Well, we’ve dug in.
We are building a straw bale addition onto our little living quarters, and increasing our space from just over 200 sq ft, to almost 500 sq ft! We’ve worked with a local drafts person and a structural engineer to come up with a set of plans and it is exciting to be putting those plans into action. We’re going non-toxic from the ground up as much as possible. We were able to greatly reduce the amount of concrete we used by going with a rubble trench foundation design, and we are utilizing a modified stick frame compatible with the bale dimensions, using a clay-lime plaster on the exterior, and clay on the interior. For a floor, we’re implementing an insulated earthen slab on grade.
Aside from the official help of certified electricians, and a few days of much appreciated help from friends, we’ve done everything ourselves.
This article follows our process from excavation in early September 2015 onward, and we are trying to keep it updated as we work. There is general information about each photo, and where it is appropriate we’ll be linking to other blog posts for more detail, such as the planning phase, working with our engineer, framing plan and execution, working through our building permit etc.
Click on a photo to see it enlarged, and to scroll through all photos as a slideshow.
Sept. 5 2015. We rented a digger, and leveled the ground around our addition to the grade of the existing building, then took the floor to level, which was grade, minus the thickness of the finished floor, insulation, and radon rock.
Using the laser level, with strings set on the batter boards, we were able to dig a clean trench that was quite accurate, with little need for back fill. This was good protocol for this site, as one this particular soil is disturbed, it becomes very unstable.
Using the mini digger to trench out the drain pipe from the weeping tile (left). A drain to daylight is a very effective way to get potential excess water away from your foundation. Back filling drain pipe (right). We stared at the low of the system, as the outlet of the drain was as low as it could go without interrupting the driveway.
Once the trench was dug, we lined it with geotextile fabric to prevent fines from penetrating the drain rock. We also set our perimeter insulation, in this case we went with Roxul’s Drainboard IS. It is rated for below grade applications, it is a foam free option made of rock wool and mineral slag. We then began the most fun process of moving 27,000 lbs of rock.
With the initial rock in the bottom of the trench tamped, we began by dry fitting the weeping tile, and using a 4′ level to ensure proper slope to have adequate flow towards the drain pipe & and exit the system. Once the slope was established, we glued, and back filled/ tamped drain rock around the pipe. This was really important to ensure a stable base for the foundation.
Preparing the form work for the concrete pour. We cut the Roxul to the finished height of our grade beam as it was to act as one side of the screed guide. We used plywood in the interior wall of the form, with the intention of leaving it in place permanently. We used some of the leftover rock in sacks to help stabilize the form, along with various strapping, brackets and stakes. We also cut rebar and connected it
Sept 15th 2015 the concrete truck arrives! A kind neighbour stopped by to give us a hand which was much appreciated. Pouring concrete is stressful, especially with a big truck in a tight space, but it was great to see it coming together.
And the framing begins!! We built 2 insulated box columns which will be the supports for the new beam. Rather than just using a post, and then having to notch a bale around the post, and connect it to the existing building, we decided to go with an insulated box column, which combines structural support, and insulation value. Not shown is that the plywood skin was removed so that we could attach structural screws through the column and into the existing building
We build the Larson trusses on the ground, using nailing plates and 2 x 4 gussets. Because these trusses are only made up of paired 2 x 4’s, spaced 36″ on centre (much greater spacing than in a regular stud frame wall) it was really important that the roof assembly bear down at every point along the North and South wall, but also the West wall (corner of West and South wall pictured here). In this photo we are mocking up what our truss angle will be so that we cut the wall trusses to the right height and right slope.
Cutting and nailing the webs for the TJI’s. We used 14″ TJI’s instead of 2x 12’s for our roof assembly, mostly because they allowed a deep cavity for R50 insulation in the roof, and make use of lesser quality woods. However, they were tricky to work with, required expensive hangers, and specialty blocking, and they are made of chip board which is known for containing formaldehyde. This is another element that we debated at length, and still feel like we could have gone either way.
Framing detail: connection of the rough cut beam had additional metal plates to attach it to the main frame as per the engineer. We also added additional strapping right above the main frame to connect the plywood decking directly to the TJI blocking.
Oct. 25th 2015. Getting a little help from a friend. This fall, anytime we had a visitor, we added a ‘labour tax’ to the visit, and usually roped the visitor into some kind of task, if briefly. This step was important. We had a clear couple of days to get the roof underlayment on which would effectively weather proof our building. Because our roof slope is 1/12 (that’s loosing 1 ft of height in 12 ft) BC building code requires a metal roof with a low slope to have a waterproof membrane under the metal. Even without the metal roofing on, we could proceed with the baling and not have a leaky roof.
