Iano's backfill

Complexities of Sustainability

LEED as the Definition of Sustainability
Can LEED Survive the Carbon-Neutral Era (Metropolis, November 2007) discusses the growing acceptance of the US Green Building Council LEED rating system while also considering future challenges to its relevance:

• USGBC claims 40,000 LEED-accredited professionals. The organization has certified only roughly 1000 buildings since its inception.
• A recent study by construction consultant Davis Langdon claims that LEED-certified buildings, at least up to the Gold certification level, need not cost more than conventionally designed buildings. Fiona Cousins of ARUP New York estimates it can cost $100,000 in service fees to document building performance for LEED.
• Until June of this year, buildings could achieve LEED certification without receiving any energy performance points associated with reductions in carbon emissions.
• ASHRAE, in conjunction with USGBC and others, is promoting its Advanced Energy Design Guides which target energy savings of 30% over current national  standards. ASHRAE intends to introduce similar mandatory standards by the year 2012. ASHRAE and the AIA are proposing national legislation that would require new buildings to be fully climate-neutral by the year 2020.

The article also discusses the pros and cons of the LEED "checklist" methodology for defining sustainability, in contrast to more ntegrated approaches to sustainable building design. And the article speculates on the possibility of LEED's broad definition of sustainability, which includes considerations of site and community development, materials and resources, and indoor air quality, being preempted in the future by the need to focus more narrowly on the conservation of water and energy.

Separately, The Battle for Green Building (Springfield Business Journal, 12/11/20067) discusses the Green Building Initiative's Green Globes sustainable building certification program, an alternative to the better know LEED. Though there are many similarities between these two programs, Green Globes is reportedly distinguished by its pending certification by the American National Standards Institute, and its lower implementation cost than LEED.

PVC as a Sustainable Material
The USGBC's February 2007 Assessment of the Technical Basis for a PVC-Related Materials Credit for LEED is the that organization's final report on the contentious issue of the use of PVC materials in building construction.

USGBC has been considering this issue since at least the year 2000. The Assessment looks at four common PVC applications: siding, drain/waste/vent piping, resilient flooring, and window frames. Each is compared with common alternatives, for example in the case of siding, with aluminum, wood, and fiber-cement. Materials are evaluated on a number of bases:

• Conventional life-cycle assessment in which all the resource and pollution inputs and outputs associated with the material-- beginning with its harvesting or extraction and ending with its reuse or disposal at the end of its service life--are considered. Impacts on both human health and the environment are included.
• Extended end-of-life analysis in which potential PVC dioxin emissions from backyard burning and accidental landfill fires are considered. Given the large uncertainties in the data for this scenario, upper, middle, and lower range estimates were evaluated.
• Risk assessments of the adverse human health effects due to exposure to toxic compounds generated throughout the life cycle of the materials.

The conclusion: No single material shows up as the best across all human health and environmental impact categories, nor as the worst.

The assessment's results resist simplistic conclusions. Material rankings vary depending on how environmental and human health impacts are prioritized. In other words, a choice of one material over another may benefit human health while increasing adverse effects for the environment, or vice-versa. Rankings also vary with the product category. Only in the resilient flooring category do PVC products rank consistently higher in both adverse human health and environmental effects than alternative materials (linoleum and cork).

Meanwhile, Schwarzenegger Bans PVC Additive In Toys (Healthy Building Network, October 25, 2007) reports that, despite claims made by the Vinyl Institute regarding the safety of PVC in children's toys, the state of California has passed legislation prohibiting the use of phthalates, a PVC plasticizer, in products intended for babies and children under three years of age. The article goes on to state:

Like the human carcinogens vinyl chloride and dioxin, phthalates are uniquely associated with PVC. It is this triple threat from PVC that distinguishes it as the worst plastic for environmental health and green building. Regrettably, there are still few restrictions on the use of vinyl in green buildings.

Evolving Measures of Material Sustainability
Shedding Light On The Pharos Project (Eco-Structure, December 2007) describes the Pharos Project, an ambitious building products rating program under development by the Healthy Building Network.

The Pharos Project is touted as a database of building materials intended to allow a more comprehensive and sophisticated evaluation of the sustainable attributes of materials than is currently offered by other rating systems. Its unique framework covers a broad range of health, environmental sustainability, and social justice criteria.The Project will also host a Wiki and online forums.

