Condensation is in every property and accounts for about 85{f898b7ccba74aedaf6f9f165b1651d39d829939f1b62e7036dcda8fdc0245a9d} of all damp surveys.

Key to condensation is ventilation

  1. bathrooms,
  2. kitchens,
  3. bedrooms,
  4. rooms with laundry.

A surge of modern property is over crowing, double glazing (when no one seems to keep the windows open – especially on the ground floor), indoor laundry, variable heating and blocking chimnies.

Sub-floor ventilation needs a special mention as it is often inadequate or allow ingress, and went inadequate or allows ingress, is often the cause of dry rot, a big issue to structural timbers in London.

Solid floors

Plasterers often plaster down to solid floors. Any water that condenses on the cold floor, spilt or otherwise sits on the solid floor will be absorbed up the plaster. This is also true of bathrooms, although not a problem.

Damaged, missing or broken rainwater goods

Penetrating damp from faulty rainwater good (gutters, hoppers, downpipes and gullies). Normally visible discolouration on the outside, although sometimes only visible during a rainstorm.

  1. Look at the outside for signs of damaged roof, gutters, hoppers, downpipes and gullies.
  2. Look for white, efflorescence (salt) streaks, dark discoloration to brickwork, often caused by rain bouncing off an object, green moss growing on damp shaded surfaces.
  3. Look internally for tea bag coloured stains to ceilings or walls, then look to the outside for the point of ingress.
  4. Imagine how the rain falls, or better still observed and film the outside during a rain storm.

Raise gardens

Owner often build onto of previous gardens, rather than remove ground. Furthermore in London the clay soil results in a certain amount of settlement of walls into the clay soil. Overtime London patios and gardens has risen relative to the ground.

The effect is exacerbated by plants, garden ornaments, piles of tiles or other objects that cause rain water to bounce high up a wall, often over the DAMP Proof Course (DPC) and often into the subfloor vents – creating ideal conditions for rot.

Roof leaks

Most roof leaks are easily identifiable by a brown teabag like stain n the ceiling, caused by water flowing round timber. Typical issues to look for with penetrating damp from roofs;

  • lower sections of roof valleys, where water funnels in greatest quantity,
  • flashing around walls and chimneys,
  • flat roofs, especially;
    1. bitumen roofs,
    2. where water ponds or
    3. pipe from another roof flows onto the flat roof,

Leaking pipes

Waste water (grey water) and pipe leaks are normally obvious. The ways to test are;

  • blue die, for waste pipe (and flat roofs),
  • turning water off and seeing if the main meter is still moving (if metered),
  • using a listening stick for below ground,

Cracks in brickwork, render or periodic ingress

The greater the width, looking two dimensionally downwards, the more water can come in. Therefore a vertical crack lets in only a small amount of water compared to a horizontal crack. Many cracks only cause internal dampness very occasionally, depending on quantity of rain and the wind direction and speed.

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