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Circle Organic Farm Tour

In 2013, Endeavour’s Sustainable New Construction program undertook the building of a large farm building for Circle Organic Farm in Millbrook, Ontario.

The building included a 1,500 square foot vegetable processing area on the main floor (built with straw bale construction) and another 1,500 square feet of living area for farm workers and a farm office on the second floor (built with double stud framing and cellulose insulation). Adjoining this building is a 2,000 square foot buried root cellar. This root cellar was recently featured in a Trent University study about low-energy root cellar systems.

The building is now in its second year of use as the hub of operations at the busy farm, and is settling into the landscape comfortably.


Project Update: A large, low-energy root cellar

Our 2013 project at Circle Organic farm involved constructing a large, root cellar-style vegetable storage facility attached to the vegetable processing barn. Our research showed us that small subterranean root cellars have a long history, but that the principle has not been applied on a larger scale. Julie and Andrew at Circle Organic want to be able to store a number of different root crops on a scale that would allow them to run their CSA (community shared agriculture) program year-round.

Subterranean storage has a lot of inherent advantages for vegetable storage, as the ground temperature is quite stable year-round (typically 12C in Ontario), minimizing the amount of energy required to create good storage temperatures in the 1-5C range. The question is: What’s the best way to build a large, subterranean building?Our usual palette of natural building materials did not offer a quick and easy answer. After exploring earth bag and compressed earth block, both proved to be too time intensive for a build of this size (25 x 80 feet), and would have required complicated formwork to make the arched roof.

In the end, we decided to use a heavy gauge steel quonset hut. This option appeared to be suitable for the loads imposed by burying and offered reasonable installation time. We decided to go with a highly sought after company with a stellar reputation, T Bailey: structural steel fabricators, In the end, the heavier gauge of steel proved to be slower to assemble than a typical quonset, but was still faster than earthbag or earthblock.

We assembled the quonset hut, leaving a number of 4-inch ventilation tubes running under the footings and up the outside of the building. These will be used to draw fresh outdoor air for ventilation of the root cellar.

At some point in the process, our structural engineer (Tim Krahn of Building Alternatives) questioned the ability of the quonset structure alone to handle the very significant loads of the soil on the building, and we needed to look for a way to reinforce the structure.

We found a product called concrete cloth that fit the bill. This material comes in rolls, and is a multi-layered fabric with cement powder embedded between the layers. It can be rolled out onto any shape, soaked with water, and then hardens into a thin concrete shell. For the quonset hut, we had to add a cage of strapping for the concrete cloth so that the seams could be fastened and waterproofed on a rigid backing.

The addition of the concrete cloth added a large expense and several extra steps on the labour side. However, the finished building still came in less expensive than any of the options we had considered.

The entire root cellar was finally covered with a dimple mat drainage plane before being backfilled. The backfill needed to be added to the building in alternating lifts. As the backhoe placed soil on one side of the building, it was mechanically tamped on the other side to ensure a stable, even loading of the building.

After a couple days of going back and forth, one side to the other, the root cellar was fully buried, just in time for the snow to start flying!

To date, the root cellar is just one large, undivided space. For next season, the space will be divided into a number of rooms, each with its own dedicated ventilation tube. Different vegetables require different storage temperature and humidity, and each space will need to be divided and sealed from the other spaces.

At this point, the root cellar is holding to a fairly constant 1-4C with no active tempering system, which is exactly what we had hoped. Ventilation is being handled by opening the large door occasionally and running a fan in the space. While this root cellar was definitely not constructed from natural, sustainable materials like all our other projects, the trade-off should be a food storage capability that requires extremely low energy input to maintain proper temperature and humidity year round. Operational energy tends to dwarf embodied energy of building materials over the long term, and we are quite confident this will be the case with the roof cellar.

We are very excited about the potential for this type of structure. In northern climates, the average moving cost calculator and through the winter is vital to providing local food security. We love the adventurous spirit of Circle Organic for recognizing that moving the local, organic food movement to a point where it can provide year-round food solutions. Coupled with the large greenhouse constructed to provide leafy greens year-round, this farm is conducting a remarkable experiment in food production and security that we are glad to have a hand in assisting.

Straw bale barn and Buried quonset hut root cellar by Endeavour Centre

Circle Organic farm building nearly finished. The “barn” houses veggie processing and packing. The connected root cellar provides storage, and the greenhouse being built in the foreground will provide year-round growing capability.

Home-made hydraulic lime plaster

One of the most exciting elements of the Circle Organic farm project is the home-made hydraulic lime plaster we successfully used on the interior and exterior walls of the building. With this new recipe, we are able to make a plaster with locally sourced materials that has a quick hydraulic set and is not affected by erosion or wear due to rain, as can happen with clay plasters.

