Rising damp (structural)
Encyclopedia
Structural dampness refers to the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation
from within the structure.
A high proportion of damp problems in buildings are caused by the "big three"; condensation, rain penetration, and rising damp, although other causes of dampness such as pipe leakage and construction moisture should not be overlooked.
. Plaster
and paint
deteriorate and wallpaper
loosens. Stains, from the water, salts and from mold
, mar surfaces. The highest airborne mold concentrations are found in buildings where significant mold infestation has occurred, usually as a result of severe water intrusion or flood damage. Molds can grow on almost any surface and occurs where there is a lot of moisture from structural problems such as leaky roofs or high humidity levels. Airborne mold concentrations have the potential to be inhaled and cause serious health effects in humans.
Externally, mortar may crumble and salt stains may appear on the walls. Steel & iron fasteners rust
. It may also cause a poor indoor air quality
and respiratory illness in occupants. In extreme cases, mortar or plaster may fall away from the affected wall.
A 2009 World Health Organisation report entitled "Children Living in Homes With Problems of Damp" stated that:
"Excess moisture leads – on almost all indoor materials – to growth of microbes such as moulds, fungi and bacteria, which subsequently emit spores, cells, fragments and volatile organic compounds into the indoor air. Moreover, dampness initiates chemical and/or biological degradation of materials, which also causes pollution of the indoor air. Exposure to microbial contaminants is clinically associated with respiratory symptoms, allergies, asthma and immunological reactions. Dampness has therefore been suggested to be a strong and consistent indicator of risk for asthma and respiratory symptoms such as cough and wheeze."
Processes for diagnosing rising Damp in buildings is set out in BRE Digest 245.
All of the above should be considered during any assessment for damp related defects in buildings.
in the form of a synthetic damp-proof course (DPC), about 15 cm above ground level, to act as a barrier through which water cannot pass. Slate or "engineering bricks" with a low porosity were often used for the first few courses above ground level, and these can in theory help minimise the problem.
There are many approaches to the treatment of dampness in existing buildings. Key to the selection of an appropriate treatment is a correct diagnosis of the types of dampness affecting a building. Details of possible treatments for specific types of dampness are covered in the sections below.
The cause of the dampness must first be eliminated, by providing better drainage or fixing leaking pipes. BRE Digest 245 describes several methods of treating rising damp, including the use of land-drains and the insertion of physical and chemical DPCs. Then, any affected plaster or mortar must be removed, and the wall treated, before replacing the plaster and repainting.
The major damp treatment authorities within the U.K. are The British Wood Preserving and Damp-proofing Association (BWPDA) and The Property Care Association
.
Human occupancy adds a significant amount of humidity to the indoor environment. Personal activity as basic as breathing and perspiration add moisture to an indoor space. Cooking and showering raise humidity levels in the indoor environment, which directly affects the structural dampness of a home. Aspects of the home can also increase the humidity of a space. Items such as aquariums, indoor swimming pools, hot tubs, and even indoor plants add to the humidity of an indoor space. All of these attributes can increase the humidity of a home beyond its recommended thirty to fifty percent.
Humidity levels in an indoor environment need to be accounted for based upon season and temperature. If humidity levels do not agree with the time of the year and the temperature during seasons, mold infestation and deterioration of the building will occur due to moisture. An acceptable humidity level in indoor spaces ranges from twenty to sixty percent year round. However, levels less than twenty percent in the winter and levels higher than sixty percent in the summer are deemed unacceptable for indoor air quality. Structural dampness is likely to occur as well as an increase of health risks associated with moisture damage.
Moisture condenses on the interiors of buildings due to specific interactions between the roof and wall. Leaks most commonly occur on flat-roofed buildings. Certain building materials and mechanisms can be used to prevent condensation from occurring in these areas, therefore reducing structural dampness and potential mold infestation. In many cases, the insulation between the roof and wall is compressed, leading to a decrease in thermal resistance. Due to the lack of thermal resistance, condensation occurs, which leads to water damage in the indoor environment. In most cases where moisture is not addressed quickly enough, mold and mildew develop. Another issue is that wind washing up into the crevice where the roof and wall intersect reduces the efficiency of the insulation. This results in condensation and risk for mold growth.
In the United Kingdom, condensation problems are particularly common between October and March - to the extent that this period is often referred to as the "condensation season."
left running for the recommended time and then further instrument tests made. If the dampness has disappeared, then condensation is very likely the problem.
Alternatively Humiditect cards or dataloggers (measuring air humidity, air temperature, and surface temperature) can be used as tools for diagnosing a condensation problem.
