Structural alterations cover the work that changes how a building carries its own weight: new openings, removed walls, altered floors, basements and lofts. Each one needs an engineer's calculations and a building control sign off. We appoint the engineer, build to what they issue, and coordinate the application and the inspections. We do not produce structural calculations, and we are not surveyors or architects. This page sets out the Windsor specifics.
The Royal Borough of Windsor and Maidenhead is both your planning and your building control authority
The local planning authority and building control authority for Windsor is the Royal Borough of Windsor and Maidenhead, based at the Town Hall, St Ives Road, Maidenhead SL6 1RF. One council therefore handles the planning side and the building control side of a structural job, although they remain separate applications on separate timescales. We make the building control application and book the inspections.
On the planning side, the borough formally adopted its National and Local Validation Requirements on 5 February 2026, and published the policy document in March 2026. Those requirements set out what has to accompany an application before the council will validate it. Where your alterations need planning permission as well as building control, we tell you which documents that policy calls for before you commit to a programme.
The ground under Windsor changes within a few streets
British Geological Survey 1:50,000 mapping shows Seaford Chalk Formation and Newhaven Chalk Formation, undifferentiated, as the bedrock beneath the castle ridge at Castle Hill, High Street, Park Street, Thames Street and the northern end of Sheet Street. The same mapping shows Lambeth Group, described as clay, silt and sand, beneath Peascod Street, Victoria Street, Arthur Road, Sheet Street away from that northern end, and Duke Street at Gardner Cottages.
Above the bedrock, BGS 1:50,000 mapping shows Shepperton Gravel Member, sand and gravel, at Alma Road, Trinity Place, Clarence Crescent, Vansittart Road, Helston Lane, Goslar Way and the riverside near Thames Street. The council's own conservation area appraisal describes the medieval core of the town centre as sitting on a prominent chalk outcrop directly south of the River Thames, overlooking an open, flat floodplain. Where a new pier or pad is called for, what sits beneath it is a question to answer before steel is ordered.
Cellars, basements and roof work each carry their own requirements
Windsor's older housing already has space below and above the main floors. The council's appraisal describes buildings in the Trinity Place and Clarence Crescent area as three storeys in height, or two storeys with attics and basements. For alterations to extend or create a basement of up to 100 square metres, the council publishes a charge from 1 April 2026. On full plans it is £495.00 plan charge plus £882.00 inspection charge, and on a building notice £1,583.56, both inclusive of VAT.
The drawings are specified as well. The borough's validation requirements call for cross sections at 1:20, 1:50 or 1:100 on all basement proposals, and note they may also be required for a loft extension. They ask for site levels and finished floor levels with above Ordnance datum points on all basement proposals, and on any site in Flood Zone 2 or Flood Zone 3. The Windsor Neighbourhood Plan design guide states that L-shaped rear dormers on terraced cottages with rear projections should normally not cover more than half of the rear projection. For the Laing Estate it says dormers should be constructed only on rear elevations, and that hipped roofs should not be turned into gable roofs.
Older and listed fabric limits what can be altered at all
Windsor Town Centre Conservation Area contains over 130 listed buildings and structures, with the oldest remaining buildings in the medieval streets of Castle Hill, Church Street, Market Street and St Alban's Street. The council's appraisal records that the largest collection of timber framed medieval structures in Windsor is near the Castle, some dating back to the early sixteenth century, and that these have been re-fronted in the eighteenth and nineteenth centuries. A re-fronted timber frame does not behave like a solid brick wall, and that has to be established before anything is cut.
The Windsor Neighbourhood Plan records that around 70 listed buildings are spread across its area, concentrated in the Clewer Corridor, Clewer Village, the fringe of the town centre and the edge of the Great Park. It also carries a Local List of Non-Designated Heritage Assets at Appendix 4, compiled with the Windsor and Eton Society and the borough conservation officer. The borough's validation requirements ask for a Structural Survey by a suitably qualified person where a proposal involves substantial demolition and change of use, or significant alterations or works to the historic fabric of a listed building.
- Drainage diversion and build-over agreements where required
- Steel beam and RSJ installation
- Temporary works, propping and needling
- Lintel replacement and repair over failed openings
- Wall plate, joist hanger and restraint strap installation
Trusted Structural Alterations in Windsor
We coordinate structural alterations rather than design them. The structural engineer we appoint issues the calculations, we build to them, and we never produce them ourselves. In Windsor that means dealing with a single authority, the Royal Borough of Windsor and Maidenhead, for both the planning side and the building control side. It also means knowing which documents its validation policy asks for before an application goes in. We make the building control application, book the inspections at the stages the council specifies, and give you one point of contact for the engineer, the trades and the sign off. GS Renovation Ltd is fully insured and registered in England, company number 14611254, and quotations are free and without obligation.
- Materials priced at options, so you choose the finish
- Building control inspected at foundation, steel and completion
- Straight advice on what is and is not worth spending money on
- The engineer's calculations obtained and worked to on site
- Dust screens and floor protection in occupied homes
- Honest updates if a date or a detail has to move