Building Scotland (Amendment) Regulations 2022 - ventilation and overheating: presentation

An update on the 2022/23 changes to building regulations

Ventilation and overheating standards from 1 February 2023

Introduction

Provisions within The Building Scotland (Amendment) Regulations 2022 on energy performance will come into force on 1 February 2023. The regulations were laid on 22 April 2022 and their in-force date subsequently amended on 17 June 2022 and 17 November 2022. This was in recognition of current delays in delivery of calculation tools elsewhere in the UK.

Changes to the regulations, standards and supporting guidance within section 3 (environment) were published in revised Technical Handbooks on 15 June 2022 and subsequently reformatted with minor amendments on 23 February 2023.

There are also changes within section 6 (energy) addressing energy and emissions performance and a consequential update to Aspect 2 (carbon dioxide emissions) within standard 7.1 (separate presentation available).

This presentation covers key changes to ventilation provision and the new overheating standard for dwellings and similar non-domestic residential buildings.

Background

• 2021 Programme for Government: “We will also review energy standards within current building regulations to deliver further improvement in energy efficiency and emissions reductions in new buildings, helping make homes more affordable to heat and tackling fuel poverty”.
• 1990 to 2015: 75-80% reduction in carbon emissions for new build – but it is now not ‘how far we have gone’ but ‘what more we can now do’.
• consultation on Energy Standards ran from July to November 2021.
• 176 responses received. These and consultation analysis published online

Key changes from February 2023

• revision of guidance for Domestic ventilation to clarify solutions and approaches for lower infiltration dwellings, revision of guidance on openable ventilators (purge
• ventilation) and background ventilation, changes to guidance on commissioning and written information on systems.
• incorporation of separate ‘Domestic Ventilation Guide’ as an Annex to Section 3.
• revision of guidance for Non-domestic ventilation to identify specific provisions around commissioning and written information on systems.
• introduction of new standard and supporting guidance on mitigating summer overheating risk in new homes and in new non-domestic residential buildings of a similar form.

Ventilation - changes to guidance

Changes are primarily to recognise the likelihood of a further reduction in designed infiltration levels in new homes in response to the section 6 (energy changes). The opportunity has also be taken to offer clearer guidance on ventilation levels generally and align terminology with that used elsewhere in the UK.

Domestic buildings

• clearer guidance on considering the ventilation solution in the context of the intended infiltration level of the new dwelling and the hierarchy of solutions used.
• clarification on whole dwelling ventilation rates which should be achieved, relating this to dwelling area and number of apartments. Noting that both supply and extract rates would be measured on completion for mechanical supply & extract solutions.
• reference now to ‘background ventilators’ rather than ‘trickle ventilators’. Emphasis on the need to provide effective ventilation pathways within the dwelling.
• guidance on openable ventilators now discussed as ‘purge ventilation’ and guidance on achieving adequate ventilation expanded. Previous provision at 1/30th of apartment floor areas now set at 1/20th (aligns with rest of the UK).

Guidance clause provided on each of the three most common ventilation solutions:

• natural ventilation with intermittent mechanical extract - basically unchanged.
• provision of continuous mechanical extract confirmed as whole-dwelling system only, implemented via central or decentralised extract system (cMEV or dMEV). Background ventilator areas aligned with provision in the rest of the UK.
• continuous mechanical supply and extract continues to be recommended for very low infiltration dwellings to give assurance of air supply to apartments and effective operation. Presence of heat recovery noted as likely but not mandated.

Domestic and Non-domestic buildings

• new guidance clause setting out summary information sought on commissioning and reporting on installed ventilation systems. Drawn mainly from provisions already set out in the commissioning sections of the BSD Domestic Ventilation Guide.

Domestic Ventilation Guide

• guide revised and updated - now included within the Domestic Technical Handbook as Annex 3.A for ease of reference.
• provides more detail on the ventilation solutions discussed in guidance to standard 3.14. Again emphasises the need for ventilation solution to be compatible with level of infiltration proposed for a new dwelling. Clarity on dMEV as a whole dwelling solution only. Detailed information on passive stack ventilation as an option removed.

