*ARCHIVE* - Preliminary report: BIA Overview Group on Weathertightness of Buildings - 20 May 2002

On 18 February 2002, the Building Industry Authority appointed a Weathertightness Overview Group to inquire into the weathertightness of buildings in New Zealand in general, and in particular into the current concerns regarding housing that is leaking with consequent decay. 

The Overview Group consists of Don Hunn (Chair) former Chief Executive of the State Services Commission, Ian Bond, Civil Engineer and David Kernohan, Architect.  Broadly, the Overview Group's Terms of Reference require them to identify:

• The nature, extent and effect of the current inability of some buildings to adequately deal with moisture in and through their wall cladding systems
• Potential contributing causes
• Whether failures are attributable to deficiencies in the Building Act, the Building Regulations, or in the manner in which these are administered.
• Any other relevant matters.

The Overview Group has met formally on four occasions to date.  It has undertaken a literature search to learn more of the nature and extent of the problem both within New Zealand and beyond.  It has met with experts on the matter both from within New Zealand and from Canada where there is experience with similar difficulties, especially in British Columbia.  The Overview Group is aware of and welcomes the work of the Building Research Association of New Zealand (BRANZ)'s Weathertightness Steering Group and has met with its Chair and members of the Group. 

One of the Overview Group's meetings was held in Auckland over two days.  The Overview Group visited a number of affected buildings and met with representatives from different sectors of the building industry including building owners, building developers, building contractors, product manufacturers and building inspectors and certifiers.  The Overview Group will continue with a process of wide consultation.

Although it is too early for the Overview Group to have come to any definitive conclusions, the Group  made a preliminary oral report to the Building Industry Authority on 10 May 2002.  Their early findings suggest:

Nature, Extent and Effect

There is some evidence of a growing number of new housing constructions showing signs of water damage.  The incidences noted are characteristically building types using monolithic cladding systems  and designed in a style that commonly includes features that exacerbate the problem, such as complex major and minor roof forms, much reduced and in many cases no eaves, balconies both external and internal to the outer wall plane, and, often, flush windows and doors with inadequate flashings and in some reported cases without flashings.

At present, for a number of reasons, it is difficult to know the extent of the problem.  It is a "hidden" problem literally, hidden within the walls of buildings.  It is becoming less hidden as the growing incidence of water damage is recorded.  However, there is anecdotal evidence that it is also hidden by other circumstances.  These may include, among others, the concerns of:

• building owners that their house values may be affected by adverse publicity
• builders that they may be liable for repair and reparation
• insurers that they may be liable for the costs of repair and reparation.

To date, the effects of the problem, that is repairing the damage, have been largely dealt with by building owners and their builders though not without incidences of frustration and/or litigation.   Issues of reparation involving insurance companies are being largely settled out of Court.  At present, the effects of the problem are being seen largely as a matter of costs and liabilities.  However, the Building Industry Authority is concerned that in addition to the cost implications of the lack of good practice, there are potential dangers for health and safety if the issue is not addressed systematically and quickly.   For instance, water damaged timber is a breeding ground for fungal growths.  There is some evidence of toxic fungal growth being evident during some repair work.  There is clearly a potential risk from toxic fungal growths for repair workers and home-owners.  The extent of this risk is not known.  Further, water damaged timber will become structurally unsound and fail if undetected. The extent of this risk is also not known.

Potential contributing causes

A preliminary view of the Overview Group is that from their limited investigations to date the principal causes of the problem are both societal and technical. 

Societal refers to the economy and the housing market.  The market is highly competitive. There is a desire for inner city dwellings on land that is at a premium.  The preference for inner city multi-unit housing projects in the major New Zealand cities in particular is a phenomenon of the last ten to fifteen years.  The availability of new and potentially cheaper forms of building construction, notably monolithic cladding systems, has led to owner and developer preferences, also influenced by overseas imagery, for a certain style of building.  Holding prices down (cost cutting) both in terms of the finished product and its construction is paramount and appears to have led to some inadequate practices.

Technical has to do with building in this style.   Monolithic cladding systems used are promoted as being low maintenance and providing a sealed and waterproof outer skin. The desire to seal buildings dates back to the energy crisis of the 1970s.  Energy efficiency is advocated in the Building Act.  The complexity of the building forms of the style means there are a multiplicity of junctions and penetrations.  The importance of and in some cases even the need for flashings at junctions and penetrations (even at windows and doors) is not always well understood and their use is in some cases minimal or non-existent.  Thus, there are systemic problems in the way in which component products are put together rather than necessarily any specifically identifiable problem with one product. 

When water penetrates monolithic cladding systems, the water is held and cannot get back out easily.  Trapped water affects all the materials involved.  Primary of these is untreated timber commonly used for framing although steel frame and strapped masonry construction could also be affected.  While treated timber will deteriorate in wet conditions, untreated timber seems particularly susceptible.  There is some evidence that where untreated timber has become wet, the spread and rate of decay or fungal growth has been faster and more widespread than might have been expected otherwise.

In addition, a combination of societal and technical causes manifests itself in the comment that "no-one takes overall responsibility for the project anymore".  The respective roles and responsibilities of architects, main contractors and project managers are unclear.  There can be over 50 sub-contractors on a large site.  The co-ordination and sequencing of cladders, flashers, plumbers for instance is often difficult and not given adequate priority due to time and cost constraints.  This all contributes to a system failure - and buildings that leak.

