Under The Building (Scotland) Act 2003, the Scottish Building Standards system sets minimum standards applicable where new building work is proposed. These mandatory standards, and guidance on how they may be complied with, are published in the Building Standards Technical Handbooks. The building standards system is administered by local authorities who are appointed as the verifiers for their own geographical areas.
Standard 3.14, Ventilation, in Section 3, Environment, of the Building Standards Technical Handbook 2020: non-domestic, states: 'every building must be designed and constructed in such a way that ventilation is provided so that the air inside the building is not a threat to the building or the health of the occupants'. This requirement is applied at the point construction work takes place and does not apply retrospectively to buildings constructed to lesser previous standards. As such, existing buildings require to have their ventilation systems effectively managed by their owners, operators and occupiers to ensure good levels of indoor air quality are maintained.
Evidence suggests that in poorly ventilated indoor spaces, airborne aerosols are a possible transmission route of COVID-19. It is recognised that the higher the rate of ventilation, the lower the risk of airborne transmission. However, occupant thermal comfort, energy demands and associated carbon emissions will also need to be considered as part of a building ventilation strategy. This short, focussed project gathered evidence to assess whether application of the current ventilation guidance in the Non-Domestic Technical Handbook provides adequate basis for simple operational practices that can be used to effectively mitigate the indoor airborne transmission of diseases such as COVID-19.
An industry survey was conducted to establish what ventilation guidance was being used by industry in practice when designing new or maintaining existing non-domestic buildings. The results indicate a wide range of ventilation design guides and technical literature are being used in practice, from various sources including CIBSE, BB101, ASHRAE, HTM, BSRIA and BS 16798-3.
Examples measures for effective ventilation to mitigate the spread of airborne contaminants have been identified. These include the following: i) CO2 monitoring (as a proxy for ventilation), ii) examination and maintenance of installed ventilation systems, iii) maximising outdoor airflow by increasing natural ventilation provision, intermittent purge ventilation, extending operation of intermittent ventilation systems and/or installing new passive or mechanical ventilation systems (whilst maintaining setpoints for thermal comfort), iv) diverting direct airflow away from groups of individuals, v) avoiding recirculation of air, vi) use of enhanced filtration and/or air cleaning devices, vii) provision of breaks / fallow periods between occupants, and viii) ensuring negative pressure in toilets.
Whilst current industry standards for ventilation may be acceptable to minimize the risks of COVID-19 transmission if implemented correctly, a principal issue is whether these are being met a) in use and b) maintained over time. There remains virtually no reliable data on ventilation performance in practice for non-domestic buildings. Therefore, in order to provide greater assurance that adequate ventilation is provided in new non-domestic buildings, the following recommendations for change are provided:
- The phasing out of recirculation of air and replacement over time with heat exchanger systems which prohibit the mixing of intake and extract air to avoid airborne pathogen transmission.
- An increase in the recommended mechanical ventilation supply rate in building regulations from 8 l/s/p to 10 l/s/p is suggested for occupied rooms, in addition to the need for greater clarity in the definition of supply rates and consideration of occupancy limits, based on the capacity of ventilation systems.
- The introduction of requirements for CO2 monitoring in multi-occupancy high risk spaces to help identify airborne transmission risk related to poor ventilation and/or high occupancy, to prompt and inform behaviour change. This should be provided with clear guidance and appropriate information specifically tailored to the user group, to enable monitors to be used effectively.
- The consideration of infectious disease transmission in building ventilation regulations through the provision of explicit advice on the risk of far-field (>2m) aerosol airborne transmission. The importance of ventilation in mitigating this risk should be highlighted (e.g. in Section 3.14.1).
- The identification of ventilation performance standards and enhanced measures to ensure that compliance is achieved in use (building regulations) and maintained over time (other legislation). The introduction of a performance-based framework for assessing ventilation performance in non-domestic buildings (e.g. through an annual building 'health-check' / 'MOT', or for new retrofit works), would help ensure regular assessment of performance and verification of compliance over time.
- The requirement for a building ventilation maintenance plan, to support the regular inspection, cleaning and maintenance of ventilation systems in practice.
- Provision of a communications / labelling strategy for building ventilation systems (like the domestic energy 'quick start guides') to provide a clear, simple explanation to building users on what the ventilation strategy is, and how to use it. Whilst Standard 3.14.10 requires key information on the ventilation system to be provided on completion, the provision of short, visual instructions (for instance, next to ventilation systems or controls) would help ensure accessibility to all users and support understanding and effective operation of ventilation systems in practice.
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