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High-straw earthen plaster recipe

It’s no secret that we love clay plasters at Endeavour, and the best case scenario is being able to use a clay soil right from the building site. It just so happens that we lucked into this for the teachers’ union office project!

After digging some test holes on the site early in the spring, we discovered that there was a strata in the site soil that was quite clay-rich and appeared to have almost no stone in it (which is very rare in this part of the world). We made some plaster samples from this soil and found that a wide range of recipes seemed to be viable. We left the samples face up into the elements for the whole summer, and one in particular held up really well so we knew we had a workable site plaster.

Our approach to earthen plasters has changed over the years, with the addition of more and more chopped straw over the years so that we have reached a point where we have a very high-straw content in the plaster. We have found that the high-straw recipe allows us to build up the entire thickness of the plaster in a single application. The volume of chopped straw supplies a huge amount of tensile support for the clay, and means that we don’t need to add nearly as much sand as we used to do when our plasters used less chopped straw.

The result is a mix that is very sticky thanks to the high clay content, and has a huge amount of “inner cohesion” that allows it to be applied at almost any thickness (4-5 inches is not unreasonable, if necessary!) with no cracking.

Rather than applying a very runny slip coat via sprayer or dipping the bales, we’ve found that a layer of the same mix minus the straw works well as a “primer”. We apply the primer to the bales, and then follow it immediately with the high-straw “body coat.” It’s sort of a two-part, one-coat system. It’s great to be able to apply the full desired amount of plaster and achieve the final look we want in a single application. Less time, and much less concern for de-lamination between successive coats.

The mix stays moist for a day or two, so it allows a lot of time to get the walls looking how we want, and the mix is very intuitive for those just starting to learn to plaster, while being fast to apply for those with more experience.

Our recipe (by volume) for this plaster is:

  • One part high-clay content soil
  • One part chopped straw (1/4 – 1 inch)
  • 3/4 part rough sand

There’s nothing like playing in the mud and making a viable building at the same time!

New system for straw bale walls

Over 20 years of building with straw bales, I have constantly experimented with new ways to integrate bale walls into buildings that are simple, cost-effective and energy/resource efficient. From load bearing to prefab panels to a variety of framing systems, I thought I’d tried them all.

But we were introduced to a new idea by the excellent builders at New Frameworks Natural Building, and we liked the idea so much we decided to try it ourselves.

Their “StrawCell” approach involves building a conventional stud frame wall for the building which acts as the exterior frame and main load bearing element. One immediate advantage is that this system fits into the regular code structure and should not require special engineering or design considerations, which can really ease the permitting process and help to lower costs. The straw bale wall is then built to the inside of the frame wall, with the bales pressed against the framing. The stud wall cavities are then insulated with dense packed cellulose, and sheathed with a permeable board material. Any kind of siding/rainscreen can be created as the final finish on the exterior.

On the interior the bales are very easy to install. The only framing that interrupts the straw is for window and door openings – very similar to the easy installation for load-bearing designs. At the top of the wall there is no beam or framing to notch around, just a plywood plate on the underside of the roof. We tied each bale through to the framing, so the wall was very straight and solid right away.

While the amount of lumber used in this system was initially a red flag for me, an actual calculation showed that we were using no more lumber than any of the other bale wall systems that use a frame of some sort. A conventional frame wall is actually a very effective and efficient way to use lumber, and only some load bearing systems actually use less lumber than this frame wall approach.

One major difference between this system and other straw bale approaches is the lack of exterior plaster. This can be seen as both a plus or a minus. We have been shying away from exterior plaster finishes for clients, especially commercial clients like the teachers’ union. While we love plaster, it is both a high maintenance finish and one that is susceptible to moisture issues unless well detailed, well protected and well maintained. While we definitely have not sworn off using exterior plaster, we are certainly glad to use siding when the client and/or conditions make it appropriate. On the plus side, this system reduces the amount of plastering material and labour required by half (actually, more than half since the interior plastering is always easier). Interior plastering can happen at any time of year, while exterior requires the right weather conditions.

The addition of the cellulose in the exterior wall brings this wall system into the super-insulated category, capable of reaching PassiveHouse standards even in our cold climate (something a single, two-string bale wall cannot do). The cost of the cellulose and siding together are quite similar to the cost of the material and labour for exterior plastering.

All in all, we like this system so far. We’ll continue to report as we finish preparing the walls for plastering and complete the remainder of the system.

Craning a Finished Roof

Building a roof can be intimidating, and statistically the most dangerous element of making a building. The heights involved add risk, time and a lot of effort.

Whenever we have the opportunity, we build our roof structures – including all sheathing and as much finishing as possible – on the ground, and then use a crane to lift the roof and place it on the building. In this way, we reduce the risks associated with working at heights, lower the amount of physical labour involved in carrying materials to roof height and bring protection to our building faster.

