CPD PROGRAMME | VENTILATION system pressure drops and increased noise; inappropriate and inadequate commissioning of ventilation systems; and poorly labelled controls and inadequate handover instruction for end users. The report highlighted that a lack of detailed specification and detailing had resulted, in some cases, of improvising on site (with no consultation back to the designer) and some checking of systems being done by ear, using noise levels as the guide to performance, not flow rates. Homes in occupation and operation have been similarly found wanting in the practical operation of ventilation. A key preparatory study undertaken by Aecom4 that contributed to the development of the Future Homes Standard covered 80 occupied homes 55 naturally ventilated and 25 with decentralised mechanical extract ventilation that had been constructed after 2010 to meet the requirements of Part F 2010, and which were studied across the winter period 2015-16. Although considering a relatively small sample of homes over a single quarter of a year, the findings were able to reveal some significant concerns; 30% of the tested homes with continuous mechanical extract were not maintaining recommended IAQ performance standards. Further analysis suggested that this resulted in part from the relative position of trickle ventilators causing short circuiting of airflow to the room extract grilles, and that the standards set by Part F were not, in themselves, inadequate. In the naturally ventilated homes, the location of trickle ventilators was again identified as being a significant contributor to poor performing ventilation and the resulting poor IAQ. Trickle ventilators that were obscured often at night behind closed curtains were considered as being the likely culprit leading to relatively high levels of carbon dioxide (CO2) and total volatile organic compounds (TVOC), particularly in bedrooms, driven by the relatively low air-change rates. Additionally, the report highlighted that noise from extract fans resulted in occupants choosing not always to switch them on when they were needed, which could potentially lead to the consequences of long-term under-ventilation. In locations with high external sound levels, there was a tendency for occupants to close (or obscure) trickle ventilators to reduce the ingress of noise, so reducing the home ventilation rate. The development of the new AD F volume 1 20215 (AD F1) was driven, at least in part, by such deficiencies described above, with an overall aim to protect the health of occupants of the building by providing adequate ventilation. It was widely considered that the ventilation rates of the previous Part F would Figure 1: Extreme example of the consequences of poor ventilaion in first-floor bedroom when room was closed up for 12 weeks during ground-floor building works in winter 2021-22. A trickle vent in the top corner had been previously plastered over (Photo source: Martin MacDonald) have likely been adequate if the installation and operation had followed through the intent. (See boxout Understanding AD F1 2021.) The important, relatively discreet, updates in AD F1 integrate with the desire to make the requirements clearer and more useable, and to align with the demands presented in the complementary ADs. So, for example, AD F1 ensures sufficient levels of ventilation are provided despite the more stringent building airtightness requirements of AD L1. The categories of ventilation are now simplified into three main types. Passive stack ventilation and natural ventilation without the use of mechanical extract are no longer specifically included. The first system type described in AD F1, natural ventilation with background ventilators and intermittent extract fans, might be considered as reasonably traditional for UK housing but is deemed as only applicable for new dwellings with a design air permeability higher than 5m3.m-2.h-1 @ 50Pa (or 3m3.m-2.h-1 @ 50Pa as built), referred to as a less airtight dwelling. (Practically, this means that it will not suit most new homes, as otherwise they are likely to struggle to comply with energy-related regulations.) Background ventilators are required with significantly greater equivalent area than in the previous AD F, which together with higher whole dwelling ventilation rates, and UNDERSTANDING AD F1 2021 As with all regulations and standards, there will be some interpretation required for the new AD F1, the need for which may not become obvious until the new ADs are applied to design, installation and operation. It is important to review the ADs directly to understand the detail (and they are freely available at www.gov.uk/government/collections/approved-documents). However, a useful general side-by-side comparison of the requirements of AD F1 2021 with the previous requirements may be seen at www.titon.com/uk/building-regs-update. 62 April 2022 www.cibsejournal.com CIBSE Apr 22 pp61-64 CPD 193.indd 62 25/03/2022 14:31