Usually once a home is built, the builder hands the keys over to the new owner and unless there’s a problem, the builder moves on to the next project. However, in the case of a straw-bale built home in Peterborough, the home has been lived in for the past year and all water and energy consumed has been recorded. The goal was to see if, in fact, the home is Canada’s greenest home. You can read all about its features in the article I wrote last year. Chris Magwood, director of the Endeavour Centre, whose students built the home emphasizes that it’s not supposed to be a competition, it’s meant to demonstrate that building a green home is achievable using currently available technology that is locally available.
Photo courtesy of Mick Paterson. Rear view, straw bale constructed home addition, before exterior cladding
About a month ago I posted an article written by Terrell Wong, an architect specializing in sustainable building and design, about a straw bale addition to a home she had designed. She was frustrated because the city of Toronto denied it even though the city had built a straw bale building in High Park. One of the reasons the structure was denied was because the design doesn’t use a vapour barrier. The theory regarding a vapour barrier is that it is necessary to prevent water vapour from permeating walls and getting stuck there leading to mould and mildew problems which could eventually cause significant structural deterioration — not to mention indoor health problems. But straw bale building has been around for a lot longer than vapour barriers and homes built from straw have been around for hundreds of years in Europe and still stand today. What that indicates is that as long as you know what you are doing, straw bale homes are perfectly safe, healthy and durable, contrary to what someone unfamiliar with straw bale building might think.
After I posted the article, I was contacted by Mick Paterson, a project manager with The Fourth Pig, a co-operative sustainable building not-for-profit group based in Baysville, Ontario. He is currently overseeing a straw bale addition to a house in Toronto. They received approval from the city just as he contacted me, so his project was good to go.
I took the opportunity to visit when I was briefly in Toronto in June, to get a feel for a straw bale home and to ask questions that tend to come to mind when thinking about straw bale building. After the tour, I sent the team my questions and concerns — which I think are fairly representative of straw bale novices like myself. So, below are my questions and concerns, followed by Mick’s and his team’s answers.
Side view of straw bale addition and original house.
1. The straw goes moldy after a while and can lead to such problems as black mould and wall collapse.
Fourth Pig: Moisture is the enemy of any type of construction. The straw bales would only become moldy once prolonged heavy exposure to moisture is seen. A straw bale home must have a breathable protective coat. Lime and clay based plasters provide protection from bulk moisture while allowing any absorbed humidity to escape from the wall.
2. Straw can’t act as an insulation material.
Fourth Pig: Straw can be classed as one of the oldest insulation types on the planet. Straw has been used in Europe for centuries for insulation in different forms but straw bales as a wall construction and insulation really took off in the US in the mid-19th century. Its r value is dependent on the bales compaction, orientation and construction detailing. The most agreed upon r value is 30 for 2 string bales or 1.4 to 2.6 per inch.
3. Its fire rating is low and therefore unsafe to use as a building material.
Fourth Pig: Both ATSM in the US and CSIRO in Australia show testing on straw bale walls to have a high resistance to fires with a 2 hour fire rating on plastered walls and 30 minute rating on an exposed strawbale. There are several examples of commercial straw bale buildings word wide. In Australia there is a veterinary hospital and in Colorado a Waldorf school chose straw bale as the only wall material for all 22,000 sq. ft. of its classrooms. 4. You need a vapor barrier to protect the straw from moisture.
Fourth Pig: Vapor barriers are not necessary for a straw bale wall as the plaster skin provides a similar function. As an added benefit lime and clay plasters allow the straw to absorb and release water vapor on both sides of the wall, preventing damage from accumulation. This happens in cold to hot climates, and dry to humid ones.
5. What is the best material to use for covering up the straw bale and why?
Fourth Pig: Natural plasters like lime and clay provide the most benefits for straw bale walls for their breathability qualities. Various factors such as design, cost, performance and historic longevity have shown the benefits of using lime and clay and avoiding cement and acrylic based plasters or covering the straw bales with drywall.
Close-up of Straw bale wall
6. Can straw bale be used for houses that are more than one story high?
Fourth Pig: The limits to how high you may build a SB wall are the same limits all buildings face. With intelligent design a skyscraper could be constructed with a façade of strawbales. (We would like to retrofit a multiple storey building with strawbales!)
7. How long does a house made with straw bale generally last?
Strawbale walls and all buildings will last as long as the buildings inhabitants make them last. All buildings require regular maintenance and upkeep as do strawbale walls. With proper design and upkeep SB walls can last for centuries or more. There are strawbale homes in the US that are still standing and in great condition from the mid to late 1800s. 8. Is it more or less expensive than building a stick built house?