Water will often penetrate the outer envelope of a building and appear inside. Common defects include.
The most common sources of indoor moisture at the base of walls in buildings is from defective ground and surface drainage. This is due to rising ground levels and the failure of ground drainage systems. These defects are common nation-wide. Additionally, plumbing leaks and flooding from defective drainage and plumbing are also sources of moisture occurring on the base of walls in buildings.
. Although rising damp of up to 5 metres in height has been observed the height of rise is typically much lower and is rarely above 1.5m. Rising damp has been a widely observed phenomenon for at least two hundred years. Rising damp is deemed controversial because it is often misdiagnosed in buildings. Many misdiagnose a wall stain as rising damp instance due to misinterpreting the visual evidence of the wall and the readings of moisture meters. There is also strong evidence to suggest that it was a problem understood by the Romans and Ancient Greeks.
In simple terms rising damp occurs when ground water travels upwards through porous building materials such as brick, sandstone, or mortar, much in the same way that oil travels upwards through the wick of a lamp. The effect can easily be seen by simply placing a piece of porous brick, stone, or mortar in a shallow tray of water and observing how the water is absorbed into the porous material and is transported above the water line.
Rising damp can be identified by a characteristic "tide mark" on the lower section of affected walls. This tide mark is caused by soluble salts (particularly nitrates and chlorides) contained in the groundwater. Due to the effects of evaporation these salts accumulate at the "peak" of the rising damp.
referred to the problem of dampness rising up walls and advised on how to construct buildings to avoid the problem.
Rising damp is widely referred to in Victorian literature and the Public Heath Act of 1875 introduced the requirement for a damp-proof course in walls to prevent rising damp. An entry in the British medical Journal from 1872 describes the phenomenon of rising damp as follows:
"Even if the rising damp be arrested by what is technically called an impervious damp-proof course, it will be frequently found that this is built in the wall too near the ground line, so that the heavy rain besplatters the ground and splashes above it. As time rolls on the surface of the ground also becomes elevated, and this damp course is soon lost to sight. Attempts have been made to remedy this evil of porous bricks by the substitution of the hard blue bricks of Staffordshire; and then it may often be noticed that the wet has only struck, sailor-like, across the mortar-joints and chequered the inside walls like a tartan plaid."
The architect and social reformer, Thomas Worthington
, described rising damp in his 1892 essay, "The Dwellings of the Poor: And Weekly Wage-Earners in and Around Towns":
"It should be borne in mind that damp walls absorb much more heat than dry ones and that they are frequent agents in causing rheumatism, kidney disease and colds. Rising damp from the ground may be prevented by most simple means. Six inches of good Portland cement concrete should cover the whole site of the dwelling, and concrete never less than nine inches thick should underlie all walls. A damp course should disconnect the whole of the foundations from the superstructure. This preventative may consist of a double layer of thick slates bedded in cement, or of patent perforated stone-ware blocks or of three-quarters of an inch of best asphalt."
The Building Research establishment (BRE) in its review concludes that Rising Damp is a real problem. Indeed, Part C of the Building Regulations for England and Wales specifically calls for the inclusion of a damp-proof course in all new properties.
Konrad Fisher's article "The Fraud of Rising Damp" points out that the historic city hall in Bamberg stands in the river Regnitz and its bridge remains dry without any chemical, mechanical or electronic damp-proof course.
However, evidence suggests that not all walls are capable of supporting rising damp, so merely observing that rising damp does not occur in a particular wall does not disprove its existence in other walls.
In 1997 staff at Lewisham Council in South London were so convinced that rising damp is extremely rare or possibly a myth that they are offered a reward of £50 to anyone who could prove them wrong.
Water intrusion into the indoor environment can be attributed from causes other than rising damp. Moisture penetration has been an ongoing problem for residences as evaporation occurs at the edge of the damp area, resulting in “tide marks” due to salt deposition. The “tide mark” is commonly distinguished as a feature of rising damp. However, even after the water intrusion has been treated, these salt accumulations still persist. This suggests that rising damp is not necessarily the cause for the water penetration.
the maximum height of rise is inversely proportional to the capillary radius. Taking a typical pore radius for building materials of 1 µm, Jurin's Law would give a maximum rise of about 15 m, however, due to the effects of evaporation, in practice the rise would be considerably lower.