Oct. 26th 2015. We headed up to Midway to collect our bales, but first we had to make them. A generous farmer, after selling all his square bales for the season, offered to unroll some of his big bales, and re-bale them, so we were along to help. The cows thought that it was lunch time. We crammed 75 bales into the van and 6 x 10 dump trailer we borrowed from a friend. We were happy to have installed the trailer brake connection in the van as we headed down Anarchist Hill, lumbering load in tow, hazard lights flashing the whole way.
Insulating the toe plate using up the leftover rigid insulation cut from the foundation perimeter. It’s hard to show in a photo, but the draining capacity (non absorbing) of this insulation is quite incredible. We’d been having some rain, and the insulation around the foundation was getting wet in a few places, and while it did get a bit wet, the moisture didn’t really absorb into the structure, it actually just flowed through. Observing this was an excellent lesson, and provided more proof that rock wool is a good choice for below grade applications.
Top of wall details are a tough thing to figure out. There are so many variables to take into account, including structural elements, insulation requirements, and it is a point where there are always dis-similar materials meeting. And where different materials meet, there is potential for air leakage where you don’t want it. There are practical considerations as well, such as the need for stuffing at the top of the wall. In this case, because of the slop at the top of our wall, we would need to do some stuffing, and needed something to stuff against. In conventional construction, the wall is narrower, and there is always a top plate to hold the assembly together. With our straw bale walls, it is thicker, and there is a top plate but in this project it was only running at the outside edge, and the inside, leaving a cavity in the middle. There are a few ways to deal with this cavity, and the effectiveness of each is up for debate in the energy efficiency/ building science world. In some cases builders allow the roof insulation to fall into the wall with no barrier. Some will add a plywood barrier. One practice that has come out of various engineering and fire reports is using drywall with fire rate caulking at the top of the wall. We did the latter, and will write a full blog on the topic, as it is deep and important.
Oct. 30 2015. End of the first day of baling. We tried hard to have as many cavities of 36″ as possible to make putting the bales in simple. 36″ slightly smaller than the average length of a square bale which allowed us to wedge in almost all the bales with very little alterations, just a quick hair cut. Of course, under and above the windows still required re-sizing.
We carefully planned the final height of the West wall in order to fit four bales exactly. It turned out this was also as high as the wall could be and still have a slope in our roof. Anyway, we designed the last bale to fit in tightly in order to add to the structural integrity of the wall. We used the van jack to compress the bales below, and we were able to easily slip in the last bale.
Sometimes resized bales, or even full size bales can be fragile, so it is possible to help slide a bale around framing, or between other bales with a few pieces of Masonite. It is a thin material that is smooth on one side which allows the bale to move into a tight space.
Window detailing Part l: First we insulated the frame with more of the Comfort Board IS. As the size of our windows filled up much of the wall height, there was no space to hang a bale above, so we applied the same process to the top of the windows, using rock wool batt insulation instead. Then, using acoustical sealant we secured house wrap to the sils to create an air seal around all the edges of the window. This is important as plaster of any kind will shrink back slightly from edges, allowing air to infiltrate your wall system. This causes a loss of efficiency, and potential harm to the building itself, especially in a cold climate situation where there is a major difference between the indoor temperatures and outdoor temperatures in winter. Warm air carries moisture in a vapor state and will turn to liquid water at some point in the wall as it cools. We take great care to ensure air sealing for the long term health, comfort and efficiency of the building. Again, air detailing is deep and expanding field, and will require a follow up blog for a more full explanation.
Window detail Part ll: Our process for flashing a window. Note that the plywood surrounding the window is there to support future window trim, and is the combined thickness of the exterior plaster layers. 1. Cut & fasten shim for bottom of window that slopes towards the exterior to encourage any water that may get in to escape. 2. Create a sort of ‘pan flashing’ with self healing flashing to prevent water infiltrating into the area below the window, and the bale below. Last step missing from photo sequence: one more strip of self healing flashing on either side and top of the window (not on the bottom), once it is level, plumb and secured in place. The house wrap around the exterior creates the air barrier, and the poly mesh gives texture for the plaster to adhere to. It also provides additional tensile strength to the plaster, as window corners are prone to cracking.
Window detailing Part lll: The interior. The house wrap tucks around all the edges with acoustical sealant to prevent air leakage where the plaster meets all edges. We secured the window sil & lintel wood slabs with small head screws, but solid enough to secure them to the frame. This is finished wood, and it was sanded and oiled before being installed. We used the same structural poly to stuff and shape out the interior window wells.
DETAILS. Getting the bales in the walls is a fairly straight forward and quick process. It took the two of us two and a half days. The next step, getting the bales, and the framing/ windows ready for plaster, what we call the Plaster Details. The objectives are to tie the wall together, make sure there is something that spans from the bales into any other material that is receiving plaster, as these areas are pron to cracking. Also, in this case we were using a clay-lime plaster, and wood needs to be protected from lime. Plaster will not stick directly to wood; wood is too smooth. There are a variety of ways to add texture (key). We went with a series of wooden lath, cut to 1/4 depth from leftover wood, and secured every few inches with staples.
