is set within the SAP calculations. It calculates a notional dwelling of the same size and shape, using a set of baseline 'notional' values.
Nowadays it is not just Building Regulations compliance that uses DER and CO2 emissions data from SAP - Many local planning authorities (LPA's) are using these to help achieve their planning objectives – e.g. by setting CO2 emissions targets or energy demand requirements as part of a planning condition. Such conditions can be satisfied by producing Energy Statements & Reports which are based on SAP data from the actual development.
To pass in SAP the DER can be no greater than the TER.
In England & Wales, homes built after April 2014 are also assessed on Fabric Energy Efficiency (FEE). FEE is a measure of energy demand, expressed in kWh/m²/yr (kilowatt-hours per m² per year).
Fabric Energy Efficiency is a measure of the thermal performance of the dwelling, rather than CO2. The FEE is mainly affected by u-values and air tightness, and reflects how much thermal energy is lost through the building fabric.
Fabric Energy Efficiency is assessed using DFEE/TFEE figures. As with TER for CO2 emissions, the target fabric energy efficiency (TFEE) is set by SAP using a set of notional values based on the size of the dwelling. DFEE, like DER for CO2 emissions, is the 'Dwelling Fabric Energy Efficiency', and is the FEE calculated by SAP for the actual dwelling. To pass in SAP the DFEE can be no greater than the TFEE.
A SAP Assessor works from architects drawings (plans, sections & elevations), together with the construction specification, including details of the heating, hot water, ventilation and renewable technologies proposed.
The SAP assessor then uses the drawings and specification to create a model of the dwelling in SAP software.
Once the basic building is entered into the software, the heating/cooling, lighting and ventilation systems are added – where known, specific products will be chosen from the database, otherwise assumptions based on best practice and experience are used.
All thermal elements (walls, floors, roofs and openings) are added in detail to the SAP software, together with all calculations for u-values & thermal bridges. Where known, any renewable technologies are also included, along with MVHR (Mechanical Ventilation with Heat Recovery) and other systems.
Once completed, a SAP calculation can produce many detailed reports and other data including: heat losses, energy demand, CO2 emissions, and renewables contributions.
For Building regulations Part L compliance the main SAP report required by Building Control is the 'Compliance Report'. This highlights the main areas of the calculation with a 'pass'. The compliance report is usually provided alongside the PEA (Predicted Energy Assessment), the Input Data Summary, and Full SAP calculation as support tdocumentation.
The short answer is 'no', however we will do all we can to help in order to achieve a pass.
Years ago very little attention was paid to SAP calculations or Part L as houses tended to pass without much fuss. This has all changed over the years along with each revision of Part L, with requirements becoming increasingly tough each time the regs are updated. Building Regulations are usually revised every 4-5 years. The changes to SAP run alongside changes to Part L, which has been revised since its inception in 1995. Revisions to SAP are normally dated one year prior to their regs version and have been made in 2001, 2005, 2010 and again in 2014 to coincide with Part L 2013, We are due another change to Part L in 2020/2021, which will again mean changes to the version of SAP we use - the next version of SAP will be called SAP 10. SAP10 will have many changes over the current version 'SAP2012'. We will keep this page updated with the changes in SAP10 as we know them.
As a consequence of regular updates SAP calcs have become increasingly hard to pass, primarily because CO2 emissions targets are getting tightened as government policy drives us towards zero-carbon homes (and the new Future Homes standard). In fact, a new build home that passed in 2012 would be unlikely to pass today's Part L regulations.
A SAP calculation contains many factors that determine whether a calc passes or fails, from the make/model of boiler to the wall type. When 2 dwellings really are identical, their orientation will also impact the SAP calculation as solar gain and thermal losses are taken into account through windows and doors that face south or north for example.
There are other factors that would be particular for a specific site, which would be beyond the control of the developer, for example having no connection to mains gas could mean using an oil or LPG system. Such fuels have a higher fuel factor within SAP, which impacts the DER (Dwelling Emission Rate) making it harder to achieve a pass.
We live and breathe SAP calcs, and have carried out thousands, gaining a lot of knowledge and experience along the way... from single eco self-builds & Passivhaus', through to 100+ unit apartment blocks and new housing developments. Sharing this knowledge is what our clients have come to expect from us. Here are a selection of our essential tips:
1. Think about SAP calculations early
Perhaps the most important tip... When we work on a development part-way through a build (or even when it's built), there isn't much that can be done to improve the fabric elements of the building that have already been built. There will be limited options available to improve the thermal performance or CO2 emissions, which could include extra renewables for example.
The best way to avoid this is by working with a SAP assessor as early in the development process as possible. This could be before planning is applied for, or before a building regs application is made, but definately before the build starts on site.
2. Maximum u-values are set to be beaten, not adhered to
Nowadays the maximum u-values specified in Part L1A and L1B are a lot higher than what actually works in SAP. Generally a good combination of decent u-values is what is required to achieve a pass.
As a guide we recommend the following u-values as a starting point:
3. Windows and doors lose a lot of thermal energy
The u values of openings have a big effect on a SAP calc - it's therefore wise to specify glazing & doors that are a maximum of 1.5 W/m²K. If you can get lower then all the better. There are a lot of new triple glazed products coming to market that don't cost much more than double-glazing, yet achieve u-values of around 1.0-1.2 W/m²K.
3. Get a decent boiler
The choice of boiler can make as much as a 5-10% difference to the DER/TER. Many modern boilers also contain integrated weather compensators or FGHR (Flue Gas Heat Recovery) systems for extra efficiency.
4. Air tightness & Air permeability
Most new builds require Air Permeability Testing on completion with the test result input into the SAP Calcs. Usually the air tightness will need to be around 5.0 m³/hour/m² for the SAP calc to pass. Make sure all gaps and joints are sealed, particularly around skirtings and behind bathroom and kitchen fittings that may be hiding large holes into the building fabric.
5. Pay attention to thermal bridging
A thermal bridge is the junction where an external building element meets another, such as a floor to wall joint, or the joints where a window is inserted into an external wall. Heat can be lost through these junctions. Junctions should be detailed to minimise heat loss. It's also possible to use Accredited Construction Details (ACD’s) which are details that have already been calculated - this allows us to avoid using defaults. We have a guide on Thermal Bridging here.