Managing Moisture Below Ground
Internationally Recognised Waterproofing Solutions

NCC Version

2022 Volume Two 

Area of NCC Requirements:

Part H2 – Damp and Weatherproofing

• H2P1 – Rainwater Management
• H2P2 – Weatherproofing
• H2P3 – Rising Damp

The Challenge

Below-ground external walls can create complex compliance issues in residential construction. Unlike typical above-ground wall systems, walls that are partially or fully located below natural ground level are exposed to increased moisture risks, including groundwater, surface water run-off, hydrostatic pressure and rising damp.

In this project, part of the external wall construction was located below ground level. The design also did not allow for the usual slab edge exposure that is often relied upon to assist with moisture management and compliance.

Because a clear Deemed-to-Satisfy pathway was not available for the specific construction arrangement, the project required further assessment to demonstrate that the wall system could achieve the required level of performance.

Without a suitable compliance pathway, the project risked water ingress, dampness, long-term deterioration of building elements and delays during the approval process.

What This Means

The NCC requires buildings to manage rainwater, prevent moisture penetration and protect the health, amenity and safety of occupants.

For below-ground wall construction, this means the building system must be able to resist moisture from the surrounding ground while also managing rainwater and dampness over the life of the building.

Where the DTS provisions do not provide a direct solution, compliance can still be achieved through a Performance Solution.

This requires a technical assessment of the proposed wall system, waterproofing strategy, drainage provisions, damp-proofing measures and long-term durability.

The focus is not simply on whether one product has been applied. The key question is whether the full wall and waterproofing system can work together to provide a dry, durable and compliant internal environment.

The Solution

A Performance Solution was prepared to assess the proposed below-ground wall construction against the relevant NCC damp and weatherproofing requirements.

The assessment considered:

• How the wall system resists water ingress below ground level
• The ability of the construction to manage groundwater and hydrostatic pressure
• Measures used to reduce the risk of rising damp
• Moisture protection where typical slab edge exposure was not available
• Long-term durability of the waterproofing strategy
• Drainage and moisture management around the wall system
• Alignment with internationally recognised waterproofing principles, including BS 8102:2022 – Protection of Below Ground Structures Against Water Ingress

Rather than relying on a single waterproofing measure, the performance-based approach considered how multiple elements could operate together as a complete system.

This included waterproofing, drainage, damp-proofing, construction detailing and supporting technical evidence to demonstrate that the proposed design could satisfy the intent of the NCC.

Why This Matters

Below-ground walls are high-risk areas when waterproofing and moisture management are not properly considered.

If water is not controlled correctly, it can lead to damp internal spaces, mould growth, damage to finishes, deterioration of building materials and costly rectification works after construction is complete.

A Performance Solution provides a practical compliance pathway where the standard DTS provisions do not directly address the specific construction method used on site.

By assessing the wall system against the relevant NCC Performance Requirements and recognised below-ground waterproofing principles, the project team was able to demonstrate that the proposed construction could provide appropriate protection against rainwater, weather exposure and rising damp.

This approach gives builders, designers, owners and certifiers greater confidence that below-ground wall systems can be assessed properly and achieve a compliant outcome.

Basement walls can lead to complex compliance issues. 
Reach out to our team for the solution.