Rising damp

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Rising damp is a term used in construction and stands for the external observation of water absorption in capillary conductive building materials in walls or floors, which is drawn upwards from the ground.

Causes of rising damp;

  • The lack of a capillary-breaking layer in the wall, under the wall or the ground. Correctly selected crushed stone or waterproof concrete have a capillary-breaking effect . Both have been common materials for the foundation of a house for a long time . The transition between grout and brick in brick walls also has a strong capillary-breaking effect in most cases, which is why rising damp in brick walls usually does not rise more than 20 cm. The prerequisite here is that the foundation is not capillary-breaking. If this is the case, a lack of rain protection or condensation is the likely cause of the moisture damage.
  • The lack of a horizontal barrier under the floor or in the walls.

Rising damp is very often confused (especially by drainage companies) with damp damage to building materials due to other causes. These causes include

  • Condensation caused by the condensation of warm, humid air on cool walls (often in the basement)
  • Very moist soil and even pressing groundwater on cellar walls
  • Uninsulated cold water pipes in or on the masonry, on which condensation water is deposited, which is drawn into the wall
  • Moisture penetration of the masonry from the outside due to poor general rain protection of the house walls (roof overhang too small, insufficient protection against driving rain, clogged rain gutters or rain pipes, unsuitable shape of the window sills, etc.)
  • An excessive load of the masonry with salts, which have a strongly hygroscopic (water-absorbing) effect ( e.g. calcium nitrate , see also saltpeter boiler ). Exclusively a problem with old buildings that have been used as stalls or drinking troughs for pets over time.

diagnosis

Correct treatment of rising damp generally requires a detailed diagnosis, after which the other causes of damp mentioned above must be safely excluded. In fact, rising damp is rarely the cause of moisture damage to the building fabric.

A decade-old brick quay wall at the port of Hamburg - without moisture damage

The measurement of the water content of a building substance damaged by moisture using the determination of the electrical conductivity using a so-called protimeter is controversial among experts. For the conductivity of a material, in addition to the water content, the content of charged and mobile particles (such as the ions in a salt solution) is also very important. However, the water content and ion concentration are not in a fixed relationship to one another, especially in the case of the materials of a wall construction. The protimeter is mainly used in the wood industry to determine the moisture content of wood, since the ratio of water content and ion concentration depends only on the type of wood and so the conductivity allows a correct conclusion about the moisture content. This is not the case with masonry.

remedy

Depending on the real cause of the moisture damage, different remedial measures are required to remedy the moisture damage. The method of choice for a correctly diagnosed problem of rising damp is to install a horizontal barrier . However, this does not bring about any improvement on a wall that is damp in the interior if the real problem is the precipitation of condensation water from warm, moist air on the cold wall. In this case, the room air near the wall must be prevented from falling below the dew point. This can be done very easily by using a plinth heater, which creates a weak warm air curtain on the wall. This always keeps the temperature of the air on the wall above the dew point. A heating cable or a heating pipe carrying hot water in the base area of ​​the damaged wall or a heating strip is sufficient for plinth heating . The energy consumption of a heating cable or heating pipe on the base is often lower than the energy loss due to regular ventilation, which lowers the humidity so that the dew point is no longer undershot. A cooling down of the wall can also be prevented by external insulation, but this measure is much more expensive than adequate ventilation or the laying of a heating cable or a heating pipe in the base area of ​​a wall.

Individual evidence

  1. ↑ Causes of damage in old buildings: rising damp, hygroscopic damp or condensation ?, H. Künzel, communication no. 337 of the Fraunhofer Institute for Building Physics, (1998), [1]
  2. ↑ Causes of damage to old buildings: rising damp, hygroscopic damp or condensation ?, H. Künzel, communication no. 337 of the Fraunhofer Institute for Building Physics, (1998), [2]
  3. ↑ The rising damp myth, Jeff Howell, Nosecone Publications (2008)
  4. ^ Diagnosing Damp, Ralph Burkinshaw, Mike Parrett, page 13, RICS Books (2002) [3]
  5. ^ Diagnosing Damp, Ralph Burkinshaw, Mike Parrett, page 13, RICS Books (2002) [4]
  6. ↑ Procedure for the renovation of a damp cellar with the help of a base heating, case study at www.haus-klinik.de [5]
  7. ↑ Local heating of thermal weak points, Dr. Martin Krus, Fraunhofer Institute for Building Physics, Building Physics 34 (2012), Issue 5, pp. 217–222, [6]
  8. ↑ Tips on preventing moisture and mold in houses, www.energie-lexikon.info [7]