Internal noise levels for a new dwelling under BS 8233
BS 8233 gives guideline internal ambient noise levels, not limits. What matters in a submission is the ventilation assumption and what you do when the values cannot be met.
The BS 8233 internal noise levels for a dwelling are guideline values, not statutory limits, and the distinction shapes how a submission should be written. The standard gives 35 dB LAeq,16hr for living rooms and other resting spaces during the day, 40 dB LAeq,16hr for dining spaces, and 30 dB LAeq,8hr in bedrooms at night. Those figures are the starting point for an assessment rather than the end of one, because the standard also recognises that development in noisier locations may be acceptable on a reasoned case. Officers read the reasoning, not just the table.
The guideline values and what they apply to
The values apply to internal ambient noise, meaning the total noise from all sources at the receptor, in the occupied room, with the windows in a stated condition.
| Space and period | Guideline value |
|---|---|
| Living rooms and resting spaces, 07:00 to 23:00 | 35 dB LAeq,16hr |
| Dining rooms and dining areas, 07:00 to 23:00 | 40 dB LAeq,16hr |
| Bedrooms, 07:00 to 23:00 | 35 dB LAeq,16hr |
| Bedrooms, 23:00 to 07:00 | 30 dB LAeq,8hr |
| External amenity areas such as gardens and balconies | 50 dB LAeq,T desirable, with 55 dB an upper guideline in noisier settings |
Note what is absent. There is no guideline for a kitchen, a bathroom, a hall or a study in the residential table, and there is no BS 8233 criterion for maximum instantaneous levels. Assessments that invent values for those spaces create arguments they did not need.
Daytime and night-time periods
The periods are fixed and they matter. Daytime is the sixteen hours from 07:00 to 23:00 and the descriptor is an equivalent continuous level across the whole of it. Night is the eight hours from 23:00 to 07:00.
A common error is to assess night-time using a shorter worst-case period and compare it with the 30 dB figure. That is not what the descriptor means. Another is to use the daytime sixteen hour average to represent an evening peak from a nearby venue, which averages a three hour problem across sixteen hours and makes it disappear. Where a source operates for part of a period only, say so and assess it appropriately, and where the character of the source is industrial or commercial, the BS 4142 method applies alongside this one.
Maximum levels in bedrooms
BS 8233 does not set a maximum level criterion, and yet most local authority environmental health teams ask for one. The convention that has developed is an assessment of LAmax,F events in bedrooms at night, often with a value around 45 dB and a stated number of exceedances, drawn from wider noise guidance rather than from BS 8233 itself.
Handle this by addressing it rather than ignoring it. Report the measured or predicted LAmax distribution at night, the number of events above the value the authority applies, and the source of each: a railway line, a service yard, refuse collection or a pub closing. On a site next to a railway the event count matters more than the average, as our note on railway noise and vibration for sites beside a line explains.
Where the authority applies a figure, say where the figure comes from. Attributing an authority's local standard to BS 8233 is the kind of slip that undermines confidence in the rest of the report.
External amenity areas
Gardens, balconies and communal amenity space carry the 50 to 55 dB guidance, and the standard is explicit that it applies to areas used for relaxation rather than to every square metre of external space. A balcony on a busy road frontage will not meet it, and a scheme that acknowledges this and provides a quieter communal garden is in a stronger position than one that claims compliance everywhere.
Three design responses carry weight: locating amenity space away from the dominant source, screening with built form rather than with acoustic fencing wherever possible, and providing a communal alternative where private space cannot be quiet. Screens work on ground level space and do very little for upper floor balconies.
Windows open or closed, and the ventilation problem
This is the question that decides most assessments. The guideline values are normally demonstrated with windows closed, because open windows offer little attenuation, which leaves the ventilation strategy to answer a separate question: how does the occupant get fresh air and purge heat without opening the window onto the noise?
The chain runs through three regimes at once. Approved Document F sets the ventilation requirement. Approved Document O sets the overheating requirement and expects purge ventilation, which usually means openable windows. And planning policy expects internal noise to be acceptable. The residential design guidance produced jointly by the acoustics and environmental health institutes was written to reconcile them, and it is the reference an acoustician will use.
