Building regulations - energy standards and associated topics - proposed changes: consultation

Part 4 – Ventilation

4.1 Introduction

Following the commissioning of research into the impact of previous 2015 ventilation amendments to ventilation standards for new homes earlier this year, it is the intent to undertake a fuller review of ventilation provision for both domestic and non-domestic buildings from 2022.

Accordingly, changes proposed at this time are focussed on domestic ventilation and limited to those which are considered to be directly relevant to the introduction of improved energy standards or (in response to published research^[25]) can better address the delivery of expected levels of ventilation and good indoor air quality:

• The expectation of further trends on reducing infiltration rates and increasing application of mechanical extract or supply/extract systems in lieu of natural ventilation.
• Reinforcement of the need for ventilation design to be properly considered and evidenced, systems designed and performance verified and recorded, post-commissioning.
• For dwellings, action to support proposals to require assessment and response to overheating risk in new residential buildings.

4.1.1 Background

At present provision for building ventilation to address air quality for occupants is addressed through standard 3.14 and associated guidance in the Domestic and Non-domestic Technical Handbooks. Further guidance on domestic ventilation is provided in a companion Domestic Ventilation Guide.

Guidance on the energy performance of ventilation systems is addressed under standard 6.6 and supporting guidance within the Building Service Compliance Guides. Updating of these provisions form part of the review of building services for Section 6 (energy).

For dwellings, a means of providing ventilation is required, by natural (background and intermittent extract) or mechanical (continuous extract) means.

As a basic provision, the following is identified:

• A manually openable ventilator and background ventilation is sought in every apartment.
• Intermittent mechanical extract (or passive extract) and background ventilation in each apartment and in kitchen/utility rooms and sanitary accommodation.

This simple prescriptive approach is deemed adequate to maintain indoor air quality in a typical dwelling where a reasonable ventilation component from fabric infiltration is present (equating to a building infiltration rate of not less than 5 m³/(h.m²)@50 Pa). At present, guidance is not provided to explain the basis for the provision of ventilation to achieve specified levels of air change.

For infiltration rates lower than this, the need for a continuous mechanical system is identified. Options identified in guidance are:

• mechanical extract ventilation (MEV) and decentralised mechanical extract ventilation (dMEV) if design air infiltration rate is not less than 3 m³/(h.m²)@50Pa.
• balanced supply and extract mechanical ventilation systems, with or without heat recovery, for very low infiltration dwellings (below 3 m³/(h.m²)@50Pa).

Guidance identifies provision of a means of monitoring and reporting on air quality, using CO₂ levels as an indicator (sought in one apartment used for sleeping).

The companion Domestic Ventilation Guide expands on the basic guidance in the Technical Handbooks to assist designers in choosing an appropriate solution for a given dwelling. It also provides detailed guidance on the component elements of a given solution that are needed to support effective ventilation. Guidance on the commissioning, testing and reporting of mechanical elements of systems is also provided.

It is noted that current guidance for dMEV is not focussed on use as a ‘whole dwelling’ system. Nor is a need to consider the dwelling layout and location/exposure identified in the design of the system.

For non-domestic buildings, again a means of providing ventilation to occupied spaces is required, by natural (background and intermittent extract) or mechanical (continuous extract) means. Where applying natural ventilation to buildings with infiltration no lower than 5 m³/(h.m²)@50Pa, a manually openable ventilator and background (trickle) ventilation is sought in every room. Background ventilation area is subject to infiltration rate limits. Mechanical extract ventilation is sought in toilets/wet areas. Alternative provision by use of BS 5925, or CIBSE Guide A or AM10. Options for the design of mechanical ventilation systems are identified, referencing BS 5720 and CIBSE Guide B2.

4.1.2 Issues to address:

A review of data on recent dwelling completions confirms that new homes are being constructed with lower levels of fabric infiltration. Out of just over 5,000 test undertaken last year, 7% of homes had a tested infiltration rate below 3 m³/(h.m²)@50Pa, 58% were between 3 and 5 m³/(h.m²)@50Pa and 35% at 5 m³/(h.m²)@50Pa or above, with the majority within 1 m³ of that value.

This indicates that the area of focus of this review should be on properties in the range of 3 to 5 m³, as a rate easily achieved via current construction. Noting that it should be anticipated that a move to improved fabric values, particularly for walls, will result in further reductions in infiltration due to increased layering and consistency of the insulation envelope and an increase in properties with infiltration rates below 3 m³/(h.m²)@50Pa.

