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This piece is based on an original blog by John Houston, Principal Scientist in BRE’s Building Technology & Fire Group

Excess water /moisture in all its forms (vapour, liquid, and flooding)  is still the most common problem in housing. It results in visible wetting of walls, ceilings and floors, blistering paint, bulging plaster, sulfate attack on brickwork and mould on surfaces and fabrics, usually accompanied by a musty smell. It can also lead to less obvious problems, e.g. thermal insulation is reduced in effectiveness or brickwork cracks because metal components embedded to corrode.

Successful treatment can only be achieved if the type of dampness is correctly diagnosed.  The complexity of existing homes and buildings means that dampness is very often misdiagnosed, leading to future damp problems, cost and disruption to the occupants.

What are the different types of damp?

  • Condensation – water vapour is produced as a result of the normal building usage and will move freely around the building and may condense on surfaces or within the fabric of the building.
  • Rising – Rising ground moisture is normally associated with missing or ineffective damp-proof courses or damp-proof membranes . It can also result from bridging of these defences by earth or ground works externally, or by thermal bridging through the structure.
  • Penetrating – water penetration is associated with walls and roofs and is indicative of either component failure (e.g. a missing roof tile, slate, damaged render or cladding) or the construction not being robust enough for the particular exposure of the building.
  • Falling – Falling covers those items  relating to  roof and abutment features.

What are the tools for identifying different types of damp?

When identifying damp and its causes architects, surveyors and project managers need to consider the current condition and the expected post-construction condition of the building.  There are four established methods for diagnosing damp.

  • Observation – manual viewing is the least costly, but potentially least reliable method of diagnosis.
  • Moisture meters – moisture meters can be used to confirm the observed diagnosis.  In skilled hands with regular site calibration moisture meters can be a good starting point, however depending on the complexity of the building, the materials used, its present condition and maintenance history, moisture meters can lead to misdiagnosis.
  • Laboratory techniques drilled samples and moisture contents can be subjected to techniques such as a carbide meter, oven drying and soluble salt analysis. However, these are always helpful but, like an MOT on a car, are only valid on the day they are taken.
  • Temperature and humidity measurement – Recording the relative humidity and temperatures in a series of rooms and outside using half hourly sampling is the most effective way of diagnosing damp.   The ‘data’ from the surveys  would help to inform the project manager on the time scale, for not only the current condition of the building, but how long it could take to dry down.  This should inform the project on the  materials and strategies that the design team should be consider prior to the beginning on site.

BRE has a number of experts that can help with the diagnosis of damp.  The expert pack Condensation and dampness: A collection of BRE expert guidance on assessing and treating dampness in buildings brings together the complete body of knowledge from 24 publications to provide comprehensive insight into assessing and treating dampness in buildings for architects and project managers on housing refurbishment projects.

BRE is also a partner in the newly launched UK Centre for Moisture in Buildings (UKCMB).  The UKCMB is an independent, not for profit, public good organisation run by University College London, the Building Research Establishment (BRE), Heriot Watt University and the London School of Hygiene and Tropical Medicine. The UKCMB works in a rigorous and transparent manner together with partners from academia, government, industry and the public to substantially improve the way moisture risk is understood and managed in the UK.

Sheila Swan
About the Author
Welcome to my blogs. Sometimes a bit quirky, my aim is to create interesting blogs about construction by connecting strands of related content. I am an editor at IHS BRE Press - BRE's publishing partner.
  1. John Plater Reply

    Four “types of damp” are listed, but isn’t ‘Falling’ damp covered by ‘Penetrating’ damp?

    Is temperature and relative humidity measurement really the most effective way of diagnosing damp? Perhaps what is meant is that it is the most effective way of determining the levels of dampness in a building, or the rate of drying out of a damp building.

    • Ana Paun
      Ana Paun Reply

      Thank you for your comment. The article you have referred to is a short form taster article aimed at the informed home owner who has a problem and is seeking high quality information and a pointer of where to go next. The article does make some broad statements to get the point over. The detail information can be found in the BRE publication Understanding Dampness (BR 466).

      The term ‘falling’ damp has been used for at least 30 years. It refers to water that permeates downwards from a parapet, balcony or roof through the wall head in a similar way to rising damp coming up from the base of a wall. ‘Falling’ damp could be covered by ‘penetrating’ damp in the same way that ‘rising’ damp could also be covered by ‘penetrating’ damp.

      Regarding temperature & relative humidity measurements, you are correct; but by themselves they are not the most effective way of diagnosing the causes of dampness. Data logging temperature(s) and humidity(s) will take several weeks and is best done during the winter period. This data logging and interpretation costs significantly more than a moisture survey. If you need more information, I am happy to put you in touch with one of our scientists who can help you further.

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