A "physical model" of rising damp was developed by Christopher Hall and William D Hoff in their paper "Rising damp: capillary rise dynamics in walls". The analysis is based on experimentally well established properties of porous building materials and the physics of evaporation from building surfaces. They state that model can be used to predict the height to which damp will rise in a wall, based on factors such as wall thickness, the sorptivity of the wall structure and the effect of evaporation. Further work has confirmed experimentally the importance of mortar properties in determining the height to which damp will rise in walls. BRE Digest 245 lists several factors that can influence the height of the rise including rate of evaporation from the wall, pore sizes of the masonry, salt content of the materials and the soil, groundwater and degree of saturation, and use of heating within the property. The effect of seasonal variations in evaporation rate on the height of moisture rise have been comprehensively described.
A review of data and publications commissioned by the Property Care Association and carried out by the University of Portsmouth concluded that "Rising damp is an age-old and ubiquitous problem." It also noted that "Records on observation and descriptions on this phenomenon date back to early
times. It was identified as a public health issue in the second half of the 19th Century." The review looked at data and studies on rising damp from a number of countries including the United Kingdom, Portugal, Germany, Denmark, the Netherlands, Greece, Australia, and Malaysia.
One method that is often used to determine if the source of dampness is rising damp (rather than other forms of dampness) is to look for the presence of salts - in particular a tell tale "salt band" or "tide mark" at the peak of the damp's rise. Although this is a useful indicator, it is not completely reliable as salts can enter the fabric of the wall in other ways - e.g. unwashed sea sand or gravel used in the construction of the wall.
If there is no damp-proof course and rising damp is suspected (tide mark, moisture confined to lower section of wall etc...) then a number of diagnostic techniques can be used to determine the source of dampness. BRE Digest 245 states that the most satisfactory approach is to obtain samples of mortar in the affected wall using a drill and then analysing these samples do determine their moisture and salt content. The fact that this technique is destructive to the wall finish often makes it unacceptable to homeowners. It is for this reason that electrical moisture meters are often used when surveying for rising damp. These instruments are unable to accurately measure the moisture content of masonry (they were developed for use on timber), however the patterns of readings that they provide can provide a useful indication of the source of dampness.
Where a rising damp problem is caused by a lack of a damp-proof course (common in buildings over approximately 100 years old) or by a failed damp-proof course (comparatively rare) there are a wide range of possible solutions available. These include:
BRE Digest 245 suggests that with the exception of replacement physical DPCs, only methods of treatment with third party accreditation (E.g. British Board of Agreement Certificate) should be considered. It then goes on to state that the only method of currently satisfying this requirement is DPC injection and that "this is the only method which BRE considers suitable where insertion of a physical DPC is not possible." The Royal Institute of Chartered Surveryors (RICS) publication "Remedying Damp" is more cautious about reliance on third party accredititation, casting doubt upon the validity of the test methods employed, arguing that trials are usually conducted using "specially built masonry panels - which do not match up in many respects to walls found in real properties," and that "if a DPC were proved to not work in a specially built masonry panel, this would be the more significant result." The MOAT No 39 test employed by the British Board of Agreement (BBA) in the UK is dismissed as "quite a clever test idea but in the author's opinion not actually replicating a real wall." Furthermore, the point is made that "BBA testing is paid for by manufacturers, and the results are not thought to be publicly available."
BS6576:2005 states that "the function of the new plaster is to prevent hygroscopic salts that might be present in the wall from migrating through to its surface, while still allowing the wall to dry." However, writing in the RICS publication "Remedying Damp", Ralph Burkinshaw claims that, "the plaster is really there for two main reasons." He accepts the need for replastering when significant amounts of ground salts have built up in the existing plaster, however he then goes on to say that replastering is often carried out to make up for an unreliable chemical DPC. He also suggests that damp-proofers have an incentive to carry out more replastering than is strictly necessary as it allows them to finish the job without having to wait for walls to dry out, resulting in faster payment.
Although the sand:cement renders typically installed as part of a rising damp treatment are very effective at holding back damp and ground salts, they have a number of disadvantages. These include an incompatibility with the soft bricks and mortars encountered in older buildings and a lack of insulation properties compared with more traditional plasters, resulting in an increased risk of condensation. Replastering is also one of the most expensive parts of a rising damp treatment.
Porous renders to German WTA specification 2-2-91 can be used as an alternative to dense sand-cement renders. These have a minimum porosity of 40% of total volume. Salts crystallise in these pores rather than on the plaster surface, avoiding decorative spoiling. Such plasters offer a better solution than dense sand-cement renders when used on moderately salt-contaminated walls as their porous nature gives them insulation properties, resulting in a warmer surface temperature and making condensation problems less likely to occur. However, when used on heavily salt contaminated walls they may need to be replaced frequently as they lose effectiveness once all the pores have become filled with crystallised salt.
