Section 6 update


New Scottish Building Regulations are live

1st Feb 2023

As of 1st February this year, Scotland has new building regulations that take us further along the road to Net Zero. The update to the Domestic Technical handbook had been expected in December, but due to delays in having the software tools that allow energy assessors to produce SAPs this was pushed back to February 1st. One week on from this date and there are still questions about how exactly SAPs will be calculated and what it means when designing new houses. This is our latest Section 6 update.

Essentially, houses will now be judged on two things:

  • their emissions (Design Emissions Rate – DER) and the delivered energy required to run the house (Design Dwelling Energy Rate – DDER – the supplied energy minus energy generated on site eg from solar PV). 

If carbon producing heating is avoided (gas, oil etc) then emissions calculations (DER) are not required and so the energy rating (DDER) is the only calculation required, the aim being to promote electric heating/hot water and reducing energy demand as much as possible.

We’ve considered the implications for SAP/Section 6 compliance as they will impact on architects, self builders, local authorities and developers.

Key changes (in detail below):

  • Tighter U-Values for external floors, walls and roofs
  • Greater focus on thermal bridging
  • Gas and oil boilers penalised in favour of electric heating (but not yet banned…)
  • Wood burning stoves still allowed (but going the same way as the gas boiler…?)
  • Overheating, and ventilation
  • SAP methodology

1. Tighter U-Values for external floors, walls and roofs

The Section 6 update now has more stringent U-Values for building elements, meaning better insulation will be required. For example, the backstop U-Values for floors have reduced from 0.18 to 0.15, external walls are reduced from 0.22 to 0.17, and roofs must achieve 0.12, reduced from 0.15.

These are only the backstop figures however – a ‘Notional Dwelling’ in the handbook that forms the aggregate of target figures in order to pass SAP uses floor, walls and roof U-Values of 0.12, 0.15 and 0.09 – missing these targets means improving on the Notional Dwelling figures elsewhere in SAP in order to pass.

(This Notional Dwelling breakdown can be found at the foot of this post.)

2. Greater focus on thermal bridging

Up until now most designers of new builds in Scotland could ignore thermal bridge detailing within SAP and go with a default setting. Occasionally Accredited Construction Details were required to help improve the SAP rating, say to qualify for an Ecology Building Society mortgage.

The default thermal bridge setting has been increased from a ‘y-value’ of 0.1 to 0.2 meaning that the assumed heat losses associated with default thermal bridges have doubled, while at the same time the Notional Dwelling – again the aggregate of target figures – uses a now stricter y-value of 0.05. In effect, thermal bridging details will now have to be calculated in the great majority of cases in order to pass SAP.

3. Gas and oil boilers penalised in favour of electric heating (but not yet banned…)

The ‘2024 New Build Heat Standard’ will see gas or oil boilers banned under Scottish Government plans. In the meantime they can still be installed in new dwellings, but to pass it is much harder and it is likely that extra measures such as enhanced fabric, waste water recovery on all showers and solar PV will be needed for such homes.

4. Wood burning stoves still allowed (but going the same way as the gas boiler…?)

There is nothing specific in the regulations about wood burning stoves and so for the time being they can be included, but we understand it’s the Scottish Government’s intention to ban them from 2024 in new builds along with gas and oil boilers as part of it’s “zero emission” strategy.

5. Overheating and ventilation

Details on how SAP assessors will calculate overheating using a simple method are yet to be made clear as this is now not something assessed by SAP. Instead, Section 3 of the Technical Handbook now covers overheating. Luths can however offer dynamic modelling using TM59 to assess overheating.

Of more relevance to the major housebuilders and local authorities, all new builds will now be tested for air permeability.

The target air permeability rate used in the Notional Dwelling is now 5m3/h/m2 which is unlikely to be a difficult target to hit for most well-built new homes and so we don’t see this as an area of concern.

6. SAP methodology

In terms of the way that SAPs will be calculated, all new building warrant applications will need to be supported by a SAP calculation meeting the new building regulations using ‘SAP10’. For any new dwellings that require a final EPC, this will be assessed using the same regulations used when the building warrant was granted and so the pre 1st Feb 2023 regulations will still be relevant for some time to come for these dwellings. In these cases ‘SAP2012’ will be used for the final EPC – just as it was for the ‘as designed’ SAP.

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