BS8102 – Waterproofing of Structures Below Ground -The British Standard has been with us for quite a few years now, and was in fact revised in 2009 some 10 years ago. However, with the advent of many new properties being built with basements and rooms below ground, the ‘practical’ element of correct design of these spaces has been sadly lacking.
This has resulted in many ‘failures’ due to poor design and workmanship and led to changes in the way organisations like the NHBC approve their members properties that have rooms below ground. After settling many claims from homeowners running to millions of pounds the NHBC have amended their own Technical Documents to reduce the amount of claims they have to pay out.
Chapter 5.4 of the NHBC Technical Document states that where the property retains more than 600mm of ground level then a combination of two type of waterproofing are required in accordance with BS8102. These are either:-
Type ‘A’ System – Barrier Protection
Where a waterproofing coating is applied to either the internal or external façade of the structure to provide an effective waterproof coating and prevent water ingress. Such a system could be a ‘mineral bonding slurry’ or ‘fibre reinforced bitumen coating’ or a sheet material like say ‘bituthene’. Type A systems are ideal for new build when installed on the external façade and under the slab before the ground is back filled as they are sited on the positive water pressure side, as opposed to being on the internal surface and subject to negative water pressure
Type B System – Structural Integral Protection
Type B systems are where the actual structure itself is waterproof and this effectively means casting waterproof concrete slabs and walls. All construction joints within the RC structure should be designed out where possible and where unavoidable, they should be detailed/waterproofed with appropriate waterstops. The concrete requires careful installation ensuring it is well vibrated to remove air entrapment which would result in voids and air pockets where water could pass through – especially on the joint.
Type ‘C System – Cavity Drainage Protection
Where water is allowed to enter the structure and the ingress is controlled on the ‘wet side’ of the cavity – often behind a cavity drain membrane with a dimpled surface and the water ingress then collected in a ‘sump chamber’ and either drained away naturally if falls allow or by submersible pumps to external drains. Type C installations are particularly successful on existing buildings because the stress created by water pressure is not increased by installing these type of waterproofing, compared to say a Type A system which could increase the loading on a building if water pressure began to build up behind the waterproof coating and could lead to collapse of the building if not designed carefully
In line with BS8102, the NHBC require a combination of two different types of these three waterproofing methods
Furthermore and to ensure the success of the ‘design element’ of the waterproofing, and to qualify for NHBC Certification the installation must be designed by a qualified person and surveyors who have passed the Property Care Association qualification for Waterproofing – the Certificated Surveyor in Structural Waterproofing (CSSW) would be deemed to meet this criteria
Premier Insurance who also provide insurance for new build properties also require this same design principle to qualify for their insurance cover
Why not come along to our Stand F42 at London Build Expo being held on 27th and 28th November at Olympia and talk to us about your own Basement Waterproofing project and make sure you ‘Get it Right First Time’. You can register for a FREE ticket to the event by clicking the image below:
