Exploring dampness

Framework for assessing damp

Framework

  • Speak to the occupiers or those who have a knowledge of the building being surveyed and find out what they know about the problems.
  • Map the area of concern in a basic sketch.
  • Look for the obvious causes.
  • Look everywhere else for what is not happening.
  • Collect evidence.
  • Eliminate the suspects - watch out for factors that cloud the cause (the 'accomplices').
  • Determine the source.
  • Consider the basic remedies
    • Get the water/moisture away faster.
    • Stop the water spreading.
    • Change how moisture is created (particularly by humans), or reduce it.
    • Cover it up.

Map the area

By sketching a cross-section through the area, you can see the relationship between the possible causes. Sketching also makes you observe elements and their relative positions. This is key to discovering essential evidence. Drawing a sketch with others observing also helps to explain or identify issues. It is not always possible to draw what is happening inside a structure, but even drawing its outline can be useful.

A floor plan drawing should always be produced to be used as the story board for recording measurements and vital pieces of information relevant to the survey investigations. Include items such as;

  • age of the building;
  • wall construction;
  • fenestration details;
  • location of window or wall vents above and below flooring;
  • mechanical ventilation and type;
  • locations of dampness and mould;
  • locations of external defects, i.e. bridged dpc, defective rainwater goods;
  • timber or solid ground supported or suspended flooring;
  • type of floor coverings;
  • heating: location of radiators and type, type of boiler, etc. location of room thermostats;
  • roof type: i.e. flat roof, pitched and type of covering/insulation;
  • anything unusual? Unvented tumble dryer, use of liquid based fuel;
  • record internal environmental conditions, heating pattern (where possible);
  • occupation level –is the dwelling overcrowded etc.;
  • local water table;
  • type of drainage, water main, etc.; and
  • internal plumbing checks.

The above list is by no means exhaustive, but serves to show that all surveys of this nature are completely holistic. See Nothing lasts forever for more information.

Look for the obvious causes

Most damp problems have obvious causes, so look around to see if it possible to see where water might be coming from. However, it is relatively rare to be able to identify an absolute cause and isolate it at this stage. There may be more than one cause, so it is prudent to keep looking, even if the most obvious cause is found. If a cause has been brought to your attention, keep an open mind as to what could be the root cause, as it is easy to become too focused on an initial theory. The sketch below shows the 4 main causes of damp.

The main causes of dampness are:

  1. leaks;
  2. water penetration;
  3. condensation; and
  4. rising water or rising damp.
See We have a problem for more information.

Look for what is not happening

The key to the diagnosis of damp on site is to make and find comparisons. What is not leaking can give insight into why a particular element has failed in another location.

What is different? If it is not a visible physical difference, it could be a difference hidden within the element. The slightest difference can tip the balance. This is particularly noticeable where the occupier's lifestyle affects the condensation levels in a house, making it appear damper than it actually is. Observe all areas in the building, possibly even neighbouring properties to establish if there are similar areas that show the same propensity to fail but are not displaying the signs of failure. Note orientation and recent weather conditions, as these all combine to build a picture.

Not all poor details leak: some very good details, however well applied, may never work in the location they are in. By assuming that all ad hoc repairs are defective and that all textbook remedies never fail, you can veer in the wrong direction. Keep an open mind until all possibilities have been considered.

Collect evidence

If there is no obvious cause, more evidence needs to be gathered in order to confirm or eliminate the prime suspects. The quality of the evidence and the correct correlation between gathering and assessing it are key to arriving at the best solution. To find the 'culprit', one must eliminate all the suspects and isolate them from their accomplices. Below are the profile characteristics of the usual 'accomplices' that can cause confusion during diagnosis.

Eliminate suspects - watch out for the accomplices

The wick: The wick moves moisture behind surfaces and can set false trails of moisture penetration.

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The fence: the fence transports water within the structure to another location. Known to move water as far as 15 metres.

The moisture meter: popular moisture meters don't actually measure moisture; they measure electrical conductivity. These resistance/conductance meters have 2 prongs that are pushed into the material. The theory is that moisture raises conductivity and so gives a higher reading. While the pattern of readings from a moisture meter may reflect the pattern of actual moisture, the readings themselves can also come into contact with conductive material and may be inconclusive. Resistance types meters are calibrated to timber and are therefore scaled (0-100%) to a wood moisture equivalent (WME). They can be used more accurately in masonry walls where the reading is very low (Dry) as a low reading indicates there is unlikely to be any conductive material present or dampness. Therefore they can be dry meters in other materials other than timber and a dampness and dry meter in timber.

Conductance meters operate in a similar way by sending a radio frequency on a scale of 1000. Some manufacturers claim that the radio frequency or search mode can penetrate surfaces by around 5mm and can be good for determining dampness trapped in a wall covered in ceramic tiles. However, these types of meters are prone to the same range of conductive material, which can result in high readings being recorded that are not representative of actual moisture content.

Both electrical resistance and capacitance meters can be a very useful mapping tool for solid floors and walls to identify potential trouble spots that will require further investigation and different forms of measurement. Without other evidence and tests, they should not be relied upon solely as a dampness meter in anything other than timber.

The problem with this method of measurement is that there are other reasons the conductivity between the prongs could rise. The presence of salts, preservatives, carbon or metal all affects readings. Metal can be found in foil backings to plaster boards, or in minute particles of aggregate. Perhaps because the meters are called 'moisture meters' it is easy to assume that the readings are of the actual moisture content of any given material they are made to test.

(Many surveyors fall foul of this misconception, and many more home-owners are falsely led to believe that they have rising damp. A common con trick with such meters is to use a meter that has a test button on it that, when pressed, gives out an alarm signal. With some practice the meter can be made to look as though it has discovered a major damp problem, when it has in fact found nothing.)

If confronted with moisture meter evidence as 'proof' of rising damp, query the values, not least to question what material was tested. Readings taken with moisture meters in plaster and brickwork can imply very high moisture content when in fact the levels are perfectly acceptable under the circumstances.

If the limitations of conductance moisture meters are understood, they can be used with great effect provided the following basic rules are followed:

  1. Make sure it is regularly calibrated.
  2. Test a wide area and a range of materials to understand the local profile. Establish a control reading from which others can be compared.
  3. Only compare readings, rather than assume that high values equate to damp.
  4. Remember the meters are primarily designed for timber, and that readings in other materials may not relate to those found in timber.
  5. Do not rely solely on the readings. Only use a meter to give additional evidence.
  6. In detailed investigations a moisture meter can be used to draw moisture reading contours, which can help you to see the intensity and spread of moisture. These profiles can be very useful in determining the most likely cause.

The unreliable witness: this is anyone who gives misleading information, whether by mistake or deliberately. Some people have reasons to give misleading information in order to benefit from making the situation sound worse than it actually is. Relying solely on anecdotal evidence may be tempting for a busy surveyor, but any surveyor who asks a contractor to attend to a damp problem based solely on a telephone conversation is usually destined to revisit the problem. Even if on site, anecdotal evidence can also be completely wrong, and all the physical evidence will need to be carefully evaluated to substantiate it. Lifestyle can be a major factor in moisture generation, so it is easy to see why someone might well play this down in order to steer the surveyor towards a conclusion that there is something wrong with the house.

The smoke screen: these are factors that help to mask the main cause, including:

  • condensation;
  • previous remedies, such as waterproof seals;
  • alterations to pipes and structure;
  • proximity of road water;
  • a high water table; and
  • the weather.

Determine the source

Once you have completed the above steps, you can reflect on your evidence and review whether you have what you need to determine the source. See Don't be afraid to ask for more information.