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The case of "Rising damp causing condensation (!)"

Background:
Ground floor flat was reported damp by its tenant. Her expert said the damp causing condensation was evaporating from the floor/wall junctions. He was also adamant that rising damp was still active in the walls following damp proofing works and this was also causing the dampness in the atmosphere.

 

mould
condens

The investigation:
In the Lounge the external rear wall (solid construction) was distinctly damp - wallpaper was clearly peeling off the wall and droplets of water forming on the underlying painted surface: a distinct localised 'tide mark' was visible along the exposed plasterwork of the external facing rear wall at around 1000 - 1100mm. The tide mark extended down onto the right flank wall.

 

Very little mould was noted in the Lounge but considerable growth had occurred in other rooms, especially in corners and other areas of stagnant air conditions.


Internal conditions were 24ºC and 71% relative humidity at the time of the inspection (internal vapour pressure = 2.1kPa, external vapour pressure = 1.1kPa)

 

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mmreads

Below 1100mm the surface temperature of the rear wall was below the dew point temperature; therefore condensation was actively forming at the time of the inspection.

 

High surface moisture meter readings were recorded from the rear wall. But on the front wall (internal) the wallpaper appeared sound yet recorded high surface meter readings. However, significantly lower readings were obtained beneath the paper.



 

 

 

 

 

 

 


 

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mstab

Moisture analyses showed the underlying wall to be basically 'dry', i.e., virtually no free (capillary) water, and therefore rising damp was not active.


A slight 'salt band' was noted at 1200 mm which indicated that rising damp had, in the past, risen to this height: it was now no longer active.

 

 

 

 

 

 

 

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cement Render analysis showed the material to be a good 1 : 3 cement to sand as specified, and highly water resistant.

 

 

 

 

 

 

 

 

 

There was no ventilation in the property and windows were double glazed Please note: other areas in the property were also examined by methods outlined above.

 

Conclusion:
Rising damp was not active, and the walls examined were 'dry'; the injected damp-proof course and associated rendering were very effective in performing their required function.


The dampness and decorative spoiling were solely due to severe localised condensation on the lower part of the cold external walls in the Lounge - this also gave rise to the 'tide mark' that was visually mistaken for rising dampness. The very high water vapour level in the property was solely the result of internal moisture production through daily activities coupled with almost absence of suitable ventilation.


Dampness in the floor/wall junction was due to condensate trickling down the wall - this was also clearly visible.


The front wall was also shown to be 'dry', the high surface moisture meter readings being the result of the wallpaper (wood based) absorbing moisture from the high moisture content of the air.


Dampness was therefore due to internal water production through daily activities which was condensing on the colder external walls; it was not due to rising dampness as the tenants expert had claimed.


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