Wind turbine noise assessment for a small rural scheme
ETSU-R-97 and the Institute of Acoustics good practice guide still govern wind turbine noise in England. For a small scheme the simplified route can remove a monitoring campaign entirely.
A small wind turbine noise planning assessment in England is still carried out to ETSU-R-97, the 1996 report on the assessment and rating of noise from wind farms, applied through the Institute of Acoustics good practice guide of 2013 and its supplementary notes. That surprises people who expect BS 4142 to apply, and it matters, because the two methods produce different answers. ETSU works in LA90 and correlates noise against wind speed. BS 4142 works in LAeq and applies character corrections. Using the wrong one is the fastest route to an objection from the environmental health officer.
Which framework applies
National planning guidance on renewable and low carbon energy points to ETSU-R-97 for wind turbine noise, and the Institute of Acoustics guide sets out how to apply it consistently. For a single farm turbine or a cluster of two or three, that framework still governs, scaled to the site.
ETSU sets noise limits as the prevailing background level plus 5 dB, subject to lower fixed limits that protect quiet locations. Day-time limits fall within a range of 35 to 40 dB LA90,10min, with the figure chosen by reference to the number of dwellings affected and the energy generated. The night-time limit is 43 dB LA90,10min, set to protect sleep with windows partly open.
There is a simplification that matters enormously for small schemes. Where predicted noise is below 35 dB LA90,10min at all wind speeds up to 10 m/s, measured at the standardised 10 metre height, ETSU allows the assessment to stop there without a background noise survey. For a modest turbine several hundred metres from the nearest house, that is often achievable, and it removes weeks of monitoring and a substantial fee from the project.
So the first question for any small scheme is whether the simplified route is available. Ask the acoustician to test it before commissioning anything else. The Noise Impact Assessment can then be a short, defensible document rather than a monitoring campaign.
Background noise and wind speed
Where the simplified route is not available, the survey is the expensive part.
Background noise is measured in LA90,10min at or near the nearest noise-sensitive property, simultaneously with wind speed data, and the two are correlated by regression. Separate curves are derived for day-time and for night-time, because rural background noise falls away after dark while the wind may not.
Four points where surveys go wrong:
- Rain affected data left in the dataset. Rain on a microphone raises measured levels and flatters the background curve.
- Too short a monitoring period, so the regression rests on a narrow band of wind speeds and has to be extrapolated.
- Wind speed measured on site at a height that is then converted to the standardised 10 metre value using a shear assumption nobody states. Wind shear at night is the single most contested variable in this field.
- Extraneous noise from farm activity, livestock, a nearby road at a time of day that is not typical.
Ask for the raw data, the exclusion criteria and the shear assumptions in the report, alongside the derived limits. An environmental health officer who has to ask for them will assume the worst.
Day and night limits in practice
| Period | Limit basis |
|---|---|
| Day-time | Background LA90 plus 5 dB, within a 35 to 40 dB LA90,10min range |
| Night-time | Background LA90 plus 5 dB, subject to 43 dB LA90,10min |
| Simplified route, all periods | 35 dB LA90,10min up to 10 m/s standardised wind speed |
| Financially involved dwellings | A higher limit may be applied where the occupier has an interest in the scheme |
Limits are expressed as a function of wind speed, not as a single number, which is why compliance is demonstrated by a curve rather than by one figure. Conditions that state a single dB limit with no wind speed reference are unenforceable in practice, and the wording that works is set out in our note on wind turbine noise and the ETSU-R-97 condition.
Amplitude modulation
The swish of a blade passing the tower becomes a problem when it is unusually pronounced, and that effect is what amplitude modulation describes. It is not captured by the ordinary LA90 limits, because a modulated signal and a steady one can share the same average level.
The Institute of Acoustics published a reference method for rating amplitude modulation, and authorities increasingly impose a condition applying a penalty to the noise limit where the rated modulation depth exceeds a threshold. For a small scheme the risk is lower than for a large wind farm, though it is not zero, and the condition costs little to accept at the outset and a great deal to argue about after installation.
Say something about it in the assessment even where you conclude the risk is low. An assessment silent on modulation invites a condition drafted by someone else.
