GROUNDWORK- Building with Straw Bale

Last year we were approached about being interviewed for a short documentary about building with straw bales.  We are excited to share our story as well as our reasons for choosing straw bales and other natural materials to build with, and it is delightful to be among other home owners and builders who share the same sentiments about the homes we create.  We are currently on this journey once again, and the reminder of why we are doing this is truely valuable in the face of the various challenges that manifest during such a large and complex project.

Our wood working shop is also featured in Episode 1-Building with Cob.

Other episodes made are Episode 2- Building with Timber and Episode 4- Building with Rammed Earth.

*Made by TELUS Optik Local~ supports compelling, original stories told by filmmakers from BC and Alberta by providing production funding, training and exposure to new audiences.

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!

Phase 2- Continuing the Build

foundationFoundationThe basis on which something stands or is supported; a base.  The basis or groundwork of anything.  An underlying basis or principle for something.

An overview–  The previous straw bale house chronicled on this blog was the first section of two parts of our whole building plan.  The first half is designed as an in-law suite for my mother, with a shared art studio space, and this second half that we are just starting will be bedrooms for us and our kids and a garden level living space.  The 3 acres that we have contains a lower open feild where the pond and gardens are situated, a forested upper area, and a sloping face of bedrock in between.  Since we don’t want to clear the forest or use up valuable growing space, we have designed the house to be built on the rock.  The first half sits at the top and overlooks the pond and gardens, and the other half is separeated into two floors, each built like a terrace from the garden level up to the existing section and attached with an enclosed walk way.  The total square footage will be about 2,000 square feet.

excavatorWe are building with as much attention to natural materials as possible.  We are using sustainably sourced or salvaged resources whenever we can.  The walls in this half will be straw bale with clay and lime plasters, with a living roof, just as in the first half.  We are aware of the imprint of building houses these days and the huge amount of toxic off gasing that occurs with many conventional materials as well as the chemically saturated waste that ends up in the landfill.  However, since we are building within the boundaries of building codes and needing to meet the requirements of engineers, architects and inspectors, there are just some things we can’t avoid.  Natural building can be a tag that is placed on our house as a whole, but I think it is important to state that not every aspect of the house is “natural”.  Such as, for example, the foundation.

The second half-  There are not many places in Canada where you could begin to build a house in November.  Of course, we didn’t plan to start at this point, but the process of aquiring the permit took longer than we expected.  We learned from our previous build that everything will take longer than expected.  Amazingly, the weather has been quite co-operative, allowing us to complete the form work in one week, and giving us the sunniest day of the month on the day we scheduled the pumper truck.

There is not much about the foundation that would fall into the “natural” category.  We hired an excavator to dig the footprint, and rented a large rock drill with a giant, gas powered compressor to drill out 140 holes in the bedrock, each ranging from 16″ to 24″ deep and filled with concrete grout and rebar.  We purchased a lot of 2×10 and 2×4 lumber as well as some plywood for the forms that we hope to re-use again in the framing if possible.  We set five runs of rebar inside the length of the footings and stem walls with a 1′ grid of rebar in the higher walls and snap ties every 2 feet, and placed knockouts of pvc in the footings wherever we need drainage, septic, and water runs.  We hired a concrete pumper truck and 3 truck loads of concrete.  We set anchor bolts every 3 feet in the top of the concrete to attach the framing.  The engineer is happy, the geo-tech is happy, the building inspector is happy.  This is not terribly extraordinary in the world of regular construction, in fact it is quite standard and even a “small” job.  To me it seems rather complex, requiring a lot of effort and money to create forms that become deconstucted and a structure that is largely unseen in the end.

However, this crucial first step is the foundation upon which we will begin to build up our visions of a beautiful, healthy, comfortable, sustainably functioning and lovingly hand built family house.   