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
from within the structure.
A high proportion of damp problems in buildings are caused by the "big three"; condensation, rain penetration, and rising damp, although other causes of dampness such as pipe leakage and construction moisture should not be overlooked.
Symptoms
Dampness tends to cause secondary damage to a building. The unwanted moisture enables the growth of various fungi in wood, causing rot or mold health issues and may eventually lead to sick building syndromeSick building syndrome
Sick building syndrome is a combination of ailments associated with an individual's place of work or residence. A 1984 World Health Organization report into the syndrome suggested up to 30% of new and remodeled buildings worldwide may be linked to symptoms of SBS...
. Plaster
Plaster
Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...
and paint
Paint
Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...
deteriorate and wallpaper
Wallpaper
Wallpaper is a kind of material used to cover and decorate the interior walls of homes, offices, and other buildings; it is one aspect of interior decoration. It is usually sold in rolls and is put onto a wall using wallpaper paste...
loosens. Stains, from the water, salts and from mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
, mar surfaces. The highest airborne mold concentrations are found in buildings where significant mold infestation has occurred, usually as a result of severe water intrusion or flood damage. Molds can grow on almost any surface and occurs where there is a lot of moisture from structural problems such as leaky roofs or high humidity levels. Airborne mold concentrations have the potential to be inhaled and cause serious health effects in humans.
Externally, mortar may crumble and salt stains may appear on the walls. Steel & iron fasteners rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...
. It may also cause a poor indoor air quality
Indoor air quality
Indoor air quality is a term referring to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants....
and respiratory illness in occupants. In extreme cases, mortar or plaster may fall away from the affected wall.
Health Effects of Damp Structural
Asthma is one of the most common health effects associated with structural dampness. Asthma is heightened due to condensation, moisture, humidity, and water intrusion, which all contribute to indoor moisture. Mold infestation is a major trigger for asthma. Aside asthma, other health concerns of mold are infections, allergenic or immunological illness, and nonallergic illness. Asthma is also triggered by the sensitization of dust mites accruing humid, wet regions of a structure. Another health effect associated with structural dampness is the presence of bacteria in an indoor environment. Bacteria requires water to grow and multiply. Bacteria is a source for the transmission of diseases, therefore putting occupants’ health at risk by water intrusion into the indoor environment. Water removal and drying of wet building materials within 2 days will likely prevent mold and bacteria growth, therefore reducing occupants’ vulnerability to disease.A 2009 World Health Organisation report entitled "Children Living in Homes With Problems of Damp" stated that:
"Excess moisture leads – on almost all indoor materials – to growth of microbes such as moulds, fungi and bacteria, which subsequently emit spores, cells, fragments and volatile organic compounds into the indoor air. Moreover, dampness initiates chemical and/or biological degradation of materials, which also causes pollution of the indoor air. Exposure to microbial contaminants is clinically associated with respiratory symptoms, allergies, asthma and immunological reactions. Dampness has therefore been suggested to be a strong and consistent indicator of risk for asthma and respiratory symptoms such as cough and wheeze."
Identification
A wide range of instruments and techniques can be used to investigate the causes of moisture in building materials. When used correctly, they can provide a valuable aid to investigation. The competence and experience of the person undertaking the damp investigations is of greater importance than the kit he or she carries.Processes for diagnosing rising Damp in buildings is set out in BRE Digest 245.
All of the above should be considered during any assessment for damp related defects in buildings.
Prevention and treatment
Most forms of dampness can be prevented by thoughtful building design and careful construction. In the UK, well built modern houses include damp proofingDamp proofing
Damp proofing in construction is a type of waterproofing applied to building foundation walls to prevent moisture from passing through the walls into interior spaces....
in the form of a synthetic damp-proof course (DPC), about 15 cm above ground level, to act as a barrier through which water cannot pass. Slate or "engineering bricks" with a low porosity were often used for the first few courses above ground level, and these can in theory help minimise the problem.
There are many approaches to the treatment of dampness in existing buildings. Key to the selection of an appropriate treatment is a correct diagnosis of the types of dampness affecting a building. Details of possible treatments for specific types of dampness are covered in the sections below.
The cause of the dampness must first be eliminated, by providing better drainage or fixing leaking pipes. BRE Digest 245 describes several methods of treating rising damp, including the use of land-drains and the insertion of physical and chemical DPCs. Then, any affected plaster or mortar must be removed, and the wall treated, before replacing the plaster and repainting.