Straw bale walls can be cheaper than regular insulated wall construction but there is so much variation of wall finishes and detailing that that need to be taken into account when trying to compare apples to apples. You will not get an R30 insulation value out of a traditional stick framed wall.
For more information on building a straw bale home, or have more questions about the material’s durability, visit the Fourth Pig’s website, or contact them directly.
My friend, Architect Terrell Wong, a passive house and green building specialist, has been having quite the time with the City of Toronto, trying to get an addition to a home built with straw bale. She figured that since the city had built its own straw bale building in High Park, they’d be open to others building straw bale structures.
For those of you who aren’t familiar with straw bale, it is a method of home building that’s been around for hundreds of years and is still common in Europe. It has a low embodied energy, is recyclable/bio-degradable at end of life, is durable, has a good R-value because it’s so thick and doesn’t need a vapor barrier…or does it? The city denied her application for a straw bale addition to a Toronto home on several grounds, including lack of a vapor barrier. I guess with the city it’s “Do as I say and not as I do.”
Chris Magwood, Executive Director of The Endeavour Centre sent me a note letting me know that Canada’s Greenest Home is now complete and up for sale. As he mentions in his blog post on the subject, being the greenest home is not a brag per se, as those people working in the green construction industry tend to work cooperatively rather than competitively. I had a long list of questions about the home that I sent Chris’ way, and he answered each one with significant detail.
If you’re not familiar with the Endeavour Centre, is an independent school that teaches green building skills and techniques. People in the program spend half their day in the classroom and the other half building a house, getting that hands-on practical experience they need.
Using criteria from both LEED and Living Building Challenge certification systems, the team at Endeavour built what is likely to be one of the greenest homes on the market today. Not only was it built with end-use in mind, it was built with materials that have a low embodied energy. For the most part, materials come from close to home, and are made, as much as possible from renewable resources.
The house is a spacious 2300 square feet of living space on two floors. There are three bedrooms (including a Master-ensuite) on the second floor, and two bathrooms. On the main floor there is another room which can be used as a fourth bedroom, den, playroom, office, etc. in addition to the kitchen, living and dining rooms and another bathroom.
Shell: The east and west walls for both the first and second floors are made from NatureBuilt straw Structural Insulated Panels. The south side of the building is “double-framed dense packed cellulose” and the north wall is site- strawbaled. Chris estimates that the SIP walls have an R30 value, the roof has an R-80 value, the basement floor has an R-16 value, while the basement walls, built from Durisol blocks are R-16. This is a very tight shell despite its vapour permeable walls, with an air exchange value of 0.63 ACH/hour at a standard pressure of 50 Pascal Pressure. Ross Elliot from Homesol Building Solutions performed the energy audits throughout construction. Chris noted that the floor joists were constructed within the structure so there is no issue with having thermal bridges around the joists. Needless to say, this is a very tight building envelope!
The windows and doors were manufactured by Inline Fiberglass. They are triple glazed (ie., three pieces of glass), argon filled with fiberglass frames. Fiberglass is one of the best materials you can use for windows and doors as the glass and fibreglass expand and contract at the same rate meaning the seal remains tight.
Because the building envelope is so tight, the house is equipped with an Air Source Heat Pump made by Mitsubishi, and an accompanying Energy Recovery Ventilator. Newer ASHPs work even in cold climates such as ours as they can find the heat in air that is -30C (provided the building envelope is tight enough). The ERV recovers heat not just from air, but also from moisture in the air so it is doubly efficient. Chris told me he wouldn’t worry about moisture in this house in any event. Because the walls are made of natural materials (straw, lime plaster, clay and wood), they are breathable and therefore can absorb moisture from the air and dry without worry of mou
Ross Eliott has estimated that with average consumption patterns the annual cost to heat the home should be about $325, taking into account average Time of Use rates in Ontario. In addition, there is a 5 kilowatt PV solar system on the roof which should generate some extra income for the homeowners as part of the microFIT program. In theory, Ross estimates that the home should run at a surplus, and that because the home is so well-insulated, it shouldn’t have any need for air conditioning (although it’s included in the ASHP). No fossil fuels are needed to run this home, and in the event that the homeowners draw more electricity than they produce, they have a contract with Bullfrog Power, a green energy retailer.
Exterior cladding is FSC pine from PurePine and are treated with Sansin stain (water-based) in the factory, and the cedar shingles were sourced in Madoc, Ontario.
