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Last edited 18 Jul 2020
Rising damp in walls - diagnosis and treatment (DG 245)
- The rate of evaporation from the wall.
- The porosity of the wall.
- The salt content of the wall and soil.
- The groundwater height and saturation.
- Heating in the building.
Some accumulation of salts can occur in the walls of old buildings even when they do not have a damp problem, so high readings from a moisture meter alone are not conclusive. Appendix A of the 12-page digest describes how to drill samples from a wall in to test for moisture content and hygroscopicity, and the interpretation of moisture gradient profiles.
If a building has a physical damp-proof course (DPC), it is unlikely that it has failed, as most dpc materials have a long life, however, defects such as mortar droppings in a cavity wall, may make a dpc ineffective by bridging it and allowing moisture to pass up through the wall. This and other mechanisms by which an existing dpc might be bridged are discussed.
The content of the digest includes:
- Mechanism of rising damp.
- Determining the source of the dampness.
- Dry lining.
- Further reading.
- Appendix: The sampling method.
 Related articles on Designing Buildings Wiki
- Assessing moisture in porous building materials.
- BRE articles on Designing Buildings Wiki.
- Building Research Establishment.
- Damp-proof course.
- Damp proof membrane.
- Defects in brickwork.
- Dew point.
- Diagnosing the causes of dampness (GR 5 revised).
- Interstitial condensation.
- Mould growth.
- Penetrating damp.
- Psychometric chart.
- Rising damp.
- Sling psychrometer.
- Treating brickwork with sealant or water repellent.
- Understanding dampness.
 External references
- BRE Digest 245, Rising damp in walls - diagnosis and treatment.
- Good Repair Guide 33 - GRG33.
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