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Teachers’ Union Office Building slideshow

In 2014, Endeavour’s Sustainable New Construction program built a new office building for the Trillium Lakelands Elementary Teachers’ Local in Lindsay, Ontario. The goal was to combine Passive House energy efficiency with low-impact, local and non-toxic materials.

The photo gallery below shows the entire build from start to finish. Click on a photo to view the slide show in full size:

A PassiveHouse Heating System

Passive House is a building certification program that focuses on dramatically improving the energy efficiency of new and renovated buildings. Overseen in this country by the Canadian Passive House Institute (CanPHI), the standard originated in Germany in the late 1980s and buildings that comply with the standard will have energy use reduced by 80-90% from current Canadian code requirements. Specifically, Passive House buildings must have an annual heating and cooling demand of not more than 15 kilowatt hours per square meter of building (15 kWh/m²) per year, and total primary energy (calculated as source energy, not metered energy at the building) must not exceed 120 kWh/m² per year. In addition, an air tight building enclosure is a requirement, with leakage no greater than 0.6 times the house volume per hour as tested with a blower door (0.6 ACH/hour at 50Pa).

The teachers’ union office is our first building designed to meet the Passive House standard, though we have used the Passive House software as our energy modelling software for the past three years. Although we were not intending to have the building certified, we wanted to meet the standard and achieve the energy reductions using our low-energy, low-impact range of building materials. We worked with Rob Blakeney of Local Impact Design to model the building and advise us on insulation levels, passive solar aspects and to design the heating system.

While the term “passive house” is an attractive one, it is quite misleading as the buildings do not feature passive (ie, non-mechanical) systems. In fact, Passive House buildings typically require a mechanical ventilation system to run 24 hours a day. The leap to Passive House standards means that conventional heating systems can often be left out of the design, and instead buildings can be heated with small amounts of heat input into the ventilation air distribution system or other low-input systems.

At the teachers’s union building, a 1 kilowatt heater is used in each of the three main ventilation air supply ducts to provide heat to the three offices. In general, this is the main source of heat for the building. A ductless mini-split air source heat pump is in place in the large meeting room and can provide additional heat capacity when required (though its inclusion in the system had more to do with meeting peak cooling demands in the summer). Through this year’s very cold February weather, the system had no problem keeping the building warm and comfortable… pretty impressive given that the heat source is the equivalent of running two toasters!

We were keen to build to Passive House standards because the most typical means to reach this level of performance has been to use a lot of foam insulation to achieve the necessary R-values and air tightness. We wanted to bring our low-impact, locally-sourced material palette to the challenge, using straw bales, cellulose, clay plaster and simple air tightness detailing to the highest levels of performance. In this way, we can lower both the energy use of the building, and also the embodied energy. Walking into the building when it is -25C outside and feeling the wash of warm, fresh air and knowing that the heat source is minuscule has been very satisfying!

Net metering PV now functional

The use of photovoltaics (PV) to generate electricity has been a common element on most of our projects. PV is affordable, easy to install, nearly maintenance free and very reliable. Once again, a PV array has been a key part of the energy strategy for an Endeavour project.

In Ontario, we are able to create grid-tied PV systems, allowing owners to sell some or all of their generated power to the utility company, and also to use grid power when necessary. Grid-tied PV can allow for systems that are sized to meet the owner’s needs, while still ensuring that power is available at all times. For PV to be used off-grid, generating capacity and storage capacity (in the form of batteries) must be sized to meet needs at the worst time of the year (mid-winter, when power needs are high and the amount of available sunlight is low), making the system expensive and likely to over-generate in the summer months.

