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ALTERNATIVE BUILDING MATERIALS, THE
EMERGENCE OF STEEL IN RESIDENTIAL CONSTRUCTION
Holly Najarian
FP 570 fall 1999
Professor J. Barnett
CONTENTS
· Introduction
· Traditional Residential Construction
· Steel Framed Construction
· The Advantages of Steel
· Barriers to Widespread Acceptance and Use
·
The Future of Steel in Residential Construction
For centuries home builders in the United States have
made wood their material of choice because of its satisfactory performance,
abundant supply, and relatively low cost. However, recent increases and
unpredictable fluctuations in the price of framing lumber, as well as concerns
with its quality, are causing builders and other providers of affordable
housing to seek alternative building products.
This is the introduction to the second edition of the
Prescriptive Method for Residential Cold-Formed Steel Framing. The members
of the National Steel Alliance and the American Iron and Steel Institute would
like that referenced alternative building product to be Steel. They are making
every effort to make steel the most logical selection of new homebuilders and
architects of residential construction. The many benefits of steel over the
traditional wood frame home would seem to make this an easy choice, but the
industry and modern day consumer is not so easily won over by facts and
statistics as the steel industry would have hoped. However, the benefits
provided by steel frame construction and the supporting statistics do provide a
solid argument to support the selection of and emergence of steel as the favored
material of new home construction.
There are many similarities in the construction of steel
and wood frame homes. The foundations, roofing, exteriors, flooring and the
piping and wiring runs for plumbing, ventilation and wiring are all areas where
the methods are similar. However, there are many areas that differ greatly.
These areas are where steel provides a clear advantage over the standard
constructed home. To look at these areas we must first examine the typical
construction of a wood framed residence.
Most single family homes in existence are of standard
frame lumber construction, Type V (frame) plank and beam as defined in the
National Fire Protection Agency (NFPA) 220 Standard on Types of Building
Construction. The most common construction methods in use today for
residential projects are the Type V, where larger main structural members are
used in place of many smaller members, or the "Platform Frame Construction". For
platform frame construction, the framing of the structure is similar at all
levels. The majority of the structure is made up of 2 inch by 4-foot pieces of
lumber, 2-by-4s. The bottom plates of the building are constructed of 2-by-4s
laid along walls and nailed through the subfloor into the joist headers. Studs
of 2-by 4 lumber are nailed upright from the bottom plates. They extend to the
base of the floor above, where they are topped with horizontal sets of 2-by-4s,
called double top plates. In load bearing walls, the studs are notched for let
in strips of light lumber, which function as braces, to limit sway. Then in most
cases, fire-stopping material is placed between the studs, joists or rafters.
Advances in mass production methods have allowed the
construction time of a home to be reduced drastically. Prefabricated wall
sheathing and framing can be constructed in units and assembled quickly on
scene. Other sections may include constructed sheathing, bottom plates,
insulation board and other construction pieces or complete walls. The pieces are
then put into place and nailed for permanent fixture.
The exterior walls of a conventional residence support
the majority of the weight of the structure. The walls are closed in and a
façade is placed over the exterior to provide the finished appearance of the
home. The facade is placed over the closed in exterior walls. This is done in
standard wood frames by the nailing of sheathing over the studs. The sheathing
can consist of lengths of flat lumber, sheets of plywood or composition panels.
The sheathing provides insulation to the home and provides additional strength.
The home is then protected from moisture by the application of vapor barriers
over the walls. These prevent the passage of condensation that could do
significant damage to structural members. (Compton’s Encyclopedia)
There are several different methods of framing used in
light construction. The most common used in the construction of residential
construction is wall-bearing framing. This type of construction allows the
weight of the building to be carried on the exterior walls or a combination of
the interior and exterior walls. This allows the builder and designer the
advantage of wide-open spaces within a residence with fewer interior walls
required for construction. It also provides the future potential of easier
remodeling or updating of the residence if desired. The basic joining method
used in steel frame construction is the joining of pieces by welding, bolting or
riveting. This method provides a distinct advantage to the joining of pieces by
nailing as is used in wood framed construction. The steel connections are less
susceptible to vibration, movement of the base material and weather induced
loads.
