Building a green roof


Last year, Peter Schmelzer of Vivus Architecture and Design, designed a wonderful addition for our 1915 Arts & Crafts bungalow.   When he got the idea to put a flat roof on it, he said “What do you think about a green roof?”  We said: “Cool!”

Despite being enthusiastic about having a green roof, we really had no idea how to construct one.  So the green roof has been a DIY project, or a rather a DIWF (Do it with Friends) project for we have had a lot of help and encouragement.

The addition from the rear
The addition from the rear

Dean Taylor and Taylor-Made Builders built the addition (and did a fabulous job -consider this a shameless plug for Dean and his crew) and the underlying structure of the green roof.  The roof was designed to support the load of the green roof  (Before you try this at home: hire a structural engineer to determine if your roof can hold the weight of the soil, plants and water/snow),  hold the soil and plants behind a shallow parapet, and sloped to allow water to drain toward two scuppers.   The roof is insulated which keeps the interior of the house warmer/cooler, of course, but also prevents heat from the house from warming the roof from below.

And, the roof is sealed with a waterproof membrane and drained by 3 scuppers.

Roof with rubber membrane
Roof with rubber membrane

Now it’s our turn.

Justin slithering around on the root barrier
Justin slithering around on the root barrier

The first (bottom) layer over the waterproof membrane is a polyethylene root barrier.  This is by far the trickiest material to install because the plastic is very slippery.   Our task was made trickier because our addition is at a 45 degree angle to the house which meant fitting the long sheets into 2 triangles.    Those of you with sewing experience can transfer what you’ve learned working with fabric (think slippery silk or satin) to fitting a poly root barrier.   Once aligned, the root barrier is anchored under a metal cap on the parapet.

J-Drain layer
J-Drain layer

Next, the drainage layer.  We used J-Drain – see the little bumps (they’re about 1/2″ high)?  They’re made of rigid plastic backed by another root barrier with filter fabric (that’s the brown part in the photo) on top to keep the soil out of the drain layer and scuppers plus it’s an additional root resistant layer.

Next, soil and this was the fun part.  Justin and I did the first two parts by ourselves, but we needed help transferring 3 yards of soil from the driveway to the roof.  For such a small project (the total roof area is only about 200 sq. ft), most of the automated solutions were not cost effective.  Fortunately, we have friends who work for coffee and food (as well as our hearty thanks). You can see Griff Wigley’s documentation of this phase over on Locally Grown.  Here are pictures from neighbor Eric Johnson:

The Soil
The Soil
Filling buckhets
Filling buckhets
Going up...
Going up…
And up
And up

Despite warnings that this job would take all day (or many days, our cheerful bucket brigade did it all in about 2 hours.

We put an excelsior (a fine term meaning, in addition to the wood shavings, “ever upward” and used as the state motto of New York)  erosion blanket to hold the soil in place until the plants are established.

Excelsior!
Excelsior!

Plants…we’ll be planting a variety of sedum (stonecrop) which is the green roof plant standard.  I’ll update this post when we reach this final step.

But now, to say thanks to the many folks who helped move the dirt and other assistance (in no particular order)

And finally, a plug for the folks at the Minnesota Green Roofs Council and Roofbloom for their information and encouragement.


6 responses to “Building a green roof”

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.