Green or “Living Roofs”
Are you thinking about putting a new roof on your home? Or perhaps you have a garage or other out-building that needs a new roof. You may want to consider installing a Green, or “Living Roof.” We were intrigued by the idea and created one on our cabin.
A Green Roof provides many benefits. It can provide increased energy efficiency by adding extra insulation to buildings. By having one less dark surface absorbing the sun’s rays, and with the addition of transpiring plants, you can help reduce the “heat island effect,” that causes increased temperatures in urban areas. The growing media and plants absorb water, decreasing the amount of water run-off to storm drains. By planting a diversity of flowering plants, your Green Roof will attract birds, butterflies and other insect pollinators, thereby creating a charming microhabitat. Finally, your Green Roof can provide a pleasant view for those who look down upon it.
There are some important questions to consider before you decide to build a Green Roof. Most importantly, will the structure withstand the weight of the plants, media, water and a snow load? Some structural reinforcement may be necessary– you should consult an engineer to be sure. If the slope of your roof is steep, special frames need to be constructed to prevent slippage. For slopes less than 2 degrees, adequate drainage is a problem.
The first step in the actual construction is to build a containment frame with drainage outlets on the lower edges. Next you will need a waterproof/ root-proof membrane. (We purchased a pond-liner on “Craig’s List.”) It is extremely important that you are careful not to make holes in this material and do a good job sealing seams. For roofs with less than a 10-degree slope, you will need a drainage layer and a filter layer (to prevent soil from clogging the drainage layer). Next is the growing media. To limit the weight load, it is recommended that 75-90% of the media is inorganic, such as pumice or expanded clay. We tested the weights of various mixes and ended up using a mix of 40% lava rock, 40% perlite, 10% compost, and 10% coconut fiber (+organic fertilizers). The depth (deeper =heavier!) of your growing media will determine what you will be able to plant. At depths of 2 inches or less, you will only be able to grow mosses and sedums. At 2-4 inches you can plant short, drought tolerant grasses, wildflowers, and small bulbs. At 4-8 inches, you can plant taller species and even small hardy shrubs.
The biggest expense is the plants and growing media constituents—for us it was the perlite (we kept buying out all the local Home Depot stores!). I planned ahead and grew most of our plants. Your costs increase dramatically, if you have to purchase plants and/or pay for the labor to install it.
There are many resources on the web such as greenroofs.com and livingroofs.org. A good book to check out is “Green Roof Plants: A Resource and Planting Guide” by Edmund and Lucie Snodgrass. One thing to keep in mind is that these resources are from other climates. When deciding on plants to include in your plan, you should choose ones that will thrive in this climate. I tried to stick mostly with beach, prairie and subalpine natives, and several varieties of sedums, but I also planted various bulbs and scattered miscellaneous herb seeds.
It was a great joy, last summer, to visit the roof and see the busy activity of the bees and butterflies visiting flowers on our living roof!
(This article was first published in the Peninsula Gateway on Mar. 18, 2009 as A Green Roof can Increase Efficiency.)
Feature Photograph: My Living Roof in 2006, newly planted; then in 2008 and 2012. (It looks very different at different times of the year–different flowers blooming from early spring and throughout the summer!)
My Living Roof –plant species list (Phase 1-west side)
Yarrow Achillea millefolium
Nodding Onion Allium cernuum
Chives Allium schoenoprasum
Pearly Everlasting Anaphalis margaritacea
Snapdragons* Antirrhinum majus
Sea Thrift Armeria maritima
Red Paintbrush Castilleja miniata
Large-flowered Collomia Collomia grandiflora
Tufted Hairgrass Deschampsia cespitosa
Showy Fleabane Erigeron speciosus
Oregon Sunshine Eriophyllum lanatum
Roemer’s Fescue Festuca idahoensis ‘Roemeri’
Beach Strawberry Fragaria chiloensis
Blanket Flower* Gaillardia x grandiflora
Common Flax* Linum usitatissimum
Spring Gold Lomatium utriculatum
Lupines Lupinus sp.
Grape Hyacinth* Muscari armenicum
Sea Blush Plectritis congesta
Silverweed Potentilla anserina
London Pride Saxifrage* Saxifraga x urbium
Different colored sedum varieties* Sedum sp.
Hens and Chicks* Sempervivum tectorum
Lime Thyme* Thymus x citiodorus ‘Lime’
Sticky False Asphodel Tofieldia glutinosa
& misc. bulbs* from a friends yard!
Seeds** direct sown:
English Daisy* Bellis perennis
Godetia Clarkia amoena
California Poppy Eschscholzia californica
Western Blue Flax Linum lewisii
Sweet Alyssum* Lobularia maritima
California Desert Bluebells Phacelia campanularia
Poppies* Papaver sp.
Violets* Viola sp.