Dampness in Buildings

Technical Article

The following offers a more technical analysis of dampness within buildings:

A damp substrate is one which contains a level of moisture above that expected under normal environmental conditions, which is about 50% relative humidity'.

There is no such thing as a dry building; indeed you don't want a dry building; materials are meant to be damp to a certain extent. However, it is a rise in this percentage of dampness which is what we generally term as damp', for example:


Typical Moisture Levels that we would consider 'dry'

Rise in percentage for the materials to be considered 'damp'



20% plus

Bricks / Mortar


5% plus

Gypsum Plaster


10% plus



70% plus

Density of Material

The density of the material also dictates its dampness, for example bricks are denser than gypsum plaster and therefore can retain more dampness.

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How is Moisture Measured

Conductivity Meter

A conductivity meter, which most surveyors have, often known by its trade name of Protimeter, has two prongs designed for timber readings, so using it in a timber skirting (unless there is salt present) will give an accurate reading. If the conductivity meter is used on anything else but timber it will not give an accurate reading on that material, but based upon timber.

Electromagnetic Solar Pulse Meter

To us as surveyors this means the back of the modern Protimeter. This is good for establishing a pattern, as it could be argued the conductivity meter is, when it is used on anything else but timber.

Types of Meter Reading


This can be obtained from a conductivity meter or electromagnetic pulse meter as discussed.


This requires oven drying test or a carbon meter or lab work of some sort for the most accurate meter reading. We would add that a surveyor with a client very keen to understand the condition of his property or a mortgage company requiring advice for a mortgage the time is usually not available and the surveyor will need to make a judgement based upon qualitative type of conductivity meter or the electromagnetic pulse meter.

Different Types of Dampness

Rising damp

Penetrating damp (also known as lateral damp)


Hydroscopic (where contaminated by salts, i.e. plasters)

We would refer you to our article that looks at these sections called Dampness in Buildings - Basics'.

Dampness is Often Condensation

We would advise that condensation is without doubt the most common form of dampness and you should carry out relative humidity meter tests first and look for obvious signs such as water ponding on the window sill! However, there are issues where it is not a clear cut case as to whether there is condensation or not, such as where mould is found within a room, although its location is usually an indicator. For example, mould at low level usually indicates condensation as mould is unlikely to grow if the plaster was contaminated with salts, which it would be for rising damp for example.

The final word on condensation and the key message to take away is that the most practicable solution is to increase ventilation.

Destructive Testing is the only way to be certain

We are advised that destructive testing into the plaster is the only way to be certain, as with condensation the plaster gets dryer as you get deeper into it whereas rising damp does not.

This article is taken from, amongst other things, a presentation carried out by Dr Peter Fitzsimons, for which we would like to thank him.

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