Seven ways to stop the rot

By SIMON COLLINS

Before they came to New Zealand six and a half years ago, Brenda and Robert Vale used to design houses to last 500 years. In Britain, where the church down the road might be 1000 years old, durability was "part of the culture".

Inside the exterior brick walls of new houses, there might be an air gap to let water escape and then an "inner skin" often made of concrete blocks. Interior timber walls had been banned since the Great Fire of London in 1666.

Costs were correspondingly high. New houses in Britain cost three times as much a square metre as New Zealand houses and, unsurprisingly, averaged only a third as big in area. But they were built for the British climate, and they did not leak.

When the Vales arrived in Auckland to lecture at the architecture school, the first thing that struck them was the 1990s Kiwi craze for coating houses with a thin layer of plaster trowelled over wood or netting, known as stucco.

Aluminium windows were being installed square-on to the flat plastered walls without the awnings and windowsills that might have carried water from the top and bottom of the windows to stop it getting into the house.

"It seemed very short-sighted in a very wet climate," says Professor Brenda Vale. "Everyone is fixated on cost - it [the house] has to be the cheapest and the biggest."

This week, after two years of increasingly alarming revelations about what one engineer called New Zealand's "Third World" building standards, the country has begun to learn an expensive lesson about the real costs of "cheapness". On Wednesday Commerce Minister Lianne Dalziel announced plans to force upgrading of earthquake-prone high-rise buildings - a move that could affect 10 per cent of all the country's buildings over two storeys high.

And yesterday the Building Industry Authority unveiled a proposed new building code to stop widespread water leakage in new houses and apartments. It will require an air gap at least 2cm wide in high-risk situations to drain water that gets in behind external claddings, and will restore compulsory chemical treatment to stop structural timber from rotting.

The problems have emerged gradually. An early warning was a survey by Unitec architecture lecturer Chris Murphy in 2000, based on 287 houses inspected by Auckland consultants Prendos between 1996 and 1999, which found an average of two defects in the exterior structure of every home built since 1990 - twice the average defects of houses built in all previous periods.

Within the post-1990 sample, defects averaged two for houses clad in materials such as Hardietex, made out of cement fortified by wood pulp, 3.2 for those clad in polystyrene foam marketed under names such as Hitex, Insulclad and Rockcote - and five for those clad in stucco.

"Stucco is much more prone to cracking because it is put up incorrectly," Murphy says.

"You don't have a manufacturer. The plasterer makes stucco on the site. I think my survey reflected the fact that there was an upsurge in activity with stucco and perhaps due consideration was not given to correct installation, particularly around windows."

Through 2001, as the Weekend Herald reported the first homeowners prepared to go public about their leaky houses, an industry steering group for the first time recommended building in a gap behind stucco outside walls so that any water could drain away.

Last year an inquiry led by former State Services Commissioner Don Hunn recommended that all "face-sealed cladding" such as fibre cement, polystyrene and stucco should be taken out of the building code's "acceptable solutions" in high-risk areas until research finds ways to handle any water that gets through.

Auckland structural engineer John Scarry wrote an independent report alleging that leaky buildings were "only the tip of an iceberg" of construction standards which had dropped to "Third World" levels, turning billions of dollars worth of high-rise blocks built since 1994 into "a severe seismic risk".

More than two years after the first Weekend Herald stories on the issue, there is now an emerging consensus on seven changes in construction techniques that are needed if we want our buildings to last.

1. ROOF SHAPES

Sloping roofs with overhanging eaves and verandas are not just traditional, they are actually the best defence against the rain in New Zealand's wet climate, provided that the guttering can cope with the water that the roof collects and is kept clear. Canadian research shows that eaves alone deflect 90 per cent of the rain away from walls.

2. WALL SHAPES

If water does hit the wall, traditional overlapping weatherboards are shaped to direct it out again. Their shape also provides natural ventilation behind them and they provide plenty of flexibility to cope with the expansion and contraction that all materials undergo with heating and cooling.

3. INTERNAL DRAINAGE

Some water will always get through an outside wall, both in storms and on damp days when moisture can seep into walls out of waterlogged air. The Canadian research shows that the remaining 10 per cent of water that is not deflected by eaves can be drained away by a "second line of defence" - a gap, or "cavity", between the outer wall and the internal structure.



In the past two or three years, polystyrene manufacturers have developed corrugations in the back of their external claddings where the water can drain away. This year Hitex Plastering has brought out a new system of raised diamond shapes. But the new draft code unveiled yesterday requires a minimum air gap of 2cm, bigger than any of these corrugations. This has been well signalled in advance, and most cladding companies have already adopted it.

