Iano's backfill

The Comparitive Sustainability of Structural Materials

Materials Matter (Architecture Record, March 2011) compares the life cycle effects of wood, steel, and concrete construction. this article provides an informative discussion of life cycle analysis techniques and interesting comparisons of these three structural materials. (Caveat: The article is sponsored by a group affiliated with the forestry industry.)

Regarding comparing the embodied effects of various building materials, the current issue of Architecture Record (March 2011, p. 115) has an article comparing the life cycle effects of wood, steel, and concrete construction. As I mentioned in my talk, this article was sponsored by a group affiliated with the forestry industry. Nevertheless, I think the material is useful.

 

The article is also available online here: http://continuingeducation.construction.com/article.php?L=221&C=754 .

World-Record Wood Structures?

Inhabitat's World's Largest Treehouse Built From Reclaimed Wood is intriguing and worth a look.

As is their post, World's Tallest Wooden Building Planned for Norway.

New Wood Preservative Treatments

Pressure-Treated Wood: The Next Generation (Journal of Light Construction, April 2009) reports on new chemical preservative treatments for wood that promise to be less corrosive than the current generation of preservatives, but that leave unanswered questions about long-term performance.

Second-Generation Preservatives
Until recently, the two most popular chemicals used to treat wood for protection from decay and insect attack were CA (copper azole) and ACQ (ammoniacal copper quaternary or alkaline copper quarternay). Both of these chemicals rely on high concentrations of dissolved copper for their resistance to attacks by fungi and and insects. But these high copper concentrations, can also cause rapid corrosion of metal fasteners and framing hardware with which the treated wood comes in contact.

For example, the article refers to tests of ACQ treated lumber with plain or galvanized steel which have shown corrosion rates 5 to 15 times that of CCA, the preservative chemical that ACQ and CA replaced but that was removed from the market in 2004 because of concerns for health hazards due to its arsenic content.

Third-Generation and Beyond Preservatives
Unlike CA and ACQ, in which the copper is in a dissolved (ionized) state and relatively free to migrate, a new family of chemicals rely on finely ground particles of copper in suspension that results in less free copper ions and less corrosion of metals. Chemical formulas, which vary with preservative manufacturer,  include uCA-C (dispersed copper azole), MCA (micronized copper azole), and MCQ (micronized copper quaternary). Manufacturers of these copper-suspension treatment chemicals claim reduced corrosion rates in comparison to copper-solution treatments. 

Preservatives which rely on boron for decay prevention are another alternative. These chemicals have no corrosive affect and no know health risks. But most are also highly water soluble, making them suitable only for applications protected from the weather such as interior wood framing for structures in areas of high termite risk. One treatment manufacturer produces a borate treatment chemically bound to the wood such that it can be used for exterior, non-ground contact applications.

The newest family of preservatives entering the market are based on organic insecticides and fungicides with no copper or other metals. These so-called "carbon-based" treatments promise much lower corrosivity than copper-based treatments. Currently available products are suitable for above-ground use only and include the chemicals EL2 (DCOI-Imidicloprid) and PTI (Propiconazole-Tebuconazole-Imidicloprid).

Performance
While new treatment chemicals must pass laboratory testing to demonstrate their effectiveness, their true long-term performance in real-world conditions won't be certain for decades. In the mean time, designers and builders must base their product selections on the results of standard testing and manufacturer certifications.

More Info
http://www.archchemicals.com/Fed/WOLW/
www.treatedwood.com
www.osmosewood.com
www.frtw.com
www.phibrowood.com

Plastic Houses

House of Plastic (ArchitectureWeek, 2005.0914) describes Japanese architect Kengo Kuma's "Plastic House", a small residential structure in Tokyo constructed in large part from glass and fiber-reinforced plastic (there is also loadbearing steel).

According to the article, the appearance and translucency of the 4 millimeter plastic panels are manipulated by varying the materials used for the fiber reinforcing, as well as by the insertion of paper sheets or insulating materials. Fiber-reinforced plastic (FRP) is used in many parts of the structure include for example, decking, cladding, screening, and stairs.

Kuma  states, "If I were to describe the architecture of the 20th century with one word, it would be 'concrete'. Its freedom and universality fit the 20th century so well that other local methods of construction were abandoned. Moreover, the strength of the solid mass achieved in transformation from thick liquid substance suited an era that desired monumentality and security of privacy. Therefore to seek for a substitute [material] is not a mere formal proposal but an attempt to suggest a principle of living that replaces the fundamentals of the 20th century — freedom (of course, in the sense of the era), strength, and security."

Life-Cycle Assessment of Light Wood Construction

The Canadian Wood Council has released its technical bulletin Energy and the Environment in Residential Construction, a comparative life cycle assessment of steel, concrete and wood in residential construction.

According to the bulletin, considering embodied energy, pollution and waste generation, and resources and energy use over a 20-year period, steel and concrete construction have the following disadvantages in comparison to wood construction:

• 12 to 20 percent more embodied and consumed energy


• 15 to 29 percent more greenhouse gas emissions
• 10 to 12 percent more air pollution


• 225 to 300 percent more water pollution
• 7 to 50 percent more resource use
• 6 to 16 percent more solid waste production

Three residential construction systems are compared: wood light frame, light gauge steel frame, and insulating concrete formwork, all in a Toronto climate. The study takes the position that life-cycle analysis provides the most comprehensive view possible of the comparative environmental impact of these systems.

Plastic/Wood Composites

Polymers in various forms continue to make inroads into traditional wood product applications.

