The ideal roof is a green one. A big part of responsible building design, green roofs are environmentally friendly, produce less waste and can save you money on your heating and cooling bills.
It's easiest to add a green roof to your home in a new build or a big renovation, but you can retrofit one on an existing roof. There are green roof possibilities for flat roof and sloped roofs - but you have to make sure your structure can support the additional load, as plants and saturated soil (or planting medium) are very heavy.
In a so-called "intensive" green roof system - one that takes up an entire roof - every part is designed to work together. The waterproof roof membrane and protective layers, the type of growing medium and plants, with the weight load and plant height are all taken into consideration. You'll usually find these green roofs in new buildings since the necessary structural support is designed in.
But when you install a green roof on an existing building, you'll have to reinforce the roof structure first. And you'll need to make damn sure it's 100 per cent waterproof.
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Designing a green roof is not something you can do yourself - you'll need the advice of professionals, including a structural engineer or architect.
Green to go
A simpler method of installing a green roof is to use a modular green roof system - like the one we used in the Lien on Me special on HGTV. Modular systems are made up of trays of plants, which are grown in a medium off-site, transported on pallets and then placed on the roof.
Another easy option is precultivated vegetation "blankets" - the most lightweight green roof system. Plants in a growing medium are contained in thin modular blankets or tiles - of varying sizes - that are rolled onto an existing roof.
Most green roofs are planted with varieties of sedum - tough little plants that can take heat and cold, and survive without irrigation. Stormwater runoff
One of the best features of a green roof is that it helps decrease the amount of rain runoff, as well as the flow of stormwater, keeping it out of municipal sewers and drains. In older areas of cities where sewer/stormwater systems have been combined, a heavy rainstorm can flood the system, basically dumping raw sewage into local waterways. Hence, those days you can't go swimming at the beach.
Green roofs retain rainwater and store it - the plants then slowly release the moisture back into the atmosphere. Any excess water that does run off the green roof has been filtered naturally by the plants.
A green roof also will improve air quality. By filtering the air moving across it, the roof can remove airborne particulates and pollution.
Urban heat island
Traditional building materials such as concrete, asphalt shingles and glass are hard and reflective. They soak up the sun's radiation and re-emit it as heat, making cities much hotter than the surrounding country.
Because plants use heat energy to evaporate the water they store, green roofs can help reduce the urban heat island and cool the air.
Insulation value
They also help insulate buildings by preventing heat from moving through the roof. They can dramatically improve a roof's insulation value by shading the external surface of the building so the sun can't heat it in the first place; if it's not getting hot, you won't need to cool it down. And in the winter, the roof doesn't get as cold either.
The soil and plants can also act as a sound insulator by absorbing or deflecting urban noise.
Natural habitat
Urban areas are growing all the time, resulting in a loss of wildlife habitat. Green roofs help provide a home for insects, birds, bees and butterflies that have limited natural space in cities.
The only drawback of a green roof seems to be its weight. Some existing buildings can't be retrofitted with one because of the weight of the soil and vegetation. That doesn't stop new-home builders, though, or homeowners who are planning a major renovation that involves a new roof.
Oh, and these roofs aren't 100 per cent maintenance free - you'll have to weed them once or twice a year.
Mike Holmes is the host of Holmes on Homes on HGTV. E-mail Mike at mikeholmes@holmesonhomes.com or go to http://www.holmesonhomes.com
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