Forthcoming changes to the SAP calculations

An update on what has been happening in the background with the forthcoming changes to SAP. There was a consultation last year on the changes to SAP methodology following general feedback from end users and Government that the system was not representative of ‘real world’ situations and was becoming more of a ‘ticking the box process’. BRE have now published their first version of “SAP 10”.

N.B. SAP 2012 is current and will remain so until there are changes in the Building Regulations which all of the respective administrations are currently investigating. So the changes that are listed here are really just tinkering ‘under the bonnet’ with no actual changes to the performance requirements.  This will take place in the next version of the Building Regulations (Section 6 / Part L).  What is important to note that the tinkering to the methodology will have an impact, but the real life implications will only come to light once the next version of the Regulations are published.

The most important changes to note in the new SAP 10 are:

1. Fuel prices and CO₂ factors

Many of the fuel types recognised in SAP have had their fuel prices, CO₂ and primary energy factors tweaked. The most common fuel types and changes from SAP 2012 to SAP 10 are shown below;

Of particular interest is electricity which has seen its CO₂ emission factor reduced from 0.519 kgCO₂/kWh to 0.233 kgCO₂/kWh in SAP 10. This is to reflect the increased influence of renewable energy technologies producing electricity for the national grid. It will be interesting to see whether the next version of regulations give further benefit to electrically heated dwellings to encourage the move away from fossil fuels.

WHAT THIS MEANS:

The data hints that electrically heated dwellings may become viable – will have to wait for an assessment tool to test in a real world situation

2. Heating pattern

Within the BEIS consultation the standardised heating patterns SAP is based on were discussed, with the option of moving to the same heating pattern for all days proposed. Previously SAP has had different heating patterns for weekdays and weekends, however studies had shown there was less of a difference between the weekdays and weekends than previously thought.

SAP 10 will move to using the same heating pattern for all days, which is on 07:00-09:00 and 16:00-23:00 hours. SAP should always follow good evidence as closely as possible, so we welcome this change. It will likely mean better ratings for homes as the heating will now be defaulted to being on less at the weekends.

WHAT THIS MEANS:

Better ratings by default – but the TER will increase proportionally (so no actual change for compliance)

3. Lighting energy

This has had a significant overhaul from the lighting energy calculation in SAP 2012. SAP 10 will calculate a ‘reference lighting capacity’ based on the dwellings floor area and solar gains. Should this capacity not be reached, or be exceeded, the predicted lighting energy will be increased as a result.

This will result in additional data entry for calculating lighting energy in SAP software. Power and efficacy of fixed lighting fittings will now be required in a similar way to the non-domestic methodology known as SBEM. Default efficacy figures are provided where information cannot be obtained.

WHAT THIS MEANS:

More accurate calculation method (more work for assessors) – May or may not have anything more than a minor impact

4. Thermal bridging

As expected from the BEIS consultation, the default y-value used in assessments where no details of thermal bridging are provided has been raised from 0.15 w/m²k to 0.2 w/m²k in SAP 10. This will create an even more severe penalty for developers who do not consider heat loss through building junctions.

The psi values for the MHCLG Accredited Construction Details (ACDs) scheme have been removed from SAP 10. Again this was expected as the consultation indicated the ACDs were inaccurate and not fit for purpose based on current building practices. This will result in assessors having to rely on other established sets of construction details, or encourage more junction details to be modelled to derive accurate psi values.

Finally many of the remaining ‘default’ psi values have been tweaked. The R1-R9 junctions in particular have been increased which will penalise room in the roof constructions. A new junction has also been added, R10, for any other roof or room in roof junction not covered by R1-R9.

WHAT THIS MEANS:

Penalising for using any default psi values with more reliance on calculated junctions

5. Hot water demand 

The calculation of hot water demand will now take into account the number of showers and baths which are present in a dwelling. This will result in a more accurate assessment of hot water demand than currently in SAP 2012.

Also electricity use from instantaneous electric showers will now be accounted for in assessments. This has not been the case in previous versions of SAP and will result in higher energy use in assessments where used.

WHAT THIS MEANS:

Penalies for using electric showers (will have an impact)

6. Photovoltaic panels

The calculation of electricity generated from PV now has the option to account for battery storage technology. Also where PV is directly heating an immersion coil in a cylinder, known as a PV diverter, this will be able to be reflected in SAP 10.

As discussed in the consultation, SAP 10 will now allow entry of MCS overshading data. The MCS procedure for assessing near and far field objects will provide a more accurate assessment of overshading and will be the preferred method of assessment where an MCS certificate is available.

Finally in SAP 2012 in blocks of flats where PV is supplying a landlord’s supply via a single inverter, the flats could claim the CO₂ savings from the electricity generated. In SAP 10 this will no longer be the case; only dwellings with their own inverters will be able to benefit from the cost (£) and CO₂ savings associated with PV. This may result in developers seeking alternative solutions for cost (£) and CO₂savings on blocks of flats.

WHAT THIS MEANS:

The get out for transferring all PV to the landlord’s supply will be removed.  Will have an impact for all flatted properties – means that all PV will now have to be fed into each property to achieve the SAP points

7. Overheating risk

The assessment of overheating contained in Appendix P of SAP has been changed to more accurately assess the potential for leaving windows open during hot weather. In SAP 10, if natural ventilation is used, assessors will be required to indicate if there is a source of noise that prevents windows being left open, and also if there is a security risk where windows are left open at night. If either of the answers to these questions is ‘yes’, ‘trickle vents only’ will be assumed for the window opening extent and the associated air change rate used in the assessment.

WHAT THIS MEANS:

More careful detailing will be required – will definitely have an impact (especially for GF windows).  Overheating is a pass/fail and the vast majority of properties will have to review glazing options.  Could mean the introduction of solar reflective glazing, which has a knock-on effect to the efficiency of a property (the more reflective the less solar gain)

8. Thermal mass parameter

As expected the indicative options of low, medium and high for thermal mass parameter have been removed from SAP 10. Therefore all dwellings will now be required to have a calculated thermal mass parameter based on their individual element areas and kappa values.

Further details on how to calculate kappa values are referenced from BS EN ISO 13786 and some typical heat capacity figures are provided for these calculations.

More accurate calculation method (more work for assessors) – Will have an impact (some good some bad)