As part of the government’s consultation on the Future Homes Standard, Approved Document F (AD F) is also out for consultation.1 This is a great opportunity for the government to go beyond the current position, in paragraph 4.34 of AD F 2010, that ‘noise caused by ventilation systems is not controlled under the Building Regulations’.
Most people have personal experience of annoying noise from mechanical ventilation systems, which causes them to turn it down or off. In older, less airtight houses, there is likely to be sufficient ventilation from infiltration to avoid really poor indoor air quality. In modern, airtight houses, however, occupants rely on the effective operation of their ventilation systems to enable good indoor air quality.
The research for our 2019 article, ‘How loud is too loud: noise from domestic mechanical ventilation systems’,2 in the International Journal of Ventilation, was issued with the consultation,3 and reinforces the risks that excessive noise causes for occupants. So how does the consultation draft AD-F help prevent this unintended adverse consequence? (See panel ‘AD F consultation draft wording’). For one thing, it omits the line that indicates noise is not controlled under the Building Regulations – but how does it propose to control noise in the future?
AD F consultation draft wording
To prevent excessive noise, the consultation draft AD F states:
In the Secretary of State’s view, requirement F1(1) will be met if the dwelling is provided with a means of ventilation which… provides… as far as reasonably practicable:
- Low levels of noise, by following guidance in paragraphs 1.5 to 1.7…
1.5 Mechanical ventilation systems, including both continuous and intermittent mechanical ventilation, should be designed and installed to minimise noise. This includes:
- 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 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.
The current proposal in the draft AD F (see panel) is entirely inadequate to address noise from mechanical systems. There are no objective standards to meet and, rather bizarrely, the issues highlighted in paragraph 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 that we can measure?
Also surprisingly, 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 it in this way. 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, contractors will quickly find out how to make sure their designs and installations work. The Building Control body can check or ask for third-party verification; measurements of noise levels can easily be made if there is any doubt about whether they comply with the criteria.
Need for regulation
The necessity to include noise from ventilation systems within the Building Regulations is evident to stop occupants suffering poor indoor environmental quality (IEQ) as a result of intolerable noise. There needs to be:
- Performance standards for sound from ventilation systems
- Demonstration of compliance at the design stage
- Demonstration of compliance on completion.
We suggest the minimum performance standard to prevent most people being annoyed is:
Whole dwelling ventilation: sound from any type of mechanical ventilation system – when measured according to BS EN ISO 16032 – should not exceed:
- 26 dB LAeq, T in bedrooms, and
- 30 dB LAeq, T living rooms.
Extract ventilation: sound from any type of mechanical ventilation system – when measured according to BS EN ISO 16032 – should not exceed:
- 26 dB LAeq, T in bedrooms, and
- 35 dB LAeq, T in living rooms, and
- 45 dB LAeq, T in kitchens, sanitary accommodation and bathrooms.
The requirement relating to whole-dwelling ventilation should include sound from mechanical extract ventilation (MEV) and mechanical ventilation with heat recovery (MVHR) systems. The one 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 be adopted for the measurements. Although recirculating kitchen canopies do not provide ventilation, they should meet the same noise standards.
Manufacturers, generally, have sound data for their products, but quote the values in different and often confusing ways – for example, quoting levels at 3m in the freefield, which may be 18dB lower than the level the same product makes in a small room.
It would be useful to have a consistent approach to describing sound levels, so designers can compare products, and building control bodies can determine compliance. For extract fans that are ‘in the room’, for example, describe the standardised sound level in a room of 15m3, to represent the probable worst-case condition of a small room.
It would be useful to have a consistent approach to describing sound levels, so designers can compare products and building control bodies can determine compliance
For MVHR systems, duct length and bends reduce the transmitted sound. A calculation can be given for a particular dwelling based on the ductwork layout and the source sound power level at the calculated operating point. Manufacturers or system designers can provide these calculations; manufacturers currently propose the operation point of their equipment, so this calculation could 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 Energy Performance Certificate, along with the airtightness 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.
Responses to the Approved Document F consultation must be received by 7 February 2020. The government needs our opinions. Let’s not waste this opportunity to help it make appropriate regulations that protect people.
- Building Regulations: Approved Documents L and F (consultation version).
- How loud is too loud? Noise from domestic mechanical ventilation systems, International Journal of Ventilation.
- Ventilation and indoor air quality in new homes, Ministry of Housing, Communities & Local Government.
Jack Harvie-Clark is founder of Apex Acoustics