Section 6 Energy 2021 Non-Domestic Buildings

11 November 2021 Kingspan Insulation UK
A Non-Domestic building in Scotland

Carbon emissions from buildings account for just under a quarter of total emissions in Scotland. As the country looks to reach net zero carbon by 2045, reducing these emissions is a major priority. One step to achieving this are the revised energy performance standards set to be introduced for all Scottish buildings in 2022. In this blog, we take a closer look at the key consultation proposals for both new and existing non-domestic buildings which include: 

  • two options for a new principal energy target; 
  • significantly tougher maximum U-values for new builds and conversions/extensions; and 
  • a greater focus on accurate detailing. 

Carbon emissions options 

As with the domestic part of the Section 6 consultation, two uplift options are proposed for the carbon emissions metric for new non-domestic buildings. The ‘Medium’ option requires a 16% reduction over existing carbon emissions targets whilst the ‘High’ standard aims for a 25% reduction. 
 

Primary or Delivered Energy 

The consultation also asks for feedback on whether to use Primary Energy or Delivered Energy as the principal metric for new non-domestic buildings. Delivered Energy looks solely at the anticipated energy demand for a building whilst Primary Energy also considers the energy used in upstream activities needed to prepare the fuel. 

Learn more about Primary Energy 

Scotland’s hesitancy in introducing Primary Energy (as is expected in England and Wales) is driven by the fact that the Primary Energy Factor (PEF) for electricity is higher than for gas. This means it could be simpler to meet a Primary Energy target for a property with an efficient gas boiler than for one with a heat pump. This seems a little counterintuitive given Scotland’s desire to move almost all new buildings to decarbonised heating, including heat pump technologies, from 2024. 
 

Raising the bar on fabric performance 

The consultation also sets lower maximum U-value requirements for new non-domestic buildings (shown in the table below). The values proposed in the Option 1 (Medium) package are similar to the current maximum U-values for new ‘shell and fit’ buildings (shown below) whilst the Option 2 (High) values are closer to the levels that a new domestic building might target under the existing (2015) standards. 

These maximum U-values will also apply to conversions and extensions on existing buildings (although conversions will be subject to an assessment to determine what changes are “reasonably practicable”). The consultation states it will look to develop a more robust and evidence led assessment to determine the optimal level of specification for specific buildings.  
 
Element type Current (2015) maximum U-values Current shell & fit (2015) maximum U-values Option 1 (Medium) maximum U-ivalues Option 2 (High) maximum values
All roof types
(W/m2K
0.20 0.15 / 0.20 0.18 0.13
Walls (W/m2K) 0.27 0.23 0.23 0.18
Floors (W/m2K) 0.22 0.20 0.18 0.15
Windows (W/m2K) 2.0 1.60 1.60 1.20
Rooflights (W/m2K) 2.0 1.60 2.10 1.90
NB It’s worth noting that the conventions for roof-light U-values have changed, so this isn’t a worsening of targets. U-value for rooflights is given for the horizontal plane. 
 

Notional buildings simplified 

The notional buildings used to set the Primary Energy and emissions targets for new non-domestic buildings in SBEM are also set to be simplified within the updated standard. Two variants are suggested based on heating type with one featuring an air source heat-pump (which will apply to building zones heated with heat pumps) whilst a specification featuring natural gas will be used for all other fuel types. The fabric requirements for these notional buildings are shown below. 

To better represent the complexity of these buildings, it is also proposed that the fuel used for domestic hot water is considered separately from space heating. This means it is possible to consider the impact of different fuel types if, for example, gas is used for hot water generation whilst heat pumps are used for general heating. 

As with for domestic buildings, the contribution of on-site renewable generation is also capped to reflect the amount anticipated to be used on site and ignoring any which will be sent on to the grid. 
 
Element type Current (2015) notional building - zone heated and naturally ventilated Current (2015) notional building - zone heated and mechanically cooled Option 1 (Medium) notional building Option 2 (High) notional building
All roof types (W/m2K) 0.18 0.16 0.15 0.11
Walls (W/m2K) 0.23 0.20 0.18 0.15
Floors (W/m2K) 0.22 0.20 0.18 0.15
Windows (W/m2K) 1.80 1.60 1.40 0.90
Rooflights (W/m2K) 1.80 1.80 1.50 1.50
Pedestrian Doors (W/m2K) 2.20 2.20 2.00 2.00
Vehicle access and large doors (W/m2K) 1.50 1.50 1.50 1.50
Air permeability (m3/m2/Hr@50Pa) 5.00 3.00 4.00 3.00
Photovoltaic panels (% of floor area) 4.5% 4.5% 13% 13%

New airtightness testing and detailing requirements 

In addition to efforts to improve the U-values of new and existing buildings, the revised standard also aims to close the performance gap between the expected and actual energy performance of buildings by raising compliance standards. 

As part of this approach, the exemption for small multiple units (those with a floor area of less than 150 m2) will be removed and the methodology in CIBSE TM 23 adopted for airtightness testing. The logic behind the latter move is to ensure the methodology is independent of any organisation with an associated competence scheme. Pulse testing will also be introduced as a testing option for these buildings. 

Significant changes are also set to be made around thermal bridges. These areas can account for as much as 30% of total emissions from a property and it was felt that this area needed to be urgently addressed to avoid underperformance in completed building. 

The Accredited Construction Details (ACDs) have been removed and the backstop psi-values, which can be used for junctions without a calculated detail in SBEM, worsened. The global Alpha value, which can be used where no details are supplied, has also been raised to 25% (adding 25% to the calculated heat loss from planar elements where no calculated psi values are used). This means it will be significantly more difficult (and costly) to reach compliance unless designers look to develop their own calculated details or adopt ones from existing libraries or from manufacturers.  
 

New Building Automation and Control Systems (BACS) requirement 

The consultation highlights BACS, which can centrally control a number of building systems including lighting, ventilation and security, as a particularly cost-effective means to saving energy in non-domestic buildings. It is therefore proposed that BACS be required for all new non-domestic buildings that have a heating or air conditioning system with an effective rated output over 290 kW. 
 

Removal of heating efficiency credits for existing buildings 

The existing Non-Domestic Building Services Compliance Guide allows heat generators in existing buildings to have a reduced seasonal efficiency, providing this is compensated through other energy efficiency measures (known as heating efficiency credits). These credits are set to be removed in the new guidance as it was felt that improvements in the efficiency of generator appliances in recent years meant this was no longer necessary.   

Additionally, where a heating system is fully replaced, the new system will need to be designed to operate at flow temperatures at, or below, 55 °C. This will allow simpler transition to heat pump technologies which perform more effectively at these lower temperatures. 
 

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