"Water migrates through the framework, saturating the framework elements including the timber framing. This creates an environment for the development of fungal decay.
"The overview group has seen evidence of substantial portions of the timber framing being rotted out within two years of construction. The process appears to be accelerated where untreated timber is used in framing.
"In some cases the decay threatens the structural integrity of the building, creating the risk of failure and collapse."
Scale of the problem
There is evidence of a growing number of new housing constructions showing signs of water damage, says the report.
The problem is worst in upmarket-style, one-off, single houses and multi-unit condominium-type apartments.
Both building types tend to use monolithic panel systems with features that exacerbate the problem. These are complicated roof forms, reduced or non-existent eaves, windows and doors flush to the wall with inadequate flashings or even no flashings for protection against the rain.
The problem is worst in Auckland where these buildings are most popular.
The report says it is still difficult to know the extent of the problem in New Zealand.
"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 include, among others, the concerns of
* Building owners that their house values may be affected by bad publicity
* Builders that they may be liable for repair and reparation
* Other parties who may be liable for the costs of repair and reparation.
"Although the full extent of the problem is not yet known, the overview group is convinced of the significance of the problem and that urgent action is required and must not be delayed while the extent is investigated further."
The report estimates the national repair bill at $120 million to $240 million for homes built in the past decade (assuming that half the apartments with monolithic cladding need repairs at an average cost of $20,000).
It says this estimate has a high degree of uncertainty. "Even at the conservative end of the range, however, the scale of the problem is unacceptably high."
Health and safety risks
The report warns of potential dangers for health and safety if the problem is not addressed quickly. It repeats its warning last month that people could be killed or seriously hurt if rotting balconies collapse.
It also notes evidence of toxic mould found during repair work on leaking buildings which poses a potential risk to workers and homeowners. It urges the Building Industry Authority and Ministry of Health to identify the health risks and any precautions that should be taken.
Causes: technical problems
Designers are using complex building forms which do not allow for "the behaviour of rain (horizontally and vertically)" in the Auckland climate, says the report. There is a general lack of understanding of the importance of flashings, even at windows and doors. Their use can often be minimal and in worst cases non-existent.
Monolithic claddings have become far more popular. These are supposed to be waterproof, but when water does get through it cannot get out easily, as it does with traditional weatherboard or brick cladding.
"Retained water or moisture affects all the materials involved," says the report. "Primary of these is the now generally used untreated kiln-dried timber used for framing, although steel frame and strapped masonry can also be affected. While treated timber will also deteriorate in wet conditions, untreated timber seems particularly susceptible."
The Forest Research Institute is running tests comparing the performance of treated and untreated timber. Preliminary results are expected this month.
Causes: social issues
The report says development of many large, inner-city, multi-unit projects now involves so many people that the comment is frequently heard that "no one takes responsibility any more".
It adds: "The respective roles and responsibilities of architects, main contractors, subcontractors, specialist sub-trades and project managers and developers become very complicated, hard to define and consequently unclear and hard to understand.
"There can be over 50 subcontractors on a large site ... Such an environment results in poor planning, co-ordination and a lack of individual responsibility and co-operation between the various sub-trades.
"It has been reported to the overview group that more and more often responsibilities and liabilities are being passed down the line to the subcontractors and sub-trades. Whatever the reality of this, the circumstances result in a collective system failure - and buildings that leak."
Developers, builders, architects
The report is scathing about the way professionals fail to work together.
"Today, project management appears to be a matter of programming and co-ordinating the arrival of materials and sub-trades on-site," it says."Quality assurance on-site appears to get lost.
"In many instances, building project managers may have little contact with, or knowledge or understanding of, the situation on-site itself. Their primary concern is with speed and minimising cost.
"Similarly, property developers often have no direct background in or even particular knowledge of the building industry. Often, their investment in building is purely financial."
Architects do not escape criticism. The report says they have "either abrogated their traditional responsibilities for supervising construction or have been pushed out by those with a different concept of value for money".
It condemns the trend in architectural education towards "art" to the detriment of science and technical aspects of building.
Workmanship
There is a perception in the industry that skill levels on building sites are declining, says the report. Reasons given include problems with the apprenticeship system, lack of skilled workers, the predominance of labour-only contracts and lack of regulation of standards and of quality assurance and accountability across the industry.
It suggests the Building Industry Authority explore some form of regulation, such as compulsory registration, although it warns that this may not cover 16,000 builders who do not belong to a recognised association.
Building practices
"Two fundamentals of good detailed construction design seem to be being bypassed in some instances," says the report.
"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."
The team urges further investigation of a water-draining cavity inside outer walls - a "second line of defence" adopted by British Columbia as a solution to its leaky building problem and first proposed in the inquiry's interim report in May.
The solution might look expensive, says the report, but the consensus from builders is that this and greater use of flashings would not add significantly to construction costs and would save money in the long run.
Overseas experience
In the United States, where 1.6 million homes are built each year, 90 per cent of them wood-framed, 29 per cent of recent homes have problems, with 6 per cent considered serious, says the report. Ninety per cent of surveyed problems are due to rainwater leaks.