The major damp treatment authorities within the U.K. are The British Wood Preserving and Damp-proofing Association (BWPDA) and The Property Care Association
Property Care Association
The Property Care Association is a trade association which represents specialists in the structural waterproofing, wood preservation, damp-proofing, flood remediation and structural maintenance industries in the UK....
.
Humidity
Humidity occurs in indoor environments due to building related causes. Porous walls, rising damp, and leaks in the building are determinants for structural dampness due to elevated humidity levels. The construction of the building can also lead to humidity and unwanted moisture in the indoor environment. Wet materials, such as lumber stored unprotected outdoors before construction, can lead to increased humidity indoors for up to the second year of occupancy in the building. Most commonly in residences, elevated relative humidity is produced by poor drainage systems. This leads to dampness in substructures such as crawlspaces and basements. The dampness results in vaporization where water vapor is transmitted into the building's interiors. Water vapor may enter the building through supply air ducts in building slabs and circulated by warm forced air. Water vapor can also enter a building through leaky return air ducts in homes with crawlspaces.Human occupancy adds a significant amount of humidity to the indoor environment. Personal activity as basic as breathing and perspiration add moisture to an indoor space. Cooking and showering raise humidity levels in the indoor environment, which directly affects the structural dampness of a home. Aspects of the home can also increase the humidity of a space. Items such as aquariums, indoor swimming pools, hot tubs, and even indoor plants add to the humidity of an indoor space. All of these attributes can increase the humidity of a home beyond its recommended thirty to fifty percent.
Humidity levels in an indoor environment need to be accounted for based upon season and temperature. If humidity levels do not agree with the time of the year and the temperature during seasons, mold infestation and deterioration of the building will occur due to moisture. An acceptable humidity level in indoor spaces ranges from twenty to sixty percent year round. However, levels less than twenty percent in the winter and levels higher than sixty percent in the summer are deemed unacceptable for indoor air quality. Structural dampness is likely to occur as well as an increase of health risks associated with moisture damage.
Prevention and Treatment
There are strategies to prevent water infiltration due to humidity into structures, as well as ways to treat human occupancy practices regarding humidity. Vapor retarders are materials that can be used to restrain uncontrolled airflow and water vapor into an indoor space. Vapor retarders are used to decrease the rate and amount of water vapor diffusion through ceilings, walls, and floors caused by humidity. It is made of thin, flexible materials and it’s coatings can be installed by trowels or brushes. Utilizing vapor retarders in a building prevents structural dampness from occurring or continuing if it already exists. A strategy for reducing humidity levels in an indoor environment is by altering occupant activity and indoor mechanics. Kitchens and bathrooms need to have their own vents. Additionally, washing machines need to be vented outdoors. Both of these are important in order to decrease indoor moisture due to humidity caused by the activities occurring in these indoor spaces. Moisture sources, such as hot tubs or indoor swimming pools, should be covered by airtight lids when not in use, thus humidity levels stay low in the indoor environment.Condensation
Condensation comes from water vapour within the building. Common sources may include cooking, bathing etc. The moisture in the air condenses on cold surfaces. Buildings with poorly insulated walls are very prone to this problem. It often causes damage similar to damp in a building and often appears in similar places. This is because it occurs in the "dead air" pockets that accumulate in both horizontal and vertical corners (i.e. out of circulating air patterns).Moisture condenses on the interiors of buildings due to specific interactions between the roof and wall. Leaks most commonly occur on flat-roofed buildings. Certain building materials and mechanisms can be used to prevent condensation from occurring in these areas, therefore reducing structural dampness and potential mold infestation. In many cases, the insulation between the roof and wall is compressed, leading to a decrease in thermal resistance. Due to the lack of thermal resistance, condensation occurs, which leads to water damage in the indoor environment. In most cases where moisture is not addressed quickly enough, mold and mildew develop. Another issue is that wind washing up into the crevice where the roof and wall intersect reduces the efficiency of the insulation. This results in condensation and risk for mold growth.
In the United Kingdom, condensation problems are particularly common between October and March - to the extent that this period is often referred to as the "condensation season."
Identification of condensation
If it is suspected that the problem is condensation, then a room should be sealed off with a dehumidifierDehumidifier
A dehumidifier is typically a household appliance that reduces the level of humidity in the air, usually for health reasons. Humid air can cause mold and mildew to grow inside homes, which pose various health risks. Very humid climates or air make some people extremely uncomfortable, causing...
left running for the recommended time and then further instrument tests made. If the dampness has disappeared, then condensation is very likely the problem.
