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My block is a 1930’s build and like most buildings (whatever their age) there are always issues with condensation (in varying degrees). Because condensation produces its own water/moisture it often shows up as water running down the windows and pooling on the sills. Windows are less thermally efficient than the surrounding walls (especially in older buildings) making their internal surface temperature cooler by a few degrees than the surface temperature of the walls. Once the dew point occurs (100% relative humidity) it will start condensing on the cooler surfaces. i.e. the windows before condensing on the surrounding walls showing as droplets and the discolouration of window panes. It can also show as black patches of mildew, wallpaper coming loose from the wall, and making soft furnishings and clothes smell musty when they have been placed in an unventilated airing cupboards.

Affected damp areas then attract black mould which grows on its surface. Moisture obtained from the condensation gives clear warning that the heating, structural insulation or ventilation (or all three) may require improvement. It also survives on emulsion paint or wallpaper.

Excess mold should be removed by wiping with a damp cloth or if it is dry, a vacuum cleaner. It must not be brushed as doing so releases spores into the air. Remaining mold needs to be wiped with a fungicidal wash or diluted bleach. Tea tree oil can also be used as it is a natural antiseptic and disinfectant.
Redecoration can then be carried out using a fungicidal paint or wall paper paste. Do not paint over using ordinary paint.

Condensation can also be found inside walls and insulation or under floors, and on occasions in cupboards and corners of rooms where ventilation and movement of air are restricted. I often see dehumidifyers in use but there some important steps to carry out when dealing with condensation:

  1. There must be some ventilation provided to all rooms to enable moist air to escape. A problem with nearly all of the flats in my block is that individual landlords have not only sealed up the fireplaces but also a number of the existing vents;
  2. Excessive use of heating (which I have come across because some flats feel like greenhouses when you walk into them) must be reduced, especially if point 1 also applies;
  3. No portable paraffin or flueless gas heaters must be used because each litre of oil used produces the equivalent of about a litre of liquid water in the form of water vapour;
  4. Condensation can also be produced where there are no cooker hoods/extractors over the cooker. If they are installed and vented to the outside air, much of the steam from the kitchen will be removed. They should be 6″ or 8″ in diameter;
  5. If condensation is produced on cold pipes it can be prevented by using moulded insulation or other efficient lagging;
  6. The internal surface temperature of walls can be increased by internally insulating with dry lining;
  7. External walls can be insulated with an insulated render system;
  8. The addition of more extractor fans such as in the bathroom;
  9. Upgrading the heating system.

Blocks of flats will have a number of pipes running through walls, under floors and through ceilings. Leaks usually are usually obvious, such as large amounts of water coming through ceilings, appearing under the floor, or wet patches showing on the wall or floor (in the driest of weather). If there is a service duct (or main stack) within the property it should be fully accessible because it provides access to valves, all main services, and rodding eyes. Some flats will share such services with the neighbouring flat.


There are a number of potential causes of plumbing leaks, with the following information sourced from the ARMA downloadable fact sheet ‘Water Leaks’

  1. Defective seals: found around baths and showers and which are white flexible beads which run around  the bath/shower and allow water to run back to the baths/showers. When the mastic seal is damaged, split, loose or curling away from the wall or bath, water can freely run down the back of the bath/shower, and eventually make its way through the ceiling and into the property below, often through a light fitting;
  2. Gaps in grouting: these can allow water in behind tiling causing damp patches, tiling to come loose and again, the risk of water leaking into the property below;
  3. Unconnected waste pipes;
  4. Incorrect installation of appliances: these can be a cold feed to hot supply, or ill-fitted power shower pumps etc, causing joints to fail;
  5. Unsupported pipes: this leads to sagging then to blockages and unpleasant smells;
  6. Incorporation of too many bends; this, along with an inadequate number of fixings can lead to noise and performance issues;
  7. Poor and/or over-notching to joists: these can cause floors to become ‘springy’ and in extreme cases could potentially lead to floor failure and collapse;
  8. No insulation on cold feed pipes
  9. Badly supported tanks and pipes: these can be susceptible to leaks or splitting;
  10. Irregular noise from a toilet: This can be theflush cycle taking longer than it normally does and is often remedied by adjusting the valve or replacing the inlet valve washer. A constant running sound on the other hand can cause damage to the exterior of the building because the external overflow is allowing water to escape onto the walkways below. In icy conditions this could cause a hazard. Staining will occurr on walls, damage mortars and lead to possible water ingress somewhere else, as well as encourage vegetative growth;
  11. Degraded seals: When found around the kitchen worktop and around the sink, the gaps they create can often cause water to penetrate down the back or into other properties;
  12. Frequent vibrations: these can cause the outlet connections of dishwashers and washing machines (found under the kitchen sink) can come loose due to frequent vibrations  so these connections should be regularly checked. Frequent checks should also be carried out on the washing machine hose as this is a major cause of leaks.
  13. Leaking hot/cold supply pipes, supply and waste pipes including traps, hot water pump or boiler;
  14. Repairs to central heating systems (unless the system is for a communal area of the development);
  15. Dripping taps: These can often repaired by replacing a washer;
  16. Corrosion of the plumbing or joints not fully water-tight: Corrosion can be internal as result of more than one type of metal being used in the plumbing, or external  which is often as a result of concrete or cement coming into contact with copper pipes. It can also be caused by flexible tumble dryer vents extracting into a room rather than outside of it. It typically manifests itself as a small isolated damp patch, without any brown staining, that gradually grows, ‘bubbly’ plaster at the edge of the patches with water appearing if the leak is near (or above) the surface.

In theory leaks and burst pipes are easier to correct than penetrating damp.
If there is no obvious signs of a leaking pipe, then cutting off the incoming water at the stopcock and draining the hot water system (by turning all the taps on) will quickly empty the pipework and dripping water should cease. Leaks which are more difficult to trace are ones in storage tanks, cylinders and waste pipes, and but small steady leaks that are difficult to find (or not even known about) can be slowly causing extensive damage.

Our block had a major situation with an undetected leak which occurred not long after we took over. The ceiling of a flat at the rear of the property had partially collapsed in the kitchen due to a slow, steady leak from the flat above.

Other leaks which may affect the property are faulty roofs and broken or badly fitted gutters, which may soak an external wall sufficiently to allow moisture to pass through a solid wall or find a possible “bridge” in a cavity wall.

Damp Meters

The use of damp meters to measure the amount of moisture is widely used but they do not actually record moisture, rather they read conductivity of salts in whatever the meter is pushed onto. In most cases it will be pushed about a millimetre into the plaster on the surface of the walls. So, even if the wall is dry, a high reading will be because of salts (which are highly conductive) having been drawn into the wall by moisture. Whilst the surface of walls are often wet  because they covered in cold water that has condensed there, it is highly likely that the wall underneath it will be dry.

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