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CSSW Waterproofing Specialist

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CSSW Waterproofing Specialist

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For a good while now the British Standard when it comes to waterproofing a structure below ground recognises the need for a Waterproofing Specialist (typically stating this person should be CSSW qualified).

This still doesn’t seem to have caught on in practice – just yesterday I was on a site with a whole bunch of waterproofing in place which was not designed by appropriately qualified persons.

The following is some very brief footage of the site:

On this site the architect/structural engineer came up with some structural waterproofing designed (strongly influenced by a structural waterproofing manufacturer).

This led to use of ALL THREE structural waterproofing systems:

  1. Type A – (barrier protection; in this case a sodium bentonite sheet to the exterior of earth retaining walls)
  2. Type B – Reinforced Concrete designed to be completely waterproof (I’m yet to confirm compliance with BS EN 1992)
  3. Type C – A cavity drain membrane system

In addition to all three of the above there is a land drain installed just below the foot of the earth retaining walls.

A combination of two of the above systems is right (even necessary given the context); but issues are created in using all three. Firstly, this construction is FAR more expensive than it needs to be – I think if I’d been involved at design stage the construction cost would have been ~£100k lower! Secondly, there can be a tendency to assume that because there are so many ‘lines of defense’ that they don’t necessarily have to be done perfectly.

This brings me on the main issue I noted:

The Land Drain

It is absolutely necessary that a land drain is maintainable. This one is designed with two geofabric liners to keep silt out, but that’s not enough! A land drain must have roding points and it must be possible to jet wash the land drain in order to clear out debris which will inevitably collect over decades. Here’s a photo of one module of the land drain:

There is no way this system can be flushed or maintained (and there are no access points over a 60m run).

This means that in considering this structure’s structural waterproofing design I should completely disregard the land drain. What a waste, this land drain could have been so useful if it had just been designed correctly 🙁

The knock on effect of disregarding the land drain means that upward pressure on the underside of the floor slab (heave) must be given serious consideration. Unfortunately I don’t have time to go into that right now – I’ll save it for another post.

Conclusion

Getting an appropriately qualified structural waterproofing specialist in at design stage is a must.

Using a CSSW qualified structural waterproofing specialist is a requirement in order to be compliant (for NHBC, LABC and the relevant British Standards) and you will be caught out x months down the road when you try and get a warrantee on the structure.

Not only that, but using an independent specialist is likely to SAVE YOU A LOT OF MONEY rather than having manufacturers scare you into using all of their products at the same time!

Property Care Consultants provides structural waterproofing consultancy through CSSW.LONDON


About Author

Ben

I'm a specialist surveyor dealing with dampness in buildings incorporating issues such as: rising damp, timber decay, underground waterproofing and flood resistance.

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