Three forms of protection, not three grades
BS 8102:2022, the code of practice for protecting below-ground structures against water ingress, describes three forms of protection: Type A, barrier protection applied to the structure; Type B, protection integral to the structure itself; and Type C, drained protection that manages water which enters. They are strategies, not quality rankings, and the right one depends on the structure, the water and the use of the space.
Type A: resist the water at the face
A barrier system — cementitious multi-coat tanking, a liquid-applied membrane or a bonded sheet — resists water at the surface of the structure. It needs no power, has no moving parts and takes up very little space. What it depends on is a sound, properly prepared substrate and absolute continuity: water under pressure will find the metre that was not treated or the pipe penetration that was not detailed.
Type C: accept the water and manage it
Drained protection lines the structure with a studded membrane that holds a drainage void against the wall. Water entering the structure runs down that void into a perimeter channel and away to a sump and pump, or to a gravity outfall. Because nothing depends on bonding to dry masonry, it tolerates the imperfect substrates older basements almost always have.
What each one asks of you afterwards
A barrier system asks very little, provided it was correctly applied — but if it does fail, finding and repairing the breach behind finished surfaces is disruptive. A drained system asks for maintenance: channels rodded through inspection points, the sump chamber and pump checked and cleaned, the alarm tested, typically annually. It also usually depends on electricity, which is why back-up matters where the consequences of failure are real.
How the choice is made
By assessing the water the structure faces, the condition and form of the structure, the consequence of any element underperforming, and the environment the finished space has to provide. A store room and a habitable bedroom justify different levels of protection. Where the consequences of water entering are significant, combining two forms of protection is common and sensible.
The honest summary
Tanking suits sound structures, modest water conditions and simple geometry, and it is a poor choice on friable, salt-laden or rubble-filled masonry. Drained protection suits retrofit work in older basements and tolerant substrates, provided the maintenance and the discharge route are accepted as part of the design. Anyone offering one system for every basement is selling a product rather than designing waterproofing.
Limitations of general guidance
This article is general guidance. It cannot confirm the cause of dampness in a specific property. Recommendations should follow an inspection of the building, its external environment and its internal conditions.
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