A visit to the Project's web site leaves one questioning whether the Project is alive and well. The most recently dated content appears to be from November of 2006. According to Eco-Structure, the next working version of the Project is scheduled for release in the spring of 2008.

Measures of Sustainable Buildings
Energy Performance Data Largely Lacking (ENR, November 12, 2007) reports that, despite the attention being given to green building design, there is a lack of standards for collecting and analyzing building energy performance data, and, though newer buildings may be designed to be more energy efficient than older buildings, building energy use overall continues to climb:

• According to the U.S. Department of Energy, commercial buildings consumed 18 quads (18 quadrillion BTUs) in 2004, and are projected to consume 25 quads--almost a 40 percent increase--by the year 2030. The largest part of this jump is attributed to increased use of electrical equipment and the increased cooling loads that result.
• Between 1980 and 2000, energy use per square foot in commercial buildings increased by roughly 25 percent.

LEED certification does not necessarily correlate with reduced building energy consumption. On the one hand, Seattle's LEED-Silver Alley24 mixed-used development, completed in 2006, is reportedly close to achieving a 50 percent targeted reduction in CO² emissions. On the other hand, Seattle's new City Hall, also LEED-Silver, completed in 2003, is separately reported as consuming significantly more energy than the larger, older building that it replaced.

Storm-Resistant Home Design

Home Shapes And Roofs That Hold Up Best In Hurricanes (ScienceDaily, Jun. 21, 2007) reports on a research report from New Jersey Institute of Technology identifying design strategies for homes resistant to high winds and storm-driven funding. Among the findings:

• Hipped roofs with a 30-degree slope are the most resistant to wind uplift.
• Homes thats are roughly square in plan are more wind-resistant that those that are more rectangular.
• Roof overhangs should be limited to 20 inches deep.
• An elevated structure is less at risk from storm-driven flooding.

The Delivery of Design and Construction Services

AGC-AIA Dispute Represents Deeper AEC/O Rifts (Cadalyst, Oct 25, 2007) discusses how changes in methods of project delivery, such as building information modeling, are leading to changes in the traditional roles of the designer and builder--changes that do not always come easily.

The upcoming 5th Edition of Fundamentals of Building Construction (due Fall of 2008) will have an expanded discussion of the roles of the building and construction manager in the construction of buildings.

More Info
Building Futures Council
The AGC's BIM Initiatives and the Contractor's Guide to BIM (AEC Bytes)

Roofing Lessons Learned from Hurricane Katrina

Roofing Industry Committee on Weather Issues, Inc's. Hurricane Katrina Wind Investigation Report, prepared in conjunction with Oak Ridge National Laboratory, assesses damage to roofing caused by  Hurricane Katrina in August of 2005. 

One major finding: Peak gust speeds in the inspected areas were estimated at 120 - 130 mph, below the 130 - 150 mph basic design wind speeds required by current codes. As hoped, roofs constructed to current code requirements faired relatively well. Most failures of such roofs were attributable to improper installation or deterioration rather than flaws in the design methodology.

Carbon Neutral Building Design

Green Building Studio Inc. has launched version 3 of their Green Building Studio web-based software for analyzing the energy impacts of alternative building designs. According to GBS, in less than 3 hours you can register your project, submit your BIM building model, review results with your consultants, and tune building parameters to optimize the whole building energy use. The software addresses carbon neutral building, US EPA Energy Star scores, water usage, daylighting, natural ventilation, and other factors.

The BuildCarbonNeutral calculator estimates the C02 emissions of a proposed building based on its size, method of construction, and location. Jointly developed by Mithun Architects and the Lady Bird Johnson Wildflower Center, the tool purportedly:

estimates the embodied energy and subsequent carbon amounts released during construction. The measurements account for building materials, processes and carbon released due to ecosystem degradation or sequestered through landscape installation or restoration.

