New Part L 2021:
What's changed in SAP 10?
The new version of SAP:

SAP 10: The successor to SAP 2012

SAP Calculations are used to demonstrate the energy performance of dwellings in the UK and are a key part of compliance with Building Regulations Approved Document Part L.

The latest version of Building Regulations Part L (Interim Part L 2021) went live on 15 December 2021 and has been in effect since 15 June 2022.

 

Some of the changes in Part L 2021 have the potential to affect the way new dwellings are designed going forward.

Here are the u-values used to calculate the TER* and TPER* of the notional dwelling in SAP 10, plus the maximum u-values allowed for the actual dwelling (DER) in Part L 2021:

 

Element	TER Notional u-value  (Part L 2021)	DER Maximum u-value  (Part L 2021)
Walls	0.18	0.26
Floor	0.13	0.18
Roof	0.11	0.16
Doors	1.0	1.6
Windows	1.2	1.6
Fully-Glazed Doors	1.2	1.6
Roof Windows	1.2	1.4

 

Other changes to the notional dwelling target in SAP 10:

• Air test target = 5.0

• WWHR to all showers

• Mains gas boiler with efficiency of 89.5%

• Lighting efficacy = 80 lm/W (Lumens per Watt), achievable with LED fittings.

 

The values above are fairly tight and show just how much harder it is to gain a pass in SAP 10.

There is still some design flexibility however, as shown by the DER maximum u-values. These are the maximum u-values allowed, although it should be noted that any values that exceed those used in the target calculation will need to be offset elsewhere to achieve a pass.

 

NB. To achieve a pass in SAP the DER and DPER values must be lower than the TER and TPER values, which is why the changes to the notional dwelling in SAP 10 calculations are going to have a big impact going forward.

 

 

* TER = Target Emission Rate (for the Notional Dwelling)
* TPER = Target Primary Energy Rate (for the Notional Dwelling)
* DER = Dwelling Emission Rate (for the Actual Dwelling)
* DPER = Dwelling Primary Energy Rate (for the Actual Dwelling)

 

The notional dwelling in SAP10 assumes some PV is installed, as per the calculation below:

• For Houses, kW of PV = 40% of the area of lowest storey divided by 6.5

• For Flats, kW of PV = 40% of the area of lowest storey in building divided by (6.5 x no storeys in block)

 

As a guide, this equates to around 4kW for an average-sized dwelling, effectively meaning that this amount of PV should be installed, or other technologies used  to offset the energy demand of the building. Our experience of SAP 10 shows that fabric improvements alone will not be enough for the vast majority of dwellings to pass. The best way to achieve a pass is by installing Solar PV or a heat pump.

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Electric CO₂ emissions reduce significantly

The changes to the electricity related carbon emissions may be the most significant factor – reducing from 0.519 gCO₂/kWh to 0.233 gCO₂/kWh, now only slightly higher than that of mains gas (0.210).

Currently SAP assumes that any electricity used produces 2.4 times the carbon emissions of mains gas – this is because it uses an outdated carbon factor which is not reflective of the current energy mix of the electricity grid. The greening of the grid means there is now much more renewable and clean energy and much less coal.

SAP targets are based on mains gas, heavily penalising electric use in the current version of SAP (SAP 2012). Certainly any new builds with all- electric heating are incredibly difficult to pass without additional measures or renewable technologies being installed.

We are pleased to see a much more representative carbon factor for grid electricity being applied in SAP10. This will certainly give our clients much more design flexibility going forward.

The fuel prices per kWh have also been updated within SAP 10, bringing assumptions closer to the real-world.

The assumed heating pattern has changed

Currently SAP attributes a standard heating pattern which assumes that homes are heated differently on weekdays and weekends. Studies show that this is not the case in real life, and so SAP 10 has been changed to apply a consistent daily pattern for all days of the week. This will have the effect of reducing energy use and costs across the board.

Default distribution loss factors associated with heat networks have been increased.

Losses associated with decentralised heat networks have been under-estimated previously in SAP, and so this change marginally reduces the effectiveness of connection to a heat network. This may have implications for projects in London where a carbon reduction is being sought for planning requirements.

The calculation of lighting energy has been updated

The lighting simulation within SAP 2012 was rudimentary, simply accounting for the number of low energy fittings being installed. The changes in SAP10 mean that we can use a much more accurate lighting design to inform the assessment, much like in SBEM (the tool we use for commercial and public buildings). This will allow recognition of new lighting types with higher efficiencies.

The majority of current LED lighting products will work well in SAP 10.

The options for entering thermal bridges have been revised

This is a big deal. Heat losses at junctions in the construction have, up until now often been offset by using the ACD scheme (Accredited Construction Details). This gives designers and constructors a set of junction specifications to follow, which in turn allows the SAP assessor to apply improved values over defaults.

Due to concerns over the accuracy and age of ACD junctions, SAP 10 has removed the option to use them. This means using either alternative schemes (perhaps from the insulation manufacturers) or have bespoke thermal bridge psi-values calculated for each junction.

Hot water consumption has been adjusted for shower flow rate

Hot water consumption has until now been based on a standardised usage. Flow rates will now need to be entered into SAP 10 so we will start to see a certain amount of variation between shower fittings being used.

Water efficiency calculations are already required under Part G of the building regs, so there will now be some crossover between the two assessments.

The configuration of PV systems will matter

SAP 2012 used a fixed assumption for the proportion of electrical energy generated by Photovoltaic (PV) systems and consumed within the dwelling. This was attributed regardless of whether there was a direct connection to a dwelling, or whether, as is often the case on blocks of flats, only one connection exists to a landlords supply.

This has been replaced by a formula which will only factor in a PV supply to those flats directly connected. This will impact on those developments which are relying on a carbon reduction for a planning condition, and much more consideration will need to be made when designing and installing systems.

Battery Storage & PV diverters can now be included

A PV diverter prevents electricity produced from photovoltaic panels from being exported to the grid, and instead directs it to an immersion heater in the water cylinder. It will now be possible to account for these systems in SAP 10 which will provide extra design options.

Similarly, battery storage to store PV-generated electricty will now be recognised in SAP10.

MCS overshading data can now be used

An option will now exist in SAP 10 to allow the overshading factor used for the PV calculation to be taken from Microgeneration Certification Scheme data. This would overwrite the default options currently available in SAP.

 

 

To download SAP 10 and for further reading see www.bregroup.com/sap/sap10

Download the latest version of Approved Document Part L 2021 from here