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Damp (structural)

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For other uses, see Damp (disambiguation).
Detail showing some of the causes of damp penetration

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,[1] 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. Plaster and paint deteriorate and wallpaper loosens. Stains, from the water, salts and from mold, mar surfaces. Externally, mortar may crumble and salt stains may appear on the walls. Steel & iron fasteners rust. It may also cause respiratory illness in occupants. In extreme cases, mortar or plaster may fall away from the affected wall.

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[2]. 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 254.

All of the above should be considered during any assessment for damp related defects in buildings.

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 (ie out of circulating air patterns).

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."[3]

Identification of condensation

If it is suspected that the problem is condensation, then a room should be sealed off with a dehumidifer 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. [4]

Treatment

Typical remedies for condensation include increasing background heat and ventilation[5], 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).[6]

Water will often penetrate the outer envelope of a building and appear inside. Common defects include.

  • Roof defects such as faulty flashing, cracked or missing slates or tiles.
  • Faults in the brickwork or masonry such as missing or cracked pointing. Porous bricks or stones.
  • Missing or defective mastic around windows and doors.
  • Blocked weep holes.
  • 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.[7]

Rising dampness

Rising damp describes the action of ground moisture rising up a masonry wall by capillary action. It is usually identified by a charateristic "tide mark" on the lower section of affected walls.[8] 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.[9]

According to Jurin's Law the maximum height of rise is inversely proportional to the capillary radius.[10] 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.[10]

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".[11] This 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 or 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.[12]

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 called ‘true rising damp’ is a myth and chemically injected damp-proof courses (DPC) are ‘a complete waste of money’. [13]. 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.[14] In fact, evidence would suggest that not all walls are capable of supporting rising damp, so this finding is not particularly surprising.[11].[12]

These views are not reflected by the views of UK official bodies such as the Building Research establishment (BRE).[15] [16] 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.[17]

Rising Dampness References by Victorians

The issue of rising damp has been a concern since Victorian times. An entry in the British medical Journal from 1872 describes the phenomonen 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."[18]

The architect, 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 bourne 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."[19]

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 a synthetic damp-proof course (DPC), about 15cm 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.

The cause of the dampness must first be eliminated, by providing better drainage or fixing leaking pipes. BRE Digest 245[20] describes several methods of treating rising damp, including the use of land-drains and the insertion of physical and chemical damp-proof courses. 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.

References

  1. ^ Trotman, Peter. Understanding Dampness. Vol. BR466. Building Research Establishment. ISBN 1 86081 686 x. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ "Use of electrical moisture meters".
  3. ^ The Condensation Season - October until March, Peter MacDonald - Condensation Explained.
  4. ^ How can I check for condensation?, Peter MacDonald - Condensation Explained.
  5. ^ Burkinshaw, Ralf. Remedying Damp. RICS Books. p. 151. ISBN 978-1-84219-305-1.
  6. ^ Trotman, Peter. Understanding Dampness. Vol. BR466. Building Research Establishment. ISBN 1 86081 686 x. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  7. ^ Trotman, Peter. Understanding Dampness. Vol. BR466. Building Research Establishment. ISBN 1 86081 686 x. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ Trotman, Peter. Understanding Dampness. Vol. BR466. Building Research Establishment. ISBN 1 86081 686 x. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  9. ^ Oliver, Alan. Dampness in Buildings. BSP Professional Books. ISBN 0-632-01932-8.
  10. ^ a b Alfano, G (2006). "Long-term performance of chemical damp-proof courses: Twelve years of laboratory testing". Building and Environment. 41: 1060–1069. doi:10.1016/j.buildenv.2005.04.017. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ a b "Proceedings of the Royal Society - Rising damp: capillary rise dynamics in walls - Christopher Hall and William D Hoff".
  12. ^ a b "Construction and Building Materials - Rising Damp in Masonry Walls and the Importance of Mortar Properties - Eric Rirsch and Zhongyi Zhang".
  13. ^ "Rising damp is a myth, says former RICS chief".
  14. ^ "The Fraud of Rising Damp".
  15. ^ Trotman, Peter. Rising damp in walls, diagnosis and treatment. Vol. BRE Digest 245. Building Research Establishment. ISBN 978-1-84806-012-8.
  16. ^ Trotman, Peter. Understanding Dampness. Vol. BR466. Building Research Establishment. ISBN 1 86081 686 x. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  17. ^ "Building Regulations - Part C".
  18. ^ "Damp Houses," British Medical Journal, May 25th 1872, p558
  19. ^ The Dwellings of the Poor: And Weekly Wage-Earners in and Around Towns - Thomas Locke Worthington - ISBN 978-0559706295, p105
  20. ^ Trotman, Peter. Rising damp in walls, diagnosis and treatment. Vol. BRE Digest 245. Building Research Establishment. ISBN 978-1-84806-012-8.
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