national maintenance week heading

Top Tips

Getting to Grips with Damp

Damp is something that strikes a chord with anyone who cares for a property. Lack of regular maintenance can be a prime cause of this common problem, especially if blocked pipes and gutters are causing an overflow of water that is penetrating and adversely affecting a building.

Mike Parrett

In 2005 damp was a key theme of SPAB's (The Society for the Protection of Ancient Buildings) annual National Maintenance week, SPAB joined forces with national damp expert Mike Parrett, whose work to dispel some of the myths and misunderstandings around the subject were featured in the hard-hitting investigative tv programme "Raising The Roof".

His common sense approach gets to the root of the issue and can even help people to save money by helping them to recognise the causes of their problems, giving them the confidence and knowledge to take the right steps to remedy the situation.

Mike's damp busting tips:

Watch out for the following symptoms and signs of dampness.

Damp rooms usually have a distinctive and easily recognisable smell. Stale trapped air caused by poor ventilation is another good indicator.

Damp patches and patches of mould can be due to water leakage and or water penetration - look for any corresponding defects (leaking gutters, pipes, roof tiles etc) at or near the locations of the mould.

Dampness on or around a chimney breast is likely to be caused by falling damp! Rainwater directly entering the chimney mouth and filtering down through the walls below. Capping your chimney could eliminate this problem.

If your house pre-dated World War II it is likely that it was built using lime. This is a breathable material, but later additions such as modern, hard cement renders and masonry paints may actually be trapping moisture into the walls.

Crescent shape mould in the corner of two external walls is more typically due to active condensation.

Mike ParrettCauses of condensation can be due to:

  • Design, layout and construction of the building
  • Use and occupation of the building
  • Defects to the building
  • Or any combination of the above

Salt clusters on the wall surfaces can be due to water leaks, ground water and or rain water penetration. There are salts originating from the ground and natural salts in clay bricks.

Remember - rising damp, penetrating damp and condensation are not causes of damp but describe the transportation of moisture - What causes them to occur is where you start to look and not where you finish looking.

A great deal of dampness to ground floor walls is commonly referred to as being caused by rising damp necessitating a new damp proof course to be injected - But rising damp is not a cause it describes the movement of moisture in a particular direction!

 

Common causes of dampness to ground floor walls that may cause dampness to rise:

  1. Raised external ground levels against outside walls - where the ground is higher than either the physical horizontal damp proof course or higher than the internal finished floor level.
  2. Leaking high level gutters, overflow pipes and rain water pipes.
  3. Lack of adequate air flow under timber suspended floors.
  4. Rubbish and rubble placed under suspended floors, trapping moisture and affecting ventilation.
  5. Blocked cavity wall voids.
  6. Leaking potable water main supply at or near the building.
  7. Causing damp where suspended timber floors have been replaced with solid floors - rarely is the damp proof membrane under the solid floor (if one exists!) properly related to the perimeter walls, causing moisture to squeeze out from beneath and upwards.
  8. External renders applied to external walls bridging the damp proof course and in contact with the ground.
  9. Dampness to common or party walls - the adjoining property must also be checked!
  10. High local water table and or proness to flooding - check with the Environment Agency, Local water provider and or Local Authority for further information.

Traditional masonry

It may surprise you to know that the majority of so called damp guarantee's do not cover any of the above list of common causes of rising damp! And the above list is by no means exhaustive.

Physical damp proof course rarely fail - even a cracked slate damp proof course in a wall is unlikely to create a capillary by which moisture would pass through. So if they rarely fail it is not very common to require a new one!

Chemical damp proof course injections in themselves do not provide a total barrier against rising ground water and rely on the additional water proof render and plasters to be applied to the ground floor walls. Such treatments are not a total cure, but a management of the problem.

One of the World's largest manufacturer's of electrical moisture meters say that you cannot rely solely on the results of an electrical moisture meter to form a diagnosis of the cause of dampness. So if the manufacturer's say that, how can £000's of remedial treatments be recommended, determined only by the use of that single instrument?

© SPAB 2007