General Permitted Development Order (GPDO) and Acoustics 

What are Permitted Development rights? 

Introduced in 2015, the Town and County Planning (General Permitted Development) Order 2015 (the “GPDO”) grants permission for certain types of development without the requirement for a planning application. The original order covered alterations for householders such as horizontal extensions, loft conversions and installations of porches, chimneys and antennas, which has enabled low-impact home improvements to be carried out both faster and easier than previously. 

In some cases, the development rights also cover change of use in a bid to meet the Government’s aim to increase the supply of new homes. Planning permission is not required when the change use occurs within each subclass and in some cases from one class to another, for example, commercial, business and service uses (Class E) can be changed to residential use (Class C3) under Class MA of the GDPO. This means that surplus office space generated by a shift towards home working may aid in the housing shortage currently faced in the UK. It should be mentioned that new residential dwellings generated through permitted development change of use often may not subsequently use the householder permitted development rights for additional alternations. For example, Class A enlargement, improvement or alteration is not permitted where the house was created under permitted development rights to change of use, set out in classes M, N, P, PA and Q. 

Although permission is granted directly from the Government through this legislation, ‘Prior Approval’ is often required, and it is still recommended that you should seek to discuss your proposals with the Local Authority before commencing any works. It is also worth noting that the rights may not apply or are restricted in certain protected areas such as Sites of Special Scientific Interest (SSSI’s), Areas of Outstanding Natural Beauty (AONB’s), Conservation Areas, National Parks and listed buildings. Some local planning authorities have also placed Article 4 Directions over certain areas – Article 4 Directions allow local planning authorities to restrict certain classes of the GDPO such as the change of use from Class E to Class C3. 

The 2020 Update. 

In 2020 the GPDO was updated to include vertical extensions providing a maximum of up to two additional storeys to existing dwellings (Part 1 Class AA) and to create new dwellings (Part 20 Class A – AD). As with previously permitted development rights, the alterations are subject to a series of limitations which range from factors including the building’s height, use and age. Some of the main impacts sought to be avoided with upward extensions include overlooking, privacy and the loss of light on neighbouring premises with conditions in place for all classes to avoid these issues. 

The 2024 Update 

On 5th March 2024, the GPDO was updated to extend the permitted development rights under Class MA (commercial, business and service use to dwelling houses). The amendment will remove the requirement that a building must have been vacant for a continuous period of at least 3 months immediately before the date of an application for prior approval. Additionally, Class MA is amended to remove the floorspace upper limit for buildings changing use under the right. 

GPDO and Acoustics 

Conditions set for vertical extensions under Part 1 and Part 20 of the GPDO relating to noise vary depending on the use of the existing building. Where new dwellings are being built above existing commercial or mixed uses the following condition is applied: 

“Where any development under Class [AA or AB] is proposed, development is permitted subject to the condition that before beginning the development, the developer must apply to the local planning authority for prior approval of the authority as to— 

… 

impacts of noise from any commercial premises on the intended occupiers of the new dwelling houses;” 

This in most cases would be submitted in the form of a BS 4142 assessment of potential commercial and industrial noise impacts undertaken at the location of the proposed development.  

Additionally, the development of all upward extensions under permitted development rights regardless of existing building use (apart from Class AD) is also subject to the following conditions: 

“before beginning the development, the developer must provide the local planning authority with a report for the management of the construction of the development, which sets out the proposed development hours of operation and how any adverse impact of noise, dust, vibration and traffic on occupiers of the building and adjoining owners or occupiers will be mitigated” 

The two above conditions are the only areas where noise is considered under the GPDO for upward extensions. A summary of where they are required is presented in the Table below: 

Under GPDO there are no requirements for an assessment of noise impacts from transportation noise on future occupiers of extensions. Where the rights are applied in noisier environments such as in cities, this could lead to internal ambient noise levels exceeding good practice limits e.g. BS 8233 and WHO guidance. To combat this, it is recommended that the sound insulation performance of glazing, walls, ventilation and overheating strategy match those of the floors below as a minimum.  

While typically road and rail noise sources are located at ground level, in some areas in built-up environments this is not always the case (for example viaducts and road flyovers), should an extension be built close to such sources the extension may be exposed to higher noise levels than the existing building. This in turn has the potential to lead to adverse noise impacts on the future occupiers of the extension. This also applies to dwellings built close to commercial premises, where vertical extensions could lead to windows overlooking plant enclosures or barriers which were designed to avoid impacts at receptors at lower heights (currently the requirement to assess commercial noise only applies to dwellings built on top and not close to commercial buildings). 

Conclusion 

Essentially the challenge is a simple one; if your extension places habitable rooms closer to a noise source or provides a direct line of sight to a source that was previously obstructed, acoustics is likely to need further consideration than the current conditions of the GPDO. However, where this does not apply, matching the sound insulation performance of any façade openings to those of the floor below along with the GPDO conditions is likely to be adequate in avoiding any adverse noise impacts.