Water use: There is no sewer hook-up for this home. The toilets come from a composting company in Sweden called Clivus Multrum. The system only uses 0.1L of water per flush. I’ve looked at the diagram on the Clivus website and asked Chris about it. To be honest, I was a little leery about a composting system within the home itself. The system comes with a fan, and a drainage system that separates urine from excrement and by the time the compost reaches the front of the system it is only about 10% of its original size and ready for use (it takes one to two years to reach the front of the system). My two reservations with this system are sanitation and smell. However, Clivus has been in existence since the 60s and in North America since the 70s, so maybe my reservations are unfounded. Chris noted that they have installed this system in two houses before with great success. Despite my reservations, I can see a system such as this one being a great way for progressive cities to entice new buildings and retrofits to not use the city sewer system — provided there is a lot of training and some sort of certification system in place to make sure proper safety/sanitation measures are taken.
Because there is no need for water for the toilets, there is also no gray water system. There is a rainwater harvest system in place which can be used for any household uses including watering the garden. An overflow system lets excess rainwater onto the front garden.
Interior finishes are a variety of materials including non-toxic acrylic paint from Mythic, AFM Safecoat Naturals paint, a homemade Clay finish, lime plaster and Kreidezeit clay. There are no toxins in this house!
Is this Canada’s Greenest house? It is durable, made of low-embodied energy, local and attractive materials, with exceptionally low running costs, that doesn’t tax the municipal sewer or electric system. Further, it blends in with its neighbours, is a reasonable size and offers typical functionality all of which are important factors in creating any “green” house. The market will decide how desirable this house is. And desirability is a key ingredient in any green house.
In green building circles it is generally acknowledged that prefab or modular homes are more environmentally friendly than traditional stick built on site homes. Walls are constructed inside a warehouse so the materials aren’t exposed to the elements, which helps keep the materials dry; there is less material waste because excess materials from one job can be used on the next one; There is less waste on site because walls were constructed elsewhere and homes go up faster because they are already partially built.
Straw bale houses are also becoming increasing popular because of their properties of low embodied energy (straw is the waste product from wheat, the “chaff”), combined with excellent insulating properties with R-values ranging anywhere from R-20 to R-50, depending on the thickness of the wall. They are strong, durable, and the majority of the material is biodegradable at end of life.
So now imagine a building made of prefab straw bale houses. These houses combine the insulating and durability advantages of straw bale, with those of prefab, producing less waste and being built in a faster period of time. Here in Canada, staw bale SIPs (structure insulated panels) are being produced by the team at NatureBuilt Walls. The walls were the brain child of Chris Magwood, who runs the Endeavour Centre in Peterborough, and Ian Weir, who’d taken the green building course at Fleming College. They are now joined by Neeraj Jain, and Ryan McLaughlin, who bring additional specialized strengths to the company.
I had a lot of questions about the walls, so I contacted Neeraj and we talked about these SIP walls and all of their properties. (Note that the interview has been condensed and I am paraphrasing Neeraj’s answers):
Straw Bale SIPs being transported to built site
1. What are the SIPs made of?
The SIPs are made of straw bales, FSC wood for the frame and are covered with an inch of concrete on either side.
2. What is the expected lifespan of the SIPs?
There are straw bale houses in England and the US that are still standing today that are well over 100 years old, so I’d say our homes will also last over 100 years.
3. What is R-value of a Nature Built SIP wall?
We are in the middle of testing the exact R-value of our walls through a research project being carried out at Queen’s University, but we estimate that our R value will be between 35-40.
4. Can they be used for roofing as well?
No, they are too heavy. One 8’x8′ panel weighs about a ton.
5. Given that it’s an organic product, how do you protect against mould, rot and pests?
The straw bales are packed very densely, it’s like having a wall of solid wood, so there are no pockets or cracks for animals to infiltrate. Further, the straw itself has no nutrition value, so pests would not recognize it as a food source.
With respect to water infiltration, like any wood-based product, it’s how you well you seal the straw to protect it from water. Our walls are completely covered with an inch of cement on either side, so it would be hard for water to find a pathway. But, even if water did infiltrate, because the walls are breathable, there is a way for them to dry out so mould and rot won’t start.
Exterior Walls, Straw Bale SIPs.
Interior walls, Pickering Project
6. Is the straw used for the SIPs waste straw or is it grown for this purpose?
No, the straw used is the leftover stalks from wheat production. Straw is primarily used as bedding materials for animals, so it is generally considered a waste material. Also, by putting it inside walls, it is another way to capture and store carbon.
