Oct 29, 2010

Sustainable Living and Design for existing structures-3

Since, I've been rambling on and on about green roofs, thought I'd get into action and wrtite in some detail on how a green roof for a regular home dweller could become a reality. Is it really possible for us or are green roofs only for larger or expensive building projects. Even more so to those of us in Bangalore and most of India, where professional green roof services are still not common. Seems kind of visionary but it really isnt with some understanding and investment in time and money.

In most climes, a properly designed 3-inch deep vegetated roof cover will provide a durable, low maintenance system that can realize the many benefits that green roofs have to offer.

Photo from OurSquareFootGarden

There are 2 types of green roofs by standard methodology:

-Intensive green roofs have deep soil and can support trees and larger plants. Which is a definite no-no for us regular home dwellers as it requires a complex laying system and is high on maintenance. These are good for commercial, largescale residential buildings that have access to sophisticated green roof services and a maintenance team onboard.

-Extensive green roofs are more self-sustaining than intensive roofs, and require minimal maintenance. Characterized by shallow soil (~6 inches). For us home dwellers, extensive roofs are the most practical. This type can support whole patches of sedum, grasses, herbs with interweaving gravel, slate pathways for people movement. Those willing to spend more time and money could go in for turf over larger areas, but requires ongoing regular maintenance of mowing, weeding, fertilizing, and irrigating, just like any high-use area on grade.

Photo from OurSquareFootGarden

Going forward where ever "Green roofs" are mentioned in this post, I would be refering to the extensive type.

So what are the components of a green roof. Very simply put, our regular existing roof with an additional overlay of a waterproofing membrane and then a layer of soil and plants. They may also incorporate other landscape features such as walkways, patios, arbors, and other such structures. While a great many green roofs are flat or nearly flat, there are also growing numbers of sloped (some quite steeply) green roofs, as well as vertical or near-vertical green walls.

STEP 1: Start with a waterproof membrane such as asphalt or the more commonly used waterproofing liquids in Indian homes . This step is essential. Most roofs fail because of water damage.

STEP 2: Add a root barrier. Mixing the waterproof liquid with cement and plastering the roof should do·

STEP 3: Put in a drainage layer. A drainage layer is essential to carry away excess water to gutters so that it can be carried away from the roof. Typical drainage layers are made of granular materials such as gravel & fines, lava & pumice, expanded clay & slate, and different recycled materials such as crushed roofing tiles or brick. The drainage capacity has to increase closer to the gutters and roof drains.

STEP 4: Add a filter fabric The fabric has to be porous enough to allow water to flow down into the drainage area while holding the soil or growing medium in place. Sheets from polyester or polypropylene can be used. (These sheets are available on J.C road for the Bangalore folks)

STEP 5: Put in the soil. to a minimum depth of 3 inches would be best to use a mix of lightweight perlite, cocopeat and organic manure. Local soil would also be okay but could have weeds and would be heavy and not porous enough.

Photo from GreenRoofsWordpress.com

STEP 6: Building a water supply sytem. Drip irrigation would be best as will apply water directly to the roots of the plants. It's more efficient than taking a hose to your roof, using less water, which also means less weight on your roof. Drip irrigation is an easy way to supply fertilizer to your plants to get them started. Ultimately if you've chosen the appropriate plants for your climate, you'll be able to turn off the irrigation system.

STEP 7: Plant your succulents, sedum, portullacca, wild native grasses, Gazanias basically low height, shallow root drought tolerant plants· For your shrub like veggies, container planting would be the solution. If your roof is pitched, you would require a wind barrier to keep the soil and plants intact during the growing period. In a years time approximately, the root system would keep it together. Could be a net like sheet that breathes well staked on top of the roof bed.

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