Living roofs aid in insulating a house, and are ecologically sound; however, they require advance planning. They can add quite a lot of weight to a roof, requiring strong building infrastructure. If the roof is to be added to an older home, shoring up the original structure with sturdier materials will be essential for all but the lightest green roofs. Provision for watering the roof in seasons of drought must also be considered, as well as drainage from rainfall and plant watering. Wind and other climactic considerations also come into play.
Things You'll Need
- Planned or existing roof deck with moderate slope
- Prepared roof surface
- Roof membrane
- Root barrier
- Drainage/moisture retention layer
- Filter fabric
- Growing medium
- Wind erosion blanket
- Plants or seeds for plants
- Water delivery system
- Carpentry and plumbing tools
Basic Construction Steps
Build a sturdy structure, capable of upholding about 60 to 120 cubic pounds of weight (or possibly more in regions of high snowfall). If this is a retrofit, consider using one of the lighter forms of green roof, which utilize lichens or moss instead of sedum, grass or standard garden produce. Install easy access to the roof, such as a ground level walk-up slope or a permanent stair or ladder.
Prepare the sheathing. The roof surface should be clean and dry before adding the layers necessary for a green roof.
Install a water faucet connected to the house water system near the top of the roof slope. This will enable watering the roof in dry weather. "Green Building and Remodeling for Dummies" by Freed mentions on page 275 that grass fires can be a hazard in hot, dry climates. If you are using the roof for intensive gardening, a faucet will simplify watering the vegetables.
Add the waterproof membrane such as PVC sheeting. Work carefully to make sure there are not any wrinkles or tears. Next, add a root barrier. This can be copper foil, concrete or aggregate that contains a root retardant. The goal is to not allow the roots to reach the waterproof membrane or sheathing.
Add a layer of insulation, such as rigid insulation board. Over this apply egg-crate or filter fabric to allow water flow over the underlying materials. Next apply a biodegradable filter fabric such as burlap or jute to filter the water as it permeates the layers. Spread the growing medium over the filter fabric, and cover it with a biodegradable wind blanket to keep it from blowing away before the plants can take root.
Plant seeds or small plants in the growing medium. Moss and lichen are recommended for older homes where the green roof is a retrofit. They require a minimum amount of earth and therefore place less weight stress on the structure. Next in order of weight are sedums, which are sturdy, drought-resistant plants frequently found in rocky terrain where there is little soil. The most weight-intensive type of green roof is the one used for intensive gardening. Most vegetable plants require deep soil for good growth, as well as quite a bit of water.
Check plant growth periodically on all types of green roofs. Reseed and water as needed.
Mow or trim green roofs that are part of an earth-bermed home. Use small electric or gas-powered mowers or hand mowers to keep the roof matching the rest of the lawn.
Give intensive gardening green roofs the same type of maintenance as you would any garden.
Check inside and out for signs of water leaking, as this is one of the known problems with a green roof.
Tips & Warnings
- The "Earthship" series by Michael Reynolds is excellent reading for anyone seriously interested in sustainable building.
- The Environment Site: Roof and Walls
- "Green Building and Remodling for Dummies"; Erich Corey Freed; 2007.
- Green Roofs: Adapted from the Massachusetts Low Impact Development Tool Kit
- Photo Credit Efeu image by JÃ¶rg Stumpf from Fotolia.com
- "Earthship"; Michael Reynolds; 1990
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