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Common Causes of Dampness in Buildings

Dampness in buildings is common. It can be difficult to determine the exact cause however. This section lists sources of moisture ingress which we commonly find in buildings during specialist damp surveys. Please note that the source of moisture should always be correctly identified before any remedial damp control measures are undertaken.

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Condensation occurs when air with a high water vapour content comes into contact with cool surfaces (below dew point temperature). The water condenses from the air, resulting in the formation of water droplets on the cold surfaces. Excessive condensation can lead to the rotting of window sills, dampness on walls and mould growth. The presence of black spot mould on walls is an indication of excessive condensation.

Reducing the moisture loading in the air and/or improving ventilation is the most effective method of dealing with condensation. Dehumidifiers are costly to run, require emptying and should only be considered as a temporary measure. Dehumidifiers and anti-condensation paints only treat the effects and don’t remove the cause. Whole home ventilation systems on the other hand, are a cost-effective method of dealing with the causes of condensation and removing the effects.

There are many causes of excessive condensation dampness in a building including:

  • Lack of adequate ventilation
    • Trickle vents missing
    • Extractor fans not working properly
    • Ventilation system (MVHR, PIV, Passive Stack) not serviced or set up correctly
    • Occupants not using the ventilation equipment correctly
    • Ventilation gaps under doors aren’t large enough
  • Lack of adequate heating
    • Poorly positioned radiators
    • Old or ineffective heating systems
    • Lack of local heating controls such as thermostatic valves on radiators
    • Using manual control of central heating instead of using the programmer which results in unstable heating patterns
  • Poorly insulated buildings
    • Lack of loft insulation
    • Solid construction walls
    • Uninsulated solid floors
    • Cold bridging
  • Excessive moisture generation by occupant
    • Drying laundry throughout the property or venting tumble dryer into the house
    • Use of unvented gas heaters – gas produces large amounts of water vapour when burnt
    • Moisture creation through excessive cooking or bathing
Penetrating Dampness

The ingress of water into a building through the roof, floor, walls or openings is typically the result of a building defect such as:

  • Blocked or broken guttering
  • Blocked or broken downpipes
  • Blocked soak away
  • Defective external rendering or pointing – cement render/pointing on lime constructed buildings
  • Defective weatherproof seals on doors and windows
  • No weatherboard on doors
  • Bridged wall cavity
  • Roofing defects such as loose or missing tiles/slates, damaged or missing flashings or damaged coping
  • Chimney defects
  • Unventilated chimney stacks
  • Elevated ground levels
  • Lack of vertical damp/waterproofing on external face of basement walls
  • Failed external waterproofing in basements
  • Overflow pipe continuous running
  • Lack of drip beading on rendered walls or blocked drip grooves on window sills
  • Porous or cracked bricks
Water Leaks

The escape of water from pipes, tanks or drains can lead to localised or widespread dampness in a property. Common sources of water leaks include:

  • Water mains
  • Hot and cold water supply pipes
  • Central heating pipework and valves
  • Cracked or blocked drains
  • Water tanks, radiator valves, water softeners or washing machine supply pipework
  • Toilets, showers, sinks and baths

Water leaks account for a significant number of damp issues and the effects are regularly misdiagnosed as ground water rising dampness.

Rising Damp

Rising damp is the result of the movement of moisture through materials by capillary action. A number of factors can lead to rising damp including:

  • The absence of a physical damp proof course (DPC) or damp proof membrane (DPM)
  • Breakdown or failure of a physical damp proof course including incorrect installation
  • Ineffective chemical damp proofing or replastering
  • Bridging of damp proof course by increased external ground levels, external render, internal solid floors or a blocked cavity
  • Lack of ground water removal – water is retained close to the building rather than draining away
  • Lack of adequate sub floor ventilation
  • Application of inappropriate renders, plaster and paint to walls without damp proof courses or lime/traditionally constructed buildings
Internal Building Defects

Damp ingress can be the result of the failure of a water carrying appliance, the spillage of water or other sources of moisture. These may include:

  • Plumbing faults such as leaking valves, radiators, hot water tanks, washing machines or waste pipes
  • Bath or shower overflow or splashing
  • Condensation on uninsulated cold water pipes
  • Cold bridging
  • Lack of adequate roof space ventilation leading to condensation and mould growth
  • Blocked up fireplaces causing condensation to form in the void
  • Extractor fan and ventilation systems not working to the required levels
  • Combustion salt contamination of brickwork around chimneys and fireplaces
  • Incorrect or poorly fitted retrofit cavity, internal or external insulation
  • Inappropriate plaster/render/paint applied to pre-1919 properties which affects the moisture retaining ability of the structure
It is important to correctly diagnose the source of dampness before any remedial action is taken. It is common to find more than one source of moisture affecting a building. To arrange a dampness or leak detection survey please call 01189 451144.

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