Building a Living Sod Roof For a Cob House

by ziggy on May 14, 2009 -- 10 comments -- Follow

livingroof01

At long last, I have a living roof! I’ve been anticipating this day for over a year now and it’s finally done. On Monday, a group of about twelve folks assembled to help me lift sod onto the top of my roof, and in two and a half hours, it was effectively covered.

Soil Retaining Ladders

livingroof02

A few days prior to Monday, I made several soil “retaining ladders” using rope and some thin wood poles to help keep the soil in place. These poles were spaced a couple of feet apart to provide a brake for the soil from sliding down the roof. At some point I ditched the idea of using any loose soil on the roof in favor of entirely using sod, so these ladders became less important to me, but I left them up anyway.

Building the Living Roof

Since I already wrote about cutting sod for my roof, I will describe how the sod was loaded. Once the perimeter of the roof was covered with sod, we covered the rest of the roof. Doing the edge was the trickiest part, since I had the fold the EPDM underneath itself and leave a little bit exposed to protect the edge logs.

livingroof-party01

Once that was done, it was only a matter of lifting the material onto the roof. People worked at ground level to pass the turf up to folks on scaffolding and ladders, who then passed the material to others on the roof. The turf squares were packed closely together so that there were no gaps. If any awkward gaps could not be filled with sod squares, loose soil was loaded into cracks.

livingroof-party02

It was all fairly simple. Heavy heavy, but simple. I still have to load some sod up at the very top of the roof to completely cover the tractor tire skylight frame, but the roof is effectively done.

Planting the Living Roof

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On the east side of the roof, I dumped several buckets of loose soil so that I could put in several strawberry plants. I mulched the strawberries with straw to help conserve moisture.

livingroof-strawberries

Eventually, I will plant wildflowers, grasses, and edible perennials on the roof, focusing on plants that are tolerant of drier soils and full sun. Since the sod is only about four inches thick, it is likely that the roof will dry out during high summer.

Although… yesterday was an incredible first test of the integrity of my living roof. At 6:30 p.m., we were warned of a tornado headed straight for Rutledge. Within 30 minutes, an inch and a half of rain had fallen, but thankfully the tornado turned at what felt like the last minute, and we were spared. It missed us by a mere 10 miles. I was happy to find that the soil remained intact on the roof, and none of the sod slipped. I didn’t see any signs of wear on the rafters, either. Success!

It will be interesting to see how the living roof ecology develops and changes over time. It will be especially nice once the individual sods root together and get totally established.

My Living Reciprocal Roof Formula

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Here is my living reciprocal roof formula, in layers:

  1. 28 round pole rafters (black locust and pin oak, 14 primary, 14 secondary)
  2. black walnut wood decking (mostly 1-1.5x)
  3. muslin fabric
  4. double layer of cardboard
  5. EPDM
  6. four inch thick sod squares

And finally… a few more photos from the sod roof party:

  • http://www.acoolerclimate.com Peter

    Very cool!

  • liat

    hells yea!!! you are currently one of my heroes Zig. when I return home I will be happy to help w/your floor and plaster. sad that I miss all the big work parties for gob-cobatron. we need to put in a warren request so we can start working on the next project in a few months.

  • Matthew

    Hi Ziggy

    I am interested in what you have over the sky light to keep rain out (I can see the tyre). Also does your rocket stove have a flue and, if so, how is it sealed from the rain.

    In awe.

    Matt

  • http://www.small-scale.net ziggy

    Matt: I’ve yet to install the skylight so I can’t say for sure how it will work. I have an idea in mind for it, but I’m going to wait to explain until I actually do it.

    The stove has a flue, but it exits the building horizontally, so it doesn’t really get much rainwater. (There is a little elbow, but it is usually pointed east or west.)

  • phil

    Hey Ziggy, love the house and concept of the earthen interior.
    planning a trip to visit dancing rabbit aug, 22. hoping to see the house
    in person. great job!!

  • B & J Roofing

    As a
    Seattle roofing contractor
    I appreciate this kind of information. Please count me in as a new fan of this
    Blog. Thank You!

  • Steve Snowdon

    Ziggy simply amazing I love what you have shared with everyone, brilliant stuff I have learned so much thankyou.
    I live in N/E Thailand where I too have started to build a Resort / Retirement village .Completion is expected in another 12 months
    Abobe / Cob construction will feature prominently along with alot of old timber my place is named Bedrock after the Flintstones. It will comprise of 6 dwellings and the main house which is 2 storey will be 80% Cob. I,m 6 mths into the build todate and am almost ready to do the walls so I cant wait to put into practise what you have shown me.
    I will keep you posted. Well Done……….

  • richie

    hi worried the soils going to come tumbling off that end at all?? looks a little unstable! i want to do this too so just trying to be helpful!

  • Dottie

    There are two thing I’ve been trying to figure out since I began considering cob buildings. First of all, can you build the wooden beams of the roof directly into the walls? Won’t the wood and/or the cob shrink and pull away as they dry? I was also wondering how the logs are attached to each other at the peak of the roof.

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