There are two systems for owners to connect PV systems to the grid in Ontario:

  • Under the Micro-FIT program the system owner installs two meters, one for outgoing power being sold to the utility company and one for incoming power to be used in the building. The owner receives a cheque for the full value of power generated (currently 38.4 cents per kilowatt hour), and receives a bill for the full value of power consumed (currently around 11 cents per kilowatt hour). Under Micro-FIT, an owner can generate a financial profit even if production is less than consumption.
  • Under the Net Metering program the owner has a single meter, and that meter spins in two directions, “forward” when power is being consumed from the utility grid and “backward” when generation is greater than consumption. Under Net Metering, the power has the same monetary value in either direction. Should production outweigh consumption, a credit will be carried forward on the utility bill (up to a maximum of 11 months). At best, a Net Metering customer can reduce to zero the usage charges on their bill, but can never earn money.

The teachers’ union did not qualify to apply for a Micro-FIT contract, as the restrictions for the program have been growing ever narrower as it becomes more popular. However, with the cost of PV so low now, the economic argument for a Net Metering system is a reasonable one. Combine drastically lowered utility bills with reasonable pay back period and a desire to be part of a renewable energy solution, and you have the grounds for the union’s investment in this 7.5 kilowatt system.

Sean Flanagan of Flanagan and Sun came by this week to turn the system on. With the array and the outdoor connections already made, it was a simple process to turn on the inverter and make sure all the settings were right. Luckily, it was a fairly sunny day and we were able to see about 5 kilowatts of production head out onto the grid when the system became live.

The combination of the PV array and a contract with Bullfrog Power (which we strongly recommend to all our clients) means that 100% of the energy produced and used by this building is from renewable sources.

Goodbye to the class of 2014

The students of the Sustainable New Construction 2014 class said a belated goodbye to Endeavour and the teachers’ union office project.

Their departure was one month later than expected, as five of the seven stayed on through October to make up for time lost during permitting issues earlier in the summer.

The last week was about adding some fun finishing details to the building, including the cordwood entryway to the meeting room and some great bottle and hempcrete transom details in the doorways.

This was an amazing group of builders, and we wish them all the best as they move onto their new lives in the sustainable building world!

Finishing the straw-cell wall system

Our office building project for the Trillium Lakelands Teachers’ Union features a straw bale wall system that combines conventional wood stud framing with an interior straw bale wall.

Recently, we finished the exterior side of this wall system. This involved placing dense-packed cellulose insulation in the frame wall, filling the cavity so the insulation is blown tightly against the straw bales. With the cavities insulated, we add approximately R-21.5 to the R-30 of the straw bales. Our contractor for the dense-packed cellulose was Morgan Fiene at New Energy Consulting in Hastings, Ontario (705-313-2004), whose care and concern for doing a thorough job was very refreshing.

We then covered the framing with an insulative wood fibre sheathing. This 1/2 inch wood fibre sheathing has an R-value of 4 per inch, and is made from 100% recycled wood fibre and a non-toxic binder. Made by Western Louisville Fiberboard in Quebec, this product is the cleanest sheathing product we could find. Most exterior wood fibre products use an asphalt emulsion coating, but the SONOclimat product uses a proprietary coating that is water based, non-offgassing and meets stringent environmental standards.

As a means to blend conventional wood framing with straw bale walls to achieve very high insulation values, we have been very pleased with the straw-cell system. It marries low impact materials throughout (earthen plaster, straw bales, cellulose insulation, FSC framing and recycled fibre board) with high insulation value and a straightforward construction process. It’s a great way to marry the more unconventional approaches to sustainable building with mainstream approaches.


Air tightness details for straw bale walls

Straw bale wall systems have been touted for 20+ years now as a way to achieve higher insulation values with lower environmental impacts. And, having built many straw bale homes and commercial buildings now, we know this is true. However, we have also seen that without attention to air sealing details, many straw bale buildings are quite leaky and fall short of their potential level of energy efficient performance because of this.

Along with many straw bale compadres world-wide, we’ve worked to come up with details that address these issues of air tightness in straw bale buildings. Our latest project for the Trillium Lakelands Elementary Teachers’ Local offices have good examples of easy ways in which a bale wall can be built to be air tight without reliance on whole-wall vapour barriers or other sheet membranes.