What that means in practice:
- Demonstrate the internal levels with windows closed, and state the glazing specification and its acoustic performance
- Provide ventilation that does not depend on opening the window, whether acoustic background ventilators, continuous mechanical extract or mechanical ventilation with heat recovery
- Assess overheating under Approved Document O with the same window assumption, using the Overheating Risk Assessment route, and show that purge ventilation is available even if it is noisy when used
- Report the internal level with windows open as well, so the authority can see the consequence of the occupant choosing air over quiet
Reporting only the closed-window result and staying silent on the open-window level is the pattern environmental health officers distrust most.
Where the guideline values cannot be met
Some sites cannot achieve 30 dB at night in every bedroom, and the standard contemplates that. A reasoned case has four parts: the levels achieved, the mitigation applied and why nothing further is reasonable, the wider benefits of the development, and what the occupant experience will actually be.
Design-led mitigation beats specification-led mitigation in the eyes of most officers:
- Layout so that bedrooms face the quiet elevation and circulation faces the source
- No single-aspect dwellings facing the dominant noise source
- Winter gardens or acoustically screened balconies on noisy frontages
- Building form used as the barrier for the space behind it
- Enhanced glazing and ventilators as the last layer rather than the first
Where the noise comes from an existing business or venue, the agent of change principle in national policy puts the onus on the new development to provide suitable mitigation, and the existing operator should not be burdened by it. For a residential scheme next to a live music venue that is the whole argument, and it interacts with licensing as well as planning, as our note on planning control and licensing control of entertainment noise sets out.
Illustrative example: a five-storey block beside a main road where the road-facing flats are dual aspect with bedrooms to a courtyard, glazing to a stated specification on the frontage, acoustic ventilators throughout and mechanical ventilation to the top floor, achieving the night guideline in bedrooms with windows closed. Details here are illustrative only.
Presenting compliance room by room
A Noise Impact Assessment for a residential scheme should let the officer find any room and check it. That means a schedule, not prose.
Include the measured free-field or facade levels with octave band data, since glazing calculations need spectra rather than a single figure. Give the calculation per room type: source level at the facade, the element performance assumed, and the resulting internal level against the guideline. Name the glazing and ventilator products or state the performance required of them, and identify which rooms rely on which. Then set out the conditions you expect: a scheme of sound insulation to be approved, verification testing on completion, and plant noise limits where relevant. Our note on unattended noise monitoring duration, position and validity covers the survey that feeds all of this.
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Frequently asked questions
What are the BS 8233 internal noise guideline values?
For dwellings, 35 dB LAeq,16hr in living rooms and other resting spaces during the day, 40 dB LAeq,16hr in dining spaces, 35 dB LAeq,16hr in bedrooms during the day and 30 dB LAeq,8hr in bedrooms at night. External amenity areas carry 50 dB LAeq,T as desirable with 55 dB as an upper guideline.
Are the levels assessed with windows open or closed?
Normally with windows closed, because an open window gives little attenuation. The consequence is that ventilation must be provided without relying on opening the window, using acoustic background ventilators or mechanical ventilation. Report the open-window internal level as well, so the authority can see the effect of the occupant choosing air.
Does BS 8233 set a maximum noise level for bedrooms?
No. The standard gives no criterion for maximum instantaneous levels. Many local authorities apply a value for LAmax events at night, often around 45 dB with a stated number of exceedances, drawn from wider noise guidance. Address it explicitly and attribute the figure to the authority rather than to BS 8233.
What if a site cannot achieve 30 dB at night?
Make a reasoned case. Set out the levels achieved, the mitigation applied and why further measures are unreasonable, the benefits of the development, and the likely occupant experience. Design-led measures such as layout, dual aspect flats and building form used as a barrier carry more weight than glazing specifications alone.
How does the agent of change principle apply?
Where an existing business or venue generates the noise, national policy expects the new development to provide suitable mitigation rather than the existing operator to bear the burden. For residential schemes beside music venues this shapes both the acoustic design and the interaction with licensing conditions on the venue.
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.