The New Forest of Man-Made Trim, Fine Homebuilding, August/September 2004, is a full-length article covering new alternatives to traditional sawn-lumber trim. Materials discussed include PVC, wood/plastic composites, compressed wood fiber, and engineered wood products that claim greater stability, reduced maintenance, and increased longevity. Some noteworthy points:

PVC trim is manufactured by extrusion, with the final product characteristics varying with the cooling process. One process, termed "celuka", results in a material with a dense, somewhat brittle outer layer and a less homogenous core. This product type is best suited to flat trim applications. The alternative "free-form" cooling process results in a material of uniform density throughout that is more suitable to applications requiring routing, complex cutting, or other more intricate work.

Wood/plastic composites are made from the mixing of phenolic resins or PVC plastic with wood fibers. Product characteristics vary with the various manufacturing processes. Some may be homogenous and exhibit workability similar to natural wood. Others may be acrylic clad with a less dense core.

Both solid plastic and wood/plastic composite products must be installed to allow for greater thermal expansion and contraction than natural wood products.

Compressed wood fiber products are also a mixture of phenolic resins and wood fibers, but with a higher proportion of wood fiber to resin material in comparison to composites. Similar to traditional hardboard (which has a history of failures when used in exterior applications), these newly formulated products are claimed to overcome earlier limitations. In general, product characteristics are similar to traditional hardboard or medium-density fiberboard, though qualities vary with individual manufacturer's proprietary material formulations and manufacturing processes. Given the higher wood fiber content, more care must be taken to protect these products from moisture absorption at cut ends and other vulnerable locations. Some product formulations also include chemicals to prevent decay or attack by insects.

Several products consisting of plywood or OSB panel material clad with resin-impregnated waterproof paper, similar to medium density overlay plywood, are also available for use as trim material.

Finger-jointed lumber offers greater dimensional uniformity and stability in comparison to traditional sawn-lumber. It can also be manufactured from readily renewable wood species. Improvements in finger jointing technology result in joints that are invisible in finished trim.

Many proprietary trim products are also available factory-primed and/or factory-finished, offering higher finish quality and consistency, and reduced installation costs.

Wood Design & Building reports that the University of Maine's Advanced Engineered Wood Composites Center has received a patent for a reinforced building panel that offers substantial increases in structural strength in comparison to traditional structural panel products. According to the article and information provided on the University of Maine's website, fiber-reinforced polymer reinforcing at the perimeter and other nailing surfaces of plywood and OSB panels results in increases in resistance to wind and earthquake forces of up to 20 percent in traditional stick-framed construction, or more in specially engineered systems.

The Construction Specifier, July 2004, reports on the 10-year successful track record of of boardwalk decking made from recycled/reclaimed plastic and waste wood. Installed in Spring Lake, New Jersey's boardwalk after a 1992 storm damaged the previous wood deck boardwalk, the new decking material has proved successful. Claimed benefits include: freedom from rot, no risk of splinters, no periodic refinishing or sealing requirements, and elimination of popped nail heads. Reportedly, the surface is also found to be more forgiving under foot to joggers.

Bobrick, manufacturer of washroom accessories, has announced its "Siera Series" toilet partitions made from Solid Color Reinforced Composite. So-called SCRC material is made from wood fibers suspended in high-density resins, and is claimed to offer superior resistance to abuse, easier repairs, and improved surface-burning characteristics in comparison to competing products.

More Info
Plastics in Construction are discussed on pages 694 through 697 in the textbook.

Innovations in Glulam Beam Design

Innovations in composite wood manufacturing continue to appear on the market. LVL and Sawn Wood Sandwich Makes Strong "Hybrid" Glulam, Journal of Light Construction, June, 2004, describes a new proprietary glue-laminated beam product combining solid lumber laminations as used in conventional glulams with higher-strength laminated veneer lumber (LVL) laminations. The result is a product suitable for wood light frame beam and girder applications that is claimed to be stronger, lighter, and more economical than alternative solutions.

Manufactured by Rosboro under the "Big Beam" trade name, the use of LVL laminations at the top and bottom of the beam (where bending stresses are highest) results in a structural member with design stress values approximately 25% higher than achievable with comparable glulams fabricated solely from solid lumber laminations.

More Info
_The Rosboro web site's Technical Reference and Specifications page has a good selection of references related to glue-laminated members and construction.
_Glue-laminated and LVL wood members are discussed on pages 90 through 92 of the textbook.

Plastic Bridge Faring Well

One-year-old plastic bridge exceeds expectations, Structural Engineer, January 2004, reports on the current health of the nation's first all plastic bridge, the New Jersey Pine Barrens Mullica River Bridge, first covered on this site last November.

According to the article:

• After more than one year in service, the one-lane, 56-foot long bridge is so far exceeding expecations.
• The structural plastic material is a combination of polystyrene and polyethylene, recycled from items such as milk cartons, soda bottles, and foam cups.
• The bridge is rated to carry a 36-ton load and cost $75,000 to build. Costs to replace the original wood structure were estimated at $350,000.

Also according to the article, the Federal Highway Administration currently has sponsored more than 40 projects involving experimental plastic materials and sees an "incredible" market potential for these materials.

More Proprietary Wood Products

The growth of proprietary engineered wood products continues. Humber Engineered Woods is advertising its AdvanTech product line of engineered sheathing, I-joist, and rim board products. According to the manufacturer, sheathing panels surpass the APA PS-2 performance standards, and all the products provide superior weatherability.

Preservative Treated Lumber II

Pressure-Treated Wood: The Next Generation, Fine Homebuilding January 2004, has more to say about the new wood preservatives coming to market and their higher corrosiveness as discussed here previously. In summary:

• It's the high concentration of copper in alkaline copper quat and copper azole that give these preservatives their potency, and that makes them as much as 5 times more corrosive than traditional CCA-treated lumber.
• FH recommends stainless steel hardware and fasteners wherever possible. Where hot dip galvanized material is used, a G-185 rated coating is recommended. G-185 hot