Alternatively Humiditect cards or dataloggers (measuring air humidity, air temperature, and surface temperature) can be used as tools for diagnosing a condensation problem.
Treatment
Typical remedies for condensation include increasing background heat and ventilation, improving the insulation of cold surfaces and reducing moisture generation (e.g. by avoiding the drying of clothes indoors).Rain Penetration
Rain Penetration (also known as "penetrating damp") is a common form of dampness in buildings. It can occur through walls, roofs, or through openings (e.g. window reveals).Water will often penetrate the outer envelope of a building and appear inside. Common defects include.
- Roof defects such as faulty flashingFlashingFlashing may refer to:*Exhibitionism, briefly exposing one's body in a usually sexual way, acceptable or not depending on context*Flashing , construction material used to prevent the passage of water around objects...
, cracked or missing slates or tiles. - Faults in the brickwork or masonry such as missing or cracked pointingPointingPointing may refer to:* Pointing, the hand gesture * Pointing, the external part of the mortar between bricks in walling * The position accuracy of the optical axis of a directional antenna...
. Porous bricks or stones. - Missing or defective mastic around windows and doors.
- Blocked weep holeWeep holeWeep holes or "weeper holes" are small openings left in the outer wall of masonry construction as an outlet for water inside a building to move outside the wall and evaporate. The term was coined by archaeologist C. Leonard Woolley after finding evidence of weep holes in ziggurats...
s. - Missing or defective trays in cavity walls.
Walls
Rain penetration is most often associated with single-skin walls, but can also occur through cavity walls - e.g. by tracking across wall ties.The most common sources of indoor moisture at the base of walls in buildings is from defective ground and surface drainage. This is due to rising ground levels and the failure of ground drainage systems. These defects are common nation-wide. Additionally, plumbing leaks and flooding from defective drainage and plumbing are also sources of moisture occurring on the base of walls in buildings.
Rising damp
Rising damp is the common term for the slow upward movement of water in the lower sections of walls and other ground-supported structures by capillary actionCapillary action
Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...
. Although rising damp of up to 5 metres in height has been observed the height of rise is typically much lower and is rarely above 1.5m. Rising damp has been a widely observed phenomenon for at least two hundred years. Rising damp is deemed controversial because it is often misdiagnosed in buildings. Many misdiagnose a wall stain as rising damp instance due to misinterpreting the visual evidence of the wall and the readings of moisture meters. There is also strong evidence to suggest that it was a problem understood by the Romans and Ancient Greeks.
In simple terms rising damp occurs when ground water travels upwards through porous building materials such as brick, sandstone, or mortar, much in the same way that oil travels upwards through the wick of a lamp. The effect can easily be seen by simply placing a piece of porous brick, stone, or mortar in a shallow tray of water and observing how the water is absorbed into the porous material and is transported above the water line.
Rising damp can be identified by a characteristic "tide mark" on the lower section of affected walls. This tide mark is caused by soluble salts (particularly nitrates and chlorides) contained in the groundwater. Due to the effects of evaporation these salts accumulate at the "peak" of the rising damp.
Historical Evidence of Rising Damp
The issue of rising damp has been a concern since ancient times. The Roman Architect VitruviusVitruvius
Marcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....
referred to the problem of dampness rising up walls and advised on how to construct buildings to avoid the problem.
Rising damp is widely referred to in Victorian literature and the Public Heath Act of 1875 introduced the requirement for a damp-proof course in walls to prevent rising damp. An entry in the British medical Journal from 1872 describes the phenomenon of rising damp as follows:
"Even if the rising damp be arrested by what is technically called an impervious damp-proof course, it will be frequently found that this is built in the wall too near the ground line, so that the heavy rain besplatters the ground and splashes above it. As time rolls on the surface of the ground also becomes elevated, and this damp course is soon lost to sight. Attempts have been made to remedy this evil of porous bricks by the substitution of the hard blue bricks of Staffordshire; and then it may often be noticed that the wet has only struck, sailor-like, across the mortar-joints and chequered the inside walls like a tartan plaid."
The architect and social reformer, Thomas Worthington
Thomas Worthington
Thomas Worthington was a Democratic-Republican politician from Ohio. He served as the sixth Governor of Ohio.Born in Charles Town, Virginia , Worthington moved to Ross County, Ohio in 1796. The home he eventually built just outside of Chillicothe was called Adena and happens to be the namesake of...
