BS 8102:2022
A clearer way to design below-ground waterproofing.
BS 8102 is a British Code of Practice for the protection of below-ground structures against water ingress. It provides a structured, risk-based approach to understanding the building, assessing the conditions and selecting an appropriate waterproofing strategy.
In New Zealand, BS 8102 is not a Building Code compliance document in its own right. However, its structured approach can be used alongside the New Zealand Building Code to help develop, document and communicate a project-specific waterproofing solution.
BS 8102 in five simple questions.
At its heart, BS 8102 is about asking the right questions before deciding what waterproofing system to use.
A basement used for storage does not necessarily have the same waterproofing requirements as a bedroom, office, archive or high-value commercial space.
BS 8102 starts by considering the intended use of the space and the level of protection that will be required.
Not every below-ground space needs the same level of dryness. The required performance should reflect how the space will be occupied and what will be stored or installed within it.
BS 8102 uses performance grades to help establish what level of water protection is appropriate for the intended use.
This is an important step because the waterproofing strategy should be designed around the required outcome — not simply around a particular product.
Groundwater, hydrostatic pressure, drainage conditions, soil type, site history and construction methodology can all affect how a below-ground structure needs to be protected.
BS 8102 encourages the design team to consider these conditions before selecting the waterproofing approach.
In simple terms: understand the problem before choosing the solution.
BS 8102 identifies three principal approaches to protecting below-ground structures:
Barrier protection.
A waterproofing layer is used to prevent water reaching
the structure or internal environment.
Structurally integral protection.
The structure itself is designed to provide resistance
to water penetration.
Drained protection.
Water is accepted into a controlled cavity and managed
through drainage and maintenance systems.
These approaches can also be combined where the project risk or design requires it.
A good waterproofing strategy needs to be more than a product name on a drawing.
The design should clearly identify the waterproofing approach, performance requirements, interfaces, critical details, drainage provisions, inspection requirements and responsibilities.
This creates a clear basis for specification, procurement, construction and inspection.
Where does the New Zealand Building Code fit?
This is where the distinction is important.
Sets the required performance of the building.
Establishes how those requirements will be achieved.
Provides a recognised structured methodology for below-ground waterproofing design.
Drawings, specifications, calculations, product information, inspections and construction records demonstrate the solution.
The Building Code sets the requirement.
The design establishes the solution.
BS 8102 does not replace the New Zealand Building Code. Instead, it can provide a structured design methodology that helps the project team develop and document a solution that addresses the applicable Building Code requirements.
Structural design, crack control, joints, penetrations and construction methodology all influence the ability of a below-ground structure to resist water penetration.
The relevant requirements of NZ Building Code Clause B1 and associated structural design standards need to be considered as part of the overall solution.
Below-ground waterproofing is rarely a short-term consideration. Materials, interfaces and systems need to be selected with durability and the intended service life of the building in mind.
NZ Building Code Clause B2 establishes durability requirements that need to be addressed by the project design.
Depending on the building and its design, relevant Building Code provisions may include requirements relating to external moisture, internal moisture and associated building services.
The important point is that the waterproofing strategy needs to be considered as part of the building as a whole rather than treated as an isolated product selection.
Every site and building is different. Ground conditions, construction type, occupancy, water exposure and access for future maintenance all influence the appropriate solution.
BS 8102 provides a framework for considering these issues, while the project design establishes the specific solution required for the building.
Not every basement needs the same level of dryness.
One of the useful principles within BS 8102 is that waterproofing performance should reflect how the space will actually be used.
Some seepage may be acceptable.
Suitable for environments where a basic level of protection is appropriate and occasional dampness or water ingress can be tolerated.
Controlled environment.
A higher level of protection where water penetration should be controlled but some moisture or dampness may still be acceptable.
Dry environment.
Intended for spaces where a dry internal environment is required, such as habitable or higher-value occupied areas.
The appropriate performance grade should always be established from the intended use of the space and the requirements of the project.
So how can BS 8102 be used in New Zealand?
The process does not need to be complicated. The key is to establish the performance requirements first, then develop a waterproofing strategy that responds to the actual risks of the project.
Identify the applicable Building Code requirements and relevant design standards for the building and its intended use.
Establish the required performance grade and identify any project-specific requirements for the internal environment.
Consider groundwater, soil conditions, hydrostatic pressure, drainage, construction sequencing and the ability to access systems for future maintenance.
Use the principles of BS 8102 to develop a strategy that responds to the identified risks and required performance.
Clearly document the waterproofing strategy, critical details, interfaces, specifications, inspection requirements and responsibilities.
Waterproofing performance ultimately depends on what is built. Inspection, quality control and appropriate construction monitoring help identify problems before they become expensive remedial works.
The goal isn't to use BS 8102
for the sake of using BS 8102.
The goal is to make better waterproofing decisions earlier.
By combining the performance requirements of the New Zealand Building Code with a structured waterproofing methodology such as BS 8102, designers and project teams can establish a clearer basis for decision-making, documentation and construction.
Understand the risk. Define the performance. Design the solution.Important: This page is intended as a general explanation of BS 8102:2022 and its potential application alongside the New Zealand Building Code. BS 8102 is not itself a New Zealand Building Code compliance document and does not replace the requirements of the Building Code, project-specific design, consenting requirements or advice from appropriately qualified design professionals.