Ensuring a building provides shelter from the weather is one of its primary functions.
In recent times, changes in lifestyle have led to more complex building designs, new systems and construction practices. Combined with a shift away from defined building solutions and fewer apprenticeship schemes, that has put more demands on buildings to be properly designed, built and approved to ensure they remain continually weathertight throughout their lives. Increasing numbers of reports of leaks in relatively new buildings also heightened interest in weathertightness.
From early 2000, growing evidence pointed to common problems associated with design features. These included flat roofs, complex building shapes and junctions, parapets, narrow or no eaves, monolithic claddings, untreated framing, sealed decks, built-in balconies and inadequate flashings around windows and doors. Problems were often present in high-density, multi-unit developments.
In 2002, the Building Industry Authority (which became part of the new Department of Building and Housing in November 2004) commissioned the Weathertightness Overview Group to enquire into the weathertightness of New Zealand buildings and concerns about leaking and rotting houses.
Later that year, this group produced the Report of the Overview Group on the Weathertightness of Buildings (commonly known as the Hunn Report). This outlined systemic failures in the building industry that led to inadequate building practices causing leaking, and called for far-reaching changes across the construction industry.
The Hunn Report identified solutions on several fronts to improve building practices. These ranged from improved education and training schemes to the publication of more guidance information on construction practices and materials, such as how to design and build for effective weather resistance and the durability of timber framing.
The New Zealand Building Act 2004 became fully effective from April 2005. This introduced several new initiatives to improve building practices and compliance procedures.
The Department of Building and Housing was given broader powers to deal with the issues and to offer guidance. It was also given the power to initiate an amended system of certification of building methods and products (previously known as product accreditation) for compliance with the New Zealand Building Code.
The amended Acceptable Solution E2/AS1 for the Building Code Clause E2 External Moisture became operative from 1 July 2005, after a one-year lead-in. E2/AS1 includes material specifications and specific details for common wall and roof cladding materials. (It is not mandatory to use this Compliance Document, however it represents a common benchmark for achieving weathertightness.)
From 30 November 2010, builders and designers will be required to be licensed for particular aspects of building work. This licensing requirement will help raise skills and the standards of finished buildings, and ensure improved performances in weathertight building.
The Department of Building and Housing commissioned PricewaterhouseCoopers to undertake an independent report into the size and cost of the weathertightness issue.
The report, which was released in December 2009, showed there is a wide range of the possible number of homes affected, from a low of 22,000 to a high of 89,000. The wide range reflects the fact there is a high level of uncertainty about the number of homes affected that prevents an exact, and accurate, estimate to be made. Nevertheless, the report estimated it is most likely approximately 42,000 homes (called the ‘consensus forecast’) built between 1992 and 2005 have been affected.
The consensus forecast is derived from the analysis of hard data and the views of industry experts who were consulted about this report. The evidence suggests that only a minority of leaky homes have been repaired to date.
Of the leaky homes covered by the re-estimate approximately:
- 3,500 have already been repaired;
- 9,000 are likely to have failed or will fail outside the 10 year limitation period for legal liability.
Using the ‘consensus forecast’, it is therefore likely up to around 30,000 dwellings have already failed, but not been repaired, or will fail in the future (within 10 years of the date they were built).