House Extensions in Scotland: When You Need Planning Permission, and What WGA Checks First

Page title: House Extensions in Scotland: When You Need Planning Permission, and What

Residential extensions in Scotland

A house extension can improve the way a home is used without requiring a move. Common requirements include:

• Larger kitchen and dining areas

• Better connection to the garden

• Additional bedrooms or study space

• Improved circulation between existing rooms

• More usable space within an existing roof

• A clearer relationship between old and new parts of the house

The planning route depends on the property and the proposal. The same extension may be treated differently depending on whether the home is detached, semi-detached, terraced, listed, within a conservation area, or part of a flatted property.

At WGA, we establish these conditions before developing the design in detail. This reduces the risk of preparing drawings for an approach that cannot be supported.

Planning permission or permitted development

Some householder works can proceed under permitted development rights. This means that a planning application is not required if the proposal meets all relevant conditions and limitations.

For a typical dwellinghouse outside a conservation area, a single-storey rear extension may be permitted development where it:

• Sits to the rear of the house

• Does not project more than 3 metres from a terraced house, or 4 metres from another house, where the extension is within 1 metre of the boundary

• Has eaves no higher than 3 metres

• Does not exceed 4 metres in overall height

• Does not extend forward of the principal elevation or a side elevation facing a road

• Remains within the relevant limits for ground coverage and curtilage

• Does not involve a flat or a property within a conservation area

These rules include existing extensions and other development. The available allowance is not assessed only by looking at the new room in isolation.

A multi-storey extension has tighter conditions. It must generally be to the rear, remain at least 10 metres from the boundaries of the property, and not be higher than the existing house. It must also meet the relevant limits for ground coverage and curtilage.

If any condition is exceeded, a planning application may be required. A Certificate of Lawfulness can also be considered where formal confirmation of permitted development status is appropriate.

The Scottish Government’s householder permitted development guidance and the mygov.scot guidance on house extensions provide the national framework. The local planning authority remains the appropriate source for confirmation on a specific property.

The checks WGA makes first

1. Property type and status

The starting point is the property itself.

WGA checks whether the building is:

• A detached, semi-detached or terraced house

• A flat or part of a flatted property

• A listed building

• Within a conservation area

• A property created through a previous change of use

• A building subject to relevant planning conditions or restrictions

Most householder permitted development rights apply to houses rather than flats. Extensions, dormers and conservatories to flatted properties generally require planning permission.

Listed buildings require particular care. Planning permission may be required, and listed building consent will normally be necessary where the work affects the character or historic fabric of the building. This can include extensions, dormers, rooflights, window alterations and changes to roof materials.

2. Position, boundaries and height

The site plan is tested before the layout is fixed.

The location of the extension affects whether permitted development rights apply. WGA reviews:

• The rear, side and principal elevations

• Any elevation facing a road

• Distances to site boundaries

• Existing extensions and outbuildings

• Ground levels across the site

• Eaves and ridge heights

• The amount of remaining garden or curtilage

A boundary distance can change the permitted development calculation. For multi-storey extensions and roof enlargements, the 10-metre boundary requirement is particularly important.

Accurate drawings are essential. A small difference in site measurement, roof height or boundary position can affect the planning route.

Image caption: WGA’s proposal for a rear residential extension, shown as an unbuilt visualisation. The image is illustrative and does not represent a completed project.

3. Design, materials and roof alterations

The design must respond to the existing house and its setting.

Materials do not automatically determine whether planning permission is required, but they can be important to the planning assessment and to permitted development conditions. Roof coverings used under some permitted development classes should be similar in appearance to the existing roof. In conservation areas and on listed buildings, external materials and detailing require closer review.

Dormers and other roof alterations are common sources of uncertainty. A roof enlargement may qualify as permitted development on a house outside a conservation area if it meets the relevant conditions. These include limits relating to:

• The roof plane affected

• The distance to the boundary it faces

• The height of the alteration

• The proportion of the roof covered

• The distance from the roof edge

• The relationship with the principal elevation and any side elevation facing a road

A dormer on a front roof slope, a large roof enlargement, or a proposal within a conservation area will usually need a more detailed planning review. Listed building consent may also be required.

WGA tests the roof form, materials, window proportions and junctions together. This allows the planning strategy and the architectural design to develop as one process.

Neighbours, outlook and daylight

Neighbour impact is a central part of extension design.

Where planning permission is required, the planning authority will consider the effect of the proposal on surrounding properties. This can include:

• Loss of daylight

• Overshadowing

• Overlooking and privacy

• A sense of enclosure

• Visual dominance

• The outlook from neighbouring windows and gardens

Outlook is not assessed through one universal measurement. The relationship between buildings, the orientation of the site, window positions, boundary treatments, finished floor levels and the scale of the extension all matter.

WGA studies these relationships at an early stage. Options may be adjusted through the position of windows, the depth of the extension, the roof profile, boundary-facing walls and the location of external spaces.

This is not only a planning exercise. It also supports a better relationship with neighbouring properties and reduces the risk of redesign later in the process.

Planning permission is not a building warrant

Planning permission and a building warrant are separate approvals.

Planning permission considers the principle, location, scale, appearance and impact of development. A building warrant considers whether the proposed construction meets Scottish building standards. This includes matters such as:

• Structural stability

• Fire safety

• Insulation and energy performance

• Ventilation

• Drainage

• Access and facilities

• Openings formed in existing walls

• Construction details and materials

A house extension may be permitted development and still require a building warrant. An extension will normally need technical information for building standards approval, even where no planning application is necessary.

WGA coordinates the design information required for the relevant approvals. The precise requirements depend on the property and the scope of work.

A realistic process from first sketch to completion

WGA’s residential process is structured around the information needed at each stage.

Initial review

• Homeowner brief

• Existing plans and photographs

• Property status

• Site constraints

• Initial planning route

• Early design opportunities

Survey and feasibility

• Measured information

• Site and boundary review

• Existing building assessment

• Initial layouts

• Massing and height studies

• Neighbour relationship review

Design development

• Preferred layout

• External appearance

• Materials

• Roof and window strategy

• Planning drawings

• Updated cost and construction considerations

Applications and technical information

• Planning application or permitted development review

• Certificate of Lawfulness where appropriate

• Building warrant drawings

• Technical coordination

• Information for contractor pricing

Construction and completion

• Support during the construction process

• Responses to design queries

• Review of necessary changes

• Coordination with the wider project team

• Completion information where included within the agreed service

There is no universal approval period for every extension. The programme depends on the completeness of the survey and drawings, the planning route, the local authority, the need for supporting information and the complexity of the existing building.

Starting with the correct information is the most reliable way to reduce abortive design work and avoid unnecessary cost.

Image caption: WGA’s proposal for an altered residential entrance and extension, shown as an unbuilt architectural visualisation. No completed project is represented.

WGA’s approach

WGA provides architectural design, planning and technical services for residential projects. Our approach is based on clear information, careful coordination and direct communication with homeowners.

We begin by understanding the existing building and the intended use of the additional space. We then test the planning conditions, the neighbours’ relationship with the proposal and the construction implications before progressing the design.

The result is a controlled process from first sketch through to the information required for approvals and construction.

Read more about WGA or view the WGA project portfolio.

A house extension project can be discussed with WGA at an early stage, before detailed drawings or applications are prepared.

Image caption: WGA’s proposal for a contemporary residential extension and terrace, shown as an unbuilt visualisation. The image is illustrative and does not represent a completed project.

Image caption: WGA’s proposal for a rear residential extension beneath an altered roof form, shown as an unbuilt architectural visualisation.