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The Standard Assessment Procedure (SAP) is required by the government to measure the energy performance and associated CO2 (carbon) emissions of all self-contained new build homes and conversions to show compliance with Building Regulations Part L. The Republic of Ireland has a similar scheme with their own Building Energy Rating (BER).
In terms of heating, SAP takes into account the building's orientation, area and volume, construction materials, ventilation and insulation levels as well as the efficiency of the technologies used and other technical factors such as solar gains (heat from the sun coming through windows or the sun warming the fabric of the building). One of the most important considerations is the air-tightness (air permeability) of the building and this will also determine some of the essential features that your stove must have (see the section 'Your choice of stove').
From all of this information SAP will then calculate the building's heat loss and determine how much energy and heat is needed to maintain it at a comfortable temperature. It will also produce an estimate of the running costs for this based on standardised energy costs and importantly, the carbon emissions this will also produce. Obviously the more renewable technologies you can incorporate, including a wood burner, then the easier it will be for the new build to achieve the regulation's mandatory minimum annual target emissions rate (TER) for CO2.
Calculations for SAP are typically carried out at the design stage (it can also be carried out 'as built' after completion) so it's helpful to know which wood burning stove model you will be installing and its efficiency. For the purposes of the calculation Wood burning stoves are classed as 'secondary space heating' because it is highly unlikely that a stove will be your only form of heat. Unfortunately the SAP calculation software standard default for secondary heating is carbon intensive portable electric heating so this will need to be overridden and replaced by the wood burner to deliver a much better result in terms of carbon emissions. SAP energy performance is also used to calculate the rating on a new home's Energy Performance Certificate (EPC).
When the construction of the internal envelope (the foundations, exterior walls, roof, doors and glazed windows) has been completed and all the services are connected the building's air permeability is tested by specialists. Intentional ventilation such as trickle vents, extractor fans and cooker hoods are effectively sealed to avoid leakage during the test. A good quality stove with a direct external air supply (DEAS), which makes it effectively room sealed because it does not take any of its combustion air from the room, should not normally need to be sealed. There may be some small leakage from twin wall flue joints but this is usually insignificant and doesn't normally create any particular issues. The building is then put under positive and negative pressure and a range of readings are then taken and recorded.
There are plenty of companies who will produce your SAP calculation and some will also help and advise you on how you can cost-effectively achieve the best energy performance. Any elements of the new build which are likely to increase the use of energy and CO2 emissions can be balanced by greater thermal efficiency elsewhere in the house. For example, if the window areas are larger than normally expected, then higher levels of insulation with the associated increased costs may be required to offset this. This is where a wood burning stove can offer you some distinct advantages, especially if it is heating more than one room. These days many SAP consultancies will already be aware of the benefits that a wood burning stove can have on the SAP outcome, but don't necessarily assume that they will all know this.
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