For the teachers’ union office, we once again had enough room on the building site to do just this. We set up two rows of beams on the ground at the back of the property and fully erected the entire roof, including trusses, bracing, strapping, membrane, steel sheathing, light tubes and the full PV array. All of this was accomplished with the fascia less than two feet from the ground!

As we’ve found to be typical, the craning is a relatively quick process. We were slowed somewhat this year by wet conditions on site that made placing the crane in the right position difficult, but we still put all three sections of the roof on the building in a single day.

A quick look at the math makes a pretty good financial case for building roofs in this way. The cost of a day’s rental of a crane and operator is easily paid back by the efficiency and reduced labour time of building on the ground.

It’s not a carbon free practice, but when the site and conditions are appropriate – and particularly when working with student builders – it’s one place that we’re willing to let fossil fuels and mechanical advantage help us out!

Building Science: What every home owner and builder should know

Building Science is a relatively new field of study, emerging over the past decade as architects, engineers and builders examined the results of the new wave of highly insulated and energy efficient buildings. Building science attempts to see a building as a whole system, rather than an amalgam of different elements. Building enclosure (roofs, walls, floors, insulation, windows, doors and barriers) and heating/cooling systems as well as occupant loads and demands are examined within building science to achieve the highest levels of comfort, efficiency and building durability and serviceability.

At Endeavour, we think it’s important that building science isn’t just left to the scientists. Homeowners and tradespeople who understand the principles of building science will make better, more informed decisions at every turn in a project. Whether it’s a minor renovation or a complete new build, the lessons of building science will make the project more energy efficient, more durable and more comfortable.

The basics of heat and moisture movement and material properties are not hard to understand, and armed with an understanding of these basics, homeowners and builders will be able to have informed discussions with designers, building officials and HVAC suppliers and installers.

Builders involved in the natural building movement of the past two decades have played an interesting role in pushing the boundaries of building science. Lessons learned in straw bale, cob and adobe buildings have helped to inform the entire building science community as the field developed into its own branch of study. To date, buildings made with natural materials have often embodied the best principles of building science (whether knowingly or not!)

You can join one of North America’s leading natural building scientists for a workshop on the Fundamentals of Building Science at Endeavour to bring yourself up to speed for your home building project or to help you become a better builder. Jacob Deva Racusin is a principal at New Frameworks Natural Building in Vermont, and a co-author of The Natural Building Companion. His four day course is open to all, and is designed to introduce and develop the concepts of building science in both a theoretical and hands-on manner. You can read the course outline here.

If you intend to achieve a high level of performance in your own home or on your professional projects, this workshop is for you!

Paperstone countertops at Canada’s Greenest Home

We spent a lot of time considering our countertop choices for Canada’s Greenest Home. It’s an area with many options, and many factors to weigh when trying to make an environmentally sound choice. Ideally, the countertop material must be durable, aesthetically pleasing, stable, renewable and/or recyclable and not off gas any chemicals into the home.

After much deliberation, we chose to go with a material called Paperstone. This type of countertop is made from 100% recycled paper fibers (complete with FSC certification), bound with a phenolic resin to create a solid, dense material that is certified food safe by NSF and resistant to high temperatures and abrasion/scratching.

One of the main attractions to Paperstone is its workability. It can be cut with typical woodworking tools, allowing us to do our own installation. We were able to shape the pieces we needed, make the sink cut-outs and bevel the edges of the material easily.

Paperstone came in a range of attractive colours, and can be finished with natural sealants and waxes.

The phenolic resin binder gave us some cause for concern. While the material does not contain any petro chemicals or off gas in the home, the resin ingredients are not environmentally benign. However, the company documents its handling practices very convincingly and has received numerous awards for its sustainability initiatives. We would like to see the company apply for Greenguard certification to ensure its claims of zero off gassing are confirmed by a trusted third party.

We obtained our Paperstone from Living Rooms in Kingston, Ontario, allowing us to work with a supplier we know and trust. This is always an important part of any product decision. The material comes in large slabs, and we bought a 5×12 foot slab from which we cut the pieces we needed.

After a lot of use (and abuse), we have been extremely pleased with the performance of the Paperstone. We gave it an initial waxing prior to use, and have not refinished it after 10 months. It is impervious to water, easy to clean, and very scratch and dent resistant. The dark charcoal colour we chose has a nice depth to it, and doesn’t show any signs of staining or wear. Areas around the sink, where many countertops begin to show signs of failure quite quickly, don’t seem vulnerable to deterioration at this point.

