SAP calculations
These perform a key role in the design of new homes in the UK. SAP calculations are a requirement of the Building Regulations, and are required for all newly built dwellings in the UK. A SAP Rating has been required for all new homes under Part L of the building regulations since 1995.
For many first-time self-builders and developers it will be a new and often challenging aspect of the planning and building control process.
SAP Calculations do three things:
They determine a SAP Rating (the energy related running costs of a dwelling)
They demonstrate compliance with Part L of the building regs
They are used to produce an Energy Performance Certificate (EPC)
You may also need a SAP for a conversion or extension, but slightly different rules apply. Scotland also has differing requirements.
What are SAP Calculations?
SAP stands for ‘Standard Assessment Procedure’. It is the only official, government approved system for assessing the energy rating for a new home. SAP assessors must be accredited and registered with a certification body.
A SAP Rating is a way of comparing energy performance of different homes – it results in a figure between 1 and 100+ (100 representing zero energy cost and anything over means you are exporting energy). The higher the SAP rating, the lower the fuel costs and the lower the associated emissions of carbon dioxide.
The SAP Calculations establish an energy cost based on the construction of the home, its heating system, internal lighting and any renewable technologies installed. It does not include energy used for cooking or appliances.
Why are SAP Calculations important?
In order to meet current building regulations, home builders will need to gain a ‘pass’ on their SAP Calculations. Without it, building control will not sign off the development and the property cannot be let or marketed for sale.
But there are other reasons to care about SAP. A SAP assessor can help the designer or architect to shape the energy profile of a new dwelling – minimising its energy use and carbon emissions.
The effect of different construction types, heating systems and technologies can be accurately measured and in turn delivered on the ground.
Another key point is that the SAP rating broadcasts the energy performance of the property, and in turn informs the Energy Performance Certificate (EPC) which all buyers and tenants see.
A ‘pass’ is gained by meeting several compliance targets around:
How well the fabric of the dwelling contains heat
Solar gain
Quality of construction and commissioning of systems
Predicted CO2 emissions from the dwelling
Why are emissions so important?
The headline emissions target is achieved using the DER/TER figures. CO2 emissions are measured by comparing a Target Emission Rate (TER) against the predicted Dwelling Emission Rate (DER).
This target rate is set within the SAP calculations by reference to a notional dwelling of the same size and shape, using a set of baseline values.
Importantly, these CO2 figures are now increasingly used by planners and councils to drive other objectives – from meeting sustainability targets and local renewable energy policy to determining 106 – type community contributions.
Fabric Energy Efficiency
Homes built after April 2014 in England are also assessed on Fabric Energy Efficiency. This is not a measure of carbon, but energy demand in units of kilowatt-hours per m2 per year. How well a home retains the heat it produces will have an impact on its CO2 emissions as well as being assessed separately to gauge compliance.
Fabric Energy Efficiency is assessed using DFEE/TFEE figures. As with emissions the target is set within SAP using a set of baseline values depending on the size of the property.
What’s Involved?
A SAP Assessor will work from architects plans and construction detail, together with a full HVAC (heating, ventilation and air conditioning) specification. For this reason drawings need to be scaled, accurate and show all elevations, sections, floor and site plans.
The assessor will scale off of these plans either electronically or by hand to create a model of the dwelling(s) in SAP software.
Once the site form is established, the heating, lighting and ventilation systems are added – specific products will be picked from manufacturer databases where they are known.
All thermal elements (walls , floors, roofs and openings) are added in detail together with all calculations for thermal junctions. Any renewable technologies and cooling are also added.
Once complete, a SAP calculation is capable of producing a raft of detailed reporting outputs, from site form, heat losses and energy demand to seasonal variations, CO2 emissions and renewables contributions, to name just a few.
How Do I Make Sure of a Pass?
It’s fair to say that developers and architects didn’t need to pay much attention to SAP in the old days – but recent years have brought significant changes to the SAP metrics and Part L Building regs. Starting work without a design stage SAP assessment is not an option!
This is primarily because CO2 emissions targets have tightened enormously – driven as they are by European and UK climate policies. An average new build designed just 5 years age is highly unlike to pass the regulations today.
We are often asked to explain why some builds fail and some pass, and it isn’t always easy to give a straight answer. Numerous factors can play a part, from the size of a boiler to a junction in a wall, to the thickness of insulation in a floor, to which direction the house is pointing!
Some factors can be beyond the clients control – for example having no connection to mains gas could mean having to use an oil or LPG system. These fuels have higher cost and CO2 emissions factors within SAP, and as the Target Emission Rate is set based on a mains gas system, you take a hit.