Rising damp – diagnosis

Follow the science

“With a chemistry degree, background in fraud investigation and property management, my motivation is scientific truth”  Simon

I plead with surveyors who find a genuine case of rising damp, to get in touch, so I can investigate it. I always keep an open mind.

In 2017 I embarked on a mission to understand why there is so much diagnostic divergence between the Royal Institute of Chartered Surveyors (“RICS”), the Property Care Association (“PCA”), English Heritage, Society for the Protection of Ancient Buildings (“SPAB”) and surveyors who investigate dampness in houses for a living.

I’ve completed multiple courses on damp and qualified with both RICS as an expert witness and the PCA as a damp and timber surveyor. I have attended many seminars and talked in depth with academics and practitioners including the UCL, SPAB and English Heritage.

I have investigate over 1,000 cases, initially determined as being rising damp by another survey. All suspect rising damp cases have turned out to be damp from another root cause.

12 reasons why otherwise able surveyors, still misdiagnose rising damp (in my opinion):

  1. Lack of understanding that rising damp is a symptom, groundwater is the cause.
  2. Not knowing what groundwater is.
  3. Not understanding why groundwater needs to be separately classified.
  4. Failure to look for high groundwater or assess the risk.
  5. The use of analogous terms like capillary action, capillarity and wicking.
  6. No examples of rising damp available for practitioners to investigate.
  7. Limited investigation and training in recognising damp from its profile.
  8. Poor understanding of barriers such as damp proofing courses (“DPC”).
  9. Limited knowledge, training and investigation into hygroscopic salts.
  10. Insufficient training and investigation into mould and condensation.
  11. Insufficient training and investigation into salts on walls.
  12. Tendency to diagnose rising damp after eliminating other causes of damp.

+ Motivation to diagnose rising damp.

Whether financial, or lack of time, access and resources to fully investigate the root cause of damp

– or fear of being sued by owners who spent money treating misdiagnosed rising damp.

1. Rising damp is a symptom not a cause

Rising damp, mould, condensation, rot, woodworm, surface salts and damp staining are all symptoms of excess moisture. It is important to differentiate symptoms from root causes.

Dampness and the damage caused by dampness will only disappear if damp is stopped at the source of moisture.

The root causes of excess moisture are:

  1. vapour – leading to excess humidity causing mould and condensation etc.
  2. rainwater or precipitation – leading to penetrating damp or flooding
  3. leaks or piped water – from mains, heating, wastewater, cleaning, spillage 
  4. groundwater – leading to rising damp

2. What is groundwater? “Groundwater in the Environment” by Paul Younger

Groundwater is the large body of water found below ground level, in saturated porous rocks with an impermeable rock base. It is often referred to as the water table. Groundwater comes to the surface in the form of springs. 

Traditionally springs were not built on or near, but made into parks, like Wells Park in SE London. The groundwater in most cities is pumped out for drinking water, irrigation and industry.

There is over 100 times more fresh water held as groundwater, than surface water (including water held in all the world’s rivers and lakes).

 Groundwater acts like a lake, or any other body of water, because:

  • pores in rocks are saturated and 
  • there is a base, which stops gravity from drawing water further down.

A brick in contact with groundwater will absorb moisture upwards by about 200mm, with is referred to as rising damp.

3. Why does groundwater need to be separately classified from rainwater.

Water in soil is called surface water. Surface water comes from precipitation. Excess surface water should be treated by draining it away from a building.

In contrast to groundwater, water in soil is in a temporary state of suspension, held by the forces of the soil’s absorption. Water will either evaporate, be consumed by organisms or be drawn down by gravity through unsaturated porous rock to become groundwater.  Rainwater does not not act like groundwater until all the pores down to the bedrock are saturated, at which point it acts like, and becomes groundwater.

A brick in contact with damp soil may become a little moist, but this is not rising damp.

Water from any source is absorbed upwards through porous material. The rise depends on various factors including the relative absorption of the source of water, saturation and gravity. The force of gravity means that roughly 10 times more water is absorbed down, than is absorbed upwards.

Moisture from groundwater is absorbed up roughly 10 times higher than water in soil.

As the pours below groundwater are saturated down to the base rock, the force of gravity is limited to the rise above the groundwater.  As a result, the rise of groundwater is roughly 10 times greater than rise of water from soil with no bedrock.

Water found in soil comes directly from precipitation. The most effective, least risky and most economic solution is drainage.

4. Assessing the risk of a wall being in contact with groundwater

Properties have to be:

  1. built on  low lying land or built on a spring  (see https://flood-map-for-planning.service.gov.uk) AND
  2. built above a productive aquifer (http://mapapps2.bgs.ac.uk/geoindex/home.html?layer=BGSHydroMap) AND
  3. note be in a city, such as London where water is pumped out,
  4. groundwater should be visible within about 200mm of ground floor timber.

5. Analogous terms such as capillary action, capillarity and wicking can mislead

Moisture is absorbed by a porous material in every direction, but the force of gravity will act to pull about 10 times more downwards, than upwards. 

Capillaries and wicks would also draw more water down than up, but as they are normally held vertically upwards, people tend to think of the primary direction of absorption as being upwards. 

The only time when absorption is significantly upwards, is where there is groundwater within water saturated rock, sitting above bedrock. The water acts like water in a vessel, the vessel stops gravity from draw water downwards. This phenomena is known as rising damp. 

The absorption of moisture from damp soil, is known simply as absorption and falls under the category of penetrating damp.

 6. No examples of rising damp available for practitioners to investigate.

Rising damp can be replicated by placing a brick in a vessel containing water. I have not found a wall built on groundwater (presumably because that would not be very sensible). I have yet to see a genuine case of rising damp., possibly because I practice mainly in London, where groundwater is pumped out.

7. Limited investigation and training in recognising damp from its profile.

I have attended 4 courses given by the PCA and RICS, and seen photos of purported rising damp, but never once seen a replication of rising damp. I would very much like to see an actual example either in a property or in the laboratory.

8. Poor understanding of barriers such as damp proofing courses (“DPC”).

Limited knowledge, training and investigation into hygroscopic salts.

Insufficient training and investigation into mould and condensation.

Insufficient training and investigation into salts on walls.

Tendency to diagnose rising damp after eliminating other causes of damp.

 Misunderstanding the nature of groundwater compared to other sources of water.
Not determining the risks of a building being in contact with groundwater, before considering whether it is suffering from rising damp.
The use of analogous terms like capillary action, capillarity and wicking.
Limited training and investigation into the effects of hygroscopic salts.
No examples of rising damp available for practitioners to observe and test.
Insufficient training and investigation into mould and condensation.
Insufficient training and investigation into surface salts.
Tendency for rising damp to be the catch all, when all other forms of damp have been eliminated.

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