In Canada, 800 three to four-storey condominium complexes were built in Vancouver between 1980 and 1995 with over half experiencing leaks. It is estimated that 50,000 units are affected.
Repair costs range from C$35,000 ($47,140) to C$40,000 for a condominium unit valued at C$150,000. In Vancouver, condominiums are hard to sell unless the cladding has been replaced, irrespective of damage. The builders warranty scheme has collapsed.
The report also notes that polystyrene-based "chilly bin claddings" - officially known as EIF (Exterior Insulation and Finish) systems - are effectively banned in Vancouver, North Carolina and Georgia.
New Zealand does not yet have detailed figures on the scale of the problem like the US and Canada, says the report.
"There is no doubt, however, that the conditions that have produced the problems of the past decade in British Columbia and North Carolina exist in this country.
"There is clear evidence of a growing number of new housing constructions showing signs of water damage. The numbers uncovered (literally) are likely to increase, probably significantly."
Confidence in building industry
The report says there is now much greater awareness that the problem has the potential to damage public confidence in the industry, if something is not done.
It worries that so far "the reaction has been largely one of angry owners, faced with large and unexpected repair bills, seeking redress through the legal system. It would seem most of these cases are settled out of court, many of the settlements subject to confidentiality agreements, so that there is no public record of them and therefore a barrier to accruing the very information needed for preventative action".
The report calls for an industry summit of chief executives and board chairmen to look for answers. It adds that this might still be seen by some as sweeping the problem under the carpet and suggests the Government consider some form of public inquiry into the building industry - similar to one recently carried out in New South Wales.
Building inspections
The report found strong anecdotal evidence that council procedures were driven by the need to save time and money and minimise compliance costs for developers. Some councils rated their staff by numbers of consents issued in minimum time and the average time each inspection took. The report warns that this short-term cost-saving mentality could compromise the long-term value of New Zealand's homes.
It also says councils do not demand enough detail on plans before they issue consents. There is no mandatory requirement to inspect buildings as the cladding is being sealed - the crucial point for weathertightness - and some councils have suggested that "trusted" contractors should be allowed to police themselves.
"There is a lack of consistency throughout the consent, inspection, and compliance process and that this requires urgent consideration and action."
It recommends that council building inspectors and certifiers - their private sector equivalent - be required to have a tertiary-level qualification to improve their training and grasp of modern methods.
Building products
The report says the industry relies too heavily on inadequate "appraisals" of products - technical opinions by qualified, independent organisations such as the Building Research Association or a university. However, these appraisals have been criticised for relying too heavily on claims made by the supplier's trade literature.
"The current weathertightness problems relate to a large extent to cladding products that have been the subject of appraisal ... The products' function and purpose as part of a building envelope or building system is not being adequately appraised."
Independent research is urgently needed and could be financed with a surplus from the building levy, the report says.
It says research is fragmented and the main agency is the Building Research Association, which is not seen as independent of the industry. Research should focus first on multi-unit properties with monolithic cladding as these seem to have the greatest problems.
The report strongly supports one proposal to test a sample of 400 houses built since 1990 across five main centres.
How we used to build a home in New Zealand
For more than a century, building the average New Zealand home involved going to an architect, draughtsman or a builder and coming up with an agreed design. A builder was appointed, and a price agreed by the owner. The architect or builder ensured compliance with all consent processes. Work began. So did a professional relationship.
Supervision lay with the architect or the builders.
In some cases a clerk of works was employed by the owner to watch over the job.
The builder generally was responsible for the employment, supervision and quality control of subcontractors, many of whom the builder regularly worked with.
The builders would hire a relatively stable workforce of skilled carpenters and labourers, many of whom would be highly trained and qualified.
They had overall responsibility and in general took a pride in the completed product.
There was an intimate professional relationship between the owner, the designer and the builder, with a tacit sharing of responsibility among all three.
The builder might provide warranties or guarantees.
The architect took responsibility for design and supervision.
How the housing market works today
Today the housing market, particularly in the cities, has changed dramatically. Development of many large multi-unit projects will be driven in the first instance by a property developer.
The developer may employ an architect or draughtsman to prepare the minimum drawings necessary to obtain resource and building consents.
Then the developer will find a building contractor and appoint a project manager to co-ordinate all of the work on site.
Alongside the main building contractor, there will often be many "labour-only" subcontractors. This means the subcontractors and sub-trades - the actual workers - often are not well known to the main contractor and even less to the project manager and developer.
The co-ordination and sequencing of cladders, flashers and plumbers is often difficult and not given adequate priority due to time and cost constraints. The environment results in poor planning, co-ordination and a lack of individual responsibility, less co-operation between trades, and more and more responsibilities being passed "down the line".
Whatever the reality of this, the circumstances result in a collective system failure - and buildings that leak.
- Source: Building Industry Authority:
Report on Weathertightness of Buildings
* If you have information about leaking buildings,
email the Herald
or fax (09) 373-6421.
Further reading
Feature: Leaky buildings
Related links
