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Consultation on Approved Doc F: noise from domestic mechanical ventilation systems

As part of the government’s consultation on the Future Homes Standard, Approved Document F is also out for consultation – respond before 7th February 2020, or get your comments to your professional body asap for their response. This is a great opportunity for the government to go beyond the current position in para. 4.34 of Approved Doc F 2010 that:

Noise
4.34 The noise caused by ventilation systems is not controlled under the Building Regulations…

Most people have personal experience of noise from mechanical ventilation systems that is annoying. This causes people to turn ventilation systems down or off. In older, less airtight houses, there is likely to be sufficient ventilation from infiltration to avoid really poor indoor air quality as a result. In modern airtight houses, the occupants rely on the effective operation of their ventilation systems to enable good indoor air quality. We wrote about all these things in our peer-reviewed article in the International Journal of Ventilation, 2019, “How loud is too loud: noise from domestic mechanical ventilation systems“. The research that was issued with the consultation reinforces the risks that excessive noise causes for occupants. So how does the consultation draft Approved Doc F help avoid this unintended adverse consequence? Firstly, it omits the line noted above that indicates noise is not controlled under the Building Reg.s. How is it proposed to control noise in future?

The consultation draft says:

Performance

e. provides all of the following as far as reasonably practicable:
• low levels of noise, by following guidance in paragraphs 1.5 to 1.7…
Noise
1.5         Mechanical ventilation systems, including both continuous and intermittent mechanical ventilation should be designed and installed to minimise noise. This includes all of the following:
• sizing and jointing ducts correctly
• ensuring that equipment is appropriately and securely fixed
• selecting appropriate equipment, including following paragraph 1.6.
1.6         For mechanical ventilation systems, fan units should be appropriately sized so that fans operating in normal background ventilation mode are not unduly noisy.  This might require fans to be sized so that they do not operate near the maximum capacity of the fan when operating in normal background ventilation mode.
1.7         Account should be taken of outside noise when considering the suitability of opening windows for purge ventilation.

Current draft is entirely inadequate

The current proposal in the draft Approved Doc F is entirely inadequate to address noise from mechanical systems. There are no objective standards to meet, and rather bizarrely the issues highlighted in para. 1.5 don’t mention noise from the fan! Why use terms such as “minimise noise” and “not unduly noisy” rather than state objective noise levels which we can measure?

It is also surprising that reference is made to taking account of outside noise when considering the suitability of opening windows for purge ventilation. Is this purge ventilation as described in AD-F, to rapidly dilute pollutants and/or water vapour. From an acoustic perspective, there would be few concerns about external noise ingress when using purge ventilation in this way. Obviously the more common use of purge ventilation is to mitigate overheating, but that is a separate issue.

Why does this draft talk about “sizing and jointing ducts correctly” rather than simply stating noise criteria to be achieved? If noise is controlled under the Building Regulations, then contractors will quickly find out how to make sure that their designs and installations work. The Building Control body can easily check, or ask for third party verification – measurements of noise levels can easily be made if there is any doubt as to whether noise levels comply with the criteria. Indeed, Apex are UKAS-accredited for measuring noise levels in rooms, so that you can be assured of the results.

Need for regulation

The necessity to include within the Building Regulations noise from ventilation systems is evident to prevent occupants suffering poor air quality as a result of intolerable noise. To prevent noise being the constraint that prevents occupants achieving reasonable IAQ, there needs to be:

  • Performance standards for sound from ventilation systems;
  • Demonstration of compliance at the design stage;
  • Demonstration of compliance on completion.

Performance standard for sound from ventilation systems

We would suggest that the minimum performance standard to prevent the majority of people being annoyed is:

While providing whole dwelling ventilation, sound from any type of mechanical ventilation system should not exceed:
26 dB LAeq, nT in bedrooms, and
30 dB LAeq, nT living rooms
when measured according to BS EN ISO 16032.

And:

While providing extract ventilation, sound from any type of mechanical ventilation system should not exceed:
26 dB LAeq, nT in bedrooms, and
35 dB LAeq, nT  in living rooms, and
45 dB LAeq, nT in kitchens, sanitary accommodation and bathrooms
when measured according to BS EN ISO 16032.

The requirement relating to whole dwelling ventilation should include sound from MEV and MVHR systems. The requirement relating to extract ventilation should include intermittent extract fans used with natural ventilation, as well as MEV and MVHR systems. The performance requirement should apply with all doors (and windows) closed, and this be adopted for the measurements. Although re-circulating kitchen canopies do not provide ventilation, they should meet the same noise standards.

Design stage compliance

Manufacturers generally already have sound data for their products, but quote the values in different and often confusing ways (e.g. quoting levels at 3 m in the freefield, which may be 18 dB lower than the level the same product makes in a small room, for example). It would be useful to describe a consistent approach to describing sound levels, so that designers can compare products, and Building Control bodies can determine compliance.

For example, for extract fans that are “in the room”: describe the standardised sound level in a room of 15 m3, to represent likely worst case condition of a small room.

For MVHR systems, duct length and bends reduce the transmitted sound. A calculation can be provided for a particular dwelling based on the duct-work layout and the source sound power level at the calculated operating point. Manufacturers or system designers can provide these calculations – the manufacturers currently provide proposals for the operation point of their equipment, so this calculation could either be added to that or determined from the proposed ductwork layout.

Demonstrating compliance at completion

Commissioning measurements of sound should be taken at the same time as those for ventilation airflow.  All data should be lodged online in a database linked to the SAP and EPC, along with the air tightness test result and other evidence of compliance.

A less onerous regime could give Building Control bodies the power to demand commissioning sound measurements be carried out by a suitably-qualified person if they have any concerns over the sound levels, based on an aural assessment.

Make your voice heard!

Respond to the consultation directly, and to your professional body compiling a response. Members of the Institute of Acoustics may send comments to the Building Acoustics Group, who are compiling a response. Members of the Association of Noise Consultants can send comments to info@theanc.co.uk. The government is asking because it needs your opinion. Let’s not waste this opportunity to help the government make appropriate regulations that protect people.

Return to: Noise and ventilation research

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

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