How to Build a Roof for a Green Home

The California Academy of Sciences

While there are many different types of eco-friendly roofing, few are as beautiful and as good for the environment as the "Living Green Roof," which contains actual vegetation. This type of roofing is popular in Germany, the UK and Scandinavian countries because it saves owners up to 50 percent in heating, cooling and insulation costs over time. However, Americans are still picking up on the idea. One of the best examples of a living roof can be seen at the California Academy of Sciences. The 197,000-square-foot roof, which houses 1.7 million native plants, stands as a marvelous example of what modern science can achieve. Green roofs have expanded by 35 percent over the past few years, with more than 3.1 million square feet of rooftop plants installed last year alone (according to the third annual Green Roof Market Industry Survey). Chicago's 534,507 square feet make it the city with the greenest roofs, which is followed by Washington, D.C. (500,000 square feet) and New York (359,000 square feet). It can be complicated to orchestrate your own green roof, so it's best to hire a knowledgeable contractor. Yet, if you're feeling adventurous, there are easy-to-install kits you can buy. Here we'll discuss the basic steps and layers so you're informed about the project you're about to undertake.

Things You'll Need

• Experienced contractor or DIY manual Green roofing kit (like Weston Solution's Green Grid) Waterproofing layer (EPDM 1-mm-thick pond liner) Drainage layer (Pre-fab plastic, gravel or shale) Filter layer (Lightweight polyester geotextile) Prevegetated mats or blankets and plants

Instructions

1. 

   Determine if a green roof is for you. If your house is old, it's important that you meet with a structural engineer to see if your rooftop will hold under the added pressure. (With the Green Grid system, each module adds another 15 pounds to your roof.) Also, you should check with your town hall's city building codes to make sure you're allowed to complete this project in your neighborhood. Also, any leaks or repairs should be finished before the new roof is put on. The Green Grid kit cannot be used on homes with a roof slope of more than 5 percent, that are located in arid climates or that have roofs made out of tar, slate, asphalt shingles or turn-metal. Most DIY installers draw up a plan before they begin to ensure steady work flow and the most productive, efficient method. They draw out where flashing, chimneys, satellite dishes and other obstacles are. They decide whether they want to assemble the pieces on the ground and transport them up or do it layer by layer on top of the roof.

2. Retrofit your roof with a waterproof membrane. To keep excess water from pooling up and leaking in, DC Greenworks recommends using a strong, mastic sealant. Most people use 45- to 90-ml single-ply PVC, TPO or EPDM 1-mm-thick pond liner to waterproof the surface. Some people also use built-up heat-applied high-polymer asphalt or SBS modified bitumen with root barriers. Before installing your roof, you can use a technique called Electric Field Vector Mapping to see that there are no leaks. This technique costs just $1 per square foot and is 100 percent accurate in detecting pin-hole-sized leaks, so it is highly recommended that you hire a knowledgeable contractor to provide this service, even if you're installing the roof primarily yourself. Currently, International Leak Detection is the leader in providing this service world-wide (see Resources). You may also want to add insulation for added energy savings. A popular brand used in the United States, Canada and Europe is the STYROFOAM™ Brand ROOFMATE™ Insulation. Your insulation should have 1/2-by-1/4-inch drainage channels on the long edge and should be 1 to 4 inches thick. This added layer of insulation above the waterproofing membrane should be attached with metal fasteners, Grace Bitustik Tape or Chemind Chemflex sealant. The protective layer of insulation will keep your roof a steady temperature and minimize potential damage from drastic weather changes (see Resources).

3. Apply the green roof components. After the waterproofing and insulation layers are installed, you'll work on the drainage layer, filter fabric and root barrier application. The easiest way to accomplish this is with a modular green roof system like GreenGrid or GreenTech (see Resources), which provides you with a molded plastic planter tray that gets installed on the roof like a tile. The modules can be quickly preassembled on the ground and pregrown prior to installation, which is the main reason people don't mind paying a bit more for the pieces. DIY builders will also save on construction costs with this easy system. Without the kit, builders need to create layers of biodegradable blanket root barrier, gravel or pebbles for drainage and curbs made of stone, steel, concrete, aluminum or wood.

4. Add plants. After drainage and filter layers are put in place, add the soil substrate and plants to your design. It's important to note that the growing medium is a special formula composed of shale, mineral composites and mushroom compost--not topsoil. The kits will come with everything you need to ensure your plants grow healthily and happily, with very little maintenance. Ideal plants include strawberries, chives, poppies, Delosperma nubigenum (yellow ice plant), sedum varieties, roseum, spurium varieties, talinum calycinum, stonecrop, self heal, sea pink, tidy tips, miniature lupine and numerous other specialty plants. Most kits come with plants that have been specially preselected by expert horticulturists, although you can also do a little picking and choosing at websites like Mother Plants or Emory Knoll Farms (see Resources).

Tips & Warnings

• To save money on your green roof, you can install the prefabricated modules yourself, thus saving on installation costs. Also, you'd be wise to check out your state's tax credit laws regarding green roofing projects. For instance, New York City building owners can receive up to $100,000 in tax credits (or $4.50 per square foot) for green rooftops. In Philadelphia, residents receive 25 percent back for the total cost of the project (not exceeding $100,000).

• Green roofs may attract additional bugs, bees and birds. Green roofs cost 15 to 20 percent more than conventional roofs, at least initially. Green roofs do require some maintenance: watering, fertilizing and weeding. Not all homeowners' insurance companies are willing to cover green roofs. Severe weather can damage your green roof.

References

• California Academy of Sciences
• Electric Field Vector Mapping
• Roofmate Insulation

Resources

• DIY Roof Installation
• Mother Plants