The following areas of change are proposed as part of this consultation and are discussed in more detail in the next section:

• Clarification in guidance of the overall level of ventilation sought in new dwellings to reflect normal occupancy and use.
• Review of provision and citation of function of openable windows as purge ventilation.
• Greater clarity on design choices for dwellings where infiltration rates between 5 m³ and 3 m³ and below 3 m³ are proposed.
• Revision of advice on dMEV systems to reflect only ‘whole dwelling’ use as opposed to current provisions which recognise ventilation of individual rooms.
• Views on the application of mechanical supply and extract systems, including the presence of heat recovery.
• Relocation of guidance from Domestic Ventilation Guide into the Domestic Technical Handbook.
• Emphasis on commissioning and providing information is provided for air flow rate testing and, linking to commissioning of ventilation systems for energy efficiency under standard 6.6.

4.2 Proposals

4.2.1 General revision expansion of core guidance on ventilation provision

We propose to reconfigure how guidance on ventilation is presented for new buildings to emphasise the need to consider solutions in the context of low or very low infiltration buildings. This will emphasise that there are three options available to designers – an approach that will work with any dwelling, regardless of the design intent for infiltration and two approaches that will generally only be viable above a specific infiltration threshold.

Solutions based upon the presence of continuous mechanical extract must be designed to suit the building and its environment, regardless of the approach taken to both extract (centralised/decentralised) or air supply (background ventilators or balanced supply).

Table 9 Ventilation solutions for design infiltration levels.

Ventilation type	Suitable for infiltration rate:
Natural ventilation (with intermittent mechanical extract)	≥ 5 m³/(h.m²)@50Pa
Continuous mechanical extract ventilation	≥ 3 m³/(h.m²)@50Pa
Continuous mechanical supply & extract ventilation	Any

To aid understanding of objectives and to inform system design, guidance will also more clearly explain, in concise terms, what level of ventilation is sought to provide adequate indoor air quality in dwellings. Including information on minimum supply rates that are to be achieved in dwellings with continuous extract, which are also deemed to be achieved by the prescriptive specification offered for naturally ventilated dwellings (infiltration rate not less than 5 m³/(h.m²)@50Pa) which formed 39% of recent dwelling completions, based upon test data.

The proposed supply rates follow the recent review, elsewhere in the UK, of the assignment of whole dwelling ventilation rates based upon both floor area and the number of apartments (habitable rooms). This makes a standard assumption on occupancy and assumes a base supply rate of 13 litres per second plus an additional 6 litres per second for each additional apartment. Subject also to the supply rate being not less than 0.3 litres per second per square metre of the dwelling internal floor area.

It is also proposed to remove detailed information on passive stack ventilation, as a little used solution, whilst still noting it as an alternative to the use of intermittent mechanical extract.

These changes are illustrated in ‘Consultation proposals - Standard 3.14 (Ventilation) Domestic’.

Question 32 –

Do you support the proposed revisions to the presentation of guidance on ventilation and the incorporation of the ‘domestic ventilation guide’ into the Technical Handbooks?

Yes

No

Please provide a summary of the reason for your view.

4.2.2 Revision of guidance on purge ventilation

Current guidance sets a minimum recommended opening area for rooms within a dwelling, including for apartments. Provision is set at 1/30^th of the floor area of the room. The purpose of this provision, to enable intermittent increase in ventilation to remove pollutants created by occasional activities, or indeed, assist in ventilation to reduce overheating, is not explained further.

Designers working in other UK administrations will be aware that provisions are already made within Approved Document F on this topic. To assist in greater understanding of the role of ventilation elements and to underpin proposed work on summertime overheating risk, it is proposed to align provisions in Scotland with this established practice.

Guidance will explain the function of ‘purge’ ventilation as a component of ventilation provision and as a prescriptive solution deemed to support a nominal ventilation level of 4 air changes per hour. We propose to align the basic provision of openable ventilators from 1/30^th to 1/20^th of the floor area of the room served to align with practice elsewhere in the UK, noting how the degree of opening of ventilators has on effective purge ventilation.

Note: the role of purge ventilation in reducing heat gain in summer is also discussed under section 5.2.4.

Question 33 –

Do you agree with the revision of guidance to clarify the function of purge ventilation and increase provision to align with that applied elsewhere in the UK?

Yes

No

Please provide a summary of the reason for your view.

