Sod roof keeps the building warmer in winter, cooler in summer, is essentially fireproof, windproof, and grows, not degrades, in the sun.

I like to tell visitors to my home in rural Massachusetts that I built a building that creates oxygen, filters rainwater, sequesters CO2 and provides wildlife habitat. “How did you do that?” they ask. I point to the top of my hand built cedar log sauna - a green living mass of vegetation covers the structure, doing all of these things, and renewing itself every year free of charge.

Not only that, but by putting a living roof on top of my building, I conserved the productive soils and plants that my building otherwise would sit on top of. In other words, I moved the “footprint” of the building to the roof! Looks very cool too.

Green roofs are nothing new. They’ve been in use for thousands of years. Known as green roofs, living roofs, sod roofs, they are partially or completely covered with plants and soil or other growing medium, planted over a waterproof membrane. Pioneers used them - in fact built whole houses of sod in the Great Plains.

Many gorgeous old log buildings in Scandinavia and parts of Russia with sod roofs still stand today, some over 1000 years old.

Green roofs are making a comeback in many new “green” buildings as well.

Ford Rouge River plant (above) in Detroit makes Ford F-150 pickup trucks inside, but outside is covered in lightweight, hardy sedum plants.

The roof at the Gap’s corporate offices (above) near San Francisco is an undulating plain of grass and flowers. Green roofs can cover it all - from the Fortune 500 company HQ to homes, garages, outbuildings, even the dog house

Here’s one video example of a simple green roof on a toolshed.

There are two types of green roofs: intensive roofs, like the one on my sauna, which are thicker and can support a wider variety of plants but are heavier and require more maintenance, and extensive roofs, like the one at Ford which are covered in a light layer of vegetation and are lighter than an intensive green roof.

Green roofs can be used to:

• Grow fruits, vegetables, and flowers
• Reduce heating and cooling costs of a building, and green roofs concentrated in a town or city can reduce the average temperatures during the summer.
• Increase roof life span - the living part regrows itself, and the waterproof parts are protected by the soil and plants.
• Attract songbirds
• Reduce storm water run off - the roof absorbs and filters rainwater
• Remove pollutants and carbon dioxide from the air
• The soil and plants on green roofs help to insulate a building for sound; the soil helps to block lower frequencies and the plants block higher frequencies.
• Filter pollutants and heavy metals out of rainwater
• Increase wildlife habitat in built-up areas
• Reduce heat loss and energy consumption in winter conditions.

Here’s a gallery of green roofs we found, courtesy of Wikipedia:

An intensive roof garden in Manhattan

Re-creation of Viking homes - Newfoundland

Sod roofs on 1700’s Norway farm

The green roof of the Mountain Equipment Co-op store in Toronto

Green roof planted with native species at L'Historial de la Vendée, a museum in France

A modern green roof at the California Academy of Sciences

Want to grow your own green roof? First make sure your building design, old or new construction, can stand the load - green roofs are heavy, especially the traditional ones. You’ve also got to get the waterproofing right or you’ll be constructing a biodegradable building when it leaks. Do some research and check with folks who have actually built them to get an idea of what you’ll need to do for your application.

Here’s how I did mine.

The photo below gives you a cross section shot of most of the layers.

My building is made mostly of cedar logs, but I used black locust logs - very strong and decay resistant - spaced 2’ apart to support the whole roof - which weighs about 15,000 pounds soaking wet! Across the logs I screwed 2” cedar planking, and covered it with plywood to make a smooth sub roof surface. Once you’ve got your sub roof in place you can begin to put in the elements of a green roof, instead of boring old shingles.

1. Step 1

Start with a waterproof layer. This step is essential. Most roofs fail because of water damage. There are many waterproof options from bentonite clay (for purists) to asphalt to sheeting to membranes that go on as a liquid. The old-timers used birch bark, but I used a Bituthene® membrane that rolls on like contact paper - I put it over the plywood and extended it out to the drip edge. You can’t see it in this picture, but you can see the brown drip edge over the cedar planks. The membrane is installed over the wood and drip edge.

2. Step 2

Install a root barrier. Bithuthene serves this purpose, but clay or asphalt will let roots penetrate. You can use concrete, or cellular glass, but I used a layer of Styrofoam board, which adds a little insulation, and protects the Bituthene layer to boot.

3. Step 3

Water drainage. As Mr. Miyagi said in the Karate Kid, the best way to defend a blow is not to be there. If water drains away easily, it’s not there to get in your building. Start with a layer of 6 mil or thicker plastic sheeting. Then add some kind of gravel or pumice. I used 2 inches of washed pea stone. The drainage capacity of your material has to increase closer to gutters and roof drains. Mine just drips off the edges of the building.

4. Step 4

Add a filter fabric. The fabric has to be porous enough to allow water to flow down into the drainage area while holding the soil or growing medium in place. Roots will penetrate this layer. You can use polyester or polypropylene, but I went organic here and used burlap. One your plants get hold, the root systems will form a filtering mat as well.

5. Step 5

Put in a growing medium. This means dirt or something else that plants can root in. You can use local soil, (watch for local weeds), and many roofs use a mix of things like crushed clay or sand with cleaned top soil and humus to supply plant nutrients. The thinner the soil, the harder your plants will have to work. Many experts recommend a soil depth of at least three inches. I used 5 inches of local loam.

6. Step 6

Add plants or seeds. Pick appropriate plants for your local environment. Consider sun, frost, heat and drought and wind. You want low maintenance. I spread Canada ryegrass seed to get a quick cover, put another layer of burlap over that to hold moisture and secure the seed and soil from birds, wind and hard rains, watered it once, and then let nature take over. I now have a nice mix of goldenrod and wild raspberries that seem to like it just fine up there. I go up top once a year and pull out any little maple trees that want to grow up big and crush my roof.

Now you’ll see in my picture above that I’ve put logs on each side of my roof to hold the soil in place until it gets established. You can do the same with timbers or planks secured to the edge, or do like the old-timers did and use an outer edge of stones or blocks of cut sod. Again one the roof gets established, it’ll hold itself in place. I also put a little birch bark around the edges to make it look authentic.

For more information, I’d go to http://www.greenroofs.com and http://www.greenroofs.org/ and start learning and dreaming! You can find a nifty design for green roof chicken coop, or video showing the building of a green garage roof.

Here are some other great You Tube videos:

Introduction to Green Roofs

This one has a terrific Jefferson Airplane soundtrack: Green Roof

No sound, but great photos: Green Roof Images

So find or build a green roof, conserve a little air, soil, water and habitat in the process, then climb up there and smell the roses…or the raspberries, or the sedum, or the grass…….