Refer to the following reading source to learn about the sustainable choices in building materials and some criteria of their selection.
This chapter takes a tour over the key material classes used in buildings. There are conventional choices and some alternatives. As you read, take note of pros and cons of switching to "greener" alternatives.
Karolides, A., Chapter 2. Introduction to Green Building Materials and Systems (pp. 27-66), in Green Building: Project Planning and Cost Estimating, RSMeans, John Wiley & Sons Inc., 2011 [available online through PSU library system].
What to pay attention to in Chapter 2:
On pages 27-30, you read the general discussion on the existing problem with construction materials which justify the goals and criteria for choosing sustainable materials. Some of the important metrics used to classify and to characterize the materials are embodied energy (explained on p.29), durability, reuse/recycling potential, and quantified impacts on the environment and human health. Read carefully the summary on p.30, which provides a definition of sustainable building materials.
On pages 31-37, you will go through the list of the most important classes of materials used in buildings. These include: concrete, masonry, metals, wood, plastics, and composites. Scan through to learn about the typical uses of those materials.
Further, on pages 37-51, we consider different functions materials perform within the buildings - insulation, moisture protection, vapor diffusion and air flow retardation, waterproofing, ventilation, roofing, providing openings, surface protection, and decoration. The text overviews the material alternatives that exist for fulfilling those functions. This is a good background read for anyone who is not very familiar with the construction industry.
Pay attention to special metrics (R-values, U-values) used to characterize insulation materials since those are related to energy efficiency of the building. The higher R-value typically indicates a higher insulating power of a material. Be careful however checking the units, as SI and US systems work on different scales. Also, specific R-value that is a characteristic of a material is different from the total R-value of a building structure, which takes into account the thickness of insulation. You can find an additional explanation on this R-value (insulation) Wikipedia page. The values given in Figure 2.1 of the textbook are given per inch of thickness.
Pages 51-63 of the text review different types of equipment used in buildings. This is very general review; just scan through it quickly.
Pay more attention to pages 63-64, which describe less conventional green materials (with low embodied energy). Think what the pros and cons of those natural alternatives are and where those materials can be practically used.
As you can perceive from this reading, one of the overarching objectives here is to select materials that have high degrees of renewability, reusability, and durability and at the same time have low environmental impact and low embodied energy.
How would you guide your selection? The principles of selection of alternatives discussed in Lesson 4 of this course apply here as well. The process may involve lifecycle analysis for some of the materials and also multi-criteria analysis to ensure the highest feasibility and lowest impact.
Sometimes, it is not easy to make a definite conclusion about the sustainability of particular materials. The question of sustainability requires wider thinking, which not only describes the material nature, environmental properties, and possible impacts. Sustainability also assumes identifying the specific fate of that material in a particular locale.
For example, if we consider refractory (fired) bricks as a common construction material, would those be a sustainable choice for construction? It really depends on a wider view on material lifecycle. Bricks are produced from extracted earth materials (such as clay) by firing in a furnace. Energy is needed to heat that furnace. In one case, if we burn coal to fire furnace to make bricks, it does not look like a sustainable production. Coal is a fossil fuel (non-renewable), and burning creates significant carbon emission, so this makes brick production apparently not a sustainable choice. But can that furnace be heated using a renewable energy source? For instance, can we use an electric furnace with electricity produced via solar power generation? Without going deeper into feasibility of that choice, we can immediately see an opportunity to make this process sustainable. On the other end of the story, if the building gets demolished, where do the bricks go? If they contribute to deconstruction waste and are hauled to the dump, non-sustainable practice results. But if there is a plan of responsible demolishing, and if we know that those bricks will be separated from other waste, shipped to the processing facility around the corner, crushed, and re-used as new bricks or as coverage for the jogging trail in the town park, we have a much better feeling about it.
The routes defining the material fate should be outlined at the planning stage, and appropriate system analysis should help with that; and further, the material lifecycle should be regulated according to that plan. That said, sustainability is not so much about materials, but more about design and managing strategy. Also, sustainability system usually has wider boundaries than the building itself, so sustainable buildings cannot be assessed apart from their infrastructure.
Lifecycle building is known as design for disassembly and design for deconstruction. This innovative approach encourages creating buildings that provide resources for future buildings.
The lifecycle building initiative was catalyzed by a number of problems. According to U.S. EPA:
- more of the 100 million tons of building-related construction and demolition debris are sent to landfills in the United States each year;
- construction and demolition debris comprises about 40 percent of the solid waste stream;
- reusing building components reduces the energy and greenhouse gases emissions associated with producing and transporting building materials;
- between the years 2000 and 2030, an estimated 27 percent of existing buildings will be replaced, and 50 percent of the total building stock will be constructed.
Lifecycle building approach implies easier building material recovery and reuse thus reducing energy and resource consumption.
Check Your Understanding:
Which of the following are keys to sustainable use of building materials?
(a) Capacity to be recycled at the end of the building lifecycle
(b) Low toxicity towards humans
(c) Low embodied energy
(d) Local manufacturing or acquisition
(e) All of the above
Click for answer.
When we say that the embodied energy of concrete is 1.9 MJ/kg and the embodied energy of plastic is 90 MJ/kg, what does that mean?
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That means that all processes that result in the production of 1 kilogram of concrete have used 1.9 megajoules of energy; and 90 megajoules in case of plastic. Embodied energy is a kind of accounting measure to estimate the environmental cost of a product or material. Materials with lower embodied energy put less load on the environment.
If fiberglass panel has the R-value of 2.5 and straw bale has the R-value of 1.45, which of these two materials would be preferential as a thermal insulator from the standpoint of heating-cooling efficiency and related energy savings?
Click for answer.
Fiberglass panel has a higher R-value and therefore has better insulating properties. However, be careful relying on R-value alone for decision making because it only considers diffusive heat transfer with no air pressure difference.