Sustainable Elements - Steel vs. Wood

Metal in commercial buildings are commonly used for structural framing. In residential homes, it seems wood is king – but should it be?

This debate over which one is better, wood or metal has been going on for quite some time, with no clear winner.

Wood is a renewable resource it is recyclable, biodegradable and less expensive than steel. It has a lower embodied energy than steel. In this definition from Wikipedia - embodied energy is the sum of all the energy required to produce goods or services, considered as if that energy was incorporated or 'embodied' in the product itself. Building sustainably requires being just as diligent in picking the products while considering the impact on the environment in making the product. Both the steel and wood industries have had environmental challenges, e.g.- the clear cutting of forests and strip mining iron. Both industries have made improvements in helping the environment recover. The wood industry is adopting the best practice standards developed through the Forest Stewardship Council. Around the world, steel production is changing to decrease the amount of CO2 emitted, energy used to produce and replanting areas mined.

It’s true that wood is not a thermal conductor like steel, wood acts as a thermal bridge which means exterior and interior cladding can go up right against the wood with out any insulation between. However with the proper insulation and thermal breaks, the conduction of steel can be easily mitigated.

So, we know the good things about wood above, now let’s look at some of the cons:

• Wood has been on the planet for about 30 years before it is incorporated into a home.
• As wood dries, it twists reducing its structural integrity.
• It is biodegradable, and is consumed by pests that eat organic material – termites, fungus, etc…
• Three wood studs do the job of one steel stud.
• Wood absorbs moisture promoting mold growth and dry rot when leaks occur.
• Wood burns at low temperatures.
• Wood is not earthquake resistant – it bends, snaps and fractures
• While wood can be recycled, it is limited in its reuse for structural uses.

Wood has been used for centuries as the primary framing structure for buildings in the U.S. It is readily available and easy to use. Using certified wood that comes from managed forests is important in the broad scope of building sustainably.

Is there something that is better? We think so. At Healthy Buildings Technology Group, we build our framing structures with light gauge steel, technically known as cold-formed steel (CFS). CFS is more expensive than wood however we use less steel than wood. Still the cost of steel runs about 3x the cost of wood for the same size member. One would think that steel would be impractical to use for building a home, but the opposite is true. "A shorter construction time will reduce the hard costs of the project by reducing the general contractor's project overhead or general conditions, typically in the range of 8-12% of the total project costs or savings in the hundreds of thousands." (quote from Steel Framing Alliance website).  The way we build – we take the money saved in labor and put that money into green features for the homeowner.

The benefits of building with steel offset the cons of building with wood:

• Steel is a new material when it reaches the home and includes considerable recycled content.
• It is not organic, therefore it is not consumed by termites, mold or fungus.
• It is resistant to fires of low temperature.
• It is structurally solid and resistant to earthquakes.
• It does not absorb moisture or rust because it is galvanized.
• Steel can be recycled and can be reused for structural intent.

While embodied energy studies the making of a product, I can’t seem to find the durability factor online.  Some might disagree, to me the more important factor to the environment is how long something lasts before you need to address replacement or repair.

When shopping for a home several years ago, the number that had structural problems struck me. There was dry rot damage in bathrooms and kitchens, in roof eaves, in window sashes, rooflines that were sagging, termite damage in foundations and mold in a lot of places. These were homes that were at least 40 years old. Shouldn’t this big investment last more than 40 years without losing its integrity?

The benefits of steel for durability, structural integrity and speed of build, outweigh the benefits of building with wood. So at our company – Steel is the winner!

Some useful websites:

http://www.steelframing.org

http://us.fsc.org/

http://www.chinamining.org/News/2012-08-16/1345098010d58725.html

Lisa is the Vice President of Business Development at Healthy Buildings Technology Group. She is a student at the San Francisco Institute of Architecture, currently studying for a Bachelors Degree in Green Building Business and Project Management. She may be contacted at lisa@hbtg.com HBTG is an early phase company specializing in creating homes, classrooms and commercial developments to be high performance, affordable and built faster than conventional construction by utilizing their OTechnology system of hybrid construction. To learn more visit, www.hbtg.com