May 15, 2006

Forethought to green roofs key to financial success, efficient builds

Planning for cost overruns, change more efficient than corrections

TERRY TINKESS

correspondent

OTTAWA

Green roofs have great potential, but only if they are considered with much forethought and as part of the building envelope rather than a separate entity.

National Green Building Conference and Exposition panelist Douglas Fishburn, of Fishburn Building Sciences Inc., encouraged developers to “pre-think” decisions.

“Durability, inspectability and maintenance are all things that need to be considered before, not after, the roof is installed.”

Because of the need for a green roof to be watertight while at the same time, allowing sufficient moisture for the plants which allow it to thrive, there is a continuous struggle.

“We have to consider what is environmentally best for the roof while at the same time, consider what is environmentally best for the plants. It’s a constant tug-of-war.”

Fishburn stressed the need to build redundancy into design because the cost involved in correcting a problem is far greater than doing things right the first time.

“Flashings account for about 70 per cent of the roofing problems, but they only account for three per cent of the cost,” says Fishburn, who said 47 per cent of problems encountered with green roof installations are as a result of labour, while a further 16 per cent can be attributed to design.

“When we get it wrong, it’s our problem. That’s why we need to build in the redundancy.”

Brian Baird, technical specialist with Dow Chemical, stressed while care and planning are essential to a successful installation, generally, the technology involved isn’t new.

“What you are doing with green roofs involves nothing that isn’t currently practiced in low-slope roofing design,” says Baird. “You are not reinventing the wheel.”

Baird, like the speakers before him, acknowledged understanding the loads — live, dead and wind — that the roof would experience make a great deal of difference in the materials that are used.

A roof that will not be subjected to excessive live loads, such as those created by construction equipment, would not require a roofing insulation as resistant to compression factors as one that is.

“Design, obviously, will dictate your insulation choice,” says Baird.

Joe Passa of Passa and Associates Inc., along with other members of the panel, was involved in the construction of a green roof at St. Christopher School in Windsor.

The school, which features a 5,000-square-foot green roof, is recognized as the most energy efficient school in Canada.

While the school implements many energy-saving technologies, according to Passa, the green roof serves a special purpose.

“With a high-performance building, the green roof is perhaps the most visible part of it,” says Passa.

The City of Toronto recently commissioned Ryerson University to complete a multi-disciplinary green roof benefit study.

Researchers calculate adding eight per cent coverage with extensive green roofs to existing city rooftops would generate over $300 million in initial cost savings in areas such as storm water management, combined sewer overflow reduction, building energy savings, and urban heat island reduction.

Consequently, that level of coverage would reportedly result in an operational cost savings for the city of approximately $40 million per year.

“Durability, inspectability and maintenance are all things that need to be considered before, not after, the roof is installed.”

Douglas Fishburn,

Fishburn Building Sciences Inc.

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