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)

Plants:

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.