Internal Membrane Systems vs Traditional Tanking: A Comprehensive Comparison

Waterproofing is a critical aspect of building design, especially in basements, cellars, and below-ground structures. Moisture ingress can lead to structural damage, mold, and long-term deterioration. Traditionally, builders relied on tanking systems, solid barriers applied to walls and floors, to keep water out. However, internal membrane systems have emerged as a modern alternative, offering a more flexible and often cost-effective solution.

In this article, we explore the key differences between membrane systems vs tanking, examining their design principles, advantages, limitations, and practical applications to help homeowners, architects, and builders make informed decisions.

Understanding the Basics: Tanking and Membrane Systems

Before comparing them, it’s essential to understand what each system entails.

What is Traditional Tanking?

Tanking refers to applying a continuous waterproof barrier to below-ground structures, typically using:

• Cementitious coatings (cement-based renders with waterproof additives)
• Bituminous coatings (tar-based liquid membranes)
• Sheet membranes (bituminous or synthetic)

The key principle is creating an impermeable barrier to prevent water from penetrating walls and floors. Tanking is usually applied to the exterior of the structure during construction, though internal tanking can also be used in retrofit projects.

What are Internal Membrane Systems?

Internal membrane systems consist of specialised sheets or panels installed on the inside of walls and floors. They are designed to channel water to a drainage system, typically connected to a sump pump, rather than trying to stop water completely at the source.

Common types include:

• Cavity drain membranes (plastic sheets with channels)
• Modular membrane panels
• Multi-layer composite systems

Unlike tanking, internal membranes manage water rather than fully blocking it, allowing it to be safely diverted away from living spaces.

How Tanking Works

Tanking relies on creating a solid, impermeable layer on the structure’s surface.

External Tanking

• Applied to the exterior of foundations and walls
• Protects against groundwater and hydrostatic pressure
• Typically used in new builds or major renovations

Internal Tanking

• Applied to the interior surface of walls and floors
• Useful for retrofit applications where external excavation is impractical
• Includes cementitious or polymer-modified coatings

Key considerations: Tanking systems are designed to resist hydrostatic pressure, but they must be continuous and free of cracks to be effective. Any damage or gaps can compromise the system.

How Internal Membrane Systems Work

Internal membrane systems operate on a different principle: water management rather than complete prevention.

1. Installation: Sheets or panels are attached to walls and floors.
2. Channeling Water: The membrane’s channels direct any moisture that penetrates the masonry towards a drainage point, usually a perimeter drainage channel.
3. Collection & Pumping: Water is collected in a sump pit and pumped away from the building, keeping the internal space dry.

This approach allows for:

• Breathability, reducing trapped moisture and condensation
• Effective retrofitting without major excavation
• Long-term adaptability in areas with fluctuating water levels

Comparing Membrane Systems vs Tanking

Here’s a detailed comparison of the two approaches:

Feature	Tanking	Internal Membrane Systems
Principle	Impermeable barrier	Water management and drainage
Installation	Exterior (new builds) or internal (retrofit)	Interior only, retrofit-friendly
Handling Hydrostatic Pressure	Direct resistance	Channels water safely
Flexibility	Rigid; cracks can compromise system	Flexible; accommodates minor movement
Maintenance	Low, if intact	Moderate; requires sump pump maintenance
Cost	High, especially external tanking	Moderate; cheaper for retrofit projects
Lifespan	Long, but dependent on integrity	Long, can be upgraded or replaced in sections
Disruption	Major for exterior tanking	Minimal; interior works only
Breathability	Low	High, reduces condensation risk

Advantages of Traditional Tanking

1. Complete Barrier Against Water: If installed correctly, tanking stops water at the source.
2. Proven Technology: Used for decades, especially in high-water-table areas.
3. Durable: Long-lasting if maintained, particularly external systems.
4. Minimal Equipment Needed: No pumps are required for properly designed tanking.

Limitations:

• High cost and disruption, especially for external applications
• Rigid; cracking or settlement can compromise protection
• Less suitable for retrofits in confined spaces

Advantages of Internal Membrane Systems

1. Retrofit-Friendly: Ideal for existing basements where external excavation is impractical.
2. Flexible & Adaptable: Can handle minor movement or settlement in walls.
3. Water Management: Channels moisture safely, preventing hydrostatic pressure build-up.
4. Minimal Disruption: Internal installation is less invasive than external tanking.
5. Reduces Condensation: Breathable systems allow moisture to evaporate safely.

Limitations:

• Relies on sump pumps or drainage systems; failure can cause water accumulation
• Initial cost may be lower than external tanking but includes maintenance of pumps
• Slight loss of internal space due to membrane thickness (usually 10–15 mm)

When to Choose Tanking

Tanking is often preferred when:

• Constructing new buildings with high groundwater exposure
• External access is available and excavation is feasible
• Hydrostatic pressure is extreme and needs direct resistance
• Long-term, low-maintenance waterproofing is a priority

When to Choose Internal Membrane Systems

Internal membranes are ideal when:

• Retrofitting existing basements or cellars
• External excavation is impractical or too costly
• There is moderate water ingress rather than severe flooding
• Homeowners want minimal disruption during installation

Installation Process: Membrane Systems vs Tanking

Tanking Installation

1. Excavate around external walls (if external tanking)
2. Prepare the wall surface (clean, repair cracks)
3. Apply tanking materials: cementitious, bituminous, or sheet membranes
4. Ensure continuity at joints, corners, and floor-wall junctions
5. Backfill and compact soil carefully to avoid damage

Internal Membrane Installation

1. Inspect and repair wall and floor surfaces
2. Fit drainage channels around the perimeter
3. Fix cavity drain membranes or panels to walls/floors
4. Connect to sump pit and pump system
5. Finish walls with plasterboard or other decorative finishes

Cost Considerations

System	Approximate Cost	Notes
External Tanking	£150–£250/m²	Excavation and material intensive
Internal Tanking	£80–£120/m²	Less invasive but labor-intensive
Internal Membrane Systems	£60–£120/m²	Includes sump and pump installation

Note: Costs vary depending on basement size, water table, and project complexity.

Maintenance and Longevity

Tanking

• Typically maintenance-free if undamaged
• External systems may require periodic inspections for cracks or soil settlement

Internal Membrane Systems

• Sump pumps require regular checks to ensure operation
• Membranes are durable but may need inspection every 5–10 years
• Can be upgraded or repaired internally without major disruption

Conclusion

Choosing between internal membrane systems vs tanking depends on multiple factors:

• Nature of the building (new vs existing)
• Level of water exposure and hydrostatic pressure
• Budget and willingness for disruption
• Maintenance preferences

Tanking remains the gold standard for new builds with extreme water exposure, offering a complete and durable barrier. Internal membrane systems, however, provide flexibility, retrofit capabilities, and effective water management for existing basements.

Ultimately, both systems aim to achieve the same goal: a dry, safe, and usable space. Understanding their strengths and limitations ensures homeowners and builders select the best solution for their specific needs.

With careful planning and professional installation, either system can transform a damp basement into a secure, functional area, enhancing comfort, property value, and long-term durability.

Explore our internal membrane solutions here: https://www.ecodampsolutions.com/services/internal-membrane-systems/