Addressing Below Ground Walls

Internationally Recognized Solutions

NCC Version:

2019 Volume 2 – Amendment 1

Area of NCC Requirements:

Part 2.2: Damp and Weatherproofing

• P2.2.1 – Rainwater Management
• P2.2.2 – Weatherproofing
• P2.2.3 – Rising Damp 

The Challenge

Below-ground external walls present one of the most difficult compliance challenges in residential construction. In this project, portions of the external wall construction were located below natural ground level—an area where the NCC provides no Deemed-to-Satisfy (DTS) guidance for waterproofing.

Compounding the issue, the design did not allow for the typical slab edge exposure normally relied upon to manage moisture and demonstrate compliance. Without a compliant pathway, the project faced potential risks of water ingress, rising damp, long-term material deterioration, and approval delays.

What This Really Means

Even when DTS provisions are silent, the NCC still requires that buildings manage rainwater, prevent moisture penetration, and protect occupant health and amenity. For below-ground construction, this means demonstrating that the wall system can resist groundwater pressure, manage moisture over time, and remain durable for the life of the building.

Where prescriptive rules stop, performance-based solutions become essential.

The Solution

A performance-based assessment was undertaken to demonstrate that the proposed below-ground wall design achieved the intent of the NCC’s damp and weatherproofing provisions.

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 to prevent rising damp in the absence of slab edge exposure
• Long-term durability and maintenance of the waterproofing strategy
• Alignment with internationally recognised best-practice benchmarks for below-ground construction

Rather than relying on a single layer of protection, the performance pathway assessed how multiple elements work together as a system to deliver a dry, healthy internal environment consistent with NCC objectives.

Why This Matters

• How the wall system resists water ingress below ground level
• The ability of the construction to manage groundwater and hydrostatic pressure
• Measures to prevent rising damp in the absence of slab edge exposure
• Long-term durability and maintenance of the waterproofing strategy
• Alignment with internationally recognised best-practice benchmarks for below-ground construction

Rather than relying on a single layer of protection, the performance pathway assessed how multiple elements work together as a system in line with British Standard BS8102:2022 to deliver a dry, healthy internal environment consistent with NCC objectives.

Basement walls can lead to issues. 

Reach out to our team for the solution.