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Basement waterproofing solutions are required when all or part of a property is built at or below ground level. Unlike above ground rising damp it is possible that water pressure can build up behind the structure leading to water forcing it’s way through the wall, the floor or even the below ground roof. The water can come through cracks, joints and previously unknown structural weaknesses in the basement. The water ingress can sometimes be a a sudden event, perhaps following a period of heavy rain, or can be a less severe long term problem leading to mould, fungal decay and damage to personal possessions.
Basement waterproofing solutions are split into three distinct categories and each is suited to different applications depending on the type of structure being waterproofed and if it is new build or retrofit.
Damp Genius will carry out a detailed survey to work out which system would best suit your desired outcomes and budget.
Generally speaking we provide what is typically called ‘tanking’ internally and externally plus we install cavity drain membranes internally.
Type A basement waterproofing is a type of system which seeks to for a physical barrier to prevent water entering a basement. Type A waterproofing systems can be installed externally and this is typically carried out only on a new build structure at the time of construction. Some examples of this type of waterproofing membrane include RIW Sheetseal or Delta Deuxan 2C, both of which are applied to the retaining wall prior to the ground being backfilled.
On a retrofit installation, such as a basement conversion, it is possible to use a type A waterproofing solution on the internal face of the wall and often the floor as well. Commonly this is referred to as ‘tanking’ and tend be achieved using a cementitious product such as Vandex BB75 or similar.
Type B basement waterproofing solutions refer principally to admixture products which are put into concrete during the construction of a building to create the waterproof concrete structure. Type B basement waterproofing systems are not suitable for use in retrofit basement conversions and should only be used on large projects such as new housing developments.
Type C basement waterproofing takes a different approach to type A and type B systems, rather than attempting to stop water entering the structure these systems accept that water will enter the structure and then divert it away to a safe discharge point. These systems are commonly referred to as Cavity Drain Membranes.
They are often used in retro fit basement conversions and on new build projects as part of a combined type A and C system or a combined type B and C system. These combined systems are generally the type requested by house builder warranty provides such as the NHBC and LABC.
Type C cavity drain membranes come in a range of sizes and depths to suit the project as well as having a smooth back finish or mesh backed finish capable of accepting plasterboard.
In a two or three sided basement (very common in Devon and Somerset) the systems will generally discharge under gravity to a suitable drainage point. For full basements, with all walls below ground, a sump and pump system will need to be installed to take the discharge water up and away.
At Damp Genius we pride ourselves on taking a pragmatic approach to specifying the best basement waterproofing solutions. Every project is different and sometimes the clients requirements or the building requirements will lead to a type A system being opted for over a type C system. That being said it widely considered that a type C Cavity Drain Membrane is the lowest risk system possible. It stands to reason really – everyone knows the story of the boy who stuck his thumb in the damn… he couldn’t hold the water back for ever! Logically it is safer to accept this fact from the start and plan accordingly.
The British Standard BS8102 puts a number of requirements on the design of waterproofing systems. As a CSSW qualified surveyors we will look to minimise the risk of the system and ensure that on going maintenance of the basement system can be carried out.
BS8102 lists the various types of systems by risk level and this puts type C Cavity Drain Systems as the lowest risk due to it’s repairabilty and ease of ongoing maintenance. This is the official line and is backed up by our experiences in the industry.
There are some key points to keep in mind when considering any of the basement waterproofing solutions described.
Type A systems, particularly the internal tanking systems such as Vandex, rely very heavily on the surface preparation of the walls. Do not be at all surprised if a quote for the work includes more time and money on the preparation than the actual application of the tanking. Nearly all the failed systems seen over the years are due to the wall not being cleaned or repointed or scabbled down correctly. That being said if the surface is done correctly, and salt inhibitors are used on the wall, then these systems can work well.
Type B basement waterproofing systems sound absolutely great on paper, however, given a bit of thought the holes in the logic start appearing. The short version of this is that waterproof concrete is really great – except for all of the spaces where the concrete cannot be! To explain, imagine a typical concrete multi story carpark as shown in the picture, notice that the walls are made of large slab with joins between them, these are called day joints. Large concrete structures always have day joints. Light bulb going off yet? Day joints are not waterproof concrete – they are holes! To read a really great review of concrete admixtures please take a look at Newton waterproofing who have published a fantastic indepth article on this subject.
With any basement project it is always advisable to get a qualified professional to provide advice and support. Damp Genius are CSSW qualified surveyors and installers of basement waterproofing systems. We use products from a range of manufacturers including Newton, Delta, Oldroyd, RIW and Triton all installed with long term guarantees.
For a no obligation survey and quotation please contact us using any of the details at the top of the page.