Permitted Development Rights for Air Conditioning Units: A Complete Guide (Including MCS 020 Noise Rules) | Reddit Edition

As temperatures rise and energy-efficient heating and cooling systems become more common, air conditioning and air source heat pump installations are increasingly being added to both homes and commercial buildings.

However, before installing an external condenser or heat pump unit, it is essential to understand whether planning permission is required or whether the installation can proceed under Permitted Development (PD) rights.

These rights are set out in the Town and Country Planning (General Permitted Development) (England) Order 2015 (GPDO) and include specific conditions relating to size, location, appearance, and — critically — noise.

What Are Permitted Development Rights?

Permitted Development rights are a national grant of planning permission that allows certain types of development to proceed without a full planning application.

They are defined in the GPDO 2015 (as amended) and apply only where all conditions are met.

However, PD rights do not override:

• Building Regulations
• Listed Building Consent
• Lease or freehold covenants
• Environmental Health noise controls
• Article 4 Directions removing PD rights
• Existing planning conditions

Air Conditioning vs Air Source Heat Pumps (Important Distinction)

Modern Permitted Development rules introduced in 2025 mainly apply to air source heat pumps, which include many reversible systems capable of heating and cooling.

However:

• ✔ Air source heat pumps (heating + cooling) → usually covered under PD if compliant
• ⚠ Cooling-only air conditioning units → often NOT automatically covered and may still require planning permission depending on location and impact

This distinction is important because planning eligibility depends on how the system is classified under the GPDO.

Government Permitted Development Rules (Class G Summary)

The relevant legislation is found in:

GPDO 2015 – Schedule 2, Part 14, Class G

In simplified terms, Class G allows installation of an air source heat pump provided that:

• The unit meets MCS or equivalent technical standards
• The system is not installed solely for cooling
• Size and siting restrictions are met
• The installation does not adversely impact neighbours
• The unit is removed when no longer required

These rules are designed to support low-carbon heating while controlling visual and environmental impact.

Key Permitted Development Conditions (Summary)

Typical PD conditions for domestic installations include:

Requirement	Typical Rule
Maximum unit size	~1.5 m³ (houses)
Detached houses	Up to 2 units
Other houses	Usually 1 unit
Roof installation	Not allowed on pitched roofs
Flat roofs	Must be set back from edge
Listed buildings	PD does not apply
Conservation areas	May be restricted

However, the most important modern requirement is now noise compliance under MCS 020.

MCS 020 – The Noise Requirement Explained

One of the most important conditions for Permitted Development is compliance with the MCS 020 planning noise standard.

MCS 020 is a calculation methodology used to determine whether a heat pump or air conditioning system is acceptable in planning terms.

It is not a simple “distance rule” or a single measured reading. Instead, it is a predictive calculation carried out during the design stage.

What MCS 020 Actually Does

MCS 020 calculates the predicted sound level at the nearest neighbouring habitable room window or door.

It takes into account:

• Manufacturer’s sound power level (dB(A))
• Distance to neighbouring properties
• Building reflections (walls, surfaces)
• Position and orientation of the unit
• Acoustic barriers or screening
• Installation layout and surroundings

The result is a predicted noise level in dB(A) at the neighbour’s property.

The 42 dB(A) Planning Threshold

Under MCS 020, the key requirement is:

The calculated sound pressure level at the nearest neighbouring habitable room must not exceed 42 dB(A).

If the calculated level is:

• ✔ ≤ 42 dB(A) → Permitted Development allowed
• ✖ > 42 dB(A) → Full planning permission required

This is a planning compliance threshold, not a comfort guideline.

What Does 42 dB(A) Sound Like?

To put this into context:

Sound Source	Approximate Level
Quiet library	30–40 dB(A)
Modern fridge	40–45 dB(A)
MCS 020 limit	42 dB(A)
Normal conversation	55–60 dB(A)

Modern heat pumps typically operate at 40–60 dB(A) at source, but distance and positioning reduce this significantly before reaching neighbours.

Why MCS 020 Is Not a Simple Noise Measurement

A common misconception is that compliance is based on the unit’s advertised noise level. This is incorrect.

MCS 020 is a planning model, not a product specification.

It considers how sound behaves in real environments, including:

• Distance attenuation (sound reduces over distance)
• Reflection from walls and hard surfaces
• Direction of airflow and compressor noise
• Installation height and positioning
• Screening effects

This means two identical units can produce very different planning outcomes depending on where they are installed.

Who Calculates MCS 020?

The MCS 020 assessment is normally carried out by:

• The installer
• The system designer
• Or a qualified acoustic assessor

It is completed during the design stage and should form part of the installation documentation.

A compliant installer should be able to provide:

• The full noise calculation
• Evidence of compliance
• Confirmation that PD rights apply

What Happens if You Fail MCS 020?

If the calculation exceeds 42 dB(A):

• The installation does not qualify for Permitted Development
• A full planning application is required
• The council may assess:
• noise impact
• siting
• neighbour amenity
• mitigation measures

In many cases, compliance can be achieved by:

• moving the unit further away
• selecting a quieter model
• adding acoustic screening
• changing orientation

Commercial Buildings

Commercial premises often benefit from broader PD rights for mechanical plant, but still require consideration of:

• noise impact
• visual appearance
• roof or façade location
• conservation constraints

Each installation must be assessed individually.

Flats and Apartments

Flats and maisonettes usually have very limited or no Permitted Development rights for external air conditioning units.

Planning permission is often required due to:

• shared building structure
• visual impact
• lease restrictions
• proximity to neighbours

Listed Buildings and Conservation Areas

If a building is listed:

• Listed Building Consent is almost always required
• PD rights do not apply

In Conservation Areas:

• external units may require permission if visible
• stricter design controls apply
• Article 4 Directions may remove PD rights entirely

Building Regulations

Even where planning permission is not required, Building Regulations may still apply, especially for:

• electrical works
• structural mounting
• roof installations
• drainage and condensate disposal

Certificates of Lawfulness

A Certificate of Lawfulness (CLOPUD) is strongly recommended for air conditioning or heat pump installations.

It provides legal confirmation that:

• the installation is permitted development
• no planning application is required

This is especially useful when selling or refinancing a property.

Key Takeaway

Whether an air conditioning unit or air source heat pump requires planning permission depends on more than just size or location.

The decisive factor for most modern installations is now:

✔ MCS 020 noise compliance (42 dB(A) at the neighbour’s habitable room)

If the system passes this calculation and meets the GPDO conditions, it can usually proceed under Permitted Development.

Final Thoughts

Permitted Development rights have significantly simplified the installation of modern heat pump systems, but the rules are highly technical.

The most important factor is not the unit itself, but:

• how it is positioned
• how sound travels
• and whether it passes the MCS 020 planning test

Getting this right at design stage avoids planning issues, neighbour disputes, and costly redesigns later.

For certainty, a pre-installation MCS 020 assessment and Certificate of Lawfulness remain the most reliable way to confirm compliance.

 

Call DWG Plans on 0800 688 9345 or get in touch online today.