“How do you choose a building material for your house,” you ask. Some time ago everywhere, and in many places today, it was/is a rather simple choice: Take from nature what is locally available and practical for building. However, with the globalised economy and industrial methods of material production and building construction, both the "locally available" and "practical for building" have changed.
Availability and “availability”
"Locally available" more often than not translates into materials that can be purchased and delivered to your building site at an affordable price even if they were produced thousands of kilometres away. Also, the meaning of "available" has changed over time: The industrial production enables us to use quantities of energy, water, chemicals and complex processes that, a couple of centuries ago, would have made some of today’s commonplace materials essentially unavailable because it would have been unfeasible to make them out of what nature has to offer. No one would have even thought about chopping so much burnable wood and going through so much effort needed to make all the steel needed for a steel-frame house, when you can make many more houses with the wood itself. In the meantime, with the help of fossil fuels, we have become used to all sorts of different materials without questioning how they are made.
The price of the materials does not reflect their ecological and carbon footprints, i.e. the damage their production and transport cause in terms of climate change, loss of biodiversity, etc., as the damage is paid for by the taxpayers. In fact, the materials that cause great damage sometimes have a lower market price. At the same time, the damage is often invisible on the construction site, either because it seems unrelated, such as climate-change-induced overheating and storms, or because it happens somewhere else, like the pollution of a river or the destruction of a forest in another country. In a globally connected world, however, damage has a way of influencing events far beyond its immediate surroundings and far beyond the present moment. We are currently threatening much of the good that we have co-created as a species, not to mention a big part of life on Earth as a whole, i.e. that which has created and sustained us as biological beings. In addition to ecological concerns and their impact on socioeconomic systems, socioeconomic impacts of material production can be direct, too: Are the materials produced in a way that ensures human health, wellbeing and empowerment? This is an issue that is especially easy to overlook and hard to influence when the production is not local.
Therefore, in addition to advocating a better taxation policy and enforcement of regulations protecting the wellbeing of humans and wider nature, we can, as designers and investors, consciously choose materials with a lower ecological and carbon footprint that were made in a fair and non-polluting way. To do this, we need footprint data, such as in the Inventory for embodied energy and carbon in building materials. We also need to be able to interpret the data, having in mind that it is expressed in energy and carbon per kilogram of material. There will definitely be more kilograms of material in a concrete house than a steel house, and probably more in a steel house than a wooden house. This will often point us towards truly local (or bioregional) materials and towards using earth or plant-based materials such as hemp, straw and wood. In some instances, when it is not hazardous for health, it may even point us towards recycled/upcycled materials.
Practicality and “practicality”
Going back to the original question, we should still consider what "practical for building" means. Faced with the urgency of the need to have a roof over one’s head and with the prevalent building practices in one’s spatial, socioeconomic and cultural surroundings, one is always tempted to take those practices for granted, as something that is not only normal, but also “the result of a long path of progress, improvement and development”, even when faced with the reality of some of the destructive effects of those practices, as outlined above. Building materials that enable, or are able to take part in, such established practices, tend to become as established as the practices and therefore more practical than other materials because they are easy to come by, covered by regulations and procedures, and people know how to both design and build with them. Being used to building practices and to building materials are therefore parts of the same habit, which is further shaped by advertising, the fashion of architectural aesthetics, and the prevalent industrial and professional lobbying. "Prevalent", "affordable" and "within the social norm" are usually the main components of practicality when it comes to choosing building practices in real life.
Even within that range, we can still choose for health and sustainability. If we push the boundaries of the range or go beyond them, we can find additional choices. Some well known experiments are low tech, such as the big rammed-earth Sheppard Theatre at the Centre for Alternative Technology in Wales. Some experiments are high-tech, such as 3d printing of entire houses. Some experiments are combining low and high tech, such as the Conceptos Plasticos bricks made of recycled plastics. And some experiments are being developed in the biohybrid realm, such as those based on growing mycelium. Going beyond status quo sometimes requires more time and effort, and money, invested in acquiring new practices or rediscovering practices that have been forgotten. Sometimes the opposite happens: The alternative to the mainstream can actually save our own resources, but we have to be willing to depart from the norm, which may still feel like a sacrifice.
