A damp course is not permanent. The two materials Ipswich houses actually have fail in completely different ways.
Talk it throughRising Damp Ipswich arranges damp assessments across Ipswich and the western corridor.
Slate was the first material widely used, and it appears in the better Ipswich houses from the 1870s to about 1910. Slate does not rot and does not corrode, so a slate course can still be doing its job after a hundred and fifty years. What it does is crack. It is brittle and it carries the full load of the wall above, so any settlement of the footing snaps it - and it snaps at exactly the points that carry the most load.
The failure is therefore local rather than general. One section of a wall goes damp while the rest stays dry, which is a pattern that gets blamed on a leak far more often than on the damp course.
Bituminous felt courses became standard through the interwar period, and most of Ipswich's 1920s to 1950s brick has one. Bitumen is flexible when new, which solves slate's cracking problem. It then oxidises. Over sixty or eighty years it goes hard, then brittle, then powdery, and once it is powdery it is no longer a barrier.
Bitumen failure is gradual and general rather than local. A whole wall starts showing damp slowly over a few seasons, with nothing having changed outside to explain it. That is the signature.
Both materials sit inside the wall, two or three courses above the ground, under the render if there is render. Nothing about a failed course is visible externally. The evidence is always indirect: the height of the damage, whether it is one section or the whole wall, and what the ground outside is doing.
Related: chemical damp course injection.
We take enquiries across the Ipswich local government area and the western corridor.
Rising Damp Ipswich