Odour Assessment

What is an Odour Assessment?

An odour assessment is a professional evaluation of the odour conditions affecting or likely to be generated by a development site.

It establishes whether existing odour sources in the surrounding area will adversely affect future occupiers, whether the proposed development itself will create odour problems for neighbouring properties or sensitive locations, and what measures can be put in place to prevent or reduce those impacts.

For odour mitigation planning purposes, an odour assessment produces two key outputs: a formal report setting out the findings of the survey, and, where emissions are found to be significant, an Odour Management Plan (OMP) setting out how those emissions will be controlled and monitored.

Both documents may be required as part of the planning process or as a condition attached to a planning permission.

When is an Odour Risk Assessment Needed?

An odour risk assessment is required in two distinct situations.

The first is where a development proposal could generate odour that would affect people living or working nearby. This applies to a wide range of uses, including food processing and commercial catering facilities, waste management and recycling operations, composting sites, sewage treatment works, agricultural and livestock facilities, and certain industrial and manufacturing processes.

In these cases, the local authority will need evidence that odour impacts have been properly assessed through odour monitoring and that appropriate controls will be in place before it will consider granting consent.

The second situation, known in planning practice as encroachment, is where a new sensitive use, such as a residential development, care home, school or hospital, is proposed close to an existing source of odorous emissions.

Even though the new development is not itself generating the odour, future local residents and occupiers will be affected by it. A planning authority’s environmental health officers will need to be satisfied that the level of odour exposure at the proposed development is acceptable before allowing a scheme to progress.

In both cases, the earlier an odour assessment survey is commissioned, the better. Identifying odour as a potential issue before a planning application is submitted allows time to adapt the scheme design, incorporate appropriate odour mitigation planning and agree the assessment approach with the local authority at pre-application stage, all of which reduces the risk of delay once the application is under review. Odour assessment experts can carry out these requirements.

What Causes Odour Problems for Development?

Odour issues arise from a very wide range of sources. Common examples relevant to development include:

• Waste and sewage: landfill sites, transfer stations, recycling facilities and many processes from sewage treatment works and pumping stations are among the most common sources of odour complaints in planning contexts.
• Food production and catering: commercial kitchens, food manufacturing plants, abattoirs, fish processing facilities and rendering operations can generate persistent and wide-ranging odour issues.
• Agriculture and livestock: farms with intensive livestock housing, slurry storage, manure spreading and silage operations are a frequent source of many types of odour issues affecting rural and semi-rural development sites.
• Industrial processes: chemical manufacturing, paint spraying, solvent use, rubber processing and a range of other industrial activities can generate significant odour emissions.
• Composting and biomass: both open-air and enclosed composting operations can produce strong odours, particularly during active decomposition phases.
• Petrol and fuel storage: forecourts, fuel depots and associated infrastructure can generate hydrocarbon odour.

The specific characteristics of an odour – not just its strength but its frequency, duration and the degree to which it is considered offensive – are all relevant to how odour consultants assess odour in a planning context.

How is an Odour Assessment Carried Out?

Odour assessments follow an established framework.

The scope of any individual assessment will vary depending on the type of development, the nature and proximity of odour sources and the local authority’s existing processes. In general terms, the process involves the following stages.

Briefing and Scoping

Odour assessment consultants will discuss the project with the developer to understand the nature of the proposed development, the activities to be carried out on site and the odour sources or receptors likely to be relevant.

This initial scoping stage establishes the appropriate methodology for the assessment and identifies any pre-application discussions to be held with the local authority or environmental regulator.

Odour Surveys and Sampling

A site visit is carried out to assess conditions on the ground. Odour consultants will inspect the site and its surroundings, identify relevant odour sources and sensitive receptors.

Survey techniques include collecting odour samples using specialist equipment. Odour analysis of the samples will measure the intensity, concentration and character of the odour.

The FIDOL factors: Frequency, Intensity, Duration, Offensiveness and Location, provide the standard framework for characterising odour in a planning context.

This approach, set out in the IAQM Guidance on the Assessment of Odour for Planning (version 1.1, July 2018), is the principal methodology used by odour assessment consultants and accepted by local authorities.

Laboratory Testing and Analysis

Samples collected during the site survey nuisance investigation are analysed in an accredited laboratory.

The results are used to quantify odour concentrations and assess the likely impact on sensitive receptors at the development site or in the surrounding area.

Dispersion Modelling

Where emissions are likely to travel beyond the immediate site boundary, atmospheric dispersion modelling may be used to predict how odour will spread in different wind conditions and seasons.