Nevertheless, the building materials have to be able to resist the loads that we designed into the structural design, which is in turn the result of architectural design decisions. Some materials are better suited for some kinds of loads, some for others. If you want cantilevers or very big spans without posts, you might find yourselves bound to steel, for example. The materials will have to resist all sorts of environmental influences, too. This is specific to the location and includes capillary moisture from the ground, rainwater, snow and ice, thermal expansion, UV radiation, corrosion, reactions with salt, calcification and other chemical processes that may affect function and/or appearance, pests, wind loads, earthquakes, fires etc. Many potential problems, however, can be avoided by design decisions and proper craftspersonship. For example, properly dried wood can often be left untreated if it is not exposed to moisture and if any water that happens to reach its surface is able to drain away immediately. Otherwise, it needs strong chemical protection. Vanity or misguided notions about abundance can lead to design decisions that require very big quantities of materials or the use of strong materials with a very big carbon footprint. On the other end of the spectrum, overenthusiasm about alternatives to the mainstream can lead to issues with durability and maintenance if design decisions fail to take into account the peculiarities of plant-based materials.
Context and intention
The much needed awareness about the consequences of design decisions goes beyond the house to encompass a much wider context around building materials: What is locally and bioregionally available? What is sustainable, healthy and fair during production and transport? What is economically feasible in the short and long term? What is adapted to the local climate, terrain and other site conditions? Where is it sustainable to build at all, and what? What is appropriate for the challenges that the design poses in order to satisfy (true) needs? What is going to contribute to the energy efficiency of the house? What is adapted to the available construction logistics and prowess? What is legally allowed within the jurisdiction? What is safe and healthy in terms of volatile compounds, microclimatic properties etc.? What can bring joy and inspiration to the senses and a sense of connection with nature? What is durable and easy to maintain? What yields well to refurbishment and reconstruction over time? What can eventually be repurposed, upcycled, recycled or composted?
These questions have roughly followed the process of creating a building from the production of materials and the spatial/urban planning to the end of the building’s current use or even lifetime. Building-material choices have to consider all of these questions in advance and simultaneously because, as it happens in architecture, the questions are intertwined – deciding on an answer to one question in isolation would limit the available answers to other questions in ways that might be undesirable. Sometimes, the answers point in opposite directions. For example, there may be abundant stone on the site itself, and using it might be very appropriate for the local climate and the carbon footprint, and yet, it might be extremely expensive to pay skilled craftspeople to work it or even impossible to find them. Another example is thermal mass: timber-frame walls filled with insulation are great in terms of limiting the loss of heat, but are not good for buffering temperature oscillations because they have low (thermal) mass. A possible solution is positioning an extra heavy chimney located mostly within the volume of the timber-frame house. The design process includes negotiating all such situations and finding a solution that is optimal even if it is not perfect.
That is why it is important to approach the design process as a coherent whole and use its initial stages to shape clear and articulate intentions that will guide subsequent decisions, including those related to the choice of building materials. For a person interested in sustainability (as a form of enlightened self-interest, if nothing else), here are a few questions that might come in handy: How do I/we practice dwelling in a way that makes it easier and more enjoyable to regenerate my/our wellbeing and my/our natural and social environments? How do I/we create a place that supports such a dwelling practice? How can a house and the space it encompasses facilitate our communal life and remind us that we are a part of nature? How can a house be the minimal user interface that allows us to be in abundant, inspiring and pleasant contact with nature? How, and with which materials, can we create and build such a house?
To sum up
As a rule of thumb, metals and plastics are to be used extremely sparingly: e.g. metal as roof cover and plastics for waterproofing. Fired clay bricks and blocks are to be used sparingly. Concrete is to be used sparingly, mostly for foundations. Stone is to be used if truly local. Wood and bamboo are to be used if from sustainably managed forests. Earth, straw and hemp are to be used abundantly, in various forms and ways, but with a solid know-how. Recycled and upcycled materials are also good if they do not pose a health risk. It is good to keep an eye out on biohybrid, 3d-printing and nano-technological developments. In the meantime, the fewer the steps between nature and construction site, the better, but then the execution of those steps has to be better too.
Make sure that the spaces are appropriately insulated and that the construction elements are suitably breathable or vapour-proof (depending on the climate and the type of insulation), as well as that moisture cannot enter them from anywhere (the ground, the sky, the sides). Ensure enough thermal mass to balance temperature amplitudes, especially in temperate and hot-arid climates. For hot-humid climates, design for good natural ventilation. The goal should always be to minimise throwing technology or chemistry (e.g., air conditioning or poisonous coating) at problems that could have been prevented by design. Choose materials, building techniques and builders that will ensure quality, durability and ease of maintenance in your particular context. Again, rather than creating problems that have to be solved, choose a site that is well drained, stable, sufficiently protected from the wind, but allowing for good ventilation, with enough sun exposure in the part of the year when that is needed.
