The Roof of the Cob Workshop

As we move into the first week of October, it remains the driest summer on record here on our west coast island, parching the gardens, drying up wells, and raising the fire danger all around us.  The one thing that the clear sunny skies have been perfect for is drying out the cob walls of Colin’s workshop and giving us lots of time to get the roof on and the walls protected for when the rains finally do pour down.  In the meantime, Colin is splitting all the cedar shakes that he needs for finishing the roof, and I am getting ready to start troweling on the scratch coat of earthen plaster on the walls.

The construction of the roof began with the laying of the rafters onto the top of the cob walls, radiating outwards from the central post and beam structure that stands in the center of the workshop to support the large skylight.  We embedded “deadmen” (inverted wood T’s) into the top foot of the cob walls every two feet, and attached the rafters to these for extra tie down support.  Then we had a small amount of cobbing left to do- filling in around the rafters up to a finished height that closed in a small vent on the outside edge.

Colin had in mind an undulating roof line as well as a curving roof line, so the top height of the walls swept up and down as they went around in the circle, making the rafters swoop above doorways and dip into corners.  Placing plywood over the rafters required half inch as well as quarter inch plywood, doubling up the quarter inch in the places where it needed to bend around corners and into the dips, giving the roof a plywood patchwork look.  We then rolled out lengths of roofing felt and started on the skylight.  Traditionally, cedar shake roofs don’t need any plywood or roofing felt.  The shakes were just nailed right to strapping over the rafters.  Because we are building a permitted building with unconventional materials with approval from an engineer in a seismically sensitive zone, well, we had to do it.  Our engineer told us that the plywood helps to distribute the load of the roof on the load bearing walls, uniting the roof and reducing the amount of pressure directly on the walls.

The skylight required a little more finessing in terms of design.  Basically, a system of nine ribs curve over a center beam, with double walled polycarbonate sheets bent over the ribs, and cedar strips screwed down on the top.  Lots of details in between, of course, but that is the basic construction of the 8×12 skylight.  There is plywood filling in the ends of the skylight, and roof venting along the sides that moves the air through from the vents at the other ends of the rafters.  We will be filling the inside of the ceiling with rock wool insulation, leaving a two inch gap at the top of the rafters for this passage of air.

The light inside is a beautiful diffused brightness, and the gentle curves and waves of the roof line is complemented by the surrounding slope and roll of the bedrock, the arch of the lifted skylight echoes the balanced curve of the strawbale house above it.  The moments of standing and looking at the very real outcome of what was an imagining is almost surreal, as if we were imagining what was already there and had just failed to notice it before.  We still have an extensive list of big and small jobs to do before the workshop is usable, or finished, but having the foundation up to the roof constructed and becoming a part of our landscape is an amazing accomplishment.  Thanks to many helping hands, encouraging words, and loads of summer fruit dropped off by generous neighbors!


8 Comments (+add yours?)

  1. sculptingearth
    Oct 04, 2012 @ 12:25:25

    Wow! this house looks great. I like the simple elegance of the design and is great to hear that you were able to get this design permitted and up to code. I really like the skylight. It seems like one of the few skylights I have seen on a cob house that I would trust not to leak and looks relatively simple to build. And wonderful craftsmanship and attention to detail with the curved skylight, roof rafters and, and undulating wall.


    • inspirationalvillage
      Oct 11, 2012 @ 03:40:49

      Thanks, so far it hasn’t rained much, but we are pretty sure it won’t leak! Colin spent a good amount of time planning the design and going over it with his father. Always helpful to have a second pair of eyes. We have been working with an enthusiastic engineer for a few years and he trusts Colin… that seems to be a big bonus in talking about alternatives. Colin has been imagining this workshop for a few years. Wendi


  2. Custom Roofing Installation
    Oct 25, 2012 @ 06:58:43

    Thanks for sharing the post! I think this is not an easy job. However it is really a great work! Looking forward for updates.


  3. A.S
    May 17, 2013 @ 14:00:02

    dimension of the timber used? weight of the silicon/ m^2?

    thanks, the house is amazing so me and my team is trying on constructing this.


  4. waziyatawin
    Apr 14, 2015 @ 02:16:30

    Love this roof! Can you tell me how thick the plywood was that you used for the sheathing? We are creating a roof for our strawbale/cob home and, if possible, we’d like to use something malleable enough to accommodate some undulations in the roof. Many thanks!


  5. Jeremy Krieg
    Jun 14, 2016 @ 12:17:19

    Wow looks fantastic !!!

    Just wondering with your pond liner (it looks like pond liner 🙂 ), is it glued together ? did it work out a lot cheaper buying strips rather than a big size ?

    Thanks so much 🙂


    • inspirationalvillage
      Jun 18, 2016 @ 00:19:57

      That is in fact just roofing felt, layered on in strips underneath the shingles. We used pond liner on the strawbale house, because we built a living roof. I believe we used two large sections and glued the seam down the middle. I think there is a post about the living roof and its construction on the blog as well.


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