Softus said:
I hear what you're saying TM, and I bow to your wider general knowledge on the subject, but, and I have to press you on this point, do you have a real-life example of rising damp caused ONLY by a failed DPC in the wall?
Not a "failed" one, but I sorted out a problem with a Victorian terraced house that had a serious absence of dpc. in a party wall. This wall was literally dripping wet upto about two and a half feet above ground level, and this was in the middle of a fairly dry summer. Although my client had just bought the property, his neighbour assured us that, the "tide line" rose to about five feet, during the winter. Although the retrospective fitting of a dpc was a big job, the neighbour contributed to the cost.
The original reason for my client seeking assistance was the condition of his floor. During one of his visits to the property, as he stepped in through the front door, it had literally just crumbled beneath his feet, resulting in a strained groin
Oh, and while I was there, could I just give the party wall a skim to hide all the mould?
This was one of those jobs where things just went from bad to worse. Besides the damp, the ground floor turned out to be riddled with wood worm. All in all, I got quite a lot of business from this job but, the client made a massive profit when he sold up a couple of years later (with no sign of damp, anywhere in the house).
His neighbour was also astounded at the difference it made to his house. Although he had installed double glazing a couple of years previous, he had been disappointed with the results. The damp had just got worse, if anything, and the house was still rather cold. Once the DPC had been sorted it completely changed the feel of the whole house and was much cheaper to warm through. His family's health had also improved, with their constant suffering of colds and flu like symptoms finally dissipating.
Although this was quite a bad case of rising damp, it was caused by the complete asbsence of a dpc. (not the failure of an existing one). I daresay in other areas, even it's absence wouldn't have been noticable. It all depends on the local geology of your environment and prevailing weather conditions.
In the same area I have seen damp patches caused by dodgy conversions. Typically a length of wall that has been knocked through with no DPC used in the making good. Where the DPC has been left out of about a foot of wall, the damp patch of a about a square foot will result.
So far, (apart from vehicle impact sites), I have yet to see a properly installed DPC actually "fail". I have even witnessed houses that have suffered from serious subsidence, with no sign of rising damp. Penetrating damp is far more common.
I have also seen a "rising damp" issue, as diagnosed by a surveyor. Upon looking outside, I noticed that the client had built a raised flower bed up against the wall. The external wall of the house (which was of a solid construction) formed the back of this flower bed with no protection whatsoever. The surveyors confusion is understandable as he hadn't ventured into the garden, and the clients hadn't thought to mention it.