House of Straw

Posted 2014-11-28
Written by
Category Taking Action

Tom Gross, Arctic Energy Alliance’s South Slave Regional Energy Project Coordinator, recently visited a home in Fort Smith where he was intrigued to hear that a couple had constructed their home using straw bales. Not that the idea was something new, straw bale construction has been around for several hundred years in Europe and since the late 1800s in North America, but that someone took the concept and actually built their home using them had to be a first for the NWT.

Tim and Tanya Vyse moved to Fort Smith in 2004, and after purchasing an acreage lot they made plans to construct their new home. Tim got the idea of using straw bales from books he read and completed the research from a number of Canada Mortgage and Housing Corporation (CMHC) report studies on the topic that he also used to guide him through the construction.

Basically, there are two types of construction methods when it comes to using straw bales, either load bearing or non-load bearing also known as filled wall. The Vyse’s opted for the filled method using a supporting structure made of pressure treated 4x4 posts holding built up beams that supported the cathedral style truss roof system.

Their 1,120 square foot home rests on a concrete slab on grade foundation with in-floor heating. Tim bought the highly compacted straw bales from a farmer that produces them in Saskatchewan with each bale measuring 106 cm (42 inches) long, 35 cm (14 inches) high and 46 cm (18 inches) in depth. The bales are stacked on top of each other just like bricks, with the exception, that instead of using cement mortar, the bales are “stitched together” using poly twine. The straw bales are also very neatly notched out so that the structural framing ends up in the center of the bale eliminating any thermal bridging.

Interior and exterior walls are then covered with a two inch wire mesh fastened in place with large staples. In this case Tim used recycled welding rods that he retrieved from the dump which he then just bent into shape. Once the wire mesh is in place the stitching begins, and when completed makes a strong ridged wall.  Interior and exterior wall surfaces are then covered in three coats of plaster. The first, a scratch coat is a thick clay plaster that has short pieces of straw mixed in with it that acts as a binder. Tim constructed his own mixer using the bottom half of an old 250 gallon fuel tank as the tub and hand troweled the mortar onto the straw bales. The process was a lot of work and required the plaster mixture to be just right “almost elastic”, as Tim explained. Care must also be taken to ensure that no areas are exposed without plaster to prevent water and rodents from getting in but also to ensure the wall system ends up completely sealed giving it the tested two hour fire rating.

The interesting part about this construction is that there is no vapour barrier used. Once the plaster coating cures properly, it acts as a water barrier in its liquid form but water vapour will pass through and does not become trapped inside the wall. Straw bales themselves are capable of absorbing and releasing large amounts of water and will still remain below the level where decay and fungus becomes active provided they are not painted which will seal in any moisture. Pigments however can be added to the final finish plaster for colour.

Straw bales can be purchased in different sizes, most commonly 45 cm (18 inches) or 61 cm (24 inches) and depending on how tightly they are bundled for density, and amount of moisture content, can test anywhere from R30 to R36. Good R value is only part of it, since straw will also dampen sound rather than transmit it, and being a natural product has no toxic glues or resins that along with its high permeability allows any indoor toxins to escape, improving air quality.
 

Tim who works for Diavik on a two week in and out rotation spent his time off, including holidays, building their home, and between him and his wife Tanya, completed all the labour work together which included a stone feature wall 2.5 metre high, 7.5 metre long and 0.6 metre deep. The couple collected the stone from Pine Point and constructed the wall not just for aesthetics but to act as a heat sink for the wood stove located in the center of the home. The primary heating system is hydronic with in-floor slab heating fired by a propane boiler which also provides heat for an indirect domestic hot water heater. We were curious as to what the cost of heating the home was, and aside from the wood burned, and the propane energy used for the past year, one of the coldest on record, was just over 1500 liters.

When we look at straw bale construction it has a low carbon footprint. Straw is an annual renewable byproduct readily available which does not require the same energy needed to cut, mill and dry such as lumber does. Construction costs are also lower than conventional construction with bales costing less than $5.00 each. The walls also go up fast and easy and have a beautiful appearance when finished with their wide sills and rounded corners.

On the down side moisture intrusion causing decay is the number one concern so it’s important that the bales start at least 20 cm above exterior grade and 15 cm from the interior floor. This will prevent the bottom bales from getting soaked from backsplash or any interior flooding. Roof overhangs must also extend out far enough to protect the wall underneath, and special attention must be taken when installing windows and doors to ensure they are loaded to the outside of the wall or properly flashed.

Tim and Tanya have lived in their home five years and although Tim says the house still needs the finish coat it looks great. Straw bale construction as an alternate is affordable, green, energy efficient, and healthy.

Special Thanks to Tim and Tanya for allowing Arctic Energy Alliance into your home and being part of our Northerner’s taking Action.