iSAP: Elmhurst's analysis of changes

On 8th October 2018 BEIS and BRE released a SAP software product based on SAP 10 known as ‘iSAP’. This is designed to help industry get an idea of the changes and the new data fields in the SAP 10 methodology.

It is important to stress this does not give an indication on how SAP 10 will influence building regulations compliance for new dwellings. Any changes to the next version of Part L1A are expected to form part of a consultation in early 2019, with a SAP 10.1 likely to accompany this.

Elmhurst has spent some time looking at iSAP to identify data entry changes compared to SAP 2012. Many of these were expected following our analysis of the SAP 10 consultation response found here.


There have been some changes to the calculation of overheating risk in summer months. Some new questions are now asked to determine an air change rate in the dwelling.

The possibility of noise nuisance in the dwelling is asked. In SAP 10 this is defined as being in close proximity (<20 m) and line of sight to a main road, railway or industrial site. Also if the dwelling is under a major airport approach (within 6 km from an airport) or subject to any other obvious source of noise this should be assumed.

The level of security risk where windows are unattended is also required. It is assumed that any easily accessible opening in accordance with Approved Document Q cannot be left unattended unless secure night time ventilation is fitted.

If the answer to noise nuisance or security risk is yes, then assessors should assume ‘trickle vents only’. Alternatively there are options for ‘windows slightly open (50mm)’ or ‘windows open half the time’.


As expected internal lighting has undergone a significant revision. Assessors are now required to enter the efficacy (Lumens/W), power(W) and number of bulbs for each fitting type in the dwelling. This will then form the basis of the new lighting demand calculation within SAP 10, where insufficient or excessive lighting will be penalised.


Further options for chimneys and flues have been added;

  • Chimney or open flue attached to closed fire
  • Chimney or open flue attached to solid fuel boiler
  • Chimney or flue attached to other heater
  • Open chimney
  • Chimney, permanently blocked

are all new options which have different ventilation rates associated with them. Many of these ventilation rates have been increased from SAP 2012 so the presence of them will result in higher ventilation heat losses.

Water Heating

Due to the change in hot water demand calculation in SAP 10 there have been a number of changes to the water heating section in iSAP. Assessors are now required to enter the number of baths and showers in the dwelling, with the flow rate and type (unvented/vented system, instantaneous electric etc.) of showers also required.

The source of cold water is also required, options include ‘mains’ or ‘header tank’. This is used to set the temperature of cold water being used within showers, baths and WWHRS which feeds into the hot water demand calculation.

Photovoltaic Panels (PV)

As expected some changes have been made to the data entry for photovoltaic panels. If the PV installation is MCS certified the overshading factor from the MCS certificate can be used instead of the SAP overshading procedure.

There is also an option to enter a PV diverter. This is where a PV array is directly powering a heating coil located in a hot water cylinder. Finally there is also an area to enter the capacity of any battery storage in kWh/yr.

Finally for PV installations not connected to the dwellings electricity meter no benefit is assigned to either energy cost or carbon emissions. This results in communal PV arrays serving landlords supply in blocks of flats no longer contributing to the energy efficiency ratings of the flats.

Jason Hewins – On Construction Team Leader says “In conclusion many of the new data fields in iSAP were expected and some such as lighting will require a change of information from clients. Further developments to SAP 10 are expected following the consultation on changes to Part L1A due early in 2019. Elmhurst will keep all of our members informed about any future changes to Part L1A or SAP.  We will as always attempt to provide our members with ‘beta’ SAP Software when the regulations are known. Thus allowing not only the inputs to be understood, but where the bar is being set for compliance.”

Should you wish to use iSAP yourself it can be found here.

Article Published: 9th October 2018

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