Damp proofingin Stanmorebuilt for the ground it sits on

Stanmore Hill drops away sharply, and a lot of the plots either side are terraced with retaining walls to create usable garden and, in some cases, habitable space below ground level. A retaining wall without a working drainage path behind it becomes saturated over time, and that water finds its way through to the room on the other side.

Correcting this properly usually means addressing drainage at the wall, a drainage channel or land drain taking water away rather than letting it build up, alongside any waterproofing to the wall face itself. Treating only the inside face of a retaining wall without dealing with the water behind it tends to be a short-lived fix.

We survey the external ground conditions as carefully as the internal symptoms on these sites, because on a hillside plot the two are directly connected.

Larger Stanmore properties, both the established 1930s houses and newer detached homes built to a bigger footprint, increasingly include basement or lower-ground floor accommodation, sometimes original, sometimes added during a major renovation. On sloping ground these rooms can be effectively below the water table on one side, so they need to be designed as structural waterproofing rather than treated as an afterthought.

We specify cementitious tanking bonded to sound masonry, or a cavity drain membrane system with perimeter drainage and a sump and pump where gravity discharge is not possible, detailing floor-to-wall junctions, steps and service penetrations properly since that is where these systems are most likely to fail if rushed.

Ventilation and internal moisture levels are also part of the specification. A below-ground room used as a gym, cinema room or additional bedroom generates more moisture than most cellars were ever designed to handle.

Integral garages are common in Stanmore's larger detached houses, and where they have been converted to habitable rooms the original slab and wall construction rarely meet the standard needed. We survey for a floor damp proof membrane, wall damp proof course and, where necessary, tanking to the lower part of the wall before specifying a fix.

Flat roofs on rear and side extensions are another regular source of penetrating damp in this area, particularly where upstands, abutment flashings or roof coverings have aged or were poorly detailed originally. Where the roof covering itself is the issue we work alongside roofing repairs so the underlying wall and ceiling damage is not simply replastered over a fault that will return.

Mixed in among the larger detached houses, particularly closer to the top and bottom of Stanmore Hill, are smaller, older cottages and period houses. These are typically solid-walled, without a cavity, and where a damp proof course exists at all it is often an ageing slate course well past its working life.

Rising damp in these properties follows the familiar pattern, a tide mark at a consistent height, salt bloom and hollow, blown plaster, and is treated with an injected chemical damp proof course using an accredited Sovereign or Wykamol system, followed by removal of salt-contaminated plaster and salt-retardant replastering.

From Harrow we cover Stanmore, Belmont, Canons Park, Harrow Weald and the Bushey Heath fringe, along with the rest of Middlesex, Brent, Edgware, Wembley, Pinner, London and West London, and further out to Watford, Slough, Buckinghamshire, High Wycombe and Surrey.

Calls are taken Monday to Friday 8am to 8pm and Saturday 8am to 1pm, and we are straightforward about timescales where a job involves structural waterproofing rather than a standard damp proof course.