CASE STUDY No 2 PDF Print E-mail

‘Cavity wall insulation found to be transmitting moisture’
The client's building society had requsested a full timber and rising damp inspection. The property had severe visible damp problems and the client was not sure what was causing it.

Instructions: Inspect timbers within the property for possible insect attack and fungal decay and inspect ground floor walls for possible rising damp.

The property is a semi detached ex local authority residence built in the 1950s of rendered cavity brickwork under a slate roof. The property had been repossessed and showed considerable damage due to damp affecting the left flank wall. My client’s building society required the property to be inspected by a member of the Property Care Association which I am.


1 Timber inspection:

The property was empty and I located the presence of Common Furniture Beetle infestation in the roof void and throughout the first floor level. Several floorboards were raised at ground floor level and nothing serious was detected. However the client was put on notice about possible decay being present in joist ends built into damp flank wall (at first and ground floor levels) and the staircase which was also in contact with the damp flank wall.

2 Rising Damp Inspection:

I was able to locate the presence of an original physical bitumen felt damp proof course built into the ground floor load bearing walls. When I had floorboards raised I observed that the bitumen damp proof course visually appeared to be working as the brickwork beneath the damp proof course was dark and damp looking and that above it was dry and of a lighter colour. All walls examined were dry except the flank wall and walls abutting the flank wall which had visible damp staining at both first and ground floor level, severe in places.

Fig: 1 Damp stain on flank wall in first floor small front room

At ground floor level the staining was more severe. I established that the entire left flank wall of the entrance hall, under stairs area and first floor landing had been covered with plaster board using dot and dab technique. No skirting was fitted in the hall. The floor in the hall adjacent to the flank wall was physically wet where it appeared that water had run down behind the plasterboard (Fig: 2). Beneath the stairs the dabs used to fix the plaster board were clearly evident as they were very damp (Fig: 3).


Damp patches were also present above the stairs nearly up to the first floor ceiling level but these were less visible as this section of the wall had recently been painted with a silk finish paint. In the ground floor toilet (Fig: 4) the situation was severe (other slight complications in this area as well) and water stains were present over the rear entrance door (Fig: 5).


It was obvious that rising damp was not the cause of such extensive damp. Externally the render was in a very poor condition; it was severely cracked and live (hollow) in many places (Fig: 6 & 7). Moss was growing out of many of the cracks giving an indication of the level of moisture present (Fig: 8 & 9). The flank wall faced south west and therefore took the brunt of wind driven rain. As the properties were built around a circular crescent it was fully exposed and not sheltered by adjacent properties.


In the front elevation at low level near to the left flank wall a loose air vent was present which I was simply able to ‘lift it out’ (Fig: 7). I then put my hand into the cavity which had been filled with insulation material and this was found to be extremely wet.

I considered the possibility of condensation forming in the cavity but dismissed this as the property had been empty for a considerable time (no one inside producing water vapour) and very recent water stains were present on the hall floor and under the stairs area (Fig: 2 & 3). The bricks behind the render were very wet indeed, sufficient to sustain moss growth, and the inner skin of bricks were not as wet thus I concluded the water was entering the wall due to the defective rendering and being transmitted across the cavity by the cavity wall insulation which was found to be very wet.

It was suggested that all of the external render should be removed; the walls protected and allowed to dry down for a period of time by fixing protective sheeting to the scaffold. The saturated cavity wall insulation had to be removed which is a time consuming awkward job. The render should then be replaced but in view of the extreme exposure of the flank wall I suggested the use of plaster membrane and increasing natural ventilation by the introduction of passive air vents (Fig:10). All timber in contact with the damp wall should be exposed, examined and monitored as they dried down.


Extensive internal and external work was necessary. Unfortunately my client was not able to negotiate a sufficient reduction in the sale price of the property to cover the cost of work necessary and therefore withdrew from the purchase.

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