4.2.3 Clarification on ventilation solutions in low infiltration new dwellings

As improvements to energy standards have led to greater levels of air tightness in buildings to reduce space heating demand, a consequence is that the ventilation provision in modern homes now has to more commonly be designed to reflect lower levels of fortuitous ventilation through the building envelope.

Low infiltration is defined as a design intent of not less than 3 m³/(h.m²)@ 50Pa and less than 5 m³/(h.m²)@50 Pa which is realised on construction. The majority of recent dwelling completions with airtightness tests (58%) are within this category.

In current building regulations guidance, airtight buildings (below 5 m³/(h.m²)@50 Pa) should be provided with a continuous mechanical ventilation solution. The revised 2015 domestic handbook guidance included the option of decentralised or centralised Mechanical Extract Ventilation (dMEV) for dwellings with an air-tightness of between 3 and 5 m³/(h.m²)@50 Pa.

Following on from this change in guidance, we engaged with the Mackintosh Environmental Architecture Research Unit (MEARU) to carry out research into the effectiveness of dMEV to act as ‘whole-house’ ventilation in new build dwellings.

The research, published in 2018^[26], highlighted that there were a number of variables that affected performance of the dMEV system. These included the nature of the trickle vents, the window coverings, the path between the room and the dMEV (including the door opening or ‘undercut’, and the arrangement of the home) and the installation and performance of the system. Essentially homes with shorter, more open paths for air movement performed better, but rooms which relied on more remote dMEV systems frequently had poor ventilation. Whilst there are some situations where a dMEV system can assist with the ventilation provision of modern airtight homes, the ability to act as a whole house system is limited, particularly in larger more complex layouts, and where ventilation loads are high.

As such, such solutions as a whole requires the same level of care in design as a centralised mechanical extract system, taking into account the house layout, paths for air movement (including ‘undercuts’ and pass vents), the nature of the mechanical system, and consideration of remote rooms. The system will only be effective in operation where these are optimised.

On that basis, it is proposed, for design infiltrations rates of not less than 3 m³/(h.m²)@50 Pa, to be presented on the basis of a whole dwelling continuous mechanical extract system which may operate via a central fan or through a number of separate room extract fans. The solution - continuous mechanical extract ventilation must be applied and controlled to the dwelling as a whole.

Such a system must be designed to deliver the required air supply in habitable rooms, taking into account the location of extract terminals and the sizing of background ventilators. This has to be demonstrated on commissioning of the completed system. In both cases, the rate of extract at each terminal and other relevant elements will need to be reviewed to support the effective draw of air though the dwelling.

Question 34 –

Do you support reference to a single option for continuous mechanical extract ventilation which can have centralised or decentralised fans, with the same design parameters being applied to the system in each case?

Yes

No

Please provide a summary of the reason for your view.

If you have any further views on the use of continuous mechanical extract to deliver effective ventilation in both low infiltration (3-5 m³) or higher infiltration (5 m³+) buildings, we would also welcome your comments.

4.2.4 Background ventilators in continuous mechanical extract solutions

Current guidance gives no information on the sizing of background ventilators in continuous mechanical ventilation solutions. This has led to designers citing CIBSE guidance which in turn references information published within English building regulations. Such solutions, principally for whole dwelling decentralised mechanical extract ventilation, are now common.

We therefore propose to introduce guidance on background ventilator sizing to support such systems and the solution proposed reflects research undertaken for review elsewhere in the UK, including the sizing of ventilators to avoid excessive air movement rates. This proposes that the minimum equivalent area of background ventilators in each habitable room should be not less than 5000 mm².

Question 35 –

Do you support introduction of proposed guidance on default minimum size of background ventilator for continuous mechanical extract systems?

Yes

No

Please provide a summary of the reason for your view and on any specific concerns which may arise from the proposed level of background ventilation or its application in the design of systems.

4.2.5 Ventilation solutions in very low infiltration new dwellings

Very low infiltration is defined as a design intent of less than 3 m³/(h.m²)@50Pa which is realised on construction. A small proportion (7%) of recent dwelling completions with airtightness tests are within this category.

Current guidance does not offer a usefully clear recommendation on the use of continuous mechanical extract ventilation (MEV) in such situations. Guidance within section 9 of the ‘Domestic Ventilation Guide’ recommending that MEV is not suitable for very low infiltration dwellings. This is based upon concerns over the efficacy of background ventilation in dwellings which can be designed and delivered with potentially very little infiltrative ventilation component.

This leaves the advised solution for ventilation systems for very low infiltration buildings as continuous mechanical supply and extract ventilation, with or without heat recovery.

