Damp Proofing Windsor

Windsor grew up around the castle on its chalk hill above the Thames. The streets below it, around Peascod Street, Sheet Street and Park Street, have Georgian and early Victorian houses, while Clarence Road, Clewer and the roads towards Dedworth are lined with Victorian and Edwardian terraces and later semis, with Eton just across the river.

The castle stands on an outcrop of chalk, but most of the town is built on Thames terrace gravels and alluvium, with London Clay rising to the south towards Windsor Great Park. The gravels are permeable and connected to the river, so the water table rises and falls with the Thames and with rainfall across the wider valley.

That makes groundwater the defining damp issue in much of Windsor. In very wet winters, such as 2013 into 2014, groundwater in the gravels around Windsor, Old Windsor and Datchet rose high enough to come up through cellar floors and into gardens even where the river itself did not overtop its banks. Any room at or below ground level near the river needs to be designed with that in mind.

Cellars are common under the older town centre houses and in Clewer and Eton. Used for storage they may cope, but converting them into living space needs a cavity drain membrane with a sump and pump, ideally with a battery backup, designed to BS 8102:2022 for the highest likely water level rather than a dry summer.

The Georgian and early Victorian houses have solid brick walls laid in lime mortar, often with stucco fronts and no original damp proof course. Cement render, cement pointing and gypsum plaster added during past refurbishments trap moisture and cause much of the damp we see in these buildings. Many are listed or in conservation areas, so treatments need to suit the fabric.

The Victorian and Edwardian terraces typically suffer from bridged damp proof courses where paths and patios have been raised, blocked air bricks and damp floor voids, wet rot in joists, and penetrating damp from worn pointing, parapets and gutters.

Chimney breasts are another common source. Where fireplaces have been blocked without ventilation or stacks are poorly capped, moisture and salts collect in the brick and show as stubborn damp patches.

Later houses with cavity walls bring their own issues, including cavity wall insulation carrying water across the cavity, failed wall ties, and damp at the junction with extensions. Condensation and mould are common in flats and in homes with replacement windows and poor extraction.

Landlords, letting agents and managing agents make up a good share of our Windsor work, given the number of rented and leasehold homes in the town. Our reports are clear about the cause of damp and which repairs belong to the owner, the freeholder or the occupier.

Because damp in Windsor can come from groundwater, the river, the weather or the way a home is used, the survey always comes first. Our CSSW and CSRT trained surveyors take moisture readings, use thermal imaging where it helps, and check drainage, pointing, ground levels and ventilation before recommending anything. You get a written report with photos that explains the cause in plain language and sets out the fix, with no obligation.

We cover Windsor and the SL4 postcode, including the town centre, Clewer, Dedworth, Old Windsor and Eton, and nearby Datchet. Surveys are arranged from our office at Unit 78 Basepoint, Lincoln Road, High Wycombe.