Olympic Construction Ltd, Chartered Building Engineers & Certified structural waterproofing surveyors (CSSW)
Specialise in structural waterproofing of new and existing structures
BS8102: 2022 -Code of practice ‘Protection of below ground structures against water ingress section 4.2 Design team is very clear stating:
A waterproofing specialist should be appointed as part of the design team so that an integrated waterproofing solution is created. The waterproofing specialist should:
- be suitably qualified and experienced, commensurate with the type and size of the proposed project;
- be capable of devising solutions that accommodate the various project constraints and needs, with an understanding of construction forms and sequencing;
- provide the design team with information and guidance that assists with and influences the design, installation and future maintenance of the waterproofed structure.
If the RIBA stages are used, a waterproofing specialist should be appointed before the technical design stage at the latest. Those responsible for the overall waterproofing design should be identified at the planning stage or as early as possible. All decisions made by others that might have an impact on the waterproofing design should be brought to the attention of the waterproofing specialist, design team, and installing contractors. Final decisions and any recommendations should be approved by those taking overall responsibility for the design of the waterproofing.
Where waterproofing design responsibility is imparted as part of a contractual process, for example, as a Contractor’s Designed Portion, the waterproofing specialist should be appointed as early as possible. Alternatively, a waterproofing specialist may develop an outline design, which is later adopted as part of a client’s requirements and developed by a suitably experienced and qualified waterproofing specialist as a Contractor’s Designed Portion.
In the photograph to the right, the external (Positive side) of the basement wall is being waterproofed using a Koster Deuxan 2C liquid-applied waterproofing membrane, to which a Delta Geo-drain Quattro membrane will be installed to provide a waterproofing system that complies with BS8102: 2022 -Code of practice ‘Protection of below ground structures against water ingress
Water can penetrate a structure below ground level in two ways:
Where the ground is not saturated, it will move through the capillaries of the ground and structure by capillary suction. When this form of moisture comes to the internal surface of the building, surface dampness is evident but there will be no free flow (flooding) of water. Capillary moisture can enter a structure laterally, such as when a wall is earth-retaining.
Where the ground is saturated and hydrostatic pressure occurs, water will be pushed through the capillaries of the ground and structure. Where the water comes to the surface, the pressure behind it will force it into the property in the form of liquid water and flooding will occur.
Where a structure is earth-retaining, water penetration can occur through the structure. If the water table is high, such as when water is trapped in a clay sump created when the foundations are excavated, or as a result of long-term rainfall percolating down resulting in water logging of the ground, presenting a head of water under hydrostatic pressure which potentially can food the basement flood.
Podium deck and buried roof waterproofing
Any horizontal surface which is forms the roof or covering to a structure that is below ground is termed a ‘Podium deck or buried roof’
These types of structures are complex and require correctly designing with the correct falls at least 1:80 along with an adequate drainage system installed to prevent standing water which results in a hydrostatic pressure that moves water through any defects within the waterproofing membranes applied to the surface of the deck.
Waterproofing membranes applied to a horizontal surface should be fully bonded to prevent lateral water movement under the membrane system should a defect occur.
On larger structures that can be prone to thermal or structural differential movement then a flexible or decoupled system would have to be designed.
In the photograph to the right, we are using a Koster Deuxan 2C liquid-applied waterproofing membrane. This system is to be combined with a Delta Geo-drain Quattro membrane installed to provide a waterproofing system, which complies with BS8102: 2022 -Code of practice ‘Protection of below ground structures against water ingress. To allow a drained patio area to be formed above the property below.