CASE STUDY No: 4 PDF Print E-mail

‘Rising Damp – yes – but not possible to treat effectively’
This house had rising damp in virtually all walls but due to its construction and other circumstances the introduction of an effective damp proof course was not a practical option – despite the fact that two damp treatment companies thought otherwise.




Instructions: Inspect ground floor walls for possible rising damp.

Background:
This property was being purchased by my clients but a condition of their building society was that an inspection for rising damp should be conducted by a member of the Property Care Association, which I am, and the report submitted for consideration. The property was built in the late 1800s and is a mid-terrace two bedroom, two reception room weavers cottage constructed of 600 mm thick stone walls with a rubble infill. The floors through out the ground floor were of solid construction. The current owners were aware of a few ‘spots’ of damp.

Inspection:
Inside and outside the property was maintained in very good condition and inside, to the eye, there did not appear to be any obvious damp problems. The property was very small and compact hence furniture stored items etc. restricted access to some of the wall surfaces. Using a surface moisture meter I was able to detect the presence of increased levels of moisture on all wall surfaces that I was able to gain access to including the single brick under stairs cupboard dividing walls. I conducted a condensation assessment and the temperature of all wall surfaces checked were above dew point temperature thus condensation was not influencing the readings I was obtaining with a surface moisture meter.

Beneath the front window there was a recess which had been ‘boxed in’ to accommodate the gas and electric meters (see sketch plan). Within this enclosed recess the stone construction of the walls was exposed and this also recorded the presence of increased moisture content up to a height of approximately 400 mm; a similar height to that detected on other walls.

There was no original physical damp proof course present in the walls and no damp remedial works had been undertaken in the last twenty years except for a small area of dry lining in the kitchen fitted by the current owners. Abutting the rear elevation wall at both party wall junctions were large stone built garden walls creating the potential for moisture penetration to occur (see sketch plan).

I was able to see that the two ground floor fireplaces in the adjoining property on the right side (taken from standing in the road looking at the front elevation), backed on to the party wall of the reception room and kitchen (see sketch plan). I also assumed that the under stairs dividing wall in the same property abutted the right party wall. Similarly the two fireplaces of the property I was inspecting backed on to the reception room and kitchen of the attached left side property.

diagram

Discussion:
As previously stated the property was in good decorative order and there was not a pressing need to do anything immediately. It highlights a question that I have discussed on many occasions with colleagues and clients which is ‘when is damp – damp?’ This property certainly has damp present but at the time of my inspection it was not causing any significant problems to the decorative finish.

It is obviously possible to go through the motions of drilling and injecting a remedial damp proof course system into very thick stone walls with rubble infill but it is my opinion that any remedial damp proof course system (with the exception of a physical DPC) introduced into 600 mm thick stone walls with a rubble infill is only likely to have a limited effect. I therefore question whether it is worth the expense of going to this trouble with this type of wall construction. Even if a company did drill and inject a remedial DPC system into such walls they would have to apply an internal re-plastering regime which would have to hold back dampness at low level which will always be present.

In addition to the wall construction I also had to consider the additional complications of the adjoining property’s fireplaces backing onto the right party wall and the difficulties created by its own fireplaces on the left party wall. It would not be possible to effectively isolate these structures from adjoining sections of wall. Then there are the two large external garden walls abutting the rear elevation.

Remedy:
I advised my clients that there was a damp problem in virtually all walls at ground floor level but due to the wall construction, very large fireplaces, fireplaces backing on to the party wall, abutting garden walls, etc it was my opinion that to go through the process of drilling and injecting a new DPC system would be of little benefit. I therefore felt it would be more cost effective if resources were directed at providing a long term dry decorative surface and suggested that cavity drainage plaster membrane should be fixed to all ground floor level wall surfaces and plastered over (Fig: 1.). The membrane should also be dressed into the perimeter of the solid floor behind the skirting boards.
 

 
plasterer

It was agreed that the problem was not pressing and that the work could be delayed until such time as redecoration was required.

Outcome:
My clients were able to negotiate a £3000 reduction off the sale price of the property and will tackle the work in a few years time when they redecorate and fit a new kitchen. They later informed me that two damp treatment contractors had quoted to introduce a chemical DPC and neither had mentioned the chimney breasts against the right party wall in the adjoining property.

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Contact Peter: Email - info@dampdecay.co.uk - Telephone: 015242 71794