Separation distance and topography
England has no national minimum separation distance for wind turbines. Distance matters because sound attenuates with it, and because national policy on onshore wind changed during 2024, removing restrictions that had been introduced in 2015. Check the current Framework edition, published on 17 August 2026, and the adopted local plan, because some authorities carry their own separation or landscape policies.
Topography changes the answer in three ways. Downwind propagation over a valley can concentrate sound at a receptor that looks well separated on a plan. Hard surfaces such as water attenuate less than soft ground. And complex terrain increases the uncertainty in both the prediction and the wind shear assumption, which usually means a more conservative design.
Noise is rarely the only constraint on a rural turbine. Reflected light and shadow flicker near an airfield are assessed by a separate method, set out in our note on glint and glare assessment near an aerodrome, and landscape, ecology and aviation safeguarding all run in parallel.
Conditions and compliance testing
A workable set of conditions for a small scheme does four things:
- Fixes the turbine type, hub height and rotor diameter, because noise output is model specific and substitution changes the prediction.
- Sets the noise limits as a table against standardised wind speed, separately for day and night, at named receptors.
- Requires compliance measurement on the written request of the authority following a complaint, carried out by a competent person at the operator's expense, to a stated method.
- Provides for remedial action where the limits are exceeded, usually a noise reduced operating mode rather than an open obligation.
Point three is the one to read carefully. A condition allowing unlimited repeat testing on any complaint is a liability. A condition allowing one test per complaint, with a reasonable interval, is proportionate.
Note the interaction with the separate statutory regime. A turbine operating within its planning conditions can still, in principle, be the subject of a statutory nuisance complaint, and the relationship between the two is covered in our note on statutory nuisance after planning permission is granted.
Where the method is contested
Three arguments recur, and it is worth knowing which are winnable.
Wind shear at night. Objectors argue that night-time shear is higher than the standard assumption, so the turbine produces more noise at a given ground level wind speed than predicted while background noise stays low. This is a real effect and the guide addresses it. Expect a site specific shear analysis on anything marginal.
The age of ETSU-R-97. It dates from 1996, turbines have grown, and critics argue the limits no longer reflect either the technology or current understanding of sleep disturbance. National guidance nonetheless still points to it, so an assessment that departs from it needs a very good reason.
Cumulative effect with an existing turbine. Where another turbine already operates nearby, the assessment has to consider both together, and the limits apply to total noise rather than to your increment.
An honest caveat: for the smallest turbines, the acoustic work is sometimes disproportionate to the scheme, and the better answer is a quieter machine sited further from the boundary rather than a longer report defending a marginal position.
If you are scoping the documents a rural energy scheme will need, enter your postcode on PlanScope to see which reports are likely to be required.
This is general guidance, not legal advice. Wind turbine noise assessment is specialist work and councils expect a suitably qualified acoustician, so professional review is strongly advised. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
Does BS 4142 apply to wind turbines?
No. National planning guidance on renewable and low carbon energy points to ETSU-R-97, applied through the Institute of Acoustics good practice guide. ETSU works in LA90 correlated against wind speed, while BS 4142 works in LAeq with character corrections. Using BS 4142 for a turbine will attract an objection from environmental health.
What are the ETSU-R-97 noise limits?
Limits are set at the prevailing background LA90 plus 5 dB, subject to fixed lower limits. Day-time limits fall within a 35 to 40 dB LA90,10min range depending on the number of dwellings affected and the energy generated. The night-time limit is 43 dB LA90,10min, set to protect sleep with windows partly open.
Can a small turbine avoid a background noise survey?
Sometimes. Where predicted noise stays below 35 dB LA90,10min at all wind speeds up to 10 m/s at the standardised 10 metre height, ETSU allows the assessment to stop without a background survey. Ask the acoustician to test that route first, because it removes weeks of monitoring and a substantial fee.
What is amplitude modulation and is it conditioned?
It describes an unusually pronounced periodic variation in turbine noise, which average level limits do not capture. The Institute of Acoustics published a reference method for rating it, and authorities increasingly impose a condition applying a penalty to the noise limit above a threshold. Address it in the assessment even where the risk is low.
Is there a minimum separation distance in England?
There is no national minimum separation distance. National policy on onshore wind changed during 2024, removing restrictions introduced in 2015, so check the current Framework edition and the adopted local plan. Some authorities carry their own separation or landscape policies, and topography can matter more than distance.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.