Steel has the highest strength to weight ratio of any
building material, twenty-five times greater than wood. (The Steel Alliance,
Building to Battle Earthquakes.) Because of this strength, and the inorganic
nature of steel, it does not warp split or twist. Also because the steel member
is an inorganic material, it will not swell or shrink in reaction to moisture
content. This allows an architect to use true dimensions when designing without
the need to compensate for the wood’s shrinkage. Additionally, because steel is
dimensionally stable and will not "settle" as wood does in new construction dry
wall cracks or shifting walls over time including the induced strain put on
other structural members is non-existent.
The inherent strength of steel makes it a natural choice
for construction in earthquake prone regions of the country. The manufacturing
process insures the consistent strength of steel from piece to piece as opposed
to wood that can vary within lumber grade and species. The characteristics of
steel include a higher ductility than wood. Allowing it to bend. In an
earthquake, the steel would absorb more of the stresses and be less prone to
cracks or breakage. As stated previously, the connections within a steel frame
structure are less susceptible to pull out or failure and will not weaken over
time because of material shrinkage or the decrease in strength of the base
material due to age.
-
The largest fire safety selling point of steel framing
in comparison to wood is that the steel framing is non-combustible. It does
not burn and will not provide additional fuel to the fire. The structural
members will deform and will reach a critical point where eventual
failure will occur but they do not provide additional fuel, nor perpetuate the
fire growth. Residential construction regulations are the least restrictive of
the building codes. However, all major structural members and materials of a
new construction are required to be fire rated. The fire rating is based on
standardized tests and calculations conducted by the American Society for
Testing and Materials (ASTM). Additional information regarding the fire rating
of structural members can be found under the ASTM Standard E-119 or within the
National Fire Protection Association SFPE Fire Protection Handbook.
Because of the standardized production methods of steel, the fire resistance
rating provided by the structural members is consistent throughout the
structure and does not fluctuate from piece to piece. That can often be a
problem in wood construction with different quality of wood members.
The insulation materials used in steel construction
are a vital concern to the builder and consumer because of their cost and
their necessity in steel construction due to the conductive properties of
steel. In addition to the main structural members, materials used for
insulation of these members are also put through standardized tests and fire
rated under ASTM E-119. As discussed in the NFPA SFPE Fire Protection
Handbook:
- The basic intent of the various methods of
protection is to reduce the rate of heat transfer to the structural steel.
This is accomplished by using insulation, membranes, flame shielding, and/or
heat sinks.
- Insulation of the steel is achieved by surrounding
the steel with materials that preferably have the following characteristics:
- Non-combustibility and the added attribute of not
producing smoke or toxic gases when subjected to elevated temperatures;
- Thermal protective capability when tested in
accordance with the standard fire test, ASTM E-119; Product reliability
giving positive assurance of consistent uniform protection
characteristics;
- Availability in a form that permits efficient and
uniform application;
- Sufficient bond strength and durability to
prevent either dislodgment or surface damage during normal construction
operations; and
- Resistance to weathering or erosion resulting
from atmospheric conditions.
Approximately 1.1 billion dollars a year in damage is
caused by termites within American residences. This damage is devastating to
homeowners and is not usually covered in typical home insurance policies.
Termite infestation is common in warm wet regions of the country and can cost a
homeowner thousands of dollars even before it causes major structural damage.
The steel-framed construction is impervious to infestation. The main cost to the
homeowner is when the main structural members of the home are effected by
infestation. So in steel homes the auxiliary or aesthetic structure may be
damaged, but the main structural members will remain unaffected saving the
homeowner substantial financial impact. (The Steel Alliance)
Steel is North America’s most recycled material. More
than 67 million tons of scrapped steel, approximately 64%, are recycled every
year, more than all other recycled materials combined. The steel framing
production process uses a minimum of 25% recycled steel, and all new steel that
is produced contains recycled steel. (Steel the Clear Cut Alternative for
Building Homes) A recent study conducted by Baylor University assessed the
benefits of using steel framing in residential construction. The study
determined that steel should be recognized as a "green" building material based
on economic and environmental criteria:
The study concludes that the steel
industry is increasingly producing materials for the residential market that
are cost competitive, performance enhancing, and environmentally advantageous.
These products should be viewed by environmentalists as more environmentally
compatible than they have been viewed historically because the steel industry
has actively improved its environmental record in mining, processing and
recycling steel. In comparison the timber industry, while emphasizing its
"green" image, has problems associated with the environmental impacts of
growing harvesting and replanting operations, which do not show true evidence
of sustainability. Plantation style lumber production and pest management
policies have tarnished the timber industry image.
