Framing~ The Bones

roofDespite a very frigid December (for the west coast), we managed to continue building just in time to get the roof sealed up and water tight before the wet west coast winter starts in.  Here is a brief account of the structure of the frame, and the way in which we are going to insert the straw bales.

first wallOur decision to use a stick frame method as opposed to a timber frame (as we did for our first house) was mostly a compromise of time and money.  Stick framing is super fast, and we hired an experienced framer friend (thanks Danny!) to work with Colin and his design with the curved roof lines.  Dan helped Colin put his drawings into a model of the house in Sketch-Up, a computer program for architecture, so they could get accurate measurements for all the framing, especially where the lengths of the 2×4’s change subtly with the curves.  The curved roof was the main reason to use stick framing- it was eaiser and faster to frame the studs under the curved beam which is essentially two 2×8’s (cut out of 2×10’s to get the curve) overlapping all along as one continuous header the length of the roof- this also alleviates the need for headers over doors and windows.  Framing started on December 2, and was done in a month, despite a week break over Christmas.  We still have some interior shear walls to frame, as we were focused on the walls that were necessary for the roof.  Also, window and door framing will be cut in sometime in the spring.  Many people have asked us about how 2×4’s can be the only thing holding up a living roof, but the engineer says they are strong enough with the 3×8 beam on top.

The exterior walls are framed to 18 inch centres, as we will be standing the bales on end between the 2×4’s.  A lengthwise notch will be cut down each side of the bales to fit them snug around the framing, and thus hide the wood frame down the centre of the wall of bales.  The new international building code for straw bales has published findings that the bales placed 14 inches wide in the wall is the same insulation value as their 18 inch wide option, due mostly to the orientation of the straw.

All of our interior walls are shear walls (plywood on one side, and attached to the foundation directly), as required by the engineer, since our exterior walls are straw bales and not considered to have any shear strength.  The shear strength is the load that an object is able to withstand in a direction parallel to the face of the material, as opposed to perpendicular to the surface.  In walls, it is usually plywood or cross bracing that provides the shear strength, preventing any side to side movement.  So our internal walls are (or will be) sheeted with plywood and continue down to the foundation.  At the foundation, the walls are secured with hold downs to resist any upwards movement in an earthquake.

The roof is standard construction with 2×4 strapping over 2×12 joists, though in the more curvy parts of the roof we had to use double layers of 1×4.  On top of the strapping is standard 1/2″ plywood decking and a 4″ curb all around the edge to keep the dirt in.  We decided to go with a double layer torch on roof membrane this time, which should easily last a very long time, longer than us… The roof was torched on in early January and we are now secure and dry for the rest of the winter.  Colin is back to work in his shop for the next few months to get caught up with his ThujaWoodArt projects, but come the spring we hope to do the infloor heating and plumbing under the concrete slab on grade subfloor, and prepare for installing the straw bales in the summer.  We will be offering workshops for installing the straw bales and plastering in the summer through the local Heartwood Folk School, check their website for more info as we get closer!

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!

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