The Material Ecology of a House: Foundations

I spent a lot of time expanding my awareness and knowledge of what I thought to be tangential and adjacent subjects to architecture during my doctorate studies with architectural sciences. There was an emphasis on the discipline of ecology, with its origins in biology and the study of the interrelationships between living systems – symbiotic and opportunistic, cause and effect, and natural food chains and environmental forces that influence the trajectories of various plant and animal species. From this ecological basis, a translation into built ecologies was made, not in a metaphorical way but in a methodological way. The ecology of a building is the interrelationship of biotic and abiotic resources, energy, and byproducts from the process of designing, making, and inhabiting the building. The material ecology of a house focuses on these relationships that are specific to the materials utilized in construction and interiors.

There is a series of variables to consider when identifying the scope of a home’s material ecology. The first is the house itself, which is a building that is made from materials and assemblies of various components and systems. The materials are constituents, which are sourced from different places (soils, plants, minerals) and processed with different methods (heating, melting, cutting, treating). The environment also plays a role in providing the biogeochemical resources for the materials that are sourced from the earth (stones, ceramics, metals) and forests (wood products). There is labor involved in all stages of design, manufacturing, and construction, which takes on different forms – human, animal, machine. There are also chains of material resources, design, labor, and manufacturing of the specialized equipment that is used to source and produce building materials. The labor resources and forces that create the building at all stages accumulate to a large quantity of people, time, machines, and equipment involved. 

Whether you are living in a relatively new house or a very old one, the material ecology can be assessed from foundations, exterior walls, roofing, and interiors. Very old houses tend to have a material ecology that is closely connected to the natural resources of the region and early construction techniques. Newer houses in the United States have become a little more uniform in the material systems used for construction, so the material ecology has broadened and can be more difficult to trace unless you are part of the General Contractor team.

Beginning with the foundation systems, the preparation of the land requires grading and possibly excavation. Moving earth around requires heavy machinery such as bulldozers, backhoes, and excavators. Just like automobile manufacturing, these machines can be produced all over the world, including Europe, China, Russia, UAE, Japan, India, South Africa, and the US. Construction equipment manufacturing companies are often the same companies that produce agriculture and farming machinery. The cost of construction machinery is extremely high, with bulldozers ranging from one to two-million dollars for example. This is demonstrative of the design and manufacturing labor that is required for the specialized machinery, as well as the resources for components and parts. The supply chain for construction machinery is part of the material ecology for building a house. The carbon footprint of building the house encompasses a percentage of the output from the machinery manufacturing. Since metals and rubbers are most commonly employed in these machines, the carbon emissions during production are substantial. Any soil that is excavated will need to find a new placement - sometimes this can be an on-site fill location, otherwise the removed soil will need to be hauled off-site, requiring more material transport emissions.

Once the earth is ready to receive a foundation, the concrete can be poured into formwork, which is often created with wood boards, but sometimes with metal. Concrete is a combination of Portland cement, aggregate (crushed rocks and sand), and water. The cement off-gases carbon dioxides (CO²) as it cures, so the amount of concrete used for construction has a direct impact on the home’s carbon footprint. A 3,000 square-foot single-story house without a basement will have a foundation slab that requires around 50-cubic-yards of concrete. The cement in the concrete mix, which serves as the primary binding agent for concrete, produces carbon dioxides during kiln heating in the manufacturing process – both from the use of fossil fuels to heat the kiln, and from the release of CO² during calcination of the minerals. There are also CO² emissions from the transport of the concrete to the construction site.

In addition to the concrete itself, concrete foundations require steel reinforcing to account for tensile forces. Steel has its own embodied carbon footprint due to the transport of source minerals, manufacturing requiring high heat energy processing, and transport to site. Most foundation designs will also include additional gravel or aggregate as a bed over compacted soil for the preparation of the concrete pour. Finally, the foundation will include a waterproofing vapor barrier as well, which is made of plastics from polymer synthesis processes that can be energy intensive and difficult to recycle. However, the vapor barrier is necessary for the health of the home’s interior, preventing moisture from transporting into the slab and preventing ground radon and other potentially harmful vapors into the house.

While concrete is known to have an environmental impact due to its carbon emissions, it is a long-lasting and durable building material. It also contributes less CO² than other building materials on a normalized volumetric basis, but concrete is so widely used in the construction industry that overall it is the number one building material contributing to the industry’s carbon footprint. However, it should also be noted that concrete, when exposed to the air, is a carbon-absorbing material, so it is also helping to reduce some of the airborne carbon dioxides through absorption over time. At the end of useful life of the house, the concrete foundation can be demolished back into aggregate that can be utilized in new concrete mixes. The steel reinforcing can also be recycled for re-use, but it is sometimes difficult to separate these components from the concrete rubble. The new life for the old concrete and steel is part of their life-cycle, and the overall material ecology of the house.

In a future blog, part two of the material ecology of a house will discuss the exterior walls. If you are planning for any new home construction or renovation and are interested in a healthy material ecology, reach out to AIDA, LLC today for a consultation. You can always find more information and healthy home resources at Aletheia Ida Design and Architecture, LLC (AIDA, LLC) at www.aletheiaida.com.