 

Bales of Insulation- A Full Report

exterior bamboo piningWe are heading into our third season of winter in our straw bale house.  Hard to believe really – I so clearly remember the feeling that the house would just never be done – but there you have it, two years later we are really beginning to see the way the design and materials of the house perform through the seasons.  Last winter was a relatively mild winter in an already mild climate zone, and the winter before we didn’t really move in fully until January, so getting a sense of how much wood we might burn and how much our heating/electrical costs would be throughout the winter months has only just begun to be obvious.

winter sun bouncing off the pond

winter sun bouncing off the pond

Our three forms of heat are the wood stove, hydronic in-floor heating, and passive solar orientation.  The winter sun arches across the sky, sending it’s light and heat into our east and south windows (when it is out!) staying entirely above the top of the trees of the ridge across the valley of which we face.  At certain times of the spring and fall, the light of the sun bounces off the pond below us which lights up our ceiling with ripply light- an unplanned bonus!  We have an earthen floor in the front room, which noticeably absorbs the warmth and retains it into the evening.  The wood stove sits on a two foot tall stone hearth and is backed by a short cob wall, both of which absorb sun heat as well as stove heat.

In floor heating tubes covered by 3 inches of cob sub floor

In floor heating tubes covered by 3 inches of cob sub floor mass

Our in-floor heating is divided into two zones, one for the bathroom and north side of the house, and one which circulates the front south room.  They are set to come on if the temperatures of the rooms drop below 19 degrees celsius.  The front room heating has never come on, and the backroom zone clicks on early in the mornings of the coldest days of winter.  The tubes are embedded under 3 inches of cob, which then also retains heat for longer.

We primarily rely on the wood stove for immediate heat.  This year we lit our first fire on November 20th, and mostly because we were nostalgic for that first cozy fire.  We kept the fire going for about an hour, and then we were too hot.  We have found that we really only need to light a fire around four or five o’clock, depending on the temperature outside, and let it die down around nine, otherwise it gets up to 25 degrees!  upraised wood stoveWe have been having a cold spell right now, where temperatures fall towards -2 or -3 degrees at night (oh my!), and then we might light a fire at three in the afternoon.  Our evening fires keep the house sitting at 20 until late the next day.  Last year, this translated into our using less than half a cord of fire wood in the whole season.  We have an older style stove that doesn’t have any of the newer reburning/efficient innovations, and our space is 920 interior square feet.

The southerly exposed room of the house is lowered by two steps, (which is where the wood stove is) and so the heat tends to naturally move towards the north side of the house as it attempts to travel upwards.  If we leave one window open in the loft of the back room, the heat is pulled even more into that space.  Another design feature of the walls themselves are the wrap- around construction – meaning that the bales are continuously wrapped around the outside of the timber frame, leaving no thermal breaks except where there are doors and windows.  We used double pane thermal glass with argon gas and a low-E squared coating.

west side, south side

south and west side- wrapping bales, sun exposure, and roof overhang

I love the heat that a wood stove gives, but I am not excited about the amount of wood and trees that need to be burned.  It is not entirely a “clean” way of heating.  Eventually we will have three wood stoves on our property – this one, one in the work shop, and one in our addition to this house.  Luckily, Colin’s business of crafting furniture from salvaged red cedar means that we have a lot of  great kindling and fire wood just from his waste.  I am comforted to know that we can potentially heat our spaces for years on just a few dead or cleared trees.  We took out a few trees when building the house, and haven’t even started using them.  This fall, I chopped almost two cords of wood from those trees, which will potentially be three years of wood.  The less wood we go through the better – we even find that turning on the stove to make dinner warms the space efficiently some nights.  Certainly, if we have friends over in the evening, lighting a fire usually leads to opening some windows.

Straw bales reportedly  have an R value of 30-60.  The building code requires that insulation needs to have an R value of 20 in walls.  We have experienced this amazingly efficient quality of insulation, in the winter and in the summer, when the inside of the house is cool and refreshing on hot days.  With a 3 foot overhang of the roof blocking out the sun’s light in summer and the rain in the winter, I am ever more convinced that straw bales are a fantastic way of providing natural temperature control in any climate.

Workshop Update

cob workshopThings have been progressing slowly but steadily in the workshop since we finally got the roof finished in the winter.

