In the lexicon of building codes, green or eco-roofs, are called vegetative roofs. In fact, vegetative roofs are now a project elective in Oregon’s new reach code.
The Oregon Reach Code, adopted in 2011, is a set of "optional" construction standards for achieving greater energy efficiency than if a building were constructed under the statewide mandatory code. Vegetative roofs are one of seventeen project electives, or additional measures, for reducing electricity use in commercial construction.
From an energy efficiency perspective, vegetative roofs help reduce the ‘heat island’ effect in urban areas by lowering the outside air temperature and reducing demands on a building's cooling system during the summer months. Portland State University's (PSU) Green Building Research Lab (GBRL) has developed a Green Roof Energy Calculator that allows you to compare the annual energy performance of a building with a vegetative roof to same building with a conventional roof. The GBRL is also investigating the cooling effect of green roofs on solar panel efficiency.
Green roofs have other benefits as well. During western Oregon’s rainy winter, they protect the health of rivers and streams by slowing stormwater run-off. That’s the primary reason the City of Portland developed its Eco-Roof Program more than 10 years ago. In addition to technical assistance, the program provides an incentive of up to $5 per square foot for installing a vegetative roof. At this time, the city has more than 300 eco-roofs totaling nearly 15 acres.
Another reason to consider a vegetative roof is that the life span of a correctly installed and maintained green roof is roughly 40 years, double the lifespan of a conventional roof. Although green roofs cost more to install, the soil and plant layers serve to significantly extend the life of roofing materials.
Experts at Portland’s Eco-Roof Program put together a webinar on vegetative roofs for Oregon Building Codes Division’s (BCD) brown-bag lunch training series. The eco-roof webinar, which aired live on January 12, 2012, is now archived so it can be viewed any time. Just go to BCD’s webpage at: http://www.bcd.oregon.gov/external/bcd/webinar/brown_bag/index.html#reg
The eco-roof webinar focuses on:
- Overview and benefits
- Basic components
- What to look for in plan review
- Structural load requirements
- Lessons learned