Clause E2 of the New Zealand Building Code, called 'External Moisture,' helps make sure buildings stay dry, safe, and healthy. It’s especially important for restricted building work (RBW) where following moisture rules is legally required.
Licensed building practitioners (LBPs) need to fully understand Clause E2 so they can meet the rules and build weathertight homes that meet the Code.
Clause E2 – External Moisture
Clause E2 of the New Zealand Building Code, called ‘External Moisture,’ helps make sure buildings stay dry, safe, and healthy. It’s especially important for restricted building work (RBW) where following moisture rules is legally required.
Licensed building practitioners (LBPs) need to fully understand Clause E2 so they can meet the rules and build weathertight homes that meet the Code.
What is Clause E2?
Clause E2 explains how buildings should be built to keep rain and moisture out. Its main goal is to stop water from getting into parts of the building like the roof, walls, windows, and doors, so it doesn’t cause damage or dampness. The clause requires that:
- External moisture does not cause undue dampness or damage to building elements.
- Water cannot enter the building through the roof, wall claddings, and external openings.
- Any moisture that does get through is able to drain or evaporate without causing harm.
E2/AS1 is the ‘Acceptable Solution’ for meeting Clause E2. It’s a commonly used set of instructions that explains which materials, building methods, and design details will keep water out and meet the rules.
What is E2/AS1?
The Acceptable Solution E2/AS1 is a practical guide that shows how to meet the rules in Clause E2 of the Building Code. It explains how to choose and install things like roofs, walls, flashings, windows, and doors to stop water getting in. It also helps builders work out the risk of leaks based on factors such as wind zone, roof overhangs, and the complexity of the building.
The guide includes details on drainage systems, weathertight barriers, and sealing around openings to make sure moisture is managed properly. It’s an important tool for LBPs, especially when doing restricted building work.
Why Clause E2 matters for restricted building work
Restricted building work is construction or design work that is critical to the structural integrity or weathertightness of a house or a small-to-medium apartment building. This includes work on the primary structure, external moisture management systems, and fire safety systems.
Clause E2 is closely linked to RBW because weathertightness is a major part of a building’s performance. If moisture isn’t managed properly, it can lead to serious problems like:
- Structural degradation (for example, timber rot or corrosion of metal components).
- Health issues (for example, mould growth or poor indoor air quality).
- Costly remediation and legal disputes.
Any RBW involving the building envelope must comply with Clause E2. LBPs who do this kind of work are legally responsible for making sure that their designs and construction methods meet or exceed the requirements of this clause.
The role of LBPs in making sure building work follows the rules
LBPs are trusted to do or oversee RBW. This includes:
- Understanding and applying the principles of Clause E2.
- Selecting appropriate materials and systems that comply with E2/AS1 or an alternative solution.
- Making sure that construction details such as flashings, junctions, and penetrations are completed properly to stop water getting in.
LBPs also need to identify and manage risks. For example, buildings in areas with strong winds or heavy rain need better systems to keep water out. LBPs must adjust their building methods to match the environmental and design conditions of each project.
Training and competency
To keep their licence, LBPs must regularly complete professional development and stay up to date with changes to the Building Code. This means knowing about any updates to Clause E2 and its guidance documents, such as E2/AS1. These updates might include new materials, building methods, or tools for assessing risk, and LBPs need to understand and apply them in their work.
MBIE (Ministry of Business, Innovation and Employment) provides resources, training modules, and technical guidance to support LBPs in this area. However, it’s ultimately up to each builder to make sure they understand how to use Clause E2 properly and feel confident applying it on site.
Conclusion
Clause E2 isn’t just a regulatory requirement — it helps ensure buildings in New Zealand remain safe, durable, and healthy. For LBPs, understanding and applying Clause E2 is a key part of doing their job well. Whether building a new home or repairing an existing one, following E2 is essential for delivering strong, weathertight, and high-quality buildings. As materials, weather conditions, and design trends continue to evolve, Clause E2 becomes even more important. LBPs play a vital role in ensuring homes stay dry and safe — not just by following rules, but by protecting clients, earning trust, and helping build homes that stand the test of time.