This allows the odour risk assessment to establish the likely odour exposure at specific receptor locations and assess whether that exposure falls within acceptable limits.

Additional assessment methods that may be incorporated into the survey include sniff testing, olfactometry, chemical analysis of specific compounds, sensory evaluation, field inspections and complaint monitoring review where existing odour problems have already been reported.

Reporting

The findings of the odour assessment are set out in a written report covering the survey methodology, the odour characterisation results, an assessment of significance using the FIDOL framework, conclusions on the acceptability of odour exposure at sensitive receptors, and recommendations for mitigation and further investigation where needed.

The report is produced in a format suitable for submission to the local authority.

Odour Management Plan

Where the assessment concludes that odour emissions are significant or pose a potential risk to sensitive receptors, an Odour Management Plan (OMP) will be produced alongside the report.

The OMP sets out the specific control measures that will be implemented to manage odour emissions from the site, an odour abatement plan and monitoring regime that will be put in place to verify that those controls are working, the procedures for responding to odour complaints and the responsibilities of the operator for ongoing compliance.

An OMP is a live document. It should be reviewed and updated regularly to reflect changes in site operations, monitoring data and regulatory requirements.

Legislation and Regulatory Guidance

Odour in a planning context is not governed by a single statute. It is instead regulated through a combination of planning policy, environmental permitting, statutory nuisance law and regulatory guidance.

The key regulatory guidance for sites that require an environmental permit is the Environment Agency’s guidance “Odour management: comply with your environmental permit,” published in December 2025. This replaced the long-standing H4 Odour Management guidance and adopts a principles-based, risk-led approach to odour compliance.

Permitted facilities, including waste management sites, industrial processes and sewage treatment works, must manage odour in accordance with this guidance as a condition of their environmental permit. The equivalent regulatory body in Wales is Natural Resources Wales and in Scotland is the Scottish Environment Protection Agency (SEPA).

For planning purposes, the primary guidance document is the IAQM Guidance on the Assessment of Odour for Planning (version 1.1, July 2018), published by the Institute of Air Quality Management. This sets out the recognised methodology for assessing odour impacts in support of planning applications and is the document most commonly referenced by local planning authorities when specifying the requirements for an odour assessment.

Additional pieces of legislation relevant to odour and development include the Environmental Protection Act 1990, which provides the statutory nuisance framework under which local authorities can take action against odour affecting neighbouring properties; the Control of Pollution Act 1974; the Town and Country Planning Act 1990; and the Environmental Permitting (England and Wales) Regulations 2016, which govern the permit conditions applying to regulated facilities.

The National Planning Policy Framework (NPPF) requires local planning authorities to prevent new development from contributing to, or being put at unacceptable risk from, unacceptable levels of pollution, which includes odour.

Odour Assessment and Sensitive Receptors

In odour assessment, a sensitive receptor is any location where people live, work, learn or receive care, and where odour exposure is therefore a relevant consideration. Residential properties are the most common sensitive receptor in a planning context, but care homes, schools, hospitals, hotels, offices, local amenities and public open spaces can all qualify depending on the circumstances and likelihood of nuisance complaints.

The sensitivity of a receptor affects the significance of any odour impact. A small number of residential properties in close proximity to a strong source of odour or potential sources will generally be treated as a more significant receptor than a similar number of properties located further away or in an area with an existing baseline of industrial activity. The FIDOL framework provides the structure for making these judgements in a consistent and defensible way, according to best practice.

Where a development involves mixed uses, for example, a scheme that combines residential accommodation with food retail or a waste-handling facility, the odour risk assessment will need to consider the relationship between the odour-generating and odour-sensitive elements of the scheme, as well as impacts on the wider area.

Organising Your Odour Assessment

Commissioning an odour assessment early in the development process gives you the best chance of resolving any issues before they affect your planning application. The right time to start is at the pre-application stage, before the scheme design is fixed, so that the assessment findings can inform the full suite of decisions about site layout, building design and the specification of odour control systems.

Odour assessment should be carried out by a qualified air quality or environmental consultant with extensive experience in odour characterisation and planning. Membership of the Institute of Air Quality Management (IAQM) is a recognised indicator of professional competence in this field.

Odour Consultancy Services

We connect developers, housing providers and landowners with qualified odour assessment consultants who can carry out odour impact assessments and produce reports that comply with best practice and meet the full range of standards required by local planning authorities and environmental regulators across England, Scotland and Wales.

Use our free service to get fast, no-obligation quotes from trusted odour risk specialists in our network who will provide expert advice. Fill in the form at the top of this page, and we will connect you with an expert who will ask for further information about your specific needs and advise on what is required to help keep your planning application on track.