"It must always be assumed that groundwater will come to bear in a structure below ground at some point in it's life"
At the start of the new millennia, a mix of tighter regulations and manufacturers producing better systems to control and manage water below ground, meant that basement conversions and developments in the U.K. began to really catch on for those fortunate enough with unused space below ground.
Outwing Construction v. Thomas Weatherald.
On the 13th of September 1999, a high court judgement was issued from the High Court of Justice - Technology and Construction Court and the case - Outwing Construction v. Thomas Weatherald.
Thomas Weatherald Ltd. was the main contractor responsible for the design and construction of a new nursing home at Bramley Hill in Croydon. The construction of the basement structure, waterproofing and land drain was subcontracted to Outwing Construction.
The floor consisted of reinforced concrete and the walls were constructed out of two skins of concrete block, sandwiching a layer of concrete in between. The structure was waterproofed externally with a bonded sheet membrane and a land drain was positioned approximately one third of the way up the wall, and discharged to a soak away a little distance from the building.
After a period of prolonged and heavy rainfall, not long after completion of the nursing home, leaks transpired internally in the basement. Thomas Weatherald Ltd. withheld money from Outwing Construction because they had incurred additional expense installing sika tanking to stop the water penetrating the structure.
"When specifying waterproofing in today’s marketplace care must be taken to look at all implications of issues surrounding the property. Being able to access systems to repair them if a problem arises is another reason that cavity drain membranes have gained popularity. This use, internally, as a dual system is fast becoming standard practice for professionals within the construction industry."
Outwing then sued Thomas Weatherald for the balance of money owing, and Thomas Weatherald counterclaimed for the cost of the in-situ treatment together with other damages.
The resulting decision was in favor of Outwing Construction, after expert witnesses provided their cases, Thomas Weatherald Ltd was found to be at fault for the incorrect and improper design for a waterproofing system below ground and recorder Colin Reese QC stated in his 25 page judgement that essentially:
- The self-adhesive membrane installed could not be expected to resist water penetration in the event of a build up of hydro-static pressure.
- Self-adhesive membranes cannot be expected to achieve a total or absolute watertight bond capable of resisting penetration by water pressure.
- The design of perimeter land drainage to be below the lowest level of the tanking system.
An excerpt from the judgement said:
"The waterproofing system consisted of both the tanking membrane and the subsoil drainage... this design did carry with it such a risk after periods of heavy rainfall when a perched water table or perched water tables might come into existence, and the factual evidence was that the water penetration problem only became apparent after heavy rain."
This court case and subsequent ruling had significant ramifications for the waterproofing industry and now sets a precedent for future similar cases.-
Below is a full cross section of an internal 'Type C' Cavity Drainage Membrane System in accordance with BS:8102:(2009)
Hydro-static pressure is different from damp above ground therefore it is imperative that the systems installed below ground manage and divert the head of water should there be slight moisture ingress or complete flooding and for the systems to be fully maintainable.
K.T. Preservation’s surveyors and technicians are fully qualified to the highest standard and have many years of experience in the industry, whatever grade of protection needed for your basement or project, our knowledge with the control of water below ground and the systems we install will make it possible.
There are a variety of options when dealing with waterproofing a structure that depend on the grade of protection needed, as outlined in BS:8102:(2009), you might not always need a full 'Type C' cavity drainage membrane system installed internally. A 'Type A' external/ barrier membrane will be incorporated with the installation of a 'Type C' system if the structure is to be used for habitable accommodation however if some seepage or dampness is permitted then a sole use of the 'Type A' system is okay as depicted below at an estate in Berkshire. This farm building was converted into a hunting lodge/ changing rooms.
Here we used Wykamol Geotex external membrane, it promotes the flow of ground water away from the face of the structure, relieving hydro-static pressure and protecting it from the back-filled earth.
View our case studies to see a more extensive look at our past waterproofing contracts! If you have any questions, or are interested in having a survey in relation to anything that has been mentioned above do not hesitate to contact us.