Accessibility and the IBC

The June 2007 Building Safety Journal is devoted mostly to accessibility regulations and the International Building Code, including discussion of:

• The 2006 IBC and 2003 ICC/ANSI A117.1 accessibility standard have been accepted by the US Department of Housing and Urban Development as a safe harbor for meeting HUD's Fair Housing Act design and construction accessibility guidelines.
• The US Access Board Committee's Courthouse Access Advisory Committee has issued a written report providing guidelines for accessible design in courthouses.
• The US Access Boards ADA and ABA standard continues to move toward adoption by the DOJ. (But the discussion of the application of various Federal agency guidelines leaves this author scratching his head.)
• Accessible design for new stadiums
• Elevators and accessible egress in tall buildings discussed, including ongoing study of elevator-assisted egress
• Theater accessibility
• Accessibility of sinks within work areas
• Differences among adoption of accessibility at the state level

For those dealing with these design issues, this issue of Building Safety Journal is worth a look.

Standards: New (costly?), New (better?), and Needed(?)

ENR's Third Exit Stair Could Make Highrises Too Costly to Build (June 4, 2007) reports on the adoption of more stringent life safety requirements for tall buildings in the 2007 Supplement to the International Building Code. Both the Building Owners and Managers Association International and the American Institute of Architects oppose as too costly a new requirement for buildings taller than 420 feet to have at least 3 independent exit stairs. Other changes to tall building requirements in the 2007 Supplement, all coming in the aftermath of the 9/11 attacks on the World Trade Center Buildings in New York City, include:

• protected fire service elevators and lobbies
• photoluminescent pathway markings in exit stairwells
• inspection and greater strength requirements for spray-applied fireproofing.

Proposals for progressive collapse resistance, increased  exit stairway enclosure integrity, and requirements for a a building's ability to burn without collapse were rejected. See the ICC's Code Development page for more information about that organization's code development process and the adoption of these new requirements.

In the same issue, Energy-Efficiency Guidelines Would Be National Model reports on the American Society of Heating, Refrigerating and Air Conditioning Engineer's (ASHRAE) ongoing development of Standard 89, an enhanced building energy efficiency guideline. Standard 89, now open for comments, is intended to reduce building energy consumption by 30% in comparison to ASHRAE's long-recognized Standard 90, and is being touted as a national standard for achieving LEED certified optimized energy performance. See ASHRAE's Advanced Energy Design Guides page for more about this organization's enhanced energy performance guidelines.

Lastly, Innovative Mix with Fly Ash is Still Not Widely Used describes a concrete mix composed of lime, portland cement, and fly ash developed by Nai C. Yang of the New Port Authority 38 years ago for use in airport runway construction. The mix is claimed to provide superior concrete and a reduction in environmental impact (due to reduction in cement content and, consequently, reductions in C02 emissions). However its broader use in airport construction has been hampered by unfamiliarity and a lack of standards for its production.

Green Construction News

Greenhouse (Eco-Structure, May/June 2007) reports on the National Association of Home Builder's (NAHB) February announcement of the development of a new residential building sustainability standard. To be produced in cooperation with the International Code Council, the new National Green Building Standard will be an ANSI certified consensus standard and will replace NAHB's current Model Green Home Building Guidelines.

Unlike the Guidelines, the new standard will be administered nationally, rather than at the local level, and will apply not only to single-family residences and townhouses, but to apartments and other types of multi-unit residential construction as well. Three levels of certification will be offered, Bronze, Silver, and Gold.

The standard is planned for release in February, 2008.

Trends and Challenges in Green Building (Building Safety Journal, April 2007) discusses coordination between sustainable design standards and building codes.

Historically, building codes have focused  on life-safety concerns and regulated construction so as to achieve immediately tangible benefits (such as higher resistance to fire or improved egress). More recently, some code requirements, such as energy efficiency in buildings, have been developed with the intent to provide benefits in the longer term and extending beyond the immediate users of the building.

Outside of energy efficiency regulations, coordination between long-term sustainability goals and building codes has been limited to date. Green building techniques relying on alternative building practices (for example, rammed earth construction) are frequently not addressed in the model codes. Green building programs, such as USGBC LEED or GreenGlobes, were originally formulated and continue to operate outside of the building code regulatory infrastructure.