Plastered straw bale walls have a naturally air tight nature thanks to the continuous plaster coating. Any crack-free layer of plaster does an excellent job of stopping air movement through a wall. However, where plaster meets other materials (at the top and bottom of each wall, at each door and window opening and around through-wall vents and pipes), just plastering up to these seams does not create an air-tight barrier. All plaster types share the characteristic of shrinking as they dry or cure. Every edge of a plaster wall will pull away and leave a gap as the plaster shrinks. It may not seem like much, but even a 1/16 inch gap at the top of 100 feet of wall area is the equivalent of 75 square inches of “hole” in the wall! Add that same gap around every window and door and at the bottom of each wall and you may have a hole in your wall of up to 1.5 square feet! That’s like leaving an average sized window open full time!

Most homeowners understand that having a window open all winter long would have a negative affect on the amount of energy used to heat the home. But many people do not put the time and effort into “closing the window” around the perimeter of their straw bale walls.

For some, there is a reluctance to build air-tight because of a notion that it is unhealthy to seal a house “too tightly.” However, it is also unhealthy to be drawing outside air into your home through cracks and leaks in your walls. That infiltrating air picks up dust, spores, and anything else that is in the walls on its way into the house. Seal the house properly, and deal with the ventilation that is required in an intentional, clean way.

It’s not difficult to make an air tight bale wall. We will report on our blower door test results for this building as soon as we have performed the test!

Stop motion straw bale and earth plastering

Sustainable New Construction 2014 student Ben Bowman set up his camera and took some great sequences of the construction process at our teachers’ union office project.

Here are the two sequences of straw bale installation and earthen plastering. In many ways, these stop motion videos give a better sense of the process than an actual video, plus it makes it all look so fast and easy!

Ben also captured sequences of our earthbag foundation construction and roof craning process:



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!

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.

Off-grid job site power system

Many sustainable building projects are built in places where it is difficult or impossible to access electrical grid power, and this necessitates running a gasoline or diesel powered generator to provide power for tools. Over the course of an entire building project this can add up to a lot of fossil fuel… I have records from one job that show we used 2,250 liters of gas over a five month period! Hard to be making claims about sustainable building when that much fossil fuel is being burned in the process.

Despite our project for the teachers’ union being in a very urban location, there was no accessible grid power and we did not want to run a generator again. The cost of running a temporary electrical service (including utility fees and electrician’s time) was around $2500, and then there would be charges for the power used on top of that.

We spoke with Sean Flanagan of Flanagan and Sun about a PV (photovoltaic) based system that could run our job site, and the price tag was about $3800. More than the temporary power, but once built the system could be used again and again in the future. Our clients at the Trillium Lakelands Elementary Teachers’ Union generously agreed to put the budgeted cost of temporary power toward the system, clearing the way for the Sustainable New Construction class of 2014 to be powered by renewable energy!

The system features 480 watts of photovoltaic output, and is coupled with two large deep cycle batteries and a 3,000 watt sine wave inverter to provide power to the tools. A MPPT (maximum power point tracking) charge controller is the “brains” of the system, matching the amount of charge from the panels to the needs of the batteries.

After trouble shooting through some issues with the first charge controller (wrong unit for the PV voltage), our site now runs on 100% renewable energy, without the noise and pollution and cost of running a generator. We do face some limitations… if multiple tools try to start up at exactly the same moment the breaker on the inverter will trip. On a cloudy day with the air compressor running almost constantly, we can have difficulty running other tools. But living within limited means is all part of sustainable building and living, and it’s a good lesson to be reminded of during construction.

The silence and the clean air are well worth the small sacrifices. We’d encourage other builders to consider similar systems. The system is small enough to fit in a typical tool trailer, and we’ve also known builders to carry the batteries and inverter in their trucks, using the truck’s alternator to also charge the batteries as they drive to and from the job site. If each project can eliminate the need for hundreds of liters of fossil fuel, that would be a worthwhile impact!