Deficiencies in the Building Act?

The Building Act has as a stated purpose, that the Act must provide the necessary controls for ensuring that buildings are safe and sanitary and in achieving this, regard shall be had to the need to safeguard people from possible injury, illness, or loss of amenity.   The Building Code cites explicit requirements and criteria for a building's structural integrity.  However, it is less explicit on the requirements and criteria relating to weathertightness.  Further, it has been suggested that the enactment of the Act and its supporting documents may not be satisfactory.  Building inspectors and building certifiers are involved in the processing of building consent applications from prospective home-owners and the follow-on construction inspections and code compliance certification.   Building consent application documentation is often little more than a sketch design with little if any detail on the likes of the all-important flashings.  Engineering input is largely structural with little if any reference specifically to weathertightness.  Comment has been made that code compliance inspections during construction are more concerned with structure and drainage than with issues of weathertightness.   All of the above may reflect the lack of emphasis on weathertightness detail in the Approved Documents.

Any other relevant matters

It has been commented that Territorial Authorities prescribe criteria in relation to plot ratios and side yard provisions in their District Plans.  There is evidence that in some cases the removal of eaves is driven by developer/designer desires to maximise accommodation in relatively small urban and suburban sites to meet District Plan requirements.  This suggests the adoption of this as a preferred building design style, is not always just for aesthetic or social reasons.

Commentary

While further research into the nature and extent of the problem must be undertaken, it may be wise at this time to accept that there is a problem and that something(s) should be done now.  The causes are multi-facetted.  They may be driven by cost and economic pressures.  These affect owner and developer choice of building form and the ways by which buildings are constructed.  In addition, new materials and changes in the structure of the building industry and its on-site processes and practices are contributing further to the problem.  There are gaps in the process that are creating gaps in buildings. 

At a detailed technical level, two fundamentals of good detailed construction design are being by-passed in some instances.  Both may have cost consequences.  The first is the loss of the traditional "belt and braces" approach to construction practice.  This accepts that water will penetrate the exterior of a building and that there should be a "second line of defence", a means of getting the water away and a means of drying out any wet elements.  The second is the lack of or misuse of flashings at junctions and penetrations.  These are being dispensed with or are detailed inadequately.

It is important to note that buildings using monolithic cladding can be and are being built in a weathertight manner.  However, to do so clearly requires greater care and attention to detail by both the designer and constructor than is all too often being applied at present.  This may involve a more conservative approach to the design, such as the use of cavities within the walls as a "belt and braces" device, and the design and installation of more effective flashings at doors and windows and other junctions and penetrations.  Consideration should also be given to a return to the use of treated timber on the wall frames of outer skin walls or at least the bottom plate of the frame in cases where there is high risk of water ingress or resultant damage, for instance in monolithic clad housing without eaves or where the building will be exposed to severe wind conditions.  

There is potential for a major systemic breakdown across the industry.  While buildings have always leaked, traditional building methods have had a greater degree of redundancy in their design  - "belt-and-braces" - and have coped by providing reasonable protection and by dealing with water penetration when it occurs - even if inadvertently.  A confluence of factors has now made the systemic problem manifest.  In summary, these include in no particular order of importance:

• Changes in responsibilities and relationships of designers and builders.
• Town planning criteria relating to plot ratio and yard distances that inadvertently lead to particular building solutions or contribute to the choice of particular styles.
• Variable application of professional and trade skills and good judgements.  There has been some anecdotal comment about an identifiable decline in the levels of skills in various trades on site.
• Changes in on-site management structures and responsibilities (sub-trades).
• Imperatives of cost and speed (cutting corners).
• Emphasis among product manufacturers on product rather than building systems
• Lack of effective supervision/inspection practices.
• Lack of emphasis and detailed attention to weathertightness in building compliance documents compared to, say, structural integrity.

Overarching is the fact that the public and in particular new home purchasers can't be expected to, and more often than not don't, understand the multiplicity of issues surrounding this complex subject.  They expect the design professions and the building industry to protect them, and rightly so.  They don't expect leaking buildings. 

The Building Industry Authority is committed to:

• Informing the public of the issues.
• Ensuring the industry is responsive to the problem (coherently and cohesively).

Actions

The Overview Group has recommended to the BIA that some actions be implemented immediately.  These include that the following should be prepared or implemented by 31 July 2002:

• Performance Briefs for and initiation of research project(s) to determine the extent of the problem.
• Performance Briefs for and initiation of research project(s) to determine the nature of the problem.
• A commentary on the causes of the problem and a strategy to eliminate or reduce their incidence.
• Recommendations for action (short term and long term) to eliminate or reduce the problem.
• A means for monitoring the ongoing investigation and implementation of the Group's recommendations.
• The current review of the sections of the Building Code relating to durability and weathertightness.  This to be completed under the present industry-wide review team as a matter of urgency and put out to the wider industry for comment.  The review is to address not only the detail of the Approved Documents but also the overarching requirements of the Building Code Objectives, Functional Requirements and Performance
• Criteria relating to durability and weathertightness, that is, the provisions in Clauses B2 and E2.
• A forum of industry leaders (including the Minister) to present and debate the high-level issues surrounding the problem that has led to the current situation and to seek their pro-active support in preparing an industry-wide response that will be ongoing and lasting.
• A communications strategy to keep the public and the industry fully informed of the issues and action taken.