The physical damp proof course is traditionally a layer of impervious material incorporated at the base of the wall during construction, to prevent ground water from rising up the wall by capillary action, and were mandatory post 1875, following the Public Health Act. True rising damp can therefore only be defined as moisture rising up a wall by capillary action due to a failure of the damp proof course. In the case of a typical slate damp proof course this may occur due to significant structural movement, or on one or two occasions I have seen slate turned to a paste like consistency, due to attack by a particular combination of salts present in the surrounding sub-soil. I have also seen a Bitumen based D.P.C turned to a powdery consistency on a couple of occasions. Hi-load plastic DPC's are unlikely to ever fail, assuming they were installed defect free. In any event, whilst true rising damp may be the cause of damp in a structure, in our experience it is the least likely cause damp, and should not be diagnosed as such until all other possible sources of moisture have been ruled out, and in accordance with BS6576 see excerpt below.
If positive evidence of rising damp is being obscured by other faults such as those described in 18.104.22.168, it is preferable that those faults should first be remedied, and that an appropriate period of time should be allowed to elapse before making further checks to ascertain the presence of rising damp.
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