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Future Buildings Standard consultation: Overheating and noise

The government launched the current consultation on the Future Buildings Standard at the end of January 2021. This follows the consultation on the Future Homes Standard that was conducted during 2020. The current consultation is the second stage of the two-part consultation on proposed changes to Part L (Conservation of fuel and power) and Part F (ventilation). It also addresses overheating in residential buildings, for which a new Approved Document is proposed.

I keep saying to people – it’s not often that a new part to the building regulations comes along which is truly exciting – but this really is! Of the 31 pages, noise is covered on a single page. But the proposed regulation has huge implications, so it’s very important that we as an industry get it as right as we can. So I’d like to draw your attention to the two most important parts.

Noise levels in bedrooms

The first is the standard for noise itself, described in para 3.1

This only controls noise in bedrooms at night time. So the first question – are “bedrooms” defined, or can developers evade this by labelling a room as a “home office” instead? More importantly, the second question – are these the appropriate noise levels to protect people from noise? For Building Regulations – remembering that these are the minimum legal standards to which people are allowed to build buildings – It may be more suitable to adopt the upper limits from the Acoustics, Ventilation, Overheating: Residential Design Guide. We spent 4 years trying to work out what was an appropriate balance between thermal and acoustic comfort, and the consensus of the cross-industry committee settled on upper limits, depending on the duration of exposure, as:

42 dB LAeq, T

65 dB LAF,max, not normally exceeded.

The definition of the LAF,max criterion is described in our IOA paper, as a reference to the AVO Guide. The AVO Guide also provides a method for considering the duration for which openings are required to mitigate overheating. It suggests that a longer duration should be associated with lower internal noise levels, but this is perhaps too complicated for Approved Documents and the Building Control process. This is considered further below – the evidence that Building Control Bodies may accept.

But sticking with the noise levels, consider the mechanical system noise. Clearly the reference time, T, should be while the mechanical system is in operation – it’s inappropriate to average the noise level between periods when it is on and off, if that’s how it operates. But is 30 dBA the right level? Our paper “How loud is too loud? noise from domestic mechanical ventilation systems” was published in the International Journal of Ventilation in 2019. We assembled and considered all the evidence that we could at that time for the effects of noise from ventilation systems. It seems that the most important effect is not noise impacting on sleep (as it is for environmental noise), but rather annoyance from mechanical noise when trying to fall asleep. If a ventilation system makes annoying noise when people are trying to fall asleep, they turn the ventilation system down or off until they can tolerate the noise. It turns out that a lower level than 30 dBA is necessary to protect the majority of people from becoming annoyed.

However, we found less evidence for the effect of noise from mechanical systems to mitigate overheating. The common experience in hotels in this country where there is a system to provide comfort cooling is that when you operate the cooling system, it’s noisy. People seem to accept that mechanical cooling can be noisy in hotels. Apparently that’s not the case in Japan, for example; comfort cooling systems in hotels are designed and built to be quiet, because that’s what occupants want and expect. We have little bits of evidence of people using or not using mechanical fan systems that have been provided near airports. But it’s a complicated question to unpick – the range of people’s tolerance to environmental noise if they open the windows, the mechanical noise with windows closed, the level of thermal comfort with each, as well as other factors that may affect their choice – such as the perceived electricity cost of running a fan. I haven’t seen that research yet, but at the same time it is essential that there is a noise limit on mechanical systems. Without a noise limit, it’s always cheaper to let them be noisier.

Demonstrating compliance

Three options are proposed to enable contractors to demonstrate compliance with the noise requirement. This perhaps needs a little clarification, because if there are no issues with external noise but a mechanical system is nonetheless used, that mechanical system should still meet the appropriate noise limit.

Testing on completion is allowed, but this is not likely to be a popular choice – you need to know before you’ve completed the building that it will comply with this requirement! So the third option is “modelling of the noise…”. This takes what many of us do every week for planning applications, and makes the Building Control officer the gatekeeper, and arbiter of what constitutes an appropriate prediction and assessment of environmental noise impact. I believe this places an unfair burden on the Building Control Officer – they have no education, skills or training in interpreting environmental noise impact assessments. So what could work better? I’ve been wondering if an independent, not for profit, industry-led scheme could provide this role. Establish minimum assessment and reporting standards, and evaluate reports against those standards. Record assessments in a central system that is openly accessible – so you can see if someone has already carried out an assessment for the adjacent plot. Link it with the EPC. Take the responsibility off Building Control to make that judgement. If left to Building Control, is there a serious risk that standards will fall to the bottom (how far down is that?), with the result that future residents will not be adequately protected?

There’s still time to register for the last Institute of Acoustics’ consultation workshop at 7 pm on 16th March.

Apex Acoustics Ltd Design Works, William St, Gateshead, Tyne and Wear NE10 0JP Head office: 0191 620 0750 Midlands: 0115 708 0750

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