4. SEALED WINDOWS

Most water that gets in through walls comes in around openings such as windows, doors and pipes. Small fittings (flashings) that used to fit under the outside wall and drain water away above and below openings are now coming back into fashion, and will be required by the new code.



5. GROUND CLEARANCE

Moisture also gets into buildings from the ground if walls and floors are in contact with wet earth or plants. The Building Research Association of New Zealand (Branz) recommends a minimum 15cm gap between most wall claddings and ground paving and at least 22.5cm above unpaved earth. The ground outside must also drain away from the building on a slope of at least 1:25, or a drain must be provided.

6. DECKS & BALCONIES

Murphy's survey found that 25 per cent of balconies and decks let water into the house. Branz recommends that balconies should be at least 5cm below the wall cladding and 15cm below the inside floor level, and that they should slope away from the building to at least two outlets with at least two overflows. It says handrails should be separated from the wall or fixed on to the side of solid balustrades, with the top of the balustrades cut at an angle to drain water away and capped with protective material.

7. TREATED TIMBER

From the early 1950s, when radiata pine started to replace strong native timbers, regulations required construction timber to be dipped in boron to deter both borer insects and rot.

The rules were abandoned in 1996 when Carter Holt produced research showing that kiln-dried timber did not need boron.

That short-lived experiment is now ending, with the new building code requiring that timber once again be treated with boron to a level of 0.4 per cent - four times the minimum required before 1996.

"Boron actually stops a lot of ground rot," says Phil O'Sullivan of Prendos, who has led the push for tightening the rules.

"Once you take away that boron treatment, you open the door to a lot of decay which is very, very fast. You will end up with fully rotten walls within six months [after water gets in]."

Apart from these technical changes, the leaky buildings scandal has also exposed what the Hunn report described as "a perception throughout the industry that skill levels on-site are declining".

"Even though a main contractor may be employed, there is often a multitude of 'labour-only' subcontractors engaged," it said. "This has led to comments such as, 'No one takes overall responsibility for the project any more."'

Dalziel has announced Building Act changes, due in Parliament next month, which will license builders, architects and engineers and ban any building work worth more than $10,000 unless it is done or supervised and certified by a licensed person.

Pieter Burghout, of the Building and Construction Industry Training Organisation (BCITO), reports a 32 per cent jump in trainee numbers in the past two years - "largely driven, one suspects, by the weathertightness issue and debate about industry registration".

Polystyrene cladding companies have introduced their own cladding qualification, run by the BCITO, and will require all their installers to qualify by this December.

O'Sullivan is pleased with what, in large part, his agitation has achieved. "I think we have got it as good as we can get it at the moment," he says.

Murphy agrees. "It's taken 20 years to learn how new materials should be used properly in the New Zealand climate," he says. "It just amazes me why we never thought of using a cavity before."

Yet despite this progress, some in the industry are still worried.

A technical issue is how to create the 2cm "cavity" or air gap behind the outer wall. With fibre cement or stucco, vertical wooden battens create the gap and allow water to drain as intended. But polystyrene is too weak to hold vertical battens, and horizontal ones are used instead - potentially blocking the water's escape.

More generally, the whole effort to reregulate the industry is still fighting an uphill battle against overwhelming commercial pressures to cut costs, from the forests right through to post-building maintenance.

Forestry companies are felling trees after 20 years instead of the traditional 25 or 30, on land that has already produced one or two earlier wood harvests, producing timber that is weaker than it used to be.

The same pressures apply in construction. John Munro, a veteran Auckland heating and ventilation contractor who is now an insulation consultant, says builders rush through jobs quickly and cheaply to justify low quotes.

"Eighty per cent of all residential buildings in New Zealand are spec-built [built by speculators], and they employ the cheapest labour they can," he says.

A decade ago he surveyed 70 insulation jobs for the Building Industry Authority and found only three complied with the building code. Most left gaps around the insulation which undermined its effect. Munro says local body building inspectors should pick up corners being cut, but are not given time to make proper inspections. "There is just no control, no policing of the Act," he says.

Finally, after houses are completed, many residents in our mobile society fail to maintain them. Far from thinking 500 years into the future, the average of five years that people had been in their present homes at the 2001 census suggests that many may think only around five years ahead.

"Buildings in New Zealand are severely under-maintained in terms of painting, looking after gutters and downpipes and so on," says Brenda Vale.

"The move from timber to stucco reflects a demand for low maintenance. That is not the right message to be sending."

Dr Carol Boyle of Auckland University's Centre for Sustainability Engineering and Research says the building industry's use of material resources could be cut by three-quarters if we could extend the lives of our buildings from the 50 years provided in the present building code to 400 years.

But achieving that may require more than just tighter regulations and tougher enforcement. It may need a complete change in our culture of cheapness.