Natural hydraulic lime (NHL) plasters are made from limestone deposits in which a significant amount of pozzolanic material is naturally occurring in the limestone. These limes come from large deposits in France, and to a lesser degree, Portugal. These limes can be purchased in North America, but are very expensive and it is carbon-intensive to ship heavy materials from overseas. Home made hydraulic lime plasters use the more commonly available hydrated lime available at masonry outlets, to which a pozzolan is added.

We have attempted to mix our own pozzolans with lime in the past, with mixed and mostly disappointing results. But the metakaolin we have sourced from Poraver for our sub-slab insulation and foundations is a very high quality and consistent pozzolan, fired to a high temperature and well-graded for a very reasonable cost.

Home made hydraulic lime plaster at Endeavour Centre

The recipe for the push-in and the body coat are enshrined on some scrap wood!

As with the Poraver foundation, we mix the metakaolin and lime in even quantities, and use this binder as the basis for the plaster. We first mix up a batch that is 1 part metakaolin, 1 part hydrated lime and 3.5-4 parts sand. This “push-in” mix is made quite thin and wet, and is used to quickly push into the straw bales by hand or trowel because it adheres very well to the straw. We then immediately cover this with a mix that is 5 parts metakaolin, 6 parts hydrated lime, 13 parts sand and 15 parts chopped straw. This coat is applied by hand until it has been built up to the right thickness, and then smoothed out with a magnesium or wood float. This provides a smooth surface that can suffice as a final finish, but also leaves a slightly textured surface in case a final, thin finish coat is desired.

Home made hydraulic lime plaster at Endeavour Centre

A version of the hydraulic lime plaster with no chopped straw is used to plaster the Durisol block wall

The metakaolin/lime/sand mix can be used as a plaster on smoother substrates without the use of chopped straw. We plastered the Durisol block walls on the project with this type of plaster. Such a mix could be used over a wide variety of wall types, and also used as a final finish coat over the chopped straw mix.

Home made hydraulic lime plaster has several advantages over our typical clay plasters. The hydraulic set happens quite quickly, with the plaster being hard to the touch within 24 hours. This is slower than cement-based plasters, leaving more working time and being more forgiving, but much faster than clay plasters which must dry out, often over several days or weeks. The hydraulic lime plaster is not affected by water once it has set, so the plaster can handle driving rains and repeated wettings without erosion, unlike clay plaster.

While clay plasters are safer (lime can burn skin, lungs and eyes) and more environmentally friendly (lime and metakaolin both require high temperature firing), this home made hydraulic lime uses an industrial by-product (Metapor) that is sourced locally to create a plaster that has all the weather resistance of cement-based plasters without relying on cement.

For a project like the Circle Organic farm building, where conditions are exposed on the exterior and involve lots of veggie washing and other wet activities inside, home made hydraulic lime plaster is an affordable and quite sustainable plaster that will withstand rugged, wet conditions.

Home made hydraulic lime plaster at Endeavour Centre

The home made hydraulic lime plaster is a very straw-rich mix



Framing and Bales for the Farm

We do a lot of straw bale work at Endeavour, but it’s such a normal part of what we do that there haven’t been any posts that show us putting in bales for a long time!

Over the past few years, we’ve arrived at a framing system for our bale walls that is very similar to many other professional bale builders. It’s interesting how often a certain approach will become common practice for a number of builders, even without any communication.

This system uses a fairly conventional light wood framing approach, in which we create double stud frames that are 14 inches apart (the width of our bales, on-edge) with the 2×4 studs spaced one bale length apart (for the bales we get here, it’s usually around 28-30 inches on centre). This framing system forms bale “cavities” in which a bale fits snugly. Too tight a fit and the studs will bend from the pressure (especially on 10 foot high walls like here at Circle Organic farm), too loose and there will be a lot of stuffing to do. If the fit is just right, it’s quite easy to get the bales in place, and the gap between the studs is filled with the “puffy” end of the bales. We stuff some extra straw into this space if there’s room, to ensure that there are no spaces without good insulation.

Built this way, we don’t ever have to notch a bale to fit around the framing, and the majority of the stud cavities take a whole bale. For shorter cavities, all the bales for that cavity are made to the same length which simplifies the cutting and retying process. If the math was done right during the planning process, the final bale at the top of each cavity should fit a full bale, tightly.