The countertop draws compliments from almost everybody who sees it. It looks and feels unique and attractive. While it is not inexpensive, the initial workability of the Paperstone allowed us to do the installation ourselves, saving money. And its apparent durability means that its an investment that will last a very long time. If you can afford it, we would recommend it as a good choice.

 

Framing systems for teachers’ union office

Wood framing is a conventional building practice that we use quite frequently at Endeavour. For the teachers’ union project, we are using wood framing for both the floor system and the exterior walls. The walls and floors may not look very different from conventional building, but from a sustainability point of view we’ve made choices that can make a large impact.

First, all the wood framing is certified by the Forest Stewardship Council (FSC), a third party certification organization that helps to ensure that wood products are harvested and processed according to high standards of sustainability. For this project, ensuring FSC certification meant going straight to a FSC certified distributor for our framing lumber and plywood as non of the local lumber yards are FSC certified.

The floor framing uses open web joists from TriForce. These open web joists do not use metal plates, but are finger-jointed and glued, using 2×3 top and bottom chords and 2×2 webs. This uses wood from smaller diameter, fast-growing trees and significantly less wood than solid floor joists, and significantly less glues than wooden I-beams with solid OSB centres. The floor joists are deep enough to allow us to achieve R-46 once they are filled with cellulose insulation.

The 2×6 wall framing is the load bearing exterior wall of the building, and will also be filled with cellulose, adding R-22 to the exterior of our bale walls (more on this hybrid system later), which will be installed to the interior side of the frame.

One of the great advantages of wood framing is the speed of construction and the low cost. When added to the renewability of wood when harvested and processed responsibility, it’s a great combination.

Earthbag foundation for floor system

In addition to the Durisol stem wall foundation, our project for the teachers’ union office includes two long sections of earthbag foundation to support the floor joist spans inside the building. The inherent insulation value of the Durisol blocks made them our first choice for the exterior of the building, but the extremely low environmental impact of earthbag foundations made them an easy choice for the interior.

Using continuous rolls of polypropylene bag material (this material would be cut and sewn to make rice, grain and feed bags) as a form for a variation of a rammed earth mix, earthbag is simple, durable and low cost.

A wide variety of material can be used in the bags, as long as it has an aggregate content capable of being tamped to a high degree of compaction. For this project, we used a road-base gravel and a small amount of a lime/metakaolin binder (you can read about this mixture here) to provide a mixture that tamps well and stays coherent after curing, even if the bag is damaged or removed. It is also possible to use aggregate and clay in the bags.

To facilitate the use of the continuous tubing, we built an earthbag loader based on a design by Kaki Hunter and Doni Kiffmeyer (authors of the excellent book, Earthbag Building), which uses a maple syrup bucket with the bottom removed and an insert made from a length of sonno-tube. The tubing is pulled onto the sonno-tube like a giant sock, with the “toe” of the sock pulled through the hole in the bucket. The pressure between the sonno-tube and the bucket prevents the tubing from continuing to pull through, unless the person loading the bags lifts the sonno-tube to allow more slack into the bag.

The material is added into the tube until the “shookler” (that’s a technical term!) determines that the desired amount of material is in the tube, and more tube is released. Behind the shookler is a tamper, who applies the tamping force that compresses the material until it has reached its limit and the proper level. We use a laser level to ensure that the top of the bag is at a consistent height.

Between each course of earthbag, a run of barbed wire is used to prevent the bags from sliding against one another. In the case of this building, we required three courses of earthbag. This was topped with a 2×8 sill plate on which the floor joists will be fastened. The sill plate is attached to the bags with long spikes as well as tie straps at regular intervals.

Though the process of doing earthbag can seem labour intensive, as a crew gets practiced it goes very quickly. Because there is no requirement for advanced formwork, it can actually be very competitive with forming and placing concrete. With a day’s practice, our crew was producing over 1.5 feet of finished bag per minute!

The beauty of earthbag is its simplicity. Bag material and fill as well as all the required tools can be found in almost any location in the world, and the strength and durability of earthbag foundations (or entire buildings) is remarkable. Bag on!

Helical pier foundation

The timber frame portion of our project for the teachers’ union rests outside the walls of the building, requiring individual foundation piers for each of the 14 posts. Typically, these would be poured concrete piers each with its own wide footing, resulting in a lot of concrete use and a lot of labour time to dig, form and pour each pier.

As an attractive option to digging and pouring concrete, we decided to use helical piers. This type of foundation is essentially a “ground screw,” consisting of a thick-walled metal tube with a screw plate on the tip. The helical piers are wound into the ground using a hydraulic device attached to a small backhoe. The screw plates are driven down to a depth below frost level and until the hydraulic force required to wind them reaches a pre-determined amount of torque. Once the proper torque has been achieved, the plates have sufficient bearing capacity to handle the loads that will be imposed on them.

