Checking For Damp Within A Building
IntroductionThis article highlights basic understanding of moisture and provides techniques to look for damp and how to use a digital moisture meter to diagnose moisture levels. Due to the comprehensive nature of the subject, we have segmented down the original article into bight size subjects.
- What Is Damp?
- Difference in damp of materials
- How To Pinpoint Moisture within a Structure
- Measuring Moisture
- How To Check For Condensation
1. What Is Damp?
Damp is caused by water getting into the property (structural) and moisture building up within the property causing condensation (lifestyle).
Damp is caused by water getting into the property (structural) and moisture building up within the property causing condensation (lifestyle).
a. Damp ingress into a property (Structural)
Damp occurs when water penetrates into the fabric of a building. Common causes are:
Damp occurs when water penetrates into the fabric of a building. Common causes are:
- Rainwater seeping through the roof where a tile or slate is missing, spilling from a blocked gutter or penetrating around window frames.
- Rising damp due to a defective damp-course or because there is no damp-course.
- Leaking pipes, wastes or overflows. Often you can see damp as “tide marks” on walls and ceilings.
b. Condensation (Lifestyle)
Lifestyle moisture issues are caused by normal daily activities (taking showers and baths, washing and drying clothes, cooking and boiling kettles), all produce warm air containing large amounts of water vapour.
If the warm air can’t escape through an open window or air vent, it moves around until it finds a cold surface where it cools and forms condensation.
Condensation occurs on any cold surface which records a below dew point temperature (temperature at which saturated air releases surplus moisture vapour). This can be seen on a mirror in a bathroom or a window in a kitchen when cooking.
Lifestyle moisture issues are caused by normal daily activities (taking showers and baths, washing and drying clothes, cooking and boiling kettles), all produce warm air containing large amounts of water vapour.
If the warm air can’t escape through an open window or air vent, it moves around until it finds a cold surface where it cools and forms condensation.
Condensation occurs on any cold surface which records a below dew point temperature (temperature at which saturated air releases surplus moisture vapour). This can be seen on a mirror in a bathroom or a window in a kitchen when cooking.
2. Difference in damp of materials
Building materials will absorb different levels of moisture content, some materials, like wood, can absorb more water than brick.
Commonly timber will absorb more water molecules than a brick wall. Wood is like a sponge, absorbing moisture directly from the buildings structure and retain higher levels of moisture before directly being affected by the damp process.
The follow table provides examples showing the percentage moisture and the readings interpretation.
As shown, wood can be classed as dry at 12%, but brick would be saturated at the same reading.
Example
A timber skirting which records a moisture reading of 12% (air dry), the plaster could be around 0.5% and the brick about 1%. In severe conditions you may see higher readings of skirting 22%, plaster 1% - 3% and brick around 2% - 5%.
Readings are taken on a reference scale as it is only a relative degree of dampness. Wood moisture scale (wood moisture equivalent ‘WME’) is the most common and is recognised by professional bodies. Wood is the first material to degrade due to damp.
Building materials will absorb different levels of moisture content, some materials, like wood, can absorb more water than brick.
Commonly timber will absorb more water molecules than a brick wall. Wood is like a sponge, absorbing moisture directly from the buildings structure and retain higher levels of moisture before directly being affected by the damp process.
The follow table provides examples showing the percentage moisture and the readings interpretation.
| Material | Moisture content % | Interpretation |
| Wood | Extremely dry | |
| Mortar | 4 | Dry |
| Brick | 4 | Damp |
| Plaster | 4 | Very wet |
| Wood | 12 | Air dry |
| Brick | 12 | Saturated |
| Plaster | 12 | Not possible |
As shown, wood can be classed as dry at 12%, but brick would be saturated at the same reading.
Example
A timber skirting which records a moisture reading of 12% (air dry), the plaster could be around 0.5% and the brick about 1%. In severe conditions you may see higher readings of skirting 22%, plaster 1% - 3% and brick around 2% - 5%.
Readings are taken on a reference scale as it is only a relative degree of dampness. Wood moisture scale (wood moisture equivalent ‘WME’) is the most common and is recognised by professional bodies. Wood is the first material to degrade due to damp.