The general findings of the report included the
projection that the costs of lumber will rise in the future due to costs paid by
the industry for impacts to wildlife, soil, water, and other resources. Also,
that the cost of timber will continue to rise because of increased land costs,
sustainability issues, and increased need for pest control. The cost of steel in
contrast has remained stable and is predicted to continue to remain stable in
the future. The report also discussed the effects of pollution from the timber
industry due to run-off and clear cuts of timber areas whereas, the steel
industry has made tremendous improvements to reduce the pollution produced from
mining, processing, and the actual steel making process. Finally, the report
compared the waste produced from the timber industry to the steel industry
produced waste. The timber industry produces waste from materials productions
and manufacturing, construction site waste, and demolition waste at the end of a
building’s life cycle. The steel industry however produces minimal waste. What
is produced from the industry is has scrap value and is readily accepted by
scrap yards and used as recyclable material.
Significant strides have been made within the steel
industry in the arena of not only waste limiting and recycling but energy
consumption during the manufacturing process as well. The energy consumption
during the last two decades has been reduced by almost one-half. It is obvious
that the production of steel requires a tremendous amount of energy. In blast
furnace production temperatures of over 3300 degrees are required. The energy
consumption is the most costly purchase required by the industry for the
production of steel. It is not only advantageous to the environment but to the
industry itself to reduce these tremendous costs. The industry has been
proactive in seeking energy saving approaches to the production process. Among
the concepts adopted and employed by the industry is the use of waste heat and
cogeneration. Additionally, the progression of technology has prompted the use
of oxygen furnaces vice the open-hearth furnaces used previously. Constant
improvement is sought out by the industry that has worked in collaboration with
the Department of Energy to reach new solutions and to adopt new processes.
The steel industry has accepted that it has formidable
barriers to overcome before steel can be widely accepted as the material of
choice for residential construction. The first major barrier is that the
industry lacks the basic infrastructure. Many regions of the country have not
established a distribution network to reach the areas of residential
development. Areas where this structure has developed are in the states of
Florida, California and Hawaii, due to the resistance of steel to hurricane
winds, earthquakes, and termite infestation these areas were the first to accept
steel on a limited basis. This approach of introducing steel to the consumer on
a partial basis seems the easiest for the consumer to accept. This is basically
introducing the consumer to the use of steel for the interior non-weight bearing
walls and for floor systems that are slowly gaining wide acceptance in the
residential market. These floor systems were the first to employ a solid
distribution to the market. (AISI)
Education and qualified framers that are capable of
working with steel are not available in many areas. Intensive and aggressive
efforts have been undertaken by the Steel Alliance to indoctrinate the labor
pools of carpenters unfamiliar with the methods of steel framing. The commercial
market that has used steel for many years is familiar with working with steel
but lacks the experience of residential framing. The industry must provide
training to both of these groups that have been unable to enter the new market
of residential steel framing.
Another major hurdle to cross is to convince the
builders and architects that steel framing is economically viable. This includes
the consideration of time, labor, the effect of availability to the price, and
the long-term concern of cost to operate the home as a secure and comfortable
home. This concern is mainly the concern held by builders and architects that
the thermal performance of steel will result in substantial costs to the
consumer. It is a well-known fact that steel is a much better conductor of heat
than wood, on the average of 400 times more conducive. This could in some
applications, translate into substantial costs for heating and cooling the home.
The industry asserts that this concern can be quickly nullified by the proper
application of high level insulation and the design of thermal breaks within the
original design. As discussed in the report from Baylor University, "Designing
for efficiency may be more costly than using the lower priced building material;
however, from a life cycle perspective, total costs will usually be lower
because the long term benefits will continue over the life of the home." In the
long-term comparison this cost is balanced by the other benefits of steel over
wood and will not impact the end user.
As Don Moody, the President of the North American Steel
Framing Alliance (NASFA) discussed in one of his organization’s recent
newsletters, one of the biggest hurdles to overcome is the development and
acceptance of industry standards for use of steel in residential applications.
Presently because there is not widespread acceptance by regulatory bodies, each
home is designed and examined individually which costs the builder substantial
time and money. This cost is passed along to the consumer and is not a cost that
the consumer or the industry is willing to accept. There is a focused effort to
educate code officials to the applied use of steel and the acceptance of
industry standards for its application in residential use. The industry has
developed the Prescriptive Method for Cold Formed Steel Framing. This
standard is currently in its second edition, but plans include its expansion to
include additional loading conditions and the inclusion of these load
tabulations to accepted industry standards such as the Building Officials and
Code Administrator International (BOCA) National Building Code. In addition, the
industry is developing design software to aid in the selection, design, and
application of steel frame members in alignment with prescriptive standards.