Our piers were supplied and installed by Postech Peterborough. They were sized according to the engineered loads provided on our building plans. On the ground, we provided the layout points for the piers and their crew came and performed the installation.

Despite accurate points on the ground for the piers, the piers do not necessarily enter the ground perfectly straight so the tops can sometimes be off line even if the piers were started at the right point. This happened on several of our piers, so next time around, we would definitely make sure we had batter boards and string lines ready so the tops of the piers could be accurately aligned.

The piers are left long, and we cut them to height after the installation. A wide range of pier caps can be used depending on the type of post or beam being attached. Most of the caps use a threaded rod to allow for fine adjustment of the pier height.

One of the advantages of helical piers is there is no digging required, meaning that the site is barely disturbed. The installation of our 14 piers took about 5 hours, making it a quick process. The piers are ready for use immediately upon completion. The galvanized steel used for the piers is a high embodied energy material, but relatively little material is needed compared to concrete or other alternatives.

A Durisol stem wall foundation

Over the past few years, we have turned to Durisol insulated concrete forms (ICFs) several times. They offer an attractive blend of sustainable features with the convenience of conventional methodology.

For the teachers’ union office project, we needed a short stem wall to raise the walls of the building a suitable height above grade. There is no basement, and the footing is a shallow, frost protected perimeter beam, so the stem wall is only 2 feet tall. Durisol blocks provided us with a solution that worked well for several reasons. The blocks have a high insulation value (R-21 to R-28), are made from a very high percentage of recycled content, and are produced within a reasonable distance of our building site. They form a 5.5-inch concrete wall, using much less concrete than a full foundation wall (typically 8-12 inches wide).

 

In addition, the blocks come in several widths which for this building meant that we could use the 14-inch wide blocks as the first course and 12-inch wide blocks on the second course, leaving us with a 2-inch lip on which we could rest our floor joists. By keeping the floor joists within the insulated walls, we minimize thermal bridging and simplify air tightness at this important seam.

The Durisol blocks are dry stacked on the footing and on each course, making them very fast to install. They can be cut with a regular circular saw when necessary, and take a wood screw very securely. For our curved foundation, we did not attempt to cut the blocks to match the curve. Rather, we set them so the inside edges were touching on the curve and used a site-mixed hempcrete to fill in the gaps.

A lime-cement plaster is used to coat the exterior of the blocks, and we used a water-based, no-VOC liquid rubber and a 100% recycled content plastic dimple mat to complete the waterproofing layers on the exterior.

While this foundation wall still has relatively high embodied energy (due to its cement content), its energy efficiency, the lack of foam products, durability and the ease of construction make it an excellent option.

A unique shallow frost-protected foundation (SFPF)

In the pursuit of foundations that use little or no concrete, we have two common strategies that we often use. The first is rubble trench foundations (you can see an example here), and the second is shallow frost protected foundations (SFPF). Our extremely flat and low lying site this year dictated the use of a shallow foundation to avoid potential drainage issues in a deep trench.

The teachers’ union office building has two extensive curved sections in the foundation, and this would have made a conventional footing formed with 2×8 lumber difficult to achieve. A great new product called Fastfoot allowed us to make this footing very quickly and easily, and is a product we’d definitely use again. Made from a woven polypropylene, the Fastfoot uses lightweight stakes in the ground and small dimension lumber fastened to the stakes to support a fabric formwork (in many ways similar to doing earthbag footings) into which concrete is poured.

The Fastfoot system has several advantages over conventional formwork. We were able to use lightweight stakes and 2x4s (or doubled 1x4s to achieve the curves), despite the footing being 8 inches deep, rather than needing 2×8 lumber. As the formwork is draped by the Fastfoot fabric, the footing lumber does not get covered in concrete. This means when the forms are disassembled we can reuse the lumber without having to clean it. The fabric of the Fastfoot system is also a barrier to rising dampness from the soil beneath, adding a layer of protection from underneath. We were able to wrap the “tails” of the fabric up and over the footing and tie it into the foundation wall moisture proofing layers, adding a positive lap to the intersection between footing and stem wall.

The lines stamped onto the Fastfoot fabric make it easy to line up within the forms, and allow for many different widths of footing. There is no waste with the system, as the fabric stays in place. Joints in the fabric are overlapped by about a foot, and a folding pattern allows for corners to be handled easily. Our curves required us to make folds at regular intervals, and this too was easily done.

We had a few small issues when we poured the concrete into the form and had the fabric slide to one side under the force of the concrete. This pushed the fabric out on one side and left a concave section on the other. In these areas we had to shovel the concrete a bit to get the form centred again. We wouldn’t make that mistake again as it’s easily avoided.

Fastfoot is an excellent addition to our sustainable building toolbox.