However, if truly looking for sustainability, we need to start from integrative spatial planning and see building materials as but one of the pieces of the puzzle that includes the protection of valuable land, the role of the house in the natural and technological cycles of materials (closing loops rather than creating waste), the energy efficiency of spaces, the wider logistics of transport and energy production, and the overarching economic system. There is only so much that a house can do on its own, and we may even ask whether or not a single-family house can be considered sustainable at all. The same goes for striving for energy autonomy of a single house.
Finally, the experience of dwelling shapes our ontological identities and worldviews, which in turn shape our perceived needs and intentions, and therefore the reality we create. The design of the house and the materials we choose and use take part in that process and need to be approached with appropriate awareness, in order to regenerate our wellbeing and the local and global ecosocial environments we take part in. How can a house remind us that we are alive?
I live on the edge of the Pannonian ecoregion, which encompasses a part of Croatia, the country where I reside, and parts of several other countries. The climate is temperate continental, with hot summers and relatively cold winters. Houses are mostly built with reinforced concrete and fired clay blocks. Due to EU regulations, new buildings have to be “near-Zero Energy Buildings,” but cooling is not counted towards the energy consumption of family houses.
The most abundant local plant-based material that could be used for the majority of the house’s envelope is straw, which can be used in the form of straw bales. Straw bales have great thermal insulation properties at one seventh of the carbon footprint of the equivalent (in terms of insulation) amount of mineral wool. Load-bearing straw-bale structures are not permitted by the building code and are prone to stability issues. However, straw bales are allowed as building-envelope walls connected with a wooden load-bearing structure. They can be coated on both sides with clay plaster, which is also abundantly locally available and provides protection from pests, fire and water, while regulating ambient temperature and humidity. Such walls are breathable and provide a pleasant indoor microclimate. In combination with reinforced-concrete foundations and a metal or clay roof with big roof overhangs, timber with straw bales seems to be the obvious sustainable choice hereabouts. However, it is hard to acquire services of the few builders who have experience with such construction, and without proper expertise and meticulous detailing, such houses can have problems with cracks in the earthen plaster and with gaps in the connections between different structural elements, which can lead to cumbersome maintenance. Due to the labour intensive and time-consuming construction, such houses are not cheaper than mainstream houses even though straw is relatively very cheap. Some financial savings can be achieved by investing time in self-building, even though that is not legally permitted.
If obtaining a reliable craftsperson for building with straw is not possible, and sustainability is a priority, it is probably more advisable to go for a lightweight timber-frame house with cellulose and wood-fibre insulation, which is also energy efficient, but has no ambient-climate-regulating capabilities, which calls for some heavier elements in the interior, such as concrete-screed floors or stone fireplaces or earthen partitions and benches (possibly combined with rocket stoves). Such a house can be built very quickly, but the costs are higher than for the mainstream construction. A somewhat cheaper timber alternative to this timber alternative is buying, potentially disassembling, moving and assembling, and then refurbishing an old house made of timber-plank load-bearing walls, which includes a lot of handwork and, most often, the application of pest control and thermal insulation (e.g. cellulose flakes). Refurbishing is, in general, a sustainable approach when compared to new construction, as long as the space can be reshaped to support a sense of wellbeing and be energy efficient.
The “damage-control” option entails going for mainstream materials (concrete, fired clay), but making sure that the house is very energy efficient, not only due to insulation, but primarily due to climate-conscious design based on passive principles. In this ecoregion, that means maximising glazing towards the south in a way that prevents the summer sun to enter the interior, while minimising the glazing on other facades, especially the northern one. It also means designing openings on the opposite sides of the house and near the top of the house, to enable natural ventilation by cross-ventilation and the upward movement of hot air. It is important, however, to bear in mind that spaces are more pleasant if light enters them from more than one direction. Of course, the use of renewable energy for heating and hot water (which can come from heat pumps, solar collectors and – if wood is sustainably sourced – efficient biomass stoves), is of paramount importance. And here, again, we enter the realm of the context that is wider than the choice of building materials.
A potential up-and-coming choice is “hempcrete”, i.e. blocks made of shredded hemp and lime, which can be used for the building envelope in conjunction with a load-bearing timber structure. This is similar to the straw-bale approach, but easier to work with. At the moment, however, there is no local production of such blocks because the overly strict regulation on hemp growing has just recently been eased, and producers and contractors in the building industry are very cautious when it comes to investing in new products and technologies.