"One of these software packages, known as STEEL XPERT, is based on the
prescriptive method and standard stud designators..…The program is set to
greatly shorten the amount of time needed to determine exactly what steel
framing members are needed and how many. It will also provide for an accurate
takeoff and estimate, leaving the user with less wasted material."
The development of widespread acceptable standards as
well as education and appropriate infrastructure are necessary to facilitate the
widespread use of steel framing. In order to do this; the industry has tackled
these issues by studying the emergence of the timber industry from its infancy.
One of the first things that the timber industry did, was the standardization of
framing members. The standardization allowed for the development of prescriptive
codes and the wide acceptance of these within each of the major model building
codes. The prescriptive code allowed the industry to design and build homes
without the necessity of specific engineering review across every aspect of
construction. The goal of which is to obtain building permits using the
prescriptive method in lieu of having to submit the full engineering. This not
only facilitates the regulatory acceptance of construction but also enables the
widespread distribution of standardized products. The industry sees the
progression to widespread acceptance as a series of steps, or dominoes to tumble
as further discussed by Don Moody, the President of the North American Steel
Framing Alliance:
You can begin to see the dominoes: standardized
framing members> prescriptive methods> building code adoption> ease of plan
check approval> and inspection processes> rules of thumb for local framing
practices> local inventories of members used per those local rules of thumb>
development of productivity enhancing tools and accessories> takeoff and
estimating software> widespread knowledge and use of framing products.
Although a simplified version of the process, each item affects the action of
the next.
Five years ago the steel industry entered into the
residential framing market; initial predictions by industry members had hoped
for an optimistic 25 percent of the new home market to be framed in steel by
1998. While the current numbers fall far below their initial projections,
approximately 3-6 percent, the numbers are increasing. The industry has
developed a clear-cut agenda of where they want to be in the future, and what
hurdles they need to clear to get there. In a recent newsletter of the NASFA the
Major Barriers and Strategic Objectives of the organization were outlined:
Major Barriers
- Cost of construction
- Lack of Infrastructure
- Industry standards
- Thermal performance
- Consumer Preference
Strategic Objectives
- Maximize Current Opportunities
- Reduced Cost Of Construction
- Develop Infrastructure
- Implement Standards
- Improve Thermal Performance
- Create Consumer Preference
- Develop Government Support
- Develop and Maintain Liaisons with Stakeholders and
Influencers
It is obvious that steel framing provides numerous
advantages to the standard residential wood framed construction. While there are
several concessions to these advantages with the constant effort of the industry
to minimize the costs and to develop new methods of framing unique to the
residential market these concessions can be compensated for. From an
engineering, safety, and long term financial standpoint steel should become the
best choice for architect, builder, and consumer when it comes to new home
construction.
REFERENCES
- American Iron and Steel Institute (AISI), Significant
Strides in Energy Efficiency.
- American Iron and Steel Institute (AISI), Steel
Framing-The Best Answer to Quality, Safety and Value in Houses.
http://www.steel.org/facts/power/roots/.html
- American Iron and Steel Institute AISI), Fire
Resistance Ratings of Load Bearing Steel Stud Walls, 1981.
- Compton’s Encyclopedia, Building Construction.
Compton’s online Volume 3
- Department of Environmental Studies, Baylor
University: Steeling The Residential Market: An Economic and Environmental
Assessment of Steel Framing for Residential Construction.
- Incropera, F., & DeWitt, D. (1996). Fundamentals
of Heat and Mass Transfer New York: John Wiley & Sons.
- National Fire Protection Association. (1997).
9. National Fire Protection Association. (1995).
- Post Gazette.com. Steel frames haven’t caught on with
homebuilders…yet.
- American Iron and Steel Institute, Prescriptive
Method for Cold Formed Steel Framing. 1997.
- The Steel Framing Alliance: Recycling Facts and
Figures.
http://www.steelframingalliance.com./facts/recycle.html
- The Steel Framing Alliance: Steel Framing Myths.
http://www.steelframingalliance.com./why/myths.html
- The Steel Framing Alliance: Benefits of Steel
Framing.
http://www.steelframingalliance.com/why/benefits.html
              
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