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Building Design

Green Building Materials
20110504-RD-LSC-0474 - Flickr - USDAgov Material selection is full of trade-off decisions, and effective strategies vary widely based on your goals and situation.  Sustainable materials can mean many things, and this page explains some considerations besides the materials’ energy performance.

As discussed on the Resource Use and Buildings page, good thermal performance of the materials in the building envelope can help the building save energy and is usually the most important factor in building material selection (for example, insulation or thermal mass).  

Lifecycle Assessment is the most thorough way to determine the environmental impacts of your building materials. However, LCA can be very costly, varies project-to-project, and is not yet extremely prevalent. Instead, the building and building products industries have a host of measures and “certifications” for green building products. BuildingGreen’s Green Building Product Certification Guide is a fantastic resource for understanding this (sometimes intentionally) complex world.
 
The following is a quick rundown of factors about how the material is produced and disposed of that can be important to consider.
 

Recycled Materials

photo: Jeremy Faludi

Steel recycling plant, with cranes sorting scrap

Materials using recycled content not only require less virgin resources, they also use less energy and chemicals to process.  For instance, recycled ("secondary") aluminum has 90% less embodied energy than virgin ("primary") aluminum. 

It is beneficial to both use recycled material, and design your constructions to be recycled as well.

Using Recycled Materials

To use recycled content in your building, call suppliers to source recycled materials.  Be sure to verify the physical properties (strength, stiffness, etc.) of the material with recycled content.  If they are lower-performance, you may need to alter your design to use slightly more material.  This is usually still a net benefit environmentally. 

Perhaps the easiest way to create a large improvement from recycled content is in concrete, because it is used in such large quantities.  Concrete can recycle fly ash from coal-fired power plants, and slag from the blast furnaces of steel production, among other materials.  Be aware, however, that these materials may contain toxins like mercury; if so, they should not be directly exposed to occupants.

Some building materials already have recycled content by default.  For instance, most structural steel contains 90% recycled content, while sheet steel usually contains around 25% recycled content.  Aluminum for curtain walls generally has no recycled content.

Making Recyclable Constructions

Materials are only recycled when the monetary value of the materials is greater than the cost to separate them out from other materials.

To make your building (or parts of your building) recyclable, design for disassembly.  That is, make it easy to separate different kinds of materials from each other.  Some strategies for this include using as few different kinds of materials as possible, using undoable fasteners (e.g. screws rather than nails or epoxies), and using larger assemblies that have greater value than small pieces.

Reused Materials

photo: Jeremy Faludi

Reclaimed wood often requires processing

Reused materials are even more beneficial than recycled materials, because in addition to saving natural resources, they also require far less manufacturing.  However, it may not be zero manufacturing.  Reclaimed wood, for instance, is often planed or otherwise cleaned up for reuse.

You can also make it easy to reuse the materials from your own building by designing for disassembly.  This means using constructions that are easy to separate from each other.


Sustainably Harvested Materials

Fsc-zertifizierung
Forest Stewardship Council (FSC) is the most widely recognized third party sustainable forestry certification.

Sustainable harvesting is the practice of harvesting a resource no faster than it can regrow, so that there is no net depletion of the resource or damage to the ecosystem.  

The most common form of this is sustainable forestry for wood products.  

The proof of sustainable harvesting is generally in third-party certification.  The most widely-recognized and credible international standard is Forest Stewardship Council ("FSC") certification.  

Some tropical hardwoods grow so slowly and are from such delicate ecosystems that there is controversy about whether they can be sustainably harvested while still remaining economical for use in buildings.  You may wish to avoid sourcing these, or perform extra due diligence when sourcing them.

Rapidly Renewable Materials

Rapidly-renewables get many harvests in the same time as one tree harvest

Rapidly renewable materials are those that grow back very quickly.  These can be sustainably harvested at a fairly high rate, so there is less burden of proof for certification as for wood products.

Many rapidly-renewable materials allow many harvests from the same plant.  For instance, cutting bamboo is like clipping grass, and cork trees are skinned of a layer of bark rather than cut down.  

Even some plants that do not provide more than one harvest are rapidly-renewable.  Products made from agricultural waste can qualify both as rapidly-renewable and as recycled content.

These products are generally used for interior finishes, though some buildings have used bamboo for structural elements as well.


Non-Toxic Materials

The toxicity of a material is measured and published in its Materials Safety Data Sheet (MSDS).  However, these documents can require chemistry expertise to understand.

For those without toxicology expertise, some organizations and green building certification systems have created lists of substances to avoid.  Here is once such list, from the Living Building Challenge:

  • Asbestos 
  • Cadmium 
  • Chlorinated Polyethylene and Chlorosulfonated Polyethlene
  • Chlorofluorocarbons (CFCs) 
  • Chloroprene (Neoprene) 
  • Formaldehyde (added) 
  • Halogenated Flame Retardants
  • Hydrochlorofluorocarbons (HCFCs) 
  • Lead (added) 
  • Mercury 
  • Petrochemical Fertilizers and Pesticides
  • Phthalates 
  • Polyvinyl Chloride (PVC) 
  • Wood treatments containing Creosote, Arsenic or Pentachlorophenol
  • (source)

These substances are usually not advertised in products, but can be present as fire retardants, adhesives, stabilizers, refrigerant gases ("working fluids"), and other ingredients.  Some of these substances are classified as Volatile Organic Compounds (VOCs) – which can slowly “off-gas” and can cause health risks in buildings that aren’t properly ventilated (see Indoor Air Quality).

Even materials that do not cause concerns about indoor air quality for the building's occupants can still carry toxicity risk for construction workers and manufacturing workers.  Some materials can also leach toxins to groundwater when they are rained on.

Manufacturers are starting to communicate more about the presence of VOCs in their products (like paints and composite wood products). However, some due diligence is required to ensure harmful chemicals and VOCs are not present in the products you source. 

In addition to lists referenced above, the health impacts of specific building products are becoming easier to understand and compare because of industry efforts like the Pharos Project  (from the Healthy Building Network).

Local Materials

500 mi (800 km) radius around Seattle, Washington, USA

Local materials are any kind of material grown or manufactured within a certain radius of the building site.  They are also called "regional" materials, because the radius is often large, such as 500 miles (800km).

The goal of local material use is to avoid the ecological impacts of transportation, and to support local economies.  For most materials, transportation is a much smaller impact than resource extraction and manufacturing, so it is a low priority environmentally (source – Journal of Green Building: Winter 2012, Vol. 7, No. 1).  

However, local materials’ benefit to local economies can be significant.  One of the only ways green building certifications encourage local economies is by giving credit for local materials. 

Other lifecycle considerations

  • High structural performance, being strong but lightweight.
  • High durability, giving the building a long life.  
  • High acoustical performance, absorbing or blocking sound for better occupant comfort.  (This helps lengthen building lifetime and increases use.)

For short videos that explain some material selection considerations, see: Environmental Properties of Materials and Physical Properties of Materials (which use product design examples).

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Sustainable Design

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