THE FIRST TEN LAYERS OF OUR SOD ROOF

I’ve missed 10 days of posting because of a crashed computer, and our impending move to temporary quarters between the old and new house(now 10 days away) has made life pretty hectic. 

But exciting progress has been happening at Underhill House, and I’ll start catching up, beginning with the roof.

While Underhill House is being plastered with lime stucco, it’s under wraps, but the building crew has been busy on the roof.

When we tell people who our house will have a sod roof, they are often taken aback.  Sod roofs conjure an image of roots burrowing through the ceiling and muddy water dripping on our heads.  After all, we did name our house Underhill partly because we are building into a hill, but also because we will have vegetation on our roof

Even though our roof has not been built following conventional methods, we are becoming very confident that we will be dry under a 14-layer sod sandwich.  Yes, 14!  We’ve just added the 10th and most important stratum, and we are confident that the roof is super sealed now.

WHY A SOD ROOF?

Our first idea was to have a standing seam metal roof that could last 50+ years.  But the undulating beauty of Whole Tree beams and rafters create waves both front to back and side to side across our roof.  Neither shingles nor standing seam roofs can really accommodate this much motion.  So Whole Trees Architecture and Structures has been opting for living roofs as the proper fit to their rippling roof lines.

This is the beginning of a beautiful roof and the end of conventional roofing methods.

Sod roofs also provide a great natural insulation that keeps your house warmer in winter and especially cooler in summer.  Instead of transferring heat from the roof surface to the interior of our house, much of the solar power that beats on the roof will be captured in the process of photosynthesis.   Our roof will be constantly pulling carbon dioxide out of the air to produce cellulose.  A relatively small fraction of the incoming light will radiate down into our house on hot summer days.

When the roof is watered by rain or trickle hoses, we also expect to benefit from evaporative cooling.

We’ll talk about the last layers and specific choice of plants in a later post.

Here are our first 10 roof layers.

  1.  Hemp cloth stapled to the tops of all of our exposed whole tree rafters.  This is the finished ceiling we look up at from below.At this point, the roof has tough hemp cloth stretched between the rafters in the interior of the house, and re-purposed, discarded wall-to-wall carpeting (with its interesting underside exposed) stretched over the exterior soffit parts of the roof.
  2. Reflectix.  Essentially a quarter-inch thick sandwich of bubble wrap with a foil layer on both sides to reflect heat back into the house in winter and act as the first moisture barrier.
  3. Tarps made from reused vinyl billboard material that has become a Whole Tree trademark.  (Some of the crew have suggested that an alternative name for Whole Trees could be Whole Tarps for their extensive reuse of this waste material.)  This layer imparted a relatively water-tight seal while the next intricate layer was being constructed.Alas, one layer of re-purposed billboard tarp is not entirely waterproof, but it’s a colorful start.
  4. Custom trusses (see my post The Roof at Underhill Is a Matter of Truss) This layer also includes a 12-inch thick filling of Icynene insulation, which is natural product derived from de-husked and pressed castor beans.Watching this caster bean foam expand  was like watching liquid popcorn pop.
  5. Another re-purposed  vinyl billboard tarp to provide waterproofness while the next somewhat time-consuming layer was applied.
  6. A 5/8” thick layer of pine decking milled last March (see my post Using Every Particle of Pine ) from trees that were growing a few feet from the building site.Doug and I lay awake at night considering all the possible ways to use the pines that were blocking our southern exposure. They made a beautiful  covering over the trusses.
  7. A second layer of 5/8” thick pine to provide extra structural stability with a few feet of plywood along the two long edges to conform to the irregular shape of our non-rectangular roof.  This was a perfect fit.  Our pine board supply came up short by a few feet, and the edges needed a few feet of plywood to accommodate the flowing shape.The second layer of pine decking made the roof very sturdy.
  8. A ½ inch layer of Styrofoam for further insulation and to cushion any splintery places in the pine decking .It almost hurt to cover the pine boards with styrofoam Their beauty was like Buddhist butter art. Unfortunately, I didn’t get a photo of our roof when it was an undulating pink plank.
  9. Another repurposed billboard tarp.
  10. Today we added,  a 60-mil thick EPDM synthetic rubber membrane.  This is the layer for ultimate water proofing.  This is the kind of stuff that goes under man-made ponds and over flat roofs.

    The world’s biggest bicycle tire.

    It looks and smells like a bicycle inner tube.  Joe Cole, one of the carpenters on the Whole Trees crew, advised us that if it ever sprung a leak we could scrape the bad spot down,get out our bicycle patch kit out and slap on a red, rubber patch.

All these layers have provided the crew with a lot of time to be up on the roof, which on some of the hottest days has been a bit intense.  The Reflectix had a wicked mirror like reflection off of its surface, and the black EPDM membrane definitely soaked I some solar heat.  But most of the time it is a really wonderful place to be.  Doug and I have joined them on every possible pretext.

Today as they stretched the black rubber, another crew member, Prairie Sundance, commented that constructing the roof was like the process of dissecting a whale.  It’s topped with a dark, rubbery skin, and then the blubber like insulation is held within the rib-like trusses.

Though it’s not finished, this is the day our roof became true shelter from the storm.

There was something almost whale-like up on that black, rubber roof.  Earlier, when it was covered with a blue tarp, I stood below it and felt like a huge wave was approaching me on the open sea.

Watching this house be built, and having a hand in it is one of the most absorbing projects I have ever undertaken.

Care to share your thoughts on living roofs? 

Have you seen any?  What do you think?

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3 replies

  1. Thanks, Lorijo.
    Yes, this is being a very hectic August. We move to our temporary digs in 9 days, and there is quite a lot to do. I’m glad to be back blogging.

  2. I too was beginning to wonder where the posts were. It is fascinating seeing the layers. I understand that the birch bark was once used as a waterproof layer under sod roofs in Scandinavia, but not sure how sustainable that would be in the long run. I love the re-use of the billboard tarps though.

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