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Building Weathertightness

Weather tightness has become an important issue in New Zealand. The Claddings Institute of New Zealand has been making its members aware of these problems and, in 2000, undertook a study tour to the USA and Canada.

Summary of findings fo the New Zealand Industry Study Tour to the USA and Canada, November 5-10, 2000

Study tour participants:

  • Brad Ridoutt, Manager Built Environment Programme, Forest Research;
  • Dale Knox, Systems Design Engineer, James Hardie Building Products;
  • Guy Cavanagh, Marketing Engineer, Carter Holt Harvey;
  • Kevin Golding, Manager-Future, Winstone Wallboards;
  • Philip O'Sullivan, President, Claddings Institute of New Zealand;
  • Rosemarie Knight, Development Executive, Winstone Wallboards;
  • Wayne Sharman, General Manager Science and Engineering, BRANZ.

Background

Early last century, New Zealand's residential architecture and construction was influenced greatly by North America. Timber is an abundant resource in both regions and remains the predominant structural material used in housing today.

Since the mid-1980s the range and complexity of cladding materials have flourished allowing a freedom of style and architecture that has changed our residential landscape.

However many of these recent buildings have weathertightness problems. New Zealand's pattern is strikingly similar to reported failures in North America.

A forum was held on weathertightness to help create a greater industry awareness of building leakage. The study tour was one of the outcomes. The tour focused on the PATH Conference on Duarbility and Diaster Mitigation in Housing, held in Madison, Wisconsin, and a visit to Vancouver, Canada on the return leg. This coincided with a meeting of BERC, a reserach consortium that leads weathertightness research at present. Three of the New Zealand group were able to attend that meeting.

Summary of findings

Scientific research is needed to better understand the building envelope and its role with moisture.

Such understanding will eventually lead to a rational approach for the development and design of exterior wall systems.

Technology is best transferred from research agenices to industry by creating useful tools for design and understanding.

Education is necessary for all levels and parts of the industry.

Even with improved codes, the implementation through the design, approval and construction phases will be an elusive goal.

In order to bring about successful outcomes, co-ordinated government agency and industry initiatives are best.

While timber framing is the predominant structural form in housing, it is being challenged by its perceived poor performance during hurricanes and because of reported termite and decay problems.

New Zealand can directly benefit from North American initiatives by monitoring programmes, using their knowledge and adapting this to our needs.

Problem analysis - The North America Situation

US$250 billion industry with 1.6 million new home built each year. 90% are woodframed.

29% of recent houses have problems with 6% considered serious. 90% of surveyed problems are due to rainwater leaks.

The population is increasing most rapidly in durability and disaster prone areas.

The size and complexity of houses are increasing.

Floor levels are too close to the ground.

Loss of roof eaves

Inappropriate use of vapour barriers

Omission of flashings and abuse of sealants

Abuse of claddings by other trades and poor construction sequencing.

English is a second language for many workers.

Multitude of opinions. Science is still evolving and there is a lack of good research.

Condensation within concealed spaces of airconditioned buildings eg. on the underside of floors in subfloor spaces.

Stiffening of buildings from monolithic claddings can generate earthquake damage.

Problem analysis - Canada (British Columbia)

Residential construction is stretched to allow cheaper low-rise condominiums on expensive inner suburban land.

800 three to four-storey condominium complexes were built in Vancouver between 1980 and 1995 with over half of these experiencing water leakage. It is estimated that 50,000 units are affected. Repair costs range from C$35,000 to C$40,000 per condominium unit that have a value of around C$150,000.

Condominiums are often owned by retired people on fixed incomes. They are used as their own homes or sources of income. Some emergency loans are now available.

The builders' home warranty scheme has collapsed.

Buildings are sometimes repaired more than once.

Condominiums are difficult to sell unless the cladding has been replaced, irrespective of damage. Repaired buildings are readily identified by exposed flashings at each flood level.

Leakage problems are also present in highrise buildings.

Given the level of public awareness it is surprising that nothing is being done to rectify problems in attached and detached dwellings.

Key lessons

The Consumer

Consumers expect industry to get it right.

Cheap and inappropriate construction, while seemingly lowering building costs, merely allows land values to rise often to unrealistic levels.

Increased consumer awareness promotes change.

Claddings are vulnerable to owner abuse - blocking vents and rains, inappropriate alterations and poor maintenance.

Science

All buildings leak.

More rain means more rain control is needed.

Moisture penetration is deceptive in its apparent simplicity.

The building envelope must have drying potential.

Greater building complexity leads to lower building performance.

The envelope is a climate transition zone that can provide ideal micro-ecological niches for destructive organisms.

The creation of energy efficent buildings has resulted in tight, cold and unforgiving claddings.

Poor indoor air quality is not related to external leakage. It is due to high occupant density, excessive moisture from internal sources, inadequate ventilation and excessive subfloor moisture.

Buildings are chaotic structures, created in a chaotic manner and occupied by chaotic people. Accurate prediction is not possible.

There must be robustness and a margin of safety in the way we build.

Implementation

Educating the public requires lots of time and money. In the short term industry-based solutions are required.

A common language for weathertightness is needed - simple terms that convey meaning and understanding.

To educate, first we must have knowledge, then we must educate the educators.

Problems can become institutionalised where unreasoned behaviour is not only accepted, it is difficult to change.

Most failures are due to poor implementation, often arising from simple mistakes.

Inspecting quality into building does not work.

Quality comes from personal traits such as knowledge, pride, care and attention to detail.

 

 

 
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