This system minimizes the amount of bale modification, and relies on very straightforward framing principles. This makes it easy for conventional builders or those with framing experience to frame up a bale wall with ease. Window and door openings are built with the same kind of jack studs and headers as conventional. The top of the wall is a typical doubled 2×4 top plate, so no large diameter beams or complex carpentry is required. The small gap between the top plates is easy to stuff with straw or other insulation.

The exposed sides of each wooden stud are covered with straw that is held in place by zig-zagging bale twine from the end of one bale to the end of the next bale. In this way, the wood is covered prior to plastering without having to rely on housewrap or tar paper.

This framing system uses a similar amount of wood as a conventional single 2×6 stud wall. While we are using double walls, the studs are spaced at least twice the distance apart. It’s a lot of building for a reasonable amount of framing lumber.

Flashings and plaster preparation are handled in a similar way to all other bale installations.

This system has worked well for us over a number of installations, and though we rarely do anything in a standardized way, this framing system is definitely becoming our standard approach.

Stay tuned to find out about the homemade hydraulic lime plaster used on this project!…


First Ever Poraver Foundation

Followers of the Endeavour blog may remember that last year we used an innovative new insulation based on Poraver expanded glass beads as our sub slab insulation for Canada’s Greenest Home. At the time, we were excited to find an insulation that can be reliably used below grade and uses no cement and no foam and offers a reasonable insulation value of around R2 per inch.


As we reported last year, the Poraver product is made from recycled glass that is “aerated,” giving it a cellular structure that is strong but containing enough air pockets to have a good insulation value. As a dry insulation, it can be used in many infill applications, and it is frequently mixed with cement to make lighter weight concrete. The “magic” for us, however, is that a by-product of making the Poraver balls is fired clay, called metakaolin. Metakaolin is a pozzolan, which means that it can be mixed with local hydrated lime to create a hydraulic lime. Hydraulic lime achieves a large percentage of its curing by consuming water, much like cement, meaning a much faster set time, much higher early strength and the ability to use lime in thick applications like a foundation wall. Suddenly, we have a locally produced material that is made from recycled content, and we also use the by-product of the process! Eliminating foam and cement from a foundation with side benefits!

Our positive experience with the material led us to use the Poraver material as the grade beam foundation for the Circle Organics building. With a good compressive strength rating of 0.5 N/mm² (72.5 psi) after seven days, we were keen to build a grade beam that combined structural properties and insulative properties within the same material.

Thanks to our ever-helpful structural engineer, Tim Krahn of Building Alternatives, we were able to build the world’s first expanded glass bead foundation.

We started with a thin, 3-1/2 inch concrete grade beam on top of our rubble trench. The grade beam is below the floor level of the building, and added the bending strength required for the foundation. It is possible that the Poraver could be strong enough without the concrete beam underneath it, but further testing would have been required to justify this, so we went with a thin beam. The concrete was poured in the same formwork we used for the Poraver, simplifying the construction process.

The Poraver grade beam was 16 inches wide (to match the width of the plastered bale walls it supports) and 24 inches tall. It will be partially below grade once the building has been backfilled and graded.

As reinforcement for the Poraver, we bent welded wire mesh (typically used as concrete slab reinforcement) into a square “cage” and laid that in the formwork.

The Poraver was mixed on site in a mortar mixer, using a recipe of 44kg Metapor (metakaolin) to 44kg Hydrated lime. These dry ingredients are mixed with water to make a very wet (cream-consistency) slurry, to which we add 1000l of Poraver of the 2-4mm size. For this project, the engineer suggested adding 5% portland cement to the mix. Hopefully, next time we do this, it can be completely portland cement free.

The mixed material was poured into a form, much like concrete. Once in the form, we spread it and compacted it to ensure it was fully distributed in the forms without any air pockets. The material was hard to the touch in 24 hours, and we removed the forms after 48 hours.

The Poraver material is friable (crushable), making the corners and edges of the foundation vulnerable to chipping when kicked or struck with any force from scrap metal buyers. However, beyond the very edges the material is remarkably resilient. It is able to hold a screw (as long as it isn’t over-torqued). We embedded metal tie straps to anchor the sill plates to the foundation core.

The mixing process was quite quick, as the round balls tumble well in the mixer and get coated in the slurry. Moving the material is easy, as it is very light weight.

This is a material that holds a great deal of potential for future use. It can be mixed on a commercial scale, and potentially formed into blocks or panels, as well as being used for custom pours like this one. This Poraver mix could drastically reduce the amount of styrofoam and concrete used in buildings, replacing it with materials that are much more benign and based on recycled content. We hope to do more work with Poraver in the future.