Efforts to improve coordination between the model codes and sustainability initiatives include:

• Newer provisions within the codes themselves recognizing sustainable design practices such as insulated concrete formwork construction, unvented conditioned attics, waterless urinals, and greywater recycling systems
• Incorporation of energy efficiency standards meeting green building assessment criteria into the building codes, such as the proposed Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings (ASHRAE/USGBC/IESNA Proposed Standard 189)
• The National Green Building Standard for residential construction, currently under development by the NAHB and the ICC (see above)
• Establishment of the USGBC committee Greening the Codes
• ICC's Industry Advisory Committee's comparison of Green Globes and LEED building assessment criteria (see Reports, IAC Task Group Report Green Buildings (March, 2007)

More Info
NAHB Research Center National Green Building Standard home page
ICC Green Building page

Pollution-Reducing Cement

A Concrete Step Toward Cleaner Air (Businessweek.com, 11/8/2006) reports on the use of concrete formulated with photocatalytic agents in the construction of walls and slabs at the Italian Pavilion of the Venice Biennale. In the presence of light, Italcementi Group's TX Active proprietary cement used in the concrete mix breaks down carbon monoxide, nitrogen oxide, benzene, and other pollutants into less harmful compounds such as water, nitrates, and carbon dioxide. The basic ingredient in TX Active, a blend of titanium dioxide, can be added to cement, mortar, paints, and plaster. Full-scale tests of the product in repaving projects in other locales have resulted in up to 60% reduction in measured pollutants.

The Vatican's Jubilee Church in Rome, 2003, (image above) was the first project to use TX-Active cement concrete.

Smog-Eating Concrete May Soon Cover US Buildings (ENR March 5, 2007) reports on the anticipated arrival TX-Active cement products in the United States via Italcementi Group's US subsidiary Essroc Cement Corp, though no specific projects are named. According to ENR, the titanium dioxide cement mix was first formulated to produce concrete with a brilliant white color, and it's pollution reducing properties were only appreciated later.

Superabsorber (transmaterial, March 8, 2007) describes the Superabsorber system designed by Douglas Hecker and Martha Skinner of fieldoffice that combines sound absorbing and photocatalytic air pollution reducing properties in sponge-like highway sound barrier walls. 

See also: Anti-Pollution Paint

Ultra-High Performance Concrete

Iowa Bridge Gives Glimpse Into the Future (Ascent, Designing With Precast, Summer 2006) describes the use of extraordinarily high-strength concrete in precast beams for the Mars Hill highway bridge in Wapello County, Iowa.

The "bulb tee" beams  (photo left) were cast with a proprietary concrete mix from Lafarge North America capable of producing concrete with compressive and tensile strengths as high as 30,000 psi and 7000 psi, respectively. (For comparison, conventional concrete is typically specified with compressive strength in the range of 2500 - 5000 psi, and taller buildings are being designed with concrete with compressive strengths as high as 10,000 - 20,000 psi.) Among the reported benefits are:

• A lighter, thinner structural member: The bulb tee beams used in the Mars Hill Bridge have webs 4-1/2 inches wide, compared to 6-1/2 inches for a conventional precast bulb tee, bottom flanges  5-1/2 inches deep, compared to 7-1/2 inches for a conventional tee, and top flanges 2-3/4 inches deep, compared to 3-3/4 inches for a conventional tee.
• The more dense concrete results in a structural member that is more resistant to the effects of weather and road salts, and that should be longer-laster.
• Reduction in the need for conventional steel reinforcing: Aside from the prestressing strands, the only other steel reinforcing in the Mars Hill Bridge beams are U-shaped bars used to develop bond between the precast beams and the cast-in-place concrete bridge deck. There are no stirrups or other conventional reinforcing steel.

More Info
For more about Lafarge Company's proprietary Ductal concrete, see Iano's Backfill Flexible Concrete.

Green Giant

Architecture firm SOM's very green Pearl River Tower, planned for Guangzhou, China, is described in both Super Tall and Green  (Metropolis, August 2006) and SOM's skyscraper innovation has moved to China (Architect Record, 07.06).  Included among its sustainable features are:

• An underfloor radiant cooling system that passively circulates air within the building's interior
• A sculpted building form that channels wind into turbine-driven electrical generators located on two of the building's mechanical floors
• A double-wall curtainwall system that preconditions fresh outside air and directs exhaust air to mechanical floors where excess heat is captured and reused
• Fuel cells located on-site that produce electricity more efficiently than that available from the public grid; Waste heat from the fuel cells is also recycled into the building's heating and cooling systems.
• A condensate reclamation system to reduce HVAC system water consumption

The 1000-ft tall building is scheduled for completion in Fall 2009. According to Metropolis Magazine, the building is designed to be the world's first "zero-energy supertall building in the world," though this claim is not fully explained.