7. Which type of windows and doors (brand and/or material) are best to use with your walls? Or does it matter?
It doesn’t matter which type of windows and doors are used. After quite a bit of experimenting we now design our panels around the openings, instead of cutting openings within the panels themselves. So, for instance, we will make two panels that will stop four feet apart, and the opening will be where the door will go. To fill the area above the door frame, we can do a variety of things such as add straw bales on site, or use different insulations such as Roxul mineral wool. There are a lot of options. We also build long narrow panels that can be used along the bottom of the house, then windows can be built in resting on top of the panel.
Construction of timber frame home
Straw Bale SIPs used in Timber Frame home
8. Does the wall provide any type of thermal mass for the building?
Absolutely. As I mentioned, these walls are incredibly heavy. They are also about 16″ thick when cement is applied to both sides, so there is a lot of thermal mass there to help regulate a building’s internal temperature.
9. Can you custom spec the walls or do they come in just one size? What is the largest wall that can be specified? Can you stack them for two stories?
Right now our only consistent requirements are height and depth. Walls are usually 8′ or 9.5′ high and the depth is always 16″. Lengths can vary depending on the design, however, because the walls are transported to the site on a flatbed truck, we like to limit the wall length to about 10′. Our residential designs can be up to three stories high. To build higher structures, the skeleton needs to be built in steel.
10. How thick is the final wall when it’s completed?
The wall is 16″ thick which consists of an inch of concrete on either side of an interior filling of 14″ thick straw bales.
11. How do you install wiring and plumbing behind the wall or is it best done through interior walls?
We don’t install plumbing on exterior walls, but we can make conduits for electrical wiring on the exterior walls. While it’s easier when we have the electrical plans when we’re building the walls, we can also add the conduits for the wires after the walls have been constructed.
12. Do you plaster directly over the walls, or do you apply studs and drywall?
The wall is as it is. It can be finished further, if desired, but it’s not necessary. The trick with these walls, especially on the exterior is covering the seams. One of my favourite examples of how this was done well, was our project in Red Rock, Ontario, near Thunder Bay. The architect who designed the building incorporated some architectural trim that was simple, cost effective and also covered the seams.
On the inside of the house it’s not usually much of an issue because the seams tend to line up where the rooms divide. Even if the seams are exposed, as in one of our projects, drywall can be applied directly onto the cement using drywall mud. No studs are necessary.
13. What kind of paint can be used on a Nature Built wall, which I assume is a breathable wall.
A silicate based mineral paint needs to be used on these walls particularly on the outside. Our advisor, Chris Magwood, figures it’s not too important to keep the walls breathable on the interior of the house, but it’s essential to stop mould growth and rot, to keep the building breathable on the outside in order for it to dry out. We can actually apply the paint in the factory so it’s already done by the time it gets to the site.
14. Can you please define a “breathable” wall for our readers?
A breathable wall is one that has no vapour barrier. Let’s say that water is traveling down a wall, even without the actual water infiltrating the wall, the water vapour can. If there is no way for the water to get out, it will eventually produce mould. A breathable wall such as ours, allows for water vapour to evaporate and keep the interior walls dry.
15. What is the cost of your system vs. a traditional stick-built house and a standard modular house.
We have numbers from the Toronto Real Estate Board that estimate it costs approximately $25-26 per square foot to build an average stick-built home. We can build our homes for about $18-20 per square foot, so we are definitely cost competitive.
16. Do you do the design, or do you have architects you work with?
We don’t offer design services, however, we can refer an interested client to architects, designers and architectural technologists who have experience with our material.
17. How long does it take to build the walls once the design is finalized?
A typical home’s panels can be manufactured in about 4-6 weeks depending on the size of the home. Normally we start production to coincide with the foundation being ready. This way, as soon as the foundation is ready, we come in and install the wall panels. One floor of panels can be installed in less than a day. After they are installed, the interior framing is done and if there is a second story, the floor is put in. As soon as the floor is ready we come back and install the 2nd floor panels in less than a day.
The Killaby project was very interesting. As we installed our panels, the builders crew did the necessary framing. We were able to install the 2nd floor the very next day! Imagine how much money is saved by getting the project done so quickly.
For more information on NatureBuilt Straw Bale walls, visit their website.
For the most part we rely on third party organizations to determine what is and isn't a "green building material." The only time we might not is when products are locally produced or no third party green designation is available for the product.
