Welcome to “Weekend Warriors.” Every Friday, we run a shining example of a reader’s recent makings—to say TGIF and send you off right into your own weekend’s projects.
When Diana Cohen and Wes Slaymaker added a family room to their older home in Madison, Wisconsin, they wanted the roof to work hard for the watershed.
The view from the roof.
“We live a couple blocks from an urban lake, and storm water run-off is a concern,” Diana explains.
So, instead of boring old shingles, the couple designed and installed a “green” roof: 220 square feet of hardy, low-growing plants, plus a paved walkway and room for chairs.
Think rugged and rocky, not lush. Even prickly pear cactus likes it up here, where shallow soil and wind create an almost alpine microclimate.
Say it with me: evapotranspiration. That’s the scientific term for what happens on a green roof, where layers of gravelly drainage, soil and plants absorb water and slowly release it back into the atmosphere. The natural process cools the air outside and adds an insulating layer between your roof and the baking-hot sun—reducing energy needs inside as well, in both the summer and the winter. For people like the Cohen-Slaymakers, who are concerned about reducing their contribution to the “urban heat island,” a green roof feels like the right thing to do. Then there’s the storm water run-off concern : impervious surfaces, like roofs, patios and roads, keep water from soaking into the ground. Instead, it flows unfiltered straight into the lake—carrying sediment, lawn chemicals, motor oil and other bad stuff. Green roofs can absorb up to 75% of that water. Plus a green roof absorbs sound, insulates better and lasts twice as long as a conventional roof (according to Green Roofs for Healthy Cities, the leading network of green roof experts).
Wes checks out the plantings
Green roofs are hot in the commercial sector (Chicago leads the trend) but in the U.S, residential builders have been slower to embrace them.
Diana and Wes crafted their green roof plan from scratch, based on internet research and conversations with friends, roofers, and a nursery with corporate green-roof clients. Research occupied Diana on winter evenings during January through March of this year. The roof was installed over several late spring weekends, and she was planting by June.
Sand and mulch delivered to Diana and Wes’s house by bulk
Ladder system for hauling materials to the roof
Diana cuts landscaping fabric
“A roof is not an economical project,” Diana admits. The Cohen-Slaymakers spent around $1200 on the DIY portion of their roof (a professional roofer built the underlying support). They saved on labor costs but splurged on high-quality materials for maximum performance.
The biggest benefit, so far?
“Feeling like we helped reduce the footprint of our new addition,” says Diana.
Ready to design your own cool green roof?
Tip: Hire a professional roofer to build the supporting structure and install the heavy-duty, first-layer PVC membrane all green roofs require. Says Diana: “It’s technical work and you need it done right.”
Here’s a helpful template from greenroofs.org:
Starting from the PVC waterproof, root repellant layer:
1. Install drainage and filtering layers. “We recommend the JDRain product, because it’s all-in-one,” says Diana. This tech-y product looks like a giant egg carton (the cups catch water) topped by a root-resistant filter membrane.
2. Mix a growing medium based on your climate. Diana’s formula: pea gravel, sand, compost, perlite, and a couple of commercial products: Turfus (used by golf courses) and Hydroton (used by growers of hydroponic produce). Tip: find a nursery with green roof clients.
Drainage layers on the roof-in-progress
3. Plant hardy vegetation. “We’re talking about a living system. Your plants and materials will depend on your climate.” Diana’s list: prickly pear cactus, daisies and asters, penstamons and dianthus, hardy grasses.
Diana, ready to plant
4. Mulch with weight in mind. Diana used “Arizona Mountain Bark,” a lightweight volcanic stone.
This stuff only looks super heavy
5. Sit back and enjoy. You’ve created a tranquil spot to relax, and a home improvement that will save energy–and money. Energy savings will vary depending on where you live, but a few stats put it in perspective: In summer, a black roof can get to 160 degrees Fahrenheit or more, whereas a green roof would only get to 70 degrees F under the same hot sun. Green Roofs for Healthy Cities reports that a six-inch-deep green roof reduces heat gains by 95% and heat losses by 26%. The Cohen-Slaymakers didn’t use their air conditioner once this summer (though—full disclaimer—it was so cool, nobody in Madison did). They look forward to a snug family room this winter, thanks to extra insulation from their DIY green roof.
How inspiring! We live in a mid-century modern house and 3/4 of the roof is flat. My biggest concerns are of course leakage, weight, and root damage but it’s looking more and more like with the help of a professional we actually might be able to do this as well. Living in the Sacramento, CA area I can’t imagine a much better climate for a green roof. I’m excited to look into this a little further. GREAT JOB guys!
Hi Julia,
Diana Cohen strongly recommends consulting with a professional roofer who’s knowledgeable, or at least interested in learning, about green roofs. Good luck with your project–succulents, the best plants for a green roof, will love your climate!
Greek Finance ministry ‘green roof’ saves 5,630 euros in costs
The “green roof” created on the roof the economy and finance ministry building in Syntagma Square, Athens, Greece has resulted in savings of 5,630 euros a year, the ministry announced on Tuesday. The savings arise from a reduction in power used for cooling, amounting to 3,600 euros a year, and a reduction in fuel used for heating by 2,030 euros a year.
The green roof was created in July 2008 and covers about 650 square metres, or roughly half the surface at the top of the building.
Measurements carried out by the applied thermodynamics laboratory at the National Technical University of Athens (NTUA) mechanical engineering department have shown that the difference in temperature between the areas of the roof with plants and those without are 18C, with the former reaching 37C and the latter 55C, respectively.
The measurements also confirmed that the energy savings from the planting amount to 9.6 percent for cooling and 4.4 percent for heating. For the top floor of the building, especially, the energy costs for cooling can be more than halved.
The finance ministry noted that the project was initiated to help improve the environment in central Athens, save energy and reduce the buildings operating costs, as well as acting as a model that might encourage initiatives by other private and public organisations.
http://media.causes.com/ribbon/568189
Great article! What a unique solution!
What happens when their is a cloud burst or heavy snow? I wonder there might be a point when the roof medium might become saturated fom heavy precip. One would suppose that there would have to be a drain to take care of the overflow.
Great question. The Cohen-Slaymakers used 2×10 roof joists on 12″ centers instead of 16″ centers, to help support the ’saturation weight’ calculated by the roofer. Every green roof needs an ‘overflow mechanism,’ too. The Cohen-Slaymakers installed a regular gutter and downspout.
Great article on an unique alternative roofing option. I too wonder how it will handle rain and snow over time. My not help with saving on your electric bill like solar panels would, but it is a very interesting an attractive alternative.
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I live about an hour outside of Madison and am hoping to build a green roof this year if I can find a way to afford it. We have flat roof over 2 sections of our house, so 1 section this year and if all works out well, the other will be next yrs project. Any help and suggestions on how to do this the cheapest way possible while still being durable would be greatly appreciated. My husband and I would like to do the work ourselves to help save on expense. Does anyone have suggestions for low maintenance plants or grasses that stay short? Roof access is somewhat limited so watering it every day during dry weather is not an option. Help?