Below Ground Masonry

Weatherproofing and Damp Control

NCC 2022 Volume 2

Area of NCC Requirements:

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

The Challenge

Basements are some of the most complex areas to waterproof, especially when constructed in blockwork below natural ground level. Unlike walls above ground, the NCC does not provide Deemed-to-Satisfy (DTS) provisions for these conditions.

Without a compliant pathway, issues such as water ingress, rising damp, and poor drainage can easily arise. The consequences are serious—ranging from structural deterioration of walls to mould, unhealthy living conditions, and loss of amenity for future occupants.

What This Means

The NCC’s provisions for rainwater management and weatherproofing are designed to ensure that internal spaces remain safe, dry, and healthy. But where DTS rules are silent, designers and builders need to look beyond prescriptive solutions and justify that their systems still meet performance requirements.

In below-ground construction, this typically means proving that walls can resist hydrostatic pressure, manage groundwater effectively, and remain watertight for the life of the building. International standards, are often used as benchmarks for this level of performance.

The Solution 

A performance solution was developed using expert judgement and international best practice. The strategy combined multiple layers of protection rather than relying on a single method, addressing:

• Barrier protection to stop water penetration at the surface
• Integral protection through treated or modified concrete elements
• Drained protection via concealed systems that manage any water that does get through

By integrating these approaches with appropriate membranes, additives, and drainage detailing, the system was designed to provide the highest level of watertightness—suitable for habitable basement spaces.

Why This Matters

The final assessment confirmed that the design met the NCC’s performance requirements for rainwater management, weatherproofing, and rising damp. Importantly, the layered system ensures durability and reliability where DTS provisions offer no guidance.

This highlights the value of performance solutions: they allow projects to adopt internationally recognised best practice, delivering safe, dry, and compliant basement spaces even under the most challenging site conditions.

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