Extensions and loft conversions in Slough
Slough is 1930s semi territory. Across Cippenham, Langley, Upton and Upton Lea the inter-war semi dominates, and the typical project is a two-storey side extension over the garage, a 4–6 m rear extension to create a kitchen-diner, a hip-to-gable loft with a rear dormer, or a garden room. In Chalvey and around the town centre the Victorian and Edwardian terraces take the classic moves: a rear or side-return extension and a rear dormer. On the post-war Britwell and Manor Park estates ground-floor rear extensions and garage conversions are the usual work, and near the station the work is flat layouts and office-to-residential conversions under Class MA prior approval.
Where the house is outside a conservation area, much of this is permitted development (PD) and we secure a Lawful Development Certificate (LDC) as proof. In the Green Belt to the north, west and east, anything that needs planning permission has to pass the proportionality test described below. In the Upton Park, Langley St Mary’s and Colnbrook conservation areas roof extensions lose PD rights, so a planning application designed to the character appraisal is the norm. HMO conversions need permission under the borough’s Article 4 direction. Flats in converted houses, on the estates and in the town centre blocks have no householder PD rights at all.
Planning constraints in Slough
- Green Belt to the north and west around Wexham, Britwell and the Burnham edge, and in the Colne Valley around Colnbrook and Poyle, where extensions must stay proportionate to the original house and outbuildings face a stricter test.
- Conservation areas at Upton Park, Langley St Mary’s and Colnbrook, where roof extensions lose PD rights; check the council’s constraints map for the exact boundaries.
- Heathrow Public Safety Zone and noise contours affecting parts of Colnbrook, Poyle and Langley.
- Article 4 direction removing PD for small HMO conversions across the borough.
- Jubilee River and Colne Brook flood risk along the southern edge and through Colnbrook and Poyle.
- Listed buildings in Upton, Langley and Colnbrook.
What Slough planning officers look for
Officers assess householder applications against the Core Strategy 2008, its saved policies and the council’s residential extensions guidance, with the emerging Local Plan carrying growing weight. On the semis they look for side extensions set back from the front elevation and down from the ridge, with a gap kept to the boundary; rear extensions that clear the 45-degree line to the neighbour’s nearest habitable window; dormers that are subordinate, set back from the eaves and clad in matching tile; and enough garden and off-street parking left after the work.
In the Green Belt the key test is that an extension must not be disproportionate to the original dwelling, meaning the house as first built or as it stood on 1 July 1948, counting every extension added since. Officers usually measure this by floorspace and volume, and additions beyond roughly a third to a half of the original tend to need a strong case. Outbuildings are treated as new buildings in the Green Belt and face a stricter test than extensions, so garden rooms that need permission should stay modest and close to the house; where PD applies we use the LDC route instead. Terracing effects from side extensions, full-width box dormers and extensions that leave too little garden or parking are the standard refusals. Slough offers paid pre-application advice. Council fees from April 2025 are £528 for a householder application and £264 for a proposed-use LDC; verify before applying.
Our services in Slough
- Planning documentation
- House extensions – side, rear and two-storey extensions on 1930s semis
- Loft conversions – hip-to-gable and rear dormer lofts
- Permitted development and LDCs
- Outbuildings and garden rooms
- Commercial to residential (Class MA) – office conversions around the station and town centre
- Building Regulations drawings
Example projects nearby
- Side extension in Barnet – side extension and garage conversion on a 1930s semi, the same house type as Cippenham and Langley
- Two-storey extension in Ealing – two-storey rear extension and side infill on an inter-war semi
- Loft conversion in Hackney – rear dormer on a Victorian terrace under permitted development, the same approach as the Chalvey terraces
Guides
Read Permitted development rights in London and Class MA: office to residential.
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