SAP 10 is Coming… Eventually

Darren Evans
November 19, 2018

Fuel Prices and CO2 Factors

The way that SAP deals with lighting has changed significantly, falling more into line with the process adopted within SBEM. The calculation of lighting energy use will be based on the quantity and efficiency of the fixed lighting in the building, and on the contribution of daylight. This will mean that it will be important to know more detail at design stage relating to the window and lighting specifications, to avoid the use of reference / default data within the SAP software. The new lighting procedure in SAP compares the fixed lighting design with a reference capacity range in SAP, based on the dwelling’s floor area. If the lighting design is outside of this lighting reference range, then additional top-up lighting (using default lighting values) will be automatically added within the software to meet the shortfall. It will be important to ensure that lighting designs enable the dwelling to perform within the lighting reference range within SAP, to avoid either additional ‘poor lighting’ or ‘surplus’ lighting being added to the calculation in the background. 

Thermal Bridging

The changes in this section of the assessment procedure revision feel like the next big step in positioning a true fabric-first approach at the heart of building design.

Within SAP 2012 a default y-value of 0.15 W/m2K can be selected to represent the heat lost through the thermal junctions of a dwelling. This is an arbitrary figure used where thermal junction lengths and heat losses have not been accurately considered and represented. Within SAP 10, this practice is discouraged and the default y-value will be increased to 0.2 W/m2K. 

Another change within this part of the assessment procedure is the removal of the use of Accredited Construction Details (ACDs). This suite of industry-approved values representing heat loss through building junctions has been deemed inaccurate and not fit for purpose, as efforts are made to ensure SAP more accurately reflects as-built dwelling performance. The removal of these heat loss values leaves the following options when representing a dwelling’s heat loss through thermal junctions:

  1. Measure the thermal junctions and use default heat loss values listed in SAP; 
  2. Measure the thermal junctions and use industry pre-calculated psi values (assuming the construction detail matches that which has been calculated);
  3. Measure the thermal junctions and calculate bespoke psi values accurately representing a dwellings heat loss.

This will require psi values to be considered alongside U-Values earlier in the design process. The use of accredited and specialist energy assessment organisations to provide this early design support will be key to avoiding costly changes and additional technologies later in the construction process. 

Alongside the removal of ACD values, there is an increase in the default psi values used in SAP for roof junctions (R1 – R9). These values have been increased to more accurately reflect heat loss through these parts of the building. There has also been an introduction of an R10 junction which is to be used for any roof junction occurring in a dwelling’s design that is not captured under junctions R1 – R9. This change in roof junction psi values will place increasing pressure on current building specifications for room in roof dwellings that rely on default roof psi values. 

Hot Water Demand 

SAP has not previously included an assessment of showers and baths; however, these are now included in the hot water assessment under SAP 10. This will result in an increase in a dwelling’s energy use when measured in SAP. The type and number of showers and baths designed within a dwelling will now be recorded in the SAP assessment. Electric instantaneous and mixer showers will need to be individually entered into SAP, with their associated flow rates. Flow rate restrictors can be used for mixer showers to a baseline of 6 litres / min and electric instantaneous showers need to be entered as 9kW or above. 

This change should result in a more accurate assessment of a dwelling’s actual hot water demand than is currently available through SAP 2012. 

Photovoltaic Panels 

One of the biggest changes in SAP 10 under this section relates to the way in which individual flats were able to accrue CO2 gains from a PV array, installed on the roof of a block of flats and connected only to a landlord’s supply. This is no longer possible. If a PV array is located on the roof of a block of flats and connected to landlord supply then none of the flats can accrue CO2 gains from the PV array installed on the roof. Only flats with individual inverters connected to the PV array on the roof of the block of flats will be able to accrue CO2 gains from the array. Consideration will need to be given to the impact this change has on the current design strategies in place to ensure compliance with different CO2 reduction targets.

SAP 10 will also introduce the facility to account for battery storage for electricity produced from PV, permit the use of MCS overshading data and account for gains where a PV array is directly heating an immersion coil in a cylinder.

Overheating Risk

The assessment of overheating in SAP 10 seeks to account for as-built circumstances that might affect people keeping their windows open during periods of hot weather. If natural ventilation is selected in SAP 10, there will be a set of questions for the assessor to answer relating to the presence and distance of external noise sources and potential security risks. The window opening extent and the air change rates permitted within the dwelling’s calculation will be affected by these individual, location-based circumstances. The inclusion of this change will require more coordinated consideration of the site location and ventilation strategy.

Thermal Mass Parameter (TMP)

The option witHin SAP of classifying the TMP of a dwelling as one of three indicative values (low, medium and high) has been removed. This is again in line with the desire to enable SAP to more accurately reflect the actual performance of a dwelling’s design. SAP 10 will require all assessments to be completed, including a detailed calculation of the building’s actual TMP based on the proposed building materials and constructions and their kappa values.

We’re keeping informed and prepared for every update as it arrives. To study SAP 10 in more detail, see Or to talk through how the changes might affect you, give us a call on 01454 317940.

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