Time to review E2/AS1

This Issue This is a part of the Exteriors and interiors feature

By - , Build 166

A review of Acceptable Solution E2/AS1 is needed so building design solutions reflect today’s living trends and current building science knowledge. If not, there will be future failures.

THE CURRENT BUILDING CODE Acceptable Solution E2/AS1 has been in force for nearly 13 years and has been the subject of several amendments. It was part of a significant raft of measures introduced to improve building standards and practices in 2004, such as the adoption of cavities, changes to various timber standards, the implementation of the 2004 Building Act and the New Zealand Building Code review.

Amendment 7 in August 2011 increased the requirements for cavities, but this, like the other amendments, only made minor tweaks to the rest of the document. Given the time since major amendments, we must now start to look at E2/AS1 and other building standards and practices differently.

Response to weathertightness issue

The third edition of E2/AS1 was introduced in July 2005 as part of the government’s reaction to the leaky building problem. This issue surfaced in the late 1990s and early 2000s and led to a widespread critical focus on the building industry. The changes to E2/AS1 in 2005 did serve a purpose, particularly with leaky buildings.

Before the third edition, E2/AS1 adopted the non-prescriptive character of the New Zealand Building Code and consisted of 12 pages. The third edition aimed to improve the weathertightness of residential dwellings in New Zealand by introducing a more prescriptive approach. It included detailing for a range of roof and wall cladding types and known problematic areas based on a weathertightness risk assessment of a building.

We have seen a reduction in the consequences of poor detailing and the effect of exterior moisture problems in residential dwellings constructed after 2004–05, particularly with the adoption of cavities.

Factors impacting weathertightness

However, the past changes to E2/AS1 have not provided all the answers for exterior weathertightness. In today’s building landscape, we are facing a unique combination of circumstances that may impact exterior weathertightness. These include:

  • a period of high demand for new housing, along with societal and financial pressures to better use existing land
  • a limited supply of experienced and skilled trades and appropriately skilled building design and inspection professionals
  • a push for mixed-use, multi-unit, mid-rise dwellings that introduce a new array of potential problems
  • rising building costs
  • the use of less-traditional components with unproven durability.

For E2/AS1 to achieve the objective of Building Code clause E2 External moisture, there needs to be consideration given to internal moisture, ventilation and insulation.

Consider Acceptable Solutions for moisture, ventilation and insulation

Due to reduced land supply in our cities, more residential buildings are being constructed on sites lacking in sunlight. These buildings will get limited benefits from the drying effects of the sun. They are also often built adjacent to retained ground, limiting the drying effect of air movement.

Internally, we have also developed living areas that produce more moisture — for example, multiple bathrooms, en suites, kitchens, laundries and bedrooms that are sealed up to prevent airflow into the building. These rooms are also underheated and often have inadequate ventilation systems.

This is a perfect environment for internal mould growth and the associated impacts on human and building health. Significantly increased levels of humidity are also created within the dwelling, often ending up in the roof or the wall cavities.

Fire protection is another area where both external moisture and fire protection issues need to be considered in tandem.

Holistic approach needed

I would like to see a review consider the application of E2/AS1 in a more holistic manner. The review should reflect today’s buildings and acknowledge that exterior moisture issues are interwoven with other issues such as internal moisture, ventilation, structure and fire.

We need to understand that the presence of moisture in a wall system is the manifestation of not just exterior moisture issues but also a result of how we are designing and living in our residential buildings.

Specific areas for review

There are some other specific areas I would like to see an E2/AS1 review address:

  • Reflect current cladding trends with a view to E2/AS1 covering some alternative cladding systems. In my work, I see a growing interest from homeowners in aluminium panels, aluminium plank systems and aerated concrete panels. There are alternative compliance paths for cladding systems currently falling outside the claddings covered by E2/AS1, but pursuing acceptance of alternative methods is a more costly and timely process. In my experience, with the cost of building so high, needing an alternative methods tends to be an inhibitor to the design and use of other claddings.
  • Incorporate details within E2/AS1 for junctions between different cladding systems that are commonly adopted on buildings, such as weatherboard to fibre-cement sheet.
  • Open the restrictive scope of E2/AS1 to include higher wind speed zones. I am based in Wellington, and this restriction effectively means that E2/AS1 does not cover significant areas of hilly terrain.
  • Address several issues relating to joinery/cladding junctions that do not provide adequate obstacles to the passage of air through the walls. I have always specified alternative details in this area.
  • Have a greater focus on appropriate detailing of the roof and wall junction.

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