We are interested in your views on the continued prescription on the need for continuous mechanical supply and extract in very low infiltration dwellings (less than 3 m³/(h.m²)@50Pa) and whether solutions without a mechanical supply component can be as effective.

Whilst not directly material to the provision of ventilation, we are also keen to hear you views on whether the presence of heat recovery should be prescribed for all packaged supply/extract systems in new homes, where the declared design infiltration rate will being significant benefit in reducing overall ventilate heat loss.

Question 36 –

Should continuous mechanical extract systems be considered a viable solution in very low infiltration dwellings and, if so, under what circumstances?

Yes

No

Please provide a summary of the reason for your view.

We would also like to hear your views on whether heat recovery should be mandated for packaged supply/extract systems

4.2.6 Incorporation of secondary guidance into the Handbook

The fragmentation of guidance on ventilation, particularly in respect of supporting advice for domestic installations has been noted by commentators. We intend to present a revised version of the current ‘domestic ventilation guide’ as an Annex to section 3 of the Domestic Technical Handbook.

These changes are illustrated in ‘Consultation proposals - Standard 3.14 (Ventilation) Domestic’.

In bringing the Domestic Ventilation Guide into Section 3 (environment as an annex), this review therefore emphasises:

• Design of ventilation that assesses the dwelling layout and components of the system and accounting for other key issues such as extract outlet positions and exposure/prevailing winds.
• Reinforcing the need for pass vents between rooms, fire protected where required, ideally at higher levels.
• Consistent application of cited standards for commissioning, testing in use and reporting to demonstrate the system functions as intended.
• Reinforcing advisory standards for noise from installed fans.
• Better design of occupant interfaces of mechanical systems, in particular boost modes as an occupant control element.
• Better advice and information for occupants about the ventilation system, its optimal use, and requirements for maintenance.

Question 37 –

Do you support the incorporating of this additional guidance into the Technical Handbooks?

Yes

No

We would be grateful for comment on the content of the proposed Annex and whether there are elements absent from guidance or which would be better presented within guidance to standard 3.14 itself.

4.2.7 Emphasis on design, commissioning and testing

Sections 6 to 8 of the proposed domestic ventilation annex set out the expected action to test and commission installed ventilation equipment. A summary note on expected action is also set out in clause 3.14.7, making reference to the new Annex text.

This includes verifying that the installed components are as specified, installation is complete and components are operational; controls are accessible and clearly marked; each mechanical supply or extract unit or terminal is tested for airflow at both normal and boost operation and results recorded; for supply/extract system, system balancing of airflow to achieve intended rates in each room.

These changes are illustrated in ‘Consultation proposals - Standard 3.14 (Ventilation) Domestic’.

It is proposed that reporting on such matters will be further collated as part of the Compliance Plan approach which will be consulted on later this summer. The intent being that this information is presented to the verifier. One output from this approach is a summary document, passed on to the building owner/occupier, that presents evidence of compliance with the requirements set by building regulations.

It is noted that advice is provided on limiting noise from mechanical ventilation systems but that this is not prescribed as a compliance test. It is expected that this will inform design and specification decisions.

Question 38 –

Are there other elements of the commissioning of ventilation systems that you consider are both practical to implement and useful in providing additional assurance of performance in practice?

Yes

No

If yes, please provide a summary of the topics which should also be considered.

4.2.8 Domestic and Non-domestic ventilation – intent and further review

As noted in section 4.1, a further review of standards and guidance on ventilation in buildings is programmed to commence later this year, with the intent to develop proposal for consultation in 2022/23. Topics identified for this review include:

• Subject to current research, review of CO₂ monitoring provisions introduced in 2015.
• Advice on ventilation assessment and installations as part of planned building retrofit.
• Guidance on minimising ingress of external pollutants.
• Guidance on the wider design and installation to minimise noise from mechanical ventilation systems.
• Consideration of guidance, post-COVID, on evolving good practice on enhanced ventilation provision and use of air recirculation in non-domestic buildings.

Question 39 –

We welcome your thoughts on these or broader topics which would merit consideration as part of the planned review. Please set out your thoughts below, including citation of relevant supporting evidence, where relevant.

4.2.9 General comments

Question 40 –

We welcome any other comments you wish to make on proposed changes to ventilation standards for domestic buildings.

Where practical, please with a reference to any particular issue in the context of the Domestic or Non-domestic Handbook (or both if applicable) and cite any standard or revised guidance clause relevant to the topic.