Standard 3.28 - Overheating

Issue

• consultation last year noted that overheating in buildings has been highlighted as a key future concern for the health and welfare of people across the UK. And whilst the likelihood of overheating is lower in Scotland than elsewhere in the UK, it is important that it is considered as an issue in the design of new buildings.

Scope

• initial provisions introduced under new standard 3.28 look at assessment and mitigation of this risk in all new homes and in new non-domestic residential buildings which are similar in form and occupation to dwellings – self contained residential units ‘managed’ by occupants (for example, purpose-built student accommodation).
• the standard does not apply to other residential buildings which are managed environments, such as halls of residence, residential homes or hotels.
• recognising the limitations that may exist when redeveloping an existing building, the standard is applied to conversions as far as is reasonably practicable.

Application

• the standard asks developers to consider two of the key elements of design which can contribute to or mitigate overheating risk – management of excessive solar gain through glazing and the provision of ventilation to assist in cooling.
• the approach taken at its simplest level considers just these two issues. There is also the option to undertake dynamic thermal analysis if a simple glazing/ventilation approach is not seen as viable or if there are unusual characteristics in the building.
• it is expected that most development will be able to demonstrate compliance via the simplified approach set out in clause 3.28.2.

Design to limit solar gain

• guidance identifies risk elevations (east through south to west) and defines a maximum solar gain limit by glazing area and a default g-value.
• assessment is of glazing to apartments. No action needed where apartment window faces north of the orientations above or if glazing is less than 20% of the area of the room it serves. Where glazed are is greater, adjustment is sought to show that solar gain would be no greater than occurring at the default glazing level (20% of room area and g-value of 0.6).
• measure is not intended to restrict glazing areas, but to highlight the need to mitigate solar gains through solutions such as shading or improved glazing specification. For daylighting, advice is also provided on maintaining a good light transmittance value for the glazing specified.

Ventilation provision to remove heat build-up

• ventilation to assist in reducing internal temperatures is sought in all new homes.
• however, for buildings which have adequate cross ventilation, this is deemed to be already addressed through provision of purge ventilation under standard 3.14.
• for single or adjacent-aspect dwellings, which will typically be flats, an increased ventilation provision is sought to assist in removing heat, the provision under standard 3.14 rising by 50% from 5% of the floor area to 7.5%.

Dynamic Thermal Analysis

• guidance on this option cites the CIBSE TM59 methodology and the standard assertions which should be applied when modelling overheating risk.
• it is expected that use of active cooling should be justified via the TM59 route.

Practicality of measures applied

• guidance is offered to reinforce the need for solutions to be something which building occupiers can use in practice and which will not create any additional risk or nuisance. In this respect, the focus is on the provision of ventilation and the actions in respect of overheating should not be more significant that those for use of ventilation in homes in general. Provision of openable ventilators/windows should be safe and convenient and any location or environmental risks considered early in the design process.

Written information

• advice on the approach taken to keep the building cool in summer should be produced and provided as part of handover information to the building owner. For new homes, this is include in the ‘quick start’ guide required under standard 6.8.

Standard 6.6 – mechanical ventilation and air conditioning

• guidance to standard 6.6 now refers to the overheating risk assessment applicable to new homes and new ND residential buildings. There is emphasis on the need to avoid active/mechanical cooling systems.
• the Domestic Handbook no longer makes reference to use of Appendix P of SAP which is withdrawn and no longer included in SAP 10.
• note that guidance on minimum system efficiency of ventilation and cooling systems is still addressed by reference to provisions within the two Building Services Compliance Guides.

Ongoing work

For awareness:

• a further review of ventilation standards will commence shortly, leading to consultation and reporting in 2023/24. This will include, amongst other things, feedback on the 2015 implementation of CO2 monitors in dwellings and learning from our collective COVID-19 experiences and how changes in what is considered as effective ventilation can assist in delivering ‘infection-resilient’ buildings.
• it would be the intent to review the scope and application of the initial implementation of the overheating standard over the next few years to determine if any expansion of scope or approach would be beneficial.
• further guidance on the commissioning and effectiveness of ventilation systems will form part of the broader Compliance Plan approach to design and construction.

Contact for further queries: thomas.lennon@gov.scot