, described rising damp in his 1892 essay, "The Dwellings of the Poor: And Weekly Wage-Earners in and Around Towns":
"It should be borne in mind that damp walls absorb much more heat than dry ones and that they are frequent agents in causing rheumatism, kidney disease and colds. Rising damp from the ground may be prevented by most simple means. Six inches of good Portland cement concrete should cover the whole site of the dwelling, and concrete never less than nine inches thick should underlie all walls. A damp course should disconnect the whole of the foundations from the superstructure. This preventative may consist of a double layer of thick slates bedded in cement, or of patent perforated stone-ware blocks or of three-quarters of an inch of best asphalt."
The Building Research establishment (BRE) in its review concludes that Rising Damp is a real problem. Indeed, Part C of the Building Regulations for England and Wales specifically calls for the inclusion of a damp-proof course in all new properties.
The Case and Evidence Against Rising Damp
A number of people have expressed the view that rising damp is a myth. A former chairman of the construction arm of the Royal Institution of Chartered Surveyors (RICS), Stephen Boniface, has said that ‘true rising damp’ is a myth and chemically injected damp-proof courses (DPC) are ‘a complete waste of money’.Konrad Fisher's article "The Fraud of Rising Damp" points out that the historic city hall in Bamberg stands in the river Regnitz and its bridge remains dry without any chemical, mechanical or electronic damp-proof course.
However, evidence suggests that not all walls are capable of supporting rising damp, so merely observing that rising damp does not occur in a particular wall does not disprove its existence in other walls.
In 1997 staff at Lewisham Council in South London were so convinced that rising damp is extremely rare or possibly a myth that they are offered a reward of £50 to anyone who could prove them wrong.
Water intrusion into the indoor environment can be attributed from causes other than rising damp. Moisture penetration has been an ongoing problem for residences as evaporation occurs at the edge of the damp area, resulting in “tide marks” due to salt deposition. The “tide mark” is commonly distinguished as a feature of rising damp. However, even after the water intrusion has been treated, these salt accumulations still persist. This suggests that rising damp is not necessarily the cause for the water penetration.
How Rising Damp Occurs
According to Jurin's LawJurin's Law
Jurin's Law describes the rise and fall of a liquid within a thin capillary tube. Named after its discoverer James Jurin....
the maximum height of rise is inversely proportional to the capillary radius. Taking a typical pore radius for building materials of 1 µm, Jurin's Law would give a maximum rise of about 15 m, however, due to the effects of evaporation, in practice the rise would be considerably lower.
A "physical model" of rising damp was developed by Christopher Hall and William D Hoff in their paper "Rising damp: capillary rise dynamics in walls". The analysis is based on experimentally well established properties of porous building materials and the physics of evaporation from building surfaces. They state that model can be used to predict the height to which damp will rise in a wall, based on factors such as wall thickness, the sorptivity of the wall structure and the effect of evaporation. Further work has confirmed experimentally the importance of mortar properties in determining the height to which damp will rise in walls. BRE Digest 245 lists several factors that can influence the height of the rise including rate of evaporation from the wall, pore sizes of the masonry, salt content of the materials and the soil, groundwater and degree of saturation, and use of heating within the property. The effect of seasonal variations in evaporation rate on the height of moisture rise have been comprehensively described.
A review of data and publications commissioned by the Property Care Association and carried out by the University of Portsmouth concluded that "Rising damp is an age-old and ubiquitous problem." It also noted that "Records on observation and descriptions on this phenomenon date back to early
times. It was identified as a public health issue in the second half of the 19th Century." The review looked at data and studies on rising damp from a number of countries including the United Kingdom, Portugal, Germany, Denmark, the Netherlands, Greece, Australia, and Malaysia.
Diagnosis of Rising Damp
The first step in assessing damp is to check for standing water. Removing water with good drainage will remove any form of dampness. Once done, and dampness remains, the next step is to look for the presence of a damp-proof course. If a damp-proof course is present, it is likely to be functioning, as the materials from which damp proof courses are manufactured tend to have a long lifespan. However, it should be acknowledged that there are cases where existing damp proof courses fail for one reason or another.One method that is often used to determine if the source of dampness is rising damp (rather than other forms of dampness) is to look for the presence of salts - in particular a tell tale "salt band" or "tide mark" at the peak of the damp's rise. Although this is a useful indicator, it is not completely reliable as salts can enter the fabric of the wall in other ways - e.g. unwashed sea sand or gravel used in the construction of the wall.
