Inverted roofs increasingly are becoming a popular alternative to traditional roofs as their benefits have become more apparent. Simply defined as a type of roof construction where the waterproofing layer lies beneath the insulation instead of above it — as in other forms of roofing — inverted roofs ensure that the complete roof construction, including roof covering, is kept at warm temperatures during winter months and at moderate temperates during the summer months.
Also known as a “protected membrane” or “upside down” roof, inverted roofs employ insulation which can resist water absorption, provide excellent thermal performance, be unaffected by freeze and thaw cycles, withstand surface traffic and be protected from UV and mechanical damage, among others. While traditional roofs place the insulation under the protective membrane, inverted roofs are designed with the waterproofing layer, usually a liquid-applied membrane, beneath the insulation. Insulation boards are loose-laid on top of the membrane and then weighted down with paving slabs, gravel ballast or soil medium in the case of ‘green’ or vegetative roofs.
There are many reasons why you should choose to install an inverted roof in your next building project. Here are five of their key virtues:
Roofs are significant investments, as they impact nearly every other function and feature of a building. The average life of a roof system in North America is around 16 years and the depreciation period for a commercial roof 39 years. However, deferring a roof replacement by 10 years can save hundreds of thousands of dollars. Inverted roofs typically last longer than traditional ones.
Inverted roofs have significantly lower maintenance costs than conventional low-slope roofs, thanks in large part to the insulation in the inverted assembly protecting the roof membrane from mechanical damage during and after construction, as well as temperature extremes that cause stress. It also protects against ultraviolet radiation that can lead to premature failure. This enhanced durability, combined with reduces annual energy costs, can reduce total roof-life costs up to 22 percent.
While the enhanced longevity and energy efficiency afforded by inverted roofs is good for the wallet, it’s also good for the planet. Due to the fact that the insulation, fabric and ballast are loose-laid and therefore can be more easily reused, inverted roofs help reduce downstream waste during construction, maintenance and demolition phases of a building’s life. With 5 percent of landfill waste in the U.S. coming from the roofing industry — amounting to around 50 billion pounds each year — a reduction in landfill is a huge boon for Mother Earth.
Because inverted roofs place insulation on top of the membrane, this provides a perfect foundation for a terrace, garden or green roof on the top of the building. Research shows that even on a hot and sunny day, the temperature of the roof surface below a green roof can be cooler than the ambient air around it — greatly reducing the effects of the sun’s energy on the interior temperature of the building and reducing the urban heat island effect compared to conventional roofing. Reduced energy demands lightens the burden on the grid — which in most regions means reducing the amount of fossil fuels or natural gas that must be burned to generate power. Alleviating the urban heat island effect means that less of the sun’s energy is reflected back into the atmosphere, which is a contributor to global warming.
As the impacts of climate change make weather patterns more unpredictable — often resulting in too little or too much rain — building resilience increasingly is relying on the ability to handle storm water overflow. Cities across North America, from San Francisco to Toronto, are beginning to take action to prevent sewage and storm water flows from ravaging the urban environment. With even a fraction of an inch of rain being capable of overwhelming some combined sewer systems, cities are acting to prevent overflow from polluting local rivers and waterways.
By constructing a green roof, you can help reduce the burden on your city’s sewage system by absorbing much of the rainwater that falls on your building. Green roofs typically retain between 40 and 90 percent of storm water runoff from the roof depending on the climate and are an ideal, cost effective way to reduce or eliminate overflow by slowing or absorbing runoff into combined sewer systems. Choosing a green roof or blue roof assembly capable of withstanding water-saturated vegetation without absorbing it is critical to the integrity of the roof. As the inventor of the inverted roof, Dow’s STYROFOAM™ Brand XPS Insulation has been the top choice for green roof assemblies for over 40 years to resist moisture and provide long-term thermal protection.
As more people spend more time than ever before in urban environments, there is a growing need to reconnect with nature. While traditional buildings tend to make people feel cut off from natural environments, making the roof a usable, walkable space with natural amenities can help bridge this disconnect and make your building’s occupants happier and more productive.
By adding more of an outdoor, park-like aesthetic to the building, occupants are more likely to be healthy, happy and helpful. Employees who work in environments with natural elements reported a 13 percent higher level of well-being and are 8 percent more productive overall, according to one report. Besides this being a good thing in and of itself, this also can help attract businesses and other tenants by serving as a key differentiator from traditional buildings.
Just as green roofs can make people happier, they also can benefit the local wildlife. As cities swell and continue to encroach on nature, there is a growing need to infuse urban landscapes with the elements of natural environments. With the world on track to lose two-thirds of its wildlife by 2020, this is more important than ever.
Green roofs mimic the natural environment by providing urban refuges for insects and birds migrating across cities. Meanwhile, green roofs are important for local biodiversity by creating homes for animals such as squirrels and rabbits. In Basel, Switzerland, for example, green roofs have become an important component of the city’s biodiversity strategy. On some of the green roofs in the city, dense microhabitats have formed, which support as many as 79 beetle and 40 spider species — and 13 of the beetles and 7 of the spiders are endangered.
A strong insulation choice is essential to extract the benefits and longevity of an inverted roof. An extruded polystyrene (XPS) insulation delivers the proven, long term performance for the life of the roof.
Browse our roofing solutions to find the right choice for your project and regional availability.
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