A progression of the North wall details. Top left, still fitting split bales into the framing. Top right, tar paper over wood installed, plaster stop at top of wall installed, and wood lath key installed at top of the wall rafter. Also note the mesh strip in the middle of the wall in that photo: we used structural poly mesh stuffed with a thin layer of straw over the framing, and stapled in place. We also sewed through the wall to a paired mesh panel on the interior. We did this for all the framing between the bales. This was an alternative to using a bunch more tar paper, and layers of mesh to create a key for the plaster. Centre right: overall photo of North wall detailed. Bottom left: Plaster stop installed between existing building and plaster wall, tar paper and wooden lath over wood framing installed (structural insulated column and rafter), window with air barrier (house wrap) installed, fine mesh to provide key over house wrap, and structural poly mesh to tie window edge to bale wall and bale wall to wooden framing. Bottom right: Same as bottom left photo, but including the metal flashing at the bottom of the wall installed.
Plaster detailing for North corner insulated box column. Top left: self healing flashing to tie exterior beam for North porch into wall without air leakage. Remaining photos include wood framing protected with tar paper with wooden lath for key.
With all the exterior plaster detailing done, we had a few skilled friends over to help out. We were grateful for the moral boost, and the infused energy to get the first coat of exterior plaster done before it got too cold.
Nov. 13th 2015. Looking a bit rough maybe, and still drying out, but we got the scratch coat of plaster on before freeze up, and we’ll tackle the next coat in the spring. On this day, we had sun and wind, so we opened up the tarps to invite in the elements to help dry things out. It was challenging to work on the exterior in November. We had to purchase the insulated tarps, we wired a construction heater to our electrical panel, and had fans running. We used energy to dry out the plasters and prevent freezing as the nights dipped just below zero.
This is the interior of the window on the North wall depicted the previous photos of plaster detailing. Last detail that was added after photo: sisal cord stapled to the tar paper and framing above window to provide key for the plaster (see below).Before we could plaster the interior, we needed to install the ceiling vapour barrier because it needed to tie into the wall plaster. But, before we could fully secure the vapour barrier, we needed to install the ceiling electrical, range hood vent, and insulate the ceiling. So, in order to keep working, we secured the edges of the vapour barrier, and tucked up the majority of the sheets temporarily. Photo on left: Spreading acoustical sealant for edge of vapour barrier. Top right: Example of how the ceiling drywall can fit above the plaster stop. Bottom right: top edge of North window, and top of the wall plaster stop with vapour barrier.
We had a vague plan for the kitchen, but knew that we would probably want to install some selves above our sink and counter area. In order to have something to nail to, we used the Lancelot blade on the grinder and carved out a channel in the bale to fight a 2 x 4 tightly, which we then fastened to the framing around the window, as well as a larson truss 36″ left of the window. We put mesh over these supports, and then plastered over them. Now, if we do decide to put in those upper shelves, we know exactly where our attachment points are.
Nov. 17th 2015. A few photos from the process putting the first coat of plaster on the interior North wall. You may notice that unlike the exterior, we didn’t put clay slip on the wall the wall first. We were experiencing some weather challenges, and our slip was outside, frozen. As an experiment we thought we’d try plastering right on the bales. While the final dried results have been similar to the other walls, the actual process of plastering without the slip was much more difficult.
So, the next time we had some friends visit, we put the labour tax policy back in action, and together we mixed enough plaster to finish the first coat of the interior, and we also made sure to slip the walls first. Nov. 25th 2015. With our plaster premixed, we got started on the first coat of interior plaster. As with the exterior, the first coat is the scratch coat. You can also see the insulation in the ceiling. R50 worth of rock wool insulation! It’s cozy in the winter, but we’re also excited to see how cool we’ll be in the summer.
Nov. 27th 2015. With all the new exterior windows in, a section of our wall was out. The electricians were in doing their work, as we continued to finish the first coat of interior plaster. With the electrical in the ceiling done, we were able to fully install the ceiling vapour barrier, with the exception of where our range hood will evacuate.
