External water ingress is often a contributing factor in most building failures, and avoiding rain damage can be one of the most challenging tasks that designers and builders face. Our nation’s history reminds us that designing for weathertightness should begin long before many other construction details are considered. Building properties right the first time ensures more New Zealanders have access to safe and healthy homes. Yet many new residential builds leak.
A 2020 BRANZ industry survey on resolving industry beliefs that hinder weathertightness solutions found that better-quality design, improved control processes, and cultural change are necessary within the construction industry. Improved training and education for builders and architects, more detailed plans, improved liability schemes, and increased awareness of compatible materials were other solutions proposed by survey participants.
Survey responses suggest weathertightness is especially present in structures with complex designs. Underpinning these issues is a desire for affordable homes, “prioritised above concerns about construction quality, and by the prevalence of risk-avoidant behaviour by some building professionals who seek to limit their exposure to liability”. Preventing weathertightness is a complicated issue with no single cause.
Learning from New Zealand’s past building failures, especially the leaky homes crisis of the 1990s and early 2000s, has shaped a new, more robust approach to weathertightness in residential construction. The widespread issues of that era, rooted in poor design, substandard materials, and inadequate oversight, highlighted the urgent need for clear, practical, and watertight principles.
Central to this new approach is the 4Ds framework: Deflection, Drainage, Drying, and Durability. These principles provide a comprehensive strategy for keeping water out and protecting the integrity of buildings:
Deflection is the first line of defence, focusing on preventing water from reaching vulnerable parts of the building. This is achieved through features like eaves, overhangs, and well-designed cladding systems that shed rain away from walls and openings.
Drainage recognises that some water will inevitably get past the outer defences. Effective drainage systems—such as flashings, wall wraps, and drained cavities—ensure that any water entering the building envelope is quickly directed back outside, minimising the risk of damage.
Drying addresses moisture that remains within the structure. Proper ventilation and the use of vapour barriers and insulation allow any residual water to evaporate or diffuse, preventing the build-up of moisture that can lead to mould or decay.
Durability underpins the entire approach. Selecting materials and construction methods that can withstand New Zealand’s challenging climate, characterised by wind-driven rain, humidity, and temperature swings, ensures that buildings remain weathertight over time.
These lessons from the past have been embedded into the New Zealand Building Code and industry best practices. However, ongoing vigilance is required. As architectural styles evolve and the demand for affordable housing continues, the 4Ds must remain at the forefront of every project. By prioritising these principles and building a culture of quality and accountability, the industry can avoid repeating past mistakes and provide safe, resilient homes for future generations.
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