Insulated Rammed Earth – Beautiful, Natural, and Functional, by Steven Gray
Architect Terrell Wong, owner of Stone’s Throw Design, and builder Sylvia Cook, owner of Aerecura Rammed Earth, presented their amazing work with insulated rammed earth buildings at the North American Passive House Conference in Chicago.
Too often high-performance means high-tech, with many Passive House walls incorporating space-age products and complex detailing. This look at the history, simplicity, and natural beauty of rammed earth was an excellent contrast to the world of high-tech building; and served as a reminder that natural building and high-performance can and should go together.
The project featured in the presentation is located in southern Ontario and incorporates the province’s first insulated rammed earth wall. The walls are comprised of 6″ of rammed earth, 6″ of polyisocyanurate insulation, and another 6″ of rammed earth. The inner and outer wythes are structurally connected with steel rebar; and additional steel reinforcing is rammed in as required by the structural engineer. The tallest wall built on the project measured 24′ high.
For those who are not fans of polyiso, Terrell reported that Tapial Builders are installing 15” of mineral fibre. Other innovations include the use of fibreglass reinforcing in place of steel and a split footing.
Sylvia and Terrell walked us through the building process. The earth was sourced from a nearby gravel pit; it is all-natural, abundant, economical, and locally available. The earth is “stabilized” with approximately 6 percent Portland cement and a water-repellent additive is incorporated into the mix. On site, all the components are combined using a skid steer and then rammed into forms using a hydraulic tamper. A hand tamper is used in more delicate or difficult-to-reach areas. The walls go up in 6″ lifts and can be increased in height by about 4 feet a day. Electrical conduit and plumbing runs can be rammed into the walls as well. The geometry of the building was cleverly designed such that only four forms were required to build all the walls.
The results are stunning. Dyes are added to the earth, giving the walls a striated, sedimentary look. Objects such as shells and fossils can be rammed in for enhanced visual interest. The material is textured and has a tactile element to it that is reassuring in its solidity. The completed assembly combines all the functions of a wall – interior finish, insulation, exterior finish, weather resistance, structure, air barrier, moisture management, thermal mass, and aesthetics – all into one process!
But how does it perform? After living in the home through a cold Ontario winter, Sylvia was able to share her experiences. The home’s only heating system is a “MacGyvered” hydronic radiant loop supplied by the domestic hot water tank. Sylvia reports only having to turn it on after extended periods of cold, cloudy weather. The home’s excellent passive solar design combined with the thermal properties of the insulated rammed earth keeps the interior comfortable as long as there is sufficient sunshine.
Terrell and Sylvia plan on conducting additional research to quantify the hygrothermal properties of the wall and assess how accurately the assembly can be modelled in WUFI. On an upcoming affordable housing project, they will embed temperature and relative humidity sensors at various depths in the walls to monitor performance and gather data for their research.
To read more about this amazing material, check out their websites:
By Steven Gray, Construction Manager at Greening Homes