Model Code Cooperation Falters

Reversing previous reports, the International Code Council (ICC) has announced the suspension of efforts for the joint development of a single set of coordinated mechanical and plumbing codes in place of the competing codes currently published by itself and the International Association of Plumbing and Mechanical Officials (IAPMO). According to the ICC's September 1 press release, reconciliation of the two organizations' different code development processes was the major stumbling block. 

As this author understands it, the ICC accepts code change proposals from any interested party, but limits participation in final voting to governmental representatives (that is, ICC member building code officials). IAPMO permits a broader spectrum of participants, including consumers, governmental officials, and industry/manufacturer representatives, to have a say in final decision making. The ICC views their change process as less subject to the influence of special interests. Whereas IAPMO claims their process protects against any one group gaining undue advantage.

Regardless of the merits of either organization's claims, this author views the breakdown of this joint development process as a setback for the design and construction industry.

Structural Innovations In Seattle Highrise

Banking On A Museum (ENR, July 17, 2006) describes the construction of Seattle's Washington Mutual Center-Seattle Art Museum Downtown highrise, a 42-story office tower/museum expansion with innovative structural design and construction, including:

The building is the tallest to date in the US to use performance-based methods for its seismic design. Rather than adhere to the prescriptive seismic design requirements of the building code, structural engineers Magnusson Klemencic Associates performed a more complex and lengthy analysis of the building structure to prove that their alternative design could perform to the same levels. The result is structure with fewer architecturally intrusive elements.

The building is also the first in the US to use buckling restrained braces (BRBs). In this case, 44 BRBs within the first thirteen levels of the structure link the relatively slender concrete core to a pair of outlying concrete-filled steel pipe columns. This linked composite structure increases the core's effective depth, thereby increasing its stiffness and reducing overturning forces.

Where the main structural core is located eccentrically relative to the lower, larger floor plates, additional braced and moment frame structures provide balanced lateral force resistance to these portions of the structure.

Steel reinforcing in the "ductile concrete" core was so densly placed that it was cast with self-consolidating 10,000 psi concrete. In addition, the concrete mat foundation, constructed 95 feet below grade, ranged from 7 to 14 feet thick.

Apart from the structural design, other interesting aspects of this project include unusual financial and development relationships between the building's two banking and museum tenants, provisions for structural changes in floor configurations as occupancy between these two tenants changes over time, and a variety of innovative techniques applied to the construction process.

This article is good case study in the real-world interaction of the many forces that shape buildings and the interesting designs that can result.

More Info
Tall, skinny ... stable: Using novel technology, S.F. tower should resist quakes, gales (SFGate.com, July 2, 2006) discusses another innovative tall building designed by engineers Magnusson Klemencic Associates, this one in San Francisco. The companion Back Story also links to video and a podcast, in which engineer Ron Klemencic discusses the building's design.

WUFI Hygrothermic Modeling

WUFI-ORNL/IBP is a software program designed to model the dymanic movement of heat and moisture through building wall and roof assemblies. The software, developed jointly by Oak Ridge National Laboratory (ORNL) and Germany's Fraunhofer Institute of Bauphysics (IBP), is intended as a tool for researchers and building technologists to aid in the analysis and design of building envelope assemblies. This author's first impressions of the software after trying out a freely available research and education version of the program follow.

What is WUFI?

WUFI allows the user to model various building assemblies, run these assemblies through simulations of several years of typical climatic conditions for various locales (see the image at left), and analyze the performance of the assembly in terms of moisture flow, moisture accumulation, and other factors.

WUFI is a sophisticated yet relatively easy to use program. For example, it can simulate climatic conditions for different locals and account for differences in orientation of the building assembly. Assemblies themselves are modeled by selecting and arranging in the desired order components (such as sheetrock, plywood, vapor barrier sheet, etc.) from a database into which the relevant material properties have already been inputted. Once the initial conditions are established, simulations can be run and graphically observed at the push of a button. In this user's experience, an assembly could be modeled and run through a 2-year simulation in less than 5 minutes once the basic mechanics of the program have been mastered.