Colin focused on getting the doors in right away, refining two old doors that came from his Dad’s work of deconstructing old houses on the island, and refitting a pair of salvaged french doors.  He also built a raised stone hearth from the pile of stones we have on the property, put in the stove pipe, and wired in the rough electrical circuits.  We got the insulation in the ceiling and the plastic vapour barrier secured over that and ready for the finished ceiling layer, which we think will be some kind of bamboo or sea grass mat.

rough sculptureI spent a couple of weeks on and off getting the rough coat of plaster on the inside and outside of the building.  This layer of clay plaster is the only rough coat needed on a cob wall, and is the same layer as the third layer that we put on the strawbale house.  (See my previous post called Natural Plaster for full details).  A mix of 4 parts sand, 2 parts clay, and 1 part straw with water to mix it to a troweling consistency kept me busy in the warmer days of late winter. rough plastered windows I cleaned up and shaped the sculptural aspects of the walls so they were ready for the final layer of plaster, which Tracy and I completed earlier in May, while the temperatures were still cool enough to give the plaster time to dry.  The final clay plaster took us 2 days to put on, a seemingly record pace for any one job to be completed in.  We mixed up the kaolin clay, sand, straw, paper pulp and whiting in the buckets the day before, and then added the rice flour paste, and borax and mixed multiple buckets together the morning we started plastering.  (See my older post Final Plastering for more exact details).  We got much of the simple walls done on the first day, then completed the wall with the windows and arched shelf the next day, cleaning up our tools by the afternoon.  I am always so amazed at how quickly the finishing layer goes, compared to the time it takes to get all the other layers beneath it built.final plaster

Last weekend, Colin and I built the one interior wall that separates the workshop from a small storage room.  It will also be the wall against which will be built Colin’s work bench.  It holds the majority of the electrical outlets and is a standard 2×4 construction filled with rock wool (Roxul) insulation and covered in plywood.  final plastered windows

There is not too much left to do in this simple building for Colin to finally move in and use the space for his wood working.  Right now he is coming to the end of a giant stone facing job and is looking forwards to working with the more forgiving medium of cedar wood.  I can turn my attention to finishing the outside of the building later this summer, playing with some creative designs for sculpture as well as getting the last coat of lime plaster done when the weather begins to cool off once again.     interior wall

Hand Split Cedar Roof Shakes

hand split cedar shakesBeing a splitter of cedar by trade, Colin naturally decided to split all his own shakes for the roof of his new workshop by hand.  Having many piles of cedar already collected and in need of being moved out of his old working location gave Colin a good start at the job of splitting approximately 600 square feet of coverage, or what he estimated to be 6 squares of shakes.  A square is made up of 4 bundles of shakes covering 100 square feet (each bundle covers approx. 25sq.ft. depending on length of shake and row coverage).  Using a froe and mallet, Colin split and shaped the shakes out of 18″ bolts of cedar, using the best of the shakes for the roof and saving the less than ideal (wavy, thin, less tapered, or  too narrow) for a future wall project.  froeshake splittingsplitting shakescedar shakesShakes are split by placing the froe across the grain on one end of the bolt, about 3/4″ from the edge, then hitting the froe with the mallet and peeling off the shake.  It should taper somewhat (shakes can be 24″ or 18″ long, usually the longer the better for coverage and tapering) and then you flip the bolt over and repeat the same action, flipping the bolt after splitting each shake.  stacks of shakesIt took a surprisingly long time to split the estimated amount needed, mostly because of the amount of less than perfect shakes that he was getting from the bolts he was using (of which much was old grapestakes, and other pieces of cedar that were not as usable in longer lengths anymore, as the cedar he salvages is not collected for shakes, but in longer bolts usable for furniture, gates and fencing).  Colin chose 18″ shakes partly because of the wood he had available and partly because of the curves and roundness of the roof on his shop.  layeringHe layered the shakes with an overlap of 7.5″ each row.  As the rows are applied it is important to offset the gaps between shakes from row to row.  What this means essentially is that the space between shakes never lines up directly with the gap in the row below, and better yet not for 3 rows.  The straight grains of cedar and the overlapping shakes encourages efficient water run-off, while the gaps allow for evaporation and quick drying time.  Cedar shake roofs have a life span of 50 years (though some have been known to last upwards of 80yrs).  flowing around the curvesCedar shingles differ from shakes in that they are taper sawn, thinner, and usually are rated only for 25yrs.  Cedar has excellent natural oils present in it’s wood that makes it rot resistant in it’s naturally wet climate.  Much of the northern pacific coastline, rimmed and abundant in fat old growth logs, offers ideal shake block opportunities with wide planks and tight grains.  Most shakes are collected from downed red cedars near logging clear cuts or trees not long enough to be worth milling into lumber.   roofHere we have salvaged what we can find on the beaches and then applied the best of our skills to producing by hand the beautiful and functional flow of cedar shakes.

