Sub-layers of the Floor

Getting the sub-floor completed adds a whole new level of progress, allowing the next stages of the build to continue with greater ease.  The main floor of our straw bale addition went from an 18″ deep mucky clay hole to a finished concrete surface that we can directly lay the final tile floor on.  Here is an outline of the different layers and the process of putting them in.

1.First we filled the bottom with 6″ of gravel to cover the 4″ drain tile that runs under the house (as we are on a hillside with many springs weeping from the bedrock) and will allow any water that gets under the house to drain away easily.

2.Preliminary plumbing- all the plumbing is laid out across the floors and supported by the drain rock to create a slope across the main floor towards the septic.  The bathroom, utility room and kitchen water fixtures all come together into one 4″ main drain that exits to the east where it will end up in a septic tank/lift pump to take up to our existing septic field.

3.Insulation layer- placed directly onto the drain rock, we used whole bags of perlite that we laid out tightly side by side and gently flattened (by foot) to create a solid layer of 8″ insulation, which gives a R value of 25.  We chose to use perlite because it is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently. (Rigid foam insulation is the usual building material for this use, but it is made of polystyrene.)  In some places we had to customize the bags by emptying them partially to help fill the spaces which were not the same shape as the bags.  Here is a link to the Perlite Institute which has complete information on using perlite for construction insulation below slabs – https://www.perlite.org/library-perlite-info/insulation-perlite/Perlite-underslab-insulation.pdf

4.On top of the perlite bags we put 2″ of sand, filling the spaces around the bags and then compacted the whole floor.

5.The next layer we put down on top of the sand was the 6mil construction poly vapor barrier and then laid out the metal rebar mesh that would be pulled up into the 4″ slab.

6.And the last thing we had to do before pouring the slab was attach the hydronic infloor heating Pex tubing to the metal mesh.  It is best to consult someone about the layout and spacing of your tubing as it will greatly affect the heating potential of your hydronic system.  It is also important to use sleeves to cover the Pex tubing where ever it comes up through the slab.

7.Once everything was ready we ordered the cement and Colin worked with a crew of 3 others to pour the slab in less than 3 hours.  The slab is flat, but not super finished as we will be putting 12″ mexican tiles down as the finish floor surface on the lower floor of the house.

The upstairs currently has a plywood subfloor.  We haven’t yet decided what we are going to use to finish it.

bathroom- exposed is the box with water lines for the bathtub, as well as venting and drain openings

 

The Layers Beneath Our Feet

We built our house on the top section of a bedrock slope – a perfect place for anchoring the house to a solid mass.  The concrete stem walls are pinned directly to the rock in a way that reaches around and flows over the various natural undulations that existed, allowing us to avoid any blasting.  At the south side, where the slope falls downwards, the cavity in which we back filled with shale was about 8 feet deep, and on the north wall side, it was only 2 feet.  An earth berm set back from the over hang of the roof lifts another 2 feet the length of the north wall, providing a small shawl of soil around the chilly side.  We had learned from Michael Reynolds and his design features that the planet Earth is a thermally stabilizing mass that delivers temperature without wire or pipes, and we wanted intuitively to be connected to that constantly warm, grounding energy.  “The outer few feet of the earth heats up and cools off in response to surface weather. However, deeper in the earth, about four feet and beyond, the temperature is more constant (around 58 degrees). Here, the earth can be used to both cool and stabilize temperature if the home is appropriately designed.”  earthship.com/comfort-in-any-climate.   So the fill of local shale went in, packing solid down to the bedrock below.  While it is not a true tapping in to the mass temperature of the earth, (instead of digging down, we filled the ground in below us) it felt better than an awkward crawl space and manufactured insulation.  On top of the shale went our vapour barrier of plastic, on to which we needed (by code)  a layer of insulation. Most common here is the pink foam board, but we looked around and found that mixing agriculture grade perlite with a modest amount of concrete (6 shovels perlite to 1 shovel concrete) and laying it 4 inches thick gave us the same value to code as the pink stuff.  We could also neatly pack it in around all the water pipes that we put down on the plastic layer.  We were able to easily anchor the hydronic in-floor heating pipes to the perlite layer before we continued up with a 3 inch thick cob slab as a sub floor.  We had a bobcat mix all that up for us and we hauled it in and trowelled it in place as level as we could get it.  Our original plan at that point was to finish it off with an earthen floor everywhere except in the kitchen, bathroom, mudroom and utility room, where we would tile instead.  Our search for cheap tile however, was fairly unsuccessful, as was our search for a trusted earthen floor recipe and method description.  Our time was being pushed as was our wallets, and at some intersections of journeys, there come times when priorities begin to change places.  Our three years in the trailer was wearing us thin, and with Colin back at work to uplift our bank account, time became scarce as well.  Accomplishing 800 square feet of earthen floor became daunting and expensive as we waded through the estimates of finishing oil and wax, kaolin clay and stucco sand.  Then I stumbled upon a place in Vancouver that was selling ecologically certified cork flooring at a ridiculous cheap price compared to other prices we had collected, so we put in an order that would cover all but the very front south facing room.  Colin was determined to make an attempt at an earthen floor in the room that receives all the passive solar sun, so as to keep the principle of mass heating intact without too much expense and time.  The cork flooring was beautiful to install- an interlocking system that floats above the subfloor, allowing for expansion with the temperature fluctuations of the in-floor heating.  Of course, because the cork was not as thick as we had planned for with the earthen floor, and the sub floor not at all level enough for cork tiles, we had to trowel an inch of concrete on to the whole area.  The cork floor is durable and flexible, warm and soft on the feet.  The earthen floor section was indeed another journey of experiment, a journey which I will write about in another post dedicated entirely to the process of the art of earthen floors.  We are glad to have only done the one small section, but we are also excited about repeating the process in the second half of the house.  It is wonderful to have the opportunity to test the methods that we are choosing on this half of the house, so we can learn from our experiences and navigate with more knowledge for the second half of the house.

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