When Sylvia Cook retired from being a high school physics teacher, she had the goal of building the most sustainable house possible. After a lot of very thorough research, Sylvia determined that the best material to build a house with was dirt. Think about it: it’s local, there’s plenty of it, it has a low embodied energy, it has a significant thermal mass, and is extremely durable. It was these last two criteria that sealed the deal sustainability for Sylvia. When all is said and done, Sylvia estimates that her house will last, at a minimum, for about 500 hundred years. That’s not a typo. Five hundred years is a far cry from the minimum standard Ontario’s current building code demands which, if built to minimum specifications, is only about 30 years. So I applaud Sylvia’s vision and far-sightedness to undertake the building of a home that will outlast her great, great, great grandchildren, and hope that the Policy Developers-That-Be will consider upgrading the building code so that homes are built to last even half that long.
But I digress. I confess that when I imagined a rammed earth home, I imagined something out of the wilds of northern England or Scotland, sitting on a desolate wind-blown moor amongst the heather….but as it turns out I was way off. Way, way off. Instead, this rammed earth home has a more “adobe,” southwestern feel to it, but that could also be because Sylvia tinted the mixture with natural terracotta pigment to give it a warmer tone than its natural cool gray concrete appearance.
Rammed earth walls consist of a mixture of dirt and sand with about 5% concrete mixed in. I asked if the dirt was off the property, but Sylvia said that the stones in the dirt on her property were too big to settle properly and would affect the structure of the hardened material. So, instead, she located a gravel pit about 5 km down the road from her property that has provided the dirt for her house.
Design: Sylvia worked closely with Terrell Wong, environmental architect, on the project. As this was Terrell’s first rammed earth home design, she mentioned that the design really came together when the two of them brainstormed. It was critical that Terrell knew what the material could do in order for her to design the most energy efficient home possible. The house consists of three “blocks” with rammed earth walls built on the inside of the home as well as for the exterior walls. The walls, which are 18″ thick provide a significant amount of thermal mass. Thermal mass allows for a more consistent temperature throughout the house regardless of the season. The walls have an R value in total of about R50. Because of this design, Sylvia is convinced that she will need only a heat source of a small wood stove and an ERV (energy recovery ventilator) for the entire house. She must have seen the look of skepticism on my face because she said that Terrell had incorporated some baseboard heaters into the design “just in case.” I’m cheering for her.
To help out the thermal mass walls, the design calls for some significant windows on the south east side of the house which allow for light and passive solar heating in the winter. Terrell made sure the home was oriented so that the sun was captured through the south-east facing windows from October through April only, thereby avoiding direct sunlight during the hottest months. There will be clerestory windows above the second floor, with a mezzanine that looks down to the main entry and living room. These windows will open to allow any rising heat in the summer to escape easily. All the windows were ordered from Germany and meet Passive House standards, meaning that they are the most thermally efficient windows on the market today.
In fact, with respect to the orientation of the house, Terrell had this to say:
The building faces perfectly on the cardinal compass points NSEW. The views are all to the east and the sun is to the south. What to do… So it’s 3 volumes (2 shoe boxes)set apart and splayed 8 degrees from one another and, they are also shifted so that there are south facing windows in every main room. These windows occur either in the jogs created by the shift of above in the clearstory mezzanine and those south facing windows project light and heat on the main 24’ high interior rammed earth wall. The windows facing east are for views and will require some external shading (yet to be determined) so that the building does not overheat. What we suspect though is that the rammed earth will absorb much of the excess and retain it when the reverse is true.
Construction method: Dirt, sand and concrete are mixed together in specific proportions to create a substance that will last when compacted, as mentioned, for at least 500 years. The mixture is shoveled in to a mold which is set up in 4′ x 8′ x 0.5′ sheets. About 8″ in height of dirt is added to the mold and then tamped down with a hydraulic tamper. The process is repeated until the top of the mold is reached. It’s topped off and leveled, then the next panel is constructed. Construction consists of a 6” exterior rammed earth, 6” polyiso insulation and 6” interior rammed earth, giving the entire construction an over all R value of around R-50. The roof consists of Thermapan SIPs panels, with an R-value of 40 plus the metal roofing material.
The home’s walls are now finished, but the first floor still needs to be constructed, then the windows, doors and roof. I can’t wait to see this house when it’s fully put together.
Sylvia’s home is the first of many rammed earth structures to be built by her company, Aerecura. For more information on rammed earth buildings, please contact Sylvia Cook at firstname.lastname@example.org, or, see her Facebook page.