By Mary Ellen Gabriel

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:

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.

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