Poraver foundation

Bart, a towering figure, is dwarfed by his accomplishment: The world’s first Poraver foundation!

Making a Rubble Trench Foundation

Rubble trench foundations offer a means by which to connect a building to frost-free ground in cold climates without resorting to the use of a concrete wall and footing. While rubble trench foundations have a long history, they are not a common practice as most foundations in cold climates incorporate a basement space. Rubble trench foundations cannot be used to make a basement, but they are perfectly suited for buildings with grade-based floors that require a footing below frost depth.

For the Circle Organic building, our rubble trench was 4 feet deep and about 2 feet wide (the width of a backhoe bucket). We used a grade of local crushed stone called 2-4 inch clear stone. This means the fines have been washed out, leaving a rock that is very well draining.

Water that may make it into the trench drains through the stone to a drainage tile at the base of the trench. This drainage pipe slopes around the building and terminates in a “dry sump” where any water can accumulate and percolate into the ground away from the foundation.

The trench is lined with used carpet, which is free for the taking from most carpet installation companies. On the sides of the trench, the carpet prevents wet soil from migrating into the rubble trench and blocking the free-draining rocks. It also provides a small thermal break from the soil.

On the outside of the trench, we also used Roxul Drainboard, a recycled mineral fiber board that is free draining and provides a more significant thermal break. Insulating a rubble trench foundation isn’t necessary, but we are applying solar heat to the ground under the building, and wanted to keep that heat from migrating into the surrounding soil.

The stone in the trench is compacted up to grade level. We then added a layer of 3/4 inch gravel over the trench and over the entire floor area. This stone is easy to level out and compact, and provided a base for the above-grade portion of our foundation as well as the slab floor.

In areas where locally harvested crushed stone is widely available and affordable, this type of foundation makes a lot of sense. It displaces a very large amount of concrete in a very simple and straightforward way. Rubble trench foundations only work in soils where a narrow-ish trench can be dug without the sides caving in. Very sandy or very rocky soils may not be appropriate.

By connecting the building above to frost-free ground below, a rubble trench foundation can often be the lowest embodied energy and most reliable and stable foundation in a sustainable builder’s repertoire. It certainly worked for us at Circle Organics!

Goodbye to the class of 2013

The fall has flown by so quickly that it’s hard to believe that the Sustainable New Construction class of 2013 has already been gone for over a month!

Straw bale vegetable processing facility at Circle Organic farm built by The Endeavour Centre

The class of 2013 and their almost-complete veggie processing building

This year’s class was an amazing collection of people, with Endeavour’s first international students making up half of the class. Participants from the UK, Brazil, France and the USA mixed it up with the Canadians to make it a very memorable five months of working on the farm at Circle Organic in Millbrook.

This photo gallery is a collection of just a few of the memorable moments from this year’s class… Stay tuned for more blog posts that will take you through this unique building project from start to finish!

Whoo-hoo, we're finished!

Whoo-hoo, we’re finished!

The site at foundation stage

Site view

Site view

The Da Vinci Roof

Inspired by Leonardo Da Vinci’s self-supporting bridge we decided to build a roof shelter for our work area to protect us from the elements. The idea is that a structure can easily be built by weaving wooden joists into an arch to create a self-supporting structure.

This is done by running central parallel beams with joist supporting these beams by being placed in an alternating pattern in a way that the beams and joists support each other.
The first joists brace two parallel beams and a third beam is placed centrally on top of these joists. A second row of joists attach to a this beam and run underneath one of the first beams. The joists then attach to a forth beam that once again will sit on other bracing joists. This process is continued until you reach the desired length.

We used 8′ 2×4 for joists and 16′ 2×4 fastened together for beams to span an area between two shipping containers.

Another Cord In The Wall

A cordwood wall is made of cob and cord wood; this is how we made it:
We began with a rock wall foundation to secure the cordwood and cob to it in order to avoid disintegration.
After cutting 6″ lengths of cordwood, we mixed the cob. Cob is made with clay, located on site, as well as water and straw. To help with the consistency we added saw dust, which proved to be an excellent source in helping with the application of the cob and eliminated having to dispose of it.
In application of the cob, Kara found using her dish gloves oppose to the large thick plastic gloves to be the best and the end result looked far better. Using just our hands was also effective but they became cold quickly!
To keep the wall straight we used a level and gussets, which are thin pieces of wood at only about an inch wide inset into the wall for strength. They measured the length of the cordwood wall and were inserted every few rows.
After rows and rows of cordwood and cob and we had reached a height of approximately 5 feet, the really fun part emerged!! The wall design! Collaborating ideas together a plan was made to do a zig-zag pattern and to have a window made from the old compression ring used to help set rafters for the reciprocal roof, it was a perfect fit for the window!
Different coloured bottles were set in-between the zig-zag to complement it and to be used for useful things such as your soap on a rope, loofah and towels.
Some beautiful blue bottles were put in upright and 2 growlers from The Publican Brewery in Peterborough. We felt it gave the wall a local feel. The final two rows were tapered up and a wave created sloping down towards the window to complete the wall! Presto!! A cordwood wall!