If there is no damp-proof course and rising damp is suspected (tide mark, moisture confined to lower section of wall etc...) then a number of diagnostic techniques can be used to determine the source of dampness. BRE Digest 245 states that the most satisfactory approach is to obtain samples of mortar in the affected wall using a drill and then analysing these samples do determine their moisture and salt content. The fact that this technique is destructive to the wall finish often makes it unacceptable to homeowners. It is for this reason that electrical moisture meters are often used when surveying for rising damp. These instruments are unable to accurately measure the moisture content of masonry (they were developed for use on timber), however the patterns of readings that they provide can provide a useful indication of the source of dampness.
Treatment of Rising Damp
In many cases, damp is caused by "bridging" of a damp-proof course that is otherwise working effectively. For example a flower bed next to an affected wall might result in soil being piled up against the wall above the level of the DPC. In this example, moisture from the ground would be able to ingress through the wall from the soil. Such a damp problem could be rectified by simply lowering the flower bed to below DPC level.Where a rising damp problem is caused by a lack of a damp-proof course (common in buildings over approximately 100 years old) or by a failed damp-proof course (comparatively rare) there are a wide range of possible solutions available. These include:
- Replacement physical damp proof course
- Injection of a liquid or cream chemical damp proof course (DPC Injection)
- Porous tubes
- Electrical-osmotic systems
- Land drainage
BRE Digest 245 suggests that with the exception of replacement physical DPCs, only methods of treatment with third party accreditation (E.g. British Board of Agreement Certificate) should be considered. It then goes on to state that the only method of currently satisfying this requirement is DPC injection and that "this is the only method which BRE considers suitable where insertion of a physical DPC is not possible." The Royal Institute of Chartered Surveryors (RICS) publication "Remedying Damp" is more cautious about reliance on third party accredititation, casting doubt upon the validity of the test methods employed, arguing that trials are usually conducted using "specially built masonry panels - which do not match up in many respects to walls found in real properties," and that "if a DPC were proved to not work in a specially built masonry panel, this would be the more significant result." The MOAT No 39 test employed by the British Board of Agreement (BBA) in the UK is dismissed as "quite a clever test idea but in the author's opinion not actually replicating a real wall." Furthermore, the point is made that "BBA testing is paid for by manufacturers, and the results are not thought to be publicly available."
Replastering
Replastering will often be carried out as part of a rising damp treatment. Where plaster has become severely damaged by ground salts there is little argument about the need to replaster. However there is considerable debate about:- The extent of replastering required
- The use of hard sand:cement renders to replaster as part of a rising damp treatment
BS6576:2005 states that "the function of the new plaster is to prevent hygroscopic salts that might be present in the wall from migrating through to its surface, while still allowing the wall to dry." However, writing in the RICS publication "Remedying Damp", Ralph Burkinshaw claims that, "the plaster is really there for two main reasons." He accepts the need for replastering when significant amounts of ground salts have built up in the existing plaster, however he then goes on to say that replastering is often carried out to make up for an unreliable chemical DPC. He also suggests that damp-proofers have an incentive to carry out more replastering than is strictly necessary as it allows them to finish the job without having to wait for walls to dry out, resulting in faster payment.
Although the sand:cement renders typically installed as part of a rising damp treatment are very effective at holding back damp and ground salts, they have a number of disadvantages. These include an incompatibility with the soft bricks and mortars encountered in older buildings and a lack of insulation properties compared with more traditional plasters, resulting in an increased risk of condensation. Replastering is also one of the most expensive parts of a rising damp treatment.
Porous renders to German WTA specification 2-2-91 can be used as an alternative to dense sand-cement renders. These have a minimum porosity of 40% of total volume. Salts crystallise in these pores rather than on the plaster surface, avoiding decorative spoiling. Such plasters offer a better solution than dense sand-cement renders when used on moderately salt-contaminated walls as their porous nature gives them insulation properties, resulting in a warmer surface temperature and making condensation problems less likely to occur. However, when used on heavily salt contaminated walls they may need to be replaced frequently as they lose effectiveness once all the pores have become filled with crystallised salt.
External links
- Coleman, Graham. Articles about dampness in buildings
- Howell, Jeff. The rising damp myth
- Property Care Association. UK trade association for damp-proofing professionals
- Waite, Richard (2009-06-26). Rising damp is a myth, says [Stephen Boniface, former Royal Institution of Chartered Surveyors
chief]] - World Health Organisation Damp and mould: health risks, prevention and remedial actions
- Newton Membranes. Useful Tips for Damp Problems