Waterproofing systems

In any basement there will be both vertical and horizontal zones to be waterproofed, perhaps sloping areas too. Horizontal zones could include ceilings, soffits and floors.

The suitability of the chosen waterproofing system needs to be considered with respect to all of the different wall and floor characteristics as found. So could we mix and match? Can we use combinations of waterproofing to cope with a variety of substrates or inclination/configuration of substrate? There seem to be opposing schools of thought here.

The BCA Design Guide advises against mixing hot and cold systems, stressing the risk of incompatibility when using hybrid systems. The guide advises that

'continuous horizontal, sloping or vertical waterproofing [should] be specified, and executed, in one proprietary waterproofing system'.

But it is common to find combinations of approach in remediation work as varying conditions or configurations of the subject building are addressed. In retro-fit application of cavity wall ties, we might choose to use a resin-fixed tie where areas of the inner leaf are found to be friable, but use standard expanding tie fixings where a sound substrate allows. In overcladding a tower block you might often come across a rainscreen cladding to upper floors, but note a wet system used to the ground storey – comprising insulation over-laid by render reinforced by meshing – offering improved fire protection against rubbish or accidental fires.

This issue has been discussed with some industry experts who support, for example, using a cavity-drained floor system in combination with a multi-coat render waterproofing to the surrounding walls. Such a remedy might be an option if the configuration of walls makes it difficult to use a relatively rigid studded membrane.

But there is an issue concerning guarantees, when the manufacturer of the cavity drain floor system might not approve of the detailing at the interaction of the wall renders and cavity-drained floor. You would in such a case mainly rely on the expertise of your professional adviser. There would also be problems concerning the meeting of British Standards or Agrément certificates, where hybrid systems of waterproofing will not be described.