Solar Hot Water Shower

Solar Hot Water System
Our outdoor shower makes excellent use of a handmade solar hot water system. This is a simple system that will supply hot water to the shower and also to a sink on the outside of the outhouse.

The System in a Nutshell
Designed minimally and for warmer weather, the water supply comes from the house via a hose line and into the outhouse. The main supply line connects to PEX piping and splits off at the shower and again at the sink to supply cold water. The remaining line goes into a hot water tank that rests above a handmade solar hot water panel. From the tank the water comes out and into the panel where it is heated by the sun. The water exits the panel and travels back into the tank from which it is then drawn through pipe to the sink and shower for hot water use.Our shower floor consists of  large flagstone slab with a drainage bed of gravel to fist sized rocks directly beneath the slab. The drainage bed leads down a shallow dug trench and into a small pit filled with rocks.

When hot water is not being drawn from the system, a natural thermo-siphoning occurs within the panel and the tank. Hot water that is running through the panel will enter the tank hotter than the water that is filling the tank volume. That forces the slightly cooler water to exit the tank and run back down into the panel. And so the cycle continues.

The Panel
The solar hot water panel that we made is incredibly simple and is very low cost.
A shallow plywood box topped with a piece of tempered glass from an old patio door houses the piping.
Water will run through a network of vertical pipes connected by horizontal pipes at the top and bottom.
Once the water runs through, it exits at the bottom of the panel from a pipe split off of the rest. Corrugated metal roofing that is typically used for barns makes a great housing for the piping itself. This roofing is painted black and then fastened into the bottom of the panel box. Corrugations that are a half circle shape hold half inch copper pipe very well.

copper pipe, solar hot water, corrugated iron panel

Building the solar panel.

By resting the pipe in the half circles, there is much more of the pipe in contact with the metal than if it rested on a flat sheet of metal. This is a great benefit because heat is conducted through the metal roofing and into the pipes. As the pipes heat more and more, so does the water that runs through them.

outhouse, solar hot water panel, homemade

Finished solar hot water shower and sink.

Reciprocal Roof

What is a reciprocal roof?

Reciprocal Frame Architecture by Olga Popovic Larsen

‘Reciprocal frames consist of linear members which are mutually supported and interlocking, forming either a flat, horizontal structure or a pitched three dimensional frame system.
The simplest form of a reciprocal frame is a beam system arranged around a single, central circle.
Each member is supported at the outer end by a ring, beam or column and at the inner end is supported by the adjacent member. When reciprocal frame members are arranged regularly around a central point of symmetry we get a regular reciprocal frame structure.’

We were lucky enough to be able to find roofing company albuquerque nm and find metals we could use for the rafters of our reciprocal roof.  An octagon was build on the top of our square outhouse to accommodate eight rafters, as we wanted our roof to be round.

The octagonal frame to support our rafters.

The octagonal frame to support our rafters.

Once we had sourced our rafters, that were as straight as possible and 11′ long, we had the tricky task of pulling them up on the roof and positioning them. Firstly we placed some supporting rafters to help hold our rafters in place and to make it easier and safer for us.


Positioning our rafters.

All the rafter were placed in position, one end on one point of the octagon and the other end in the centre. Each rafter rested on the previous one and they were tied together with twine. We used twine so we had some flexibility to tweak the rafters in place and to make sure they were supporting each other and that we had our desired shape. Once we were satisfied we screwed them together and the twine was cut.

We then used slab wood for sheathing the roof to create a sturdy platform that we will put straw bales and soil on to make a living green roof.

slab roof, reciprocal roof, green roof

The slab wood sheathing.




We have been building an outhouse that includes a composting toilet and solar hot water shower for the farm so that interns working and staying there will be able to use if for years to come.
The outhouse has been built mainly from pallets and any other material we could find to up cycle rather than buy. To separate the shower from the toilet we are building a cord wood wall and using tin cans and slab wood for siding on the outside wall. We bought a second hand sink and have hooked it up to the solar hot water.
For the roof we decided to build a reciprocal roof and plant a green roof on top of it.




Studying hard and getting to grips with building science!