High Performing, Low Cost Living Roofs...
with no goats needed to keep it looking beautiful!
by Sigi Koko
What is a living roof?
A living roof, or green roof, describes a system that allows plants to thrive on the surface of rooftop without access to groundwater. The idea is to create a self-sufficient ecosystem that doesn't need you to water once the plants are fully established. This type of roof does provide energy-efficiency benefits in the summer, because the plants provide a net cooling effect. Even one inch of planted soil lowers overall average roof temperatures and reduces day-to-night temperature swings on roof surface. A green roof does NOT provide insulation to speak of, so you still need to insulate your roof
, just like you normally would. Additionally, plants absorb and filter rainwater, reducing the negative impacts of excess storm runoff in watersheds, which is especially beneficial in areas with high percentage of impervious surfaces, such as cities and suburbs. (Yes, I did write suburbs! A mowed lawn only allows an average of 40% of the rain that falls on it to absorb into the groundwater table!)
The plants are the key!
The most important detail with a living roof is to select plants that will thrive in your climate and with the amount of sunlight striking your roof. (See below for a living roof plant resource.) First and foremost, your plants need to be able to survive without access to groundwater and rely just on your local rainfall. If you get tons of annual rainfall, you will want to be sure you select plants that can handle "wet feet", and be sure your roof drains well. If your roof is in full sun, you will need to select plants that will not wither under the heat of relentless summer sunshine. Etc.
full shade allows different plant varieties to thrive
Most planted roofs are installed on reasonably flat surfaces. But this is by no means a requirement. Steeper roofs (above about a 30-degree slope) do require additional erosion control, especially while the plants establish their root systems. Most commonly, I use a wooden trellis type grid that rests directly on the drainage layer (not fastened to the roof). Then plant in between the grid of the trellis. As the plants establish their root system, the wood biodegrades, providing additional nutrients for the plants. By the time the wood has composted, your plant roots become your erosion control.
plants thrive on shallow or steep slopes...even curves!
It's all in the details!
Here are the layers I have used with great success on numerous small scale roofs:
- sheathing (such as plywood) - typical roof sheathing is 1/2", but my engineer likes to bump it up to 5/8" to prevent any sagging from the weight of the soil. The sheathing is part of your structure, so I make sure an engineer approves the roof framing as well as the sheathing.
- waterproofing membrane - the lowest cost option I've found for this that has high effectiveness is 60 mil EPDM (rubber pond liner). I also recommend reading "Stoneview: How to Build an Eco-Friendly Little Guesthouse" (New Society Publishers) by Rob Roy for additional suggestions for waterproofing membranes.
- drainage/filter layer - I don't skimp on this because it keeps your soil medium up on your roof, even with heavy rainfall. My favorite drainage layer with integral filter fabric is: Enkadrain 3615 (by www.colbond-usa.com) because it is easy to cut & easy to install, especially on curvaceous roofs.
- growing medium (soil) - I have used everything from compost to an engineered mix of expanded shale & organic soil; they all seem to work well. The only advice here is to be certain, if you are using compost, that it is sterile, ie, that there are no active seeds (or you will be up there weeding like crazy) and if you use a mix with high inorganic content (such as expanded shale) be sure it's mixed with at least 60% organic soil (such as sterile compost)
- plants - I use ONLY sedums and other rock garden plants. These are plants that don't rely on ground water, but instead have ways of storing rainwater (their leaves act like a cistern) or can pull humidity from the air for moisture. Be sure to select plants that will thrive on your roof and in your climate, ie, whether your roof is in full sun or full shade and how much rainfall you get in a year. For recommendations on plants, see www.greenroofplants.com
If you have selected plants that will thrive on your roof environment, then most of your maintenance happens in the first year. When you first plant, you want to be sure your plants are watered the day they are planted, and then weekly for at least 4 to 6 weeks. This includes a good rainfall, so if it rains, you can skip the watering. Once your plants have established themselves in their new environment, you won't need to water anymore.
I also recommend checking for weeds at least twice during that first year that your plants are on the roof. Weeding takes out any competition and lets your plants take over quickly.
• Feature Article:
"High Performing, Low Cost Living Roofs"
• What's Happening
• Low Hanging Fruit
simple eco-living tips
• Recommended Reads
natural building books
Get out your calendars!
Upcoming Living Roof Workshop at Beautiful Zigbone Farm!
Craving more information on how to install a living roof...including hands-on experience? If so, join us in scenic Sabillasville, MD in October.
Dates: October 24&25
(rain dates Oct 31/Nov 1)
You will learn:
- the benefits & challenges
- design detailing
- each essential layer (and what it does)
- how to select plants
- and more...
Cost: $150 (includes a yummy, healthy lunch)
Contact Sigi Koko to register:
You can stay up-to-date by checking the workshop page on our website.
small habits that make a big difference...
Break the plastic bag habit...
I was at the store the other day and witnessed the following: a person putting a bunch of bananas in a plastic produce bag. Now, the bananas were all neatly in a cluster, so the bag didn't help this person organize her purchase. And bananas come with their own sanitary packaging (the peel!), so the bag didn't help keep the bananas sanitary. So why the bag?? It made me realize that plastic bags are so part of our lives, we don't even think about how we use them. I'm sure we've all done this or similar, but we can change that...!!
Why ditch the bags?
One million plastic bags are used every single minute, and each is used for an average of twelve minutes and then most are thrown away. Plastic bags do not readily biodegrade, lasting hundreds of years. The light bags are easily caught in the wind, resulting in bags in trees, landscapes, and waterways. Hundreds of thousands of water animals (fish, mammals, birds, and reptiles) die because they eat plastic bags, mistaking them for food. As plastic bags break down, they contaminate the environment with toxins, including PCBs, DDT, and nonylphenols. These toxins in turn threaten human health (even at low exposures), contaminate soil and waterways, threaten the health of many animals, and enter the food chain when fish and other wildlife eat the plastic.
The solution: ditch the disposable plastic bags in favor of reusable canvas bags!
Fpr shopping bags, I like large canvas totes with long handles. They hold more, don't break (even with heavy stuff inside), are washable, last for years (some of mine are over 20 years old), and long handles fit over your shoulder for easy carrying.
I also use small cotton baggies for buying produce and bulk items (beans, coffee, etc.)
And to remind myself (until bringing bags became a natural habit) I put a note on my front door and a note on the dashboard of my car to remind me to bring bags along with me.
Bag Resources: (not meant as an endorsement of any company or their products)
click the cover of each book for more info or to purchase
Small Green Roofs by Nigel Dunnett, Dusty Gedge, John Little, & Ed Snodgrass
This is a great resource for the do-it-yourselfer.
Green Roof Plants by Ed Snodgrass
Encyclopedic resource for selecting plants to insure maintenance-free green roofs
The Green Roof Manual by Linda McIntyre & Ed Snodgrass
Provides details for green roof design & installation