Some Sample Results

As an example of what WUFI can do, the results of three test scenarios are described below. All three are based on a wall modeled as follows: wood siding at the exterior, building paper, plywood sheathing, glass fiber batt insulation, and gypsum wallboard at the interior. The location is Seattle, Washington, using climate data for a relatively cold winter, with the wall assembly facing to the North. Interior conditions were set to moderate levels of relative humidity. The three scenarios differ in the placement of a polyethylene sheet vapor retarder, either close to the inside of the assembly, close to the outside of the assembly, or not included at all:

Scenario 1: Vapor retarder sheet behind the gypsum wallboard (close to interior, warm side of assembly). This is the conventionally "correct" location for a vapor retarder in the Seattle climate. To the left is a screen shot of the graphic results of the model after a 2-year simulation (click on the image to view a larger version). The exterior side of the assembly is to the left in the charts. The top chart records temperature data. The lower chart records relative humidity and moisture content. For example, the wide green band represents the range of relative humidity conditions encountered in various parts of the wall assembly throughout the two-year simulation. (Results are also presented by the program in tabulated and other graphic formats.)

Scenario 2: In this case, the vapor retarder sheet is (incorrectly) located on the exterior side of the exterior sheathing. In this configuration the vapor retarder is expected to trap condensed moisture in the plywood sheathing. Note the lower blue curve in the lower chart, representing moisture accumulation. As expected, in comparison to scenario 1, this configuration results in greater quantities of moisture accumulated in the exterior sheathing.

Scenario 3: No vapor retarder. In this scenario, the levels of moisture accumulated in the plywood sheathing fall in-between the two previous scenarios. Referring to the tabulated results provided by the software, water accumulated in the plywood sheathing for each of the scenarios is as follows: Scenario 1: 3.6 lb of water per cu. ft. of plywood Scenario 2: 8.4 lb / cu. ft. Scenario 3: 7.6 lb / cu. ft.

Interpreting WUFI Results

The WUFI anayses offer some interesting insights, and also raise additional questions.

For starters, the results seem to agree with conventional wisdom. That is, in a northern climate, a vapor retarder located toward the warm side (interior) of the assembly is beneficial in minimizing moisture accumulation in the wall: In the simulations above, Scenario 1 results in less than half the moisture accumulation of either of the other two assemblies.

A second question relates to the form of the data provided by the simulations. For example, is 3.6 lb of water per cu. ft. of plywood OK? How about 7.6 or 8.4 lb per cu. ft? To answer this question, one would have to convert these numbers to obtain moisture content as a percentage of the wood's oven dry weight, and then compare this to established standards which suggest that wood kept above a moisture content of approximately 15% to 20% is at risk of mold growth and decay. It would also be necessary to look at the moisture content data over time. For example, an occasional excess of moisture might be OK, but a long period of continuous excess moisture might not be.

On another point, this author was somewhat surprised by the results of Scenario 3 (no vapor retarder), which were almost as bad as Scenario 2. In the Seattle region, there is some question among the building technology community as to whether the use of vapor retarders is beneficial in this climate or not. The results of the Scenario 3 simulation seem to indicate that the absence of a vapor retarder is almost as detrimental as deliberately placing the retarder in the wrong part of the assembly. So the WUFI results seem somewhat in conflict with local practice.

Finally, there are some aspects of building assembly behavior that the WUFI program does not address at all. Two important ones are leakage of water due to construction defects and air flow through the assembly. In the real world, these two phenomena may very well be the most severe sources of moisture that an assembly will encounter, potentially contributing an order of magnitude more moisture to the assembly than those phenomena that WUFI does simulate. If so, to what extent are WUFI simulations useful at all? Based on conversations with other building scientists, the answer to this question seems to be that with proper use of the software, these effects can be simulated, and the results of WUFI analysis can be validly applied to actual building practice.

Despite these limitations, for those interested in the science of the building envelope, WUFI appears to be a useful tool for teaching and/or analysis.

More Info

• Oak Ridge National Laboratory WUFI website
• Fraunhofer Institute of Bauphysics WUFI website
• The WUFI Forum

More Really Small Houses

HELP Is on the Way (Dwell Magazine, Feb/Mar 2006) describes  Architect Carib Daniel Martin and builder Rob Bragans' disaster relief  HELP (Housing Every Last Person) Housing  prototype.

Martin and Bragans' housing system is intended as a mass produced emergency housing system, and was designed in response to the plight of thousands of Gulf Coast residents left homeless by the hurricane disasters of 2005.