Drainage Membranes for Below-Ground Waterproofing
Drainage membranes are used within waterproofing design to control and manage the movement of water, rather than to act as a primary waterproof barrier. These perform two distinct functions depending on where they are installed within the structure.
In below-ground construction, drainage membranes are used externally to relieve hydrostatic pressure against retaining structures, reducing the load on Type A waterproofing systems. In contrast, within deck and podium constructions, drainage membranes are installed above the waterproofing layer to manage surface water and protect the underlying membrane.
Because of this, drainage membranes must always be specified as part of a wider waterproofing design. Their role, performance requirements and detailing differ significantly depending on whether they are managing groundwater at foundation level or surface water within a deck build-up.
Drainage Membranes for External Walls
Drainage membranes installed to external walls are designed to relieve hydrostatic pressure and control groundwater movement against below-ground structures. Positioned outside the primary waterproofing layer, they create a drainage path that directs water downwards to land drains or discharge points.
These systems are critical where groundwater is present, as reducing pressure against the structure lowers the risk of water ingress and improves the long-term performance of Type A waterproofing systems.
Typical applications include:
• Basement walls and retaining structures
• Earth-retained concrete and masonry walls
• Structures requiring external drainage in conjunction with Type A waterproofing
• Projects where water must be directed to perimeter drainage systems
In this context, drainage membranes perform two key roles:
• Relieving hydrostatic pressure acting on the waterproofing layer
• Protecting the external waterproofing system from damage during backfilling
Newton HydroBond 410 GeoDrain is designed to provide consistent drainage capacity while maintaining durability in contact with the ground.
Correct specification depends on groundwater conditions, discharge routes and integration with the overall waterproofing strategy. Drainage capacity, continuity and outlet design are critical to ensuring that water is effectively removed from the structure.
Drainage Membranes for Decks and Podiums
In deck and podium constructions, drainage membranes are used to create a controlled drainage layer above the waterproofing system, allowing water to move laterally to outlets while protecting the waterproofing from mechanical damage and sustained loading.
Unlike external wall applications, these systems are not managing groundwater pressure. Instead, they deal with surface water within the build-up, ensuring that water does not accumulate above the waterproofing layer.
Typical applications include:
• Podium and plaza decks
• Buried roofs and inverted roof constructions
• Deck waterproofing systems requiring protection and drainage
• Green roof build-ups where water storage and drainage must be balanced
• Horizontal surfaces where water must be directed to outlets
In these applications, drainage membranes:
• Facilitate controlled water movement to drainage points
• Manage both drainage and, where required, water retention within the build-up
• Provide protection to the waterproofing layer during installation and in service
Newton 408 DeckDrain and 420 Reservoir are designed for use within deck build-ups. The 420 Reservoir in particular provides controlled water storage and drainage within extensive green roof systems, rather than groundwater management.
Correct specification must consider drainage capacity, falls, outlet positioning, and the interaction between the drainage layer and the overall deck or green roof construction.
Contact Newton Waterproofing
For technical advice, specifications, and support with drainage membrane selection, contact Newton Waterproofing. Our team guides detailing coordination and BS 8102:2022 compliance, ensuring the correct system is selected early in the waterproofing design process.
