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Basement Block Wall Waterproofing

Basement Block Wall Waterproofing

Waterproofing Blockwork Basements

When DTS Isn’t Enough  


NCC 2019 Volume 2, Amendment 1

Area of NCC Requirements:

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


The Challenge

Basement walls made from blockwork present a unique waterproofing challenge. Unlike roofs or above-ground walls, there are no Deemed-to-Satisfy (DTS) provisions within the NCC that directly address below-ground blockwork waterproofing.

This compliance gap raises a critical question: how do you ensure that subterranean walls remain resistant to rainwater, surface water entry, and rising damp? Without a considered approach, the risks are significant—deterioration of building materials, mould growth, and unhealthy internal environments.


What This Really Means

In practice, this means designers and builders are left without a prescriptive checklist when dealing with basement blockwork. Yet, the NCC still requires that habitable spaces be protected against water ingress and dampness.

The absence of DTS provisions doesn’t remove the obligation—it shifts the responsibility onto performance-based solutions that can prove equivalent or better compliance. For habitable basements, that means not only resisting occasional seepage but achieving a level of watertightness that ensures long-term durability and safe, healthy living conditions.


The Solution 

A performance solution was developed drawing on international standards and expert judgement. The system combined both Type A (barrier protection) and Type B (integral protection) strategies, using:

  • Treating core-filled blockwork walls.
  • External barrier protection.
  • Under-slab protection.
  • Surface and sub-surface water drainage. 
  • Protection sheets for durability.

This layered approach provided a redundancy for habitable basement spaces.

The assessment confirmed that, when compared with NCC intent, the system not only equalled but in some respects exceeded DTS expectations for above-ground weatherproofing.


Why This Matters

The report concluded that the performance solution satisfied NCC requirements for rainwater management, weatherproofing, and rising damp. More importantly, it provided builders and owners with confidence that habitable basements could remain dry, safe, and structurally sound over the long term.

When DTS provisions stop short, performance solutions open the door to international best practice and innovative detailing. For projects involving blockwork basements, this isn’t just about code compliance—it’s about safeguarding investments and creating healthy living environments.


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