A few things going on in this photo. Firstly, it is after our 2nd building inspection. The first inspection was to confirm the radon evacuation system. As per code and part of the radon evacuation system, we installed vapour barrier, sealed to the foundation, which was the second inspection. We were excited to learn about Roxul’s Technical Bulletin that claims that their ComfortBoard IS mineral wool product (similar to the stuff we used to insulate our rubble trench) could be used under a typical 4″ concrete slab. We planned to use it under our 4″ earthen slab but when the time came to install it, we got cold feet. It’s soft, maybe even best described as squishy, and we had doubts that the ‘softer’ earthen slab would behave well above it. We reached out to the wider natural building community and had discussions with our engineer and decided that it was a bit too risky to put under an earthen floor. So we compromised and decided to go with EPS foam instead of the mineral wool. EPS, as far as I’m concerned, is a much better product than the more common XPS foams because the blowing agents in EPS are far less damaging, and EPS isn’t filled with brominated flame retardants that are common in most XPS foam products. And for what it’s worth, the EPS carries the Canadian EcoLogo for these benefits. I’ll be writing a more complete analysis of this subject but every decision has tradeoffs and we figured an earthen slab with EPS was a better choice than a concrete slab with mineral wool. It certainly feels solid!
First layer of earthen sub floor! Sand and gravel mix we picked up at our local quarry, with about 18% clay added. This mix is used for road base, and once we mechanically tamped the floor out, it was easy to see why.
Second pass of earthen sub floor. We did two passes mostly because we needed 3 yards of material to fill up the floor for stability and thermal mass, and we can only haul about 1.5 yards at a time with the trailer. Of course, this is when the mixer chose to break, so we mixed the second pass by hand, in a wheelbarrow. We were thankful that a few friends stopped by to help us finish up.
Using the mechanical tamper on the earthen subfloor. For the first pass, the floor was a little on the wet side (as can been noted by the track marks left behind by the tamper)! We did another pass the next day, with very excellent results. The floor is drying really well, and is hard as can be. No cracks, no depressions from walking on it even though it was still wet. Since then, we’ve been working on the floor with no issue.
Installing the range hood! This was an exciting development. Cooking in our little space was a challenge, mostly because we were using a hot plate, but we also had no ventilation. This unit is quiet and highly functional, and didn’t totally blow our budget.
What a mess. Getting to the finishing work is a double edged sword. The end is in sight, but the details always take more time then expected. Here, we’re preparing to finish the kitchen wall so we can install the remaining cabinets, and then we can get to the ceiling.
Dec 23rd 2015. Preview of the kitchen coming together. Close up of a cabinet door. Simple, functional and elegant is our theme. Kitchen is coming together, with many many hours of precise work dedicated to cutting, assembling, sanding and oiling. Many many hours.
Dec. 24th 2015. Merry Christmas! In the foreground you can see some of the plaster sitting, all tucked in, ready to become the second coat. Also, the kitchen is coming together, and we’ve almost finished the tongue and groove ceiling. Our electricians came back to do the final tie in, and our light fixtures are in, and the light switches work! And so does the range. We have a range!
Jan. 4th 2016. Our adobe wall! Purpose: to add more thermal mass to our space. The adobes are next to our wood stove, so in the winter when we’re heating, and when the thermometer rises, it will help to offset the heat of summer. We made these blocks over the last year, using up leftover material from various projects, including our oven build, earthen floors, and plasters. For mortar, we used the same material as the second coat of plaster for the walls; simply clay, sand and straw.
A kitchen!! Lights over the sink still need shades, and we need to install the counter top, and of course there is the floor…but we are oh so close. We call this look reclaimed-industrial. The wooden panel was collected from the discard pile at our local saw mill, the metal for the back splash was the packaging that came with our metal roof, and most of the material in the cabinets came from re-configuring our former kitchen, used bits like melamine and hinges from the building reuse centre. The second coat of plaster is on, now only the colour coat left! But the range is in and hooked up, and the hood fan is fully functional.
We’ve been puttering around a bit since Christmas, and have had the pleasure of slowing down a bit, and easing off on the project schedule. However, if we actually want to enjoy the new space, we’re going to have to finish up at some point. We got our motivation back by starting with some colour plasters.
The floor. It has been a long time coming! For this install we decided to go with stabilized earth. We did a bunch of testing, starting from some of our more standard earthen floor recipes and adding a small percentage of cement to the mix. Our primary reason for this was to speed the drying process, as the cement actually takes water into its structure while it’s curing.
After a full day of non stop work, Ashley laying material and Heather running the mixer, we came in to check on the floor at 8:30pm. It was surprisingly hard! To add some character to this floor, we had planned to cut in a tile pattern. We had to get on it before things got to hard, so it was back to work for us for another few solid hours! We think it turned out really well though.
Final colour of the soycrete, after two passes with the stain. We still need to grout the ’tiles’. We are happy with how the floor turned out. It is lighter than most of our earthen floors in colour. The cement element was a pain to work with (short working time) and because we laid it in by hand like our earthen floors (much different than how concrete floors are poured) we ended up with some cracking. We felt like this was a bit out of our control, as it is the nature of cement to not like cold joints. We went back to some of the cracks and filled them with a fine clay mix, and once the stain went on, things looked really good.