Extensions and loft conversions in Windsor and Maidenhead
The Royal Borough of Windsor and Maidenhead is two towns, a string of Thames-side villages and a large Green Belt. In Windsor, Clewer and central Maidenhead the Victorian and Edwardian terraces and villas take the classic moves: a rear or side-return extension to create a kitchen-diner, and a rear dormer to add a bedroom and bathroom in the roof. In Cox Green, Furze Platt, Dedworth and Boyn Hill the 1930s semi dominates, and the typical project is a two-storey side extension over the garage, a 4–6 m rear extension, a hip-to-gable loft with a rear dormer, or a garden room. In Ascot, Sunningdale and Bray the large detached houses take two-storey rear extensions and full remodels, and in Eton, Cookham, Datchet and Old Windsor the cottages are often listed or in a conservation area, where the work is careful single-storey extension and internal alteration.
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. PD still applies to houses in the Green Belt, which covers most of the borough, but anything that needs planning permission there has to pass the Green Belt test described below. In the Windsor, Eton, Cookham, Bray and Datchet conservation areas roof extensions lose PD rights, so a planning application designed to the character appraisal is the norm, and along the Thames a flood risk assessment often travels with the drawings. Flats have no householder PD rights at all.
Planning constraints in Windsor and Maidenhead
- Green Belt across most of the borough outside Maidenhead, Windsor, Ascot and Sunningdale, where extensions must stay proportionate to the original house and outbuildings face a stricter test.
- Conservation areas in Windsor town centre, Eton, Cookham, Bray, Datchet and Old Windsor among others, where roof extensions lose PD rights; check the council’s constraints map for the exact boundaries.
- River Thames flood risk through Cookham, Maidenhead, Bray, Windsor, Eton, Datchet, Old Windsor and Wraysbury; the Jubilee River scheme protects Maidenhead, Windsor and Eton, but Datchet, Wraysbury and Old Windsor remain at risk.
- Windsor Great Park and Crown Estate land from Windsor through Old Windsor towards Ascot.
- Listed buildings in Eton, Cookham, Bray, Datchet, Old Windsor and Windsor town centre.
What Windsor and Maidenhead planning officers look for
Officers assess householder applications against the Borough Local Plan 2013–2033 and the council’s guidance on residential extensions. On the terraces they look for rear extensions that respect the pattern of the row, sit below the neighbour’s first-floor sill and clear the 45-degree line; on the semis, side extensions set back from the front elevation and down from the ridge, with a gap kept to the boundary; and everywhere, dormers that are subordinate, set back from the eaves and clad in matching materials.
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. In the Thames flood zones a flood risk assessment is expected with any ground-floor extension. Disproportionate Green Belt additions, terracing effects, roof extensions in the Windsor, Eton and Cookham conservation areas and flood zone extensions without an assessment are the standard refusals. The Royal Borough 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 Windsor and Maidenhead
- Planning documentation
- House extensions – rear, side and two-storey extensions on terraces, semis and detached houses
- Loft conversions – hip-to-gable and rear dormer lofts
- Permitted development and LDCs
- Outbuildings and garden rooms – including Green Belt plots
- Feasibility studies and pre-application advice – for Green Belt, conservation area and listed building work
- Building Regulations drawings
Example projects nearby
- Loft conversion in Richmond upon Thames – hip-to-gable and rear dormer on an Edwardian semi in a Thames-side conservation area
- Side extension in Barnet – side extension and garage conversion on a 1930s semi, the same house type as Cox Green and Furze Platt
- Garden office in Bromley – 20 m² garden office under permitted development, the model for garden rooms on suburban plots
Guides
Read Conservation areas: extensions and lofts and Permitted development rights in London.
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