At the very end of the project Colin ran out of suitable cedar to split for final part of the roof, and not wanting to waste anymore time as it was the middle of winter, we gave in and purchased the last few bundles of shakes needed to complete the roof.  Although a bit of a disappointment for Colin, this is the reality of building yourself, sometimes you just need to compromise and get it done!roof finishedfinished roof

Final Lime Plaster

Back in May (2011) we decided to get going on the final lime plaster of the outside of the house before the business of summer cob building took over.  Lime prefers to have cooler temperatures in which to dry, and requires much more attention to the timing of the drying process for a result of eveness of colour and trowel lines.  Much like the process of applying the cayolin clay plaster on the inside, lime needs to be troweled on continually until a whole section can be completed, otherwise an apparent line will be visible where the plaster dried too fast, or where troweling stopped.  There are techniques to make these lines look less visible if whole big sections are difficult to complete in one go at it. We added a beveled line that undulates around the house, dividing the wall into smaller sections and providing a place for us to stop.  That way we were able to plaster only the top section, and then only the bottom, and have the line of plaster meet under the bevel and so be hidden.

moving along in a team of three

Working with three people who are competent with the job is important.  Fixing spots as you go, running out of plaster when you need it, and being too late for the sponging part of plastering is stressful.  So is having the sun come out unexpectedly and not being able to stop to find a way of shading the work space.  Likewise, having lunch, snacks, and drinks being made available while working is a huge bonus in making lime plastering a smooth and fun thing to do.

getting those mixing muscles flexing

The right tools are also necessary.  We used Japanese trowels, hawks (easy to make-plywood board with a handle on one side), just like with the interior plaster, and mixed the plaster in 5 gallon buckets and then in a large tub for uniform colour and consistency.  A powerful drill with a paint mixer attached, measuring spoons and cups (depending on colour pigment used), a spatula, and big scooper are helpful to have on hand.  Ladders or scaffolding should be close by for high parts.

The ingredients are simple- hydrated lime, stucco sand, water, and colour pigment.  We soaked the lime in a big barrel a few weeks in advance.  We also did many colour samples using a one litre mix, adding pigments in increments of tablespoons to get an array of shades and colour blends.  We have many beautiful arbutus trees framing the house, and we wanted to make a colour that brought out a reflection of the deep red/orange/brown that we see in the twisting branches.  We also thought that such a colour would bring out the vibrant yellow of the yellow cedar window frames.  Red pigment, however, has pink tendencies, and so we ended up using ten tablespoons of red in a one litre mix, plus five tablespoons of chestnut brown.  Multiplying that up to 4 gallons in a bucket, and we were deep into a large quantity of pigment.  We ordered what we thought would be enough for the whole house, based on calculations for the area covered per bucket on the inside, but discovered partway through the job that we had only enough for just over half the house.  We spent way more money on colour pigment than we ever expected, but we were committed to the colour.  Lesson #1: estimating for natural plasters is difficult, and calculating for colour pigments is even more complicated.  Lesson #2: find a good source of affordable, bulk colour pigments.  Because we were pushing to get this job done while the weather was still cool, we just walked in to a concrete supply store and bought mortar pigments that come in small bags.  When we discovered just how much we would need, we didn’t want to take the time to find a different source because different pigments have different colour shades.  We would have needed to do the colour sampling all over again.  By the time we ran out and needed more though, I was very much wishing that we had.  However, in the end we spent about $800 in the final outside layer (incl. lime and sand), and compared to other forms of siding or paint, we have a beautiful plaster that soaks in to the landscape, accentuates the curves of the bales and the coziness of the forest, for probably less money in the end.

The very first thing we had to do, before any of the plaster went on, was to add the sculptural elements to the rough coat.  Elemental it was, too – the aspect of the house is situated very close to the four directions, and we wanted to acknowledge the directions and the elements on each side of the house.

south sun

We sculpted a large sun on the south side for fire, and a water lily on the west side for water.  My mom got to work on sculpting a tree on the north side for earth, and I placed two dragonflies on the east wall under the light that shines beside the front door for air.  Our beveled relief line that undulates through the middle of the wall flows through each of the elemental sculptures and adds a subtle shadow line.  The sculptures were made using the same mix as was used for the brown coat of the walls- 1 part clay, 2 parts sand, and 1 part chopped straw.  Fine sand and clay sifted free of rocks makes the plaster easier to shape.  We also wet down the wall and spread clay slip over the area to help with adhesion.

mixing lime, sand, and pigment

Lime plaster: 1 part lime, 3 parts sand.  For us, this meant 5 litres lime and 15 litres sand.  That is what we could mix in one 5 gallon bucket.  Spin it together with the mixer, and add colour pigment, mixing it in with a small amount of water.  Then we turned three buckets into the big tub and mixed them all together.  We worked out of this tub until we got low, then had our extra person work on mixing up more.

Before we started on the walls, I went around and plastered the sculptural areas first, thinking that it would make plastering the walls faster to do rather than having to do the intricacies at the same time as keeping ahead of the drying plaster.  Two were done in white, and two were done as the same colour as the walls.  What I discovered was this was not as straight forwards when it came time to do the walls.  Red pigment, as well as splatter from the rough coat of clay as it was being sprayed with water, got all over the finished sculpture and needed cleaning and touching up afterwards.  Also, it was hard to sponge the plaster without touching the already plastered areas, which made the transitions between the two look smudgy.  From a distance, it is not a big deal at all, and since this is the outside, we usually look at it from a certain distance.  So I recommend doing it all at the same time- just consider simple sculpture lines and expect to be slowed down considerably when plastering these areas.  Small tools are essential, as well as the all useful yogurt lid with the rim cut off.

sponging- making the finish texture smooth and uniform

The sponging part of the process comes when the plaster is tacky enough to leave finger prints but dry enough that no plaster comes off onto the fingers.  It can be a very precise moment, depending on the weather and how fast the plaster may be drying.  A damp sponge is simply moved around in circles to remove the troweling marks and give a smooth, uniform look to the whole wall.  Sponging too soon will pull at the plaster too much, and sponging too late means that the sponge needs to be wetter and a stronger motion is needed to smooth out the trowel marks.  A well troweled wall, however, won’t have very many marks to be eliminated.  We noticed that sponging on a too dry wall caused a variation in the colour pigment, making it a lighter shade, just like when we sponged near an already plastered spot and brushed up against it.

final plaster layer is about 1/4 inch thick

Our process went pretty smoothly.  Colin and I mixed what we needed for the day and did the troweling with a friend who pre-sprayed the wall sections ahead of us with water, sponged along behind us when the plaster was ready, and helped remix some of the plaster from the bottoms of the buckets when it began to dry out too much.  Getting familiar with the perfect consistency is learned simply through using the plaster, and noticing when it is too dry and difficult to spread or too wet and sliding off the trowel.

the art of troweling is challenged when ladders and awkward spaces need to be reached

The motion of getting it from hawk to trowel to wall is also a practiced motion that comes with repetition.  Generally, I would make lots of little overlapping rainbow swipes over a one foot square area, and then smooth the whole area down in larger swipes right away, and move on.  No putzing allowed!  Get it on, flatten it out, and move on.  Plastering a whole house gives lots of opportunity for repetitive motion learning…  start with the most hidden space and do the area around the front door last.

dragonflies at the front entrance

There are many details and considerations with lime plaster, and it is helpful if you have experience with some other form of earthen plastering, or if someone who does can give a hands-on lesson.  Again, we had the direction of Tracy Calvert, who has been building naturally since the 1980’s and has specialized in earthen plasters.  She has led many workshops and believes that skills of natural building are to be available for anyone willing to learn, like the traditional practices passed down from cultures around the world that enable the reality of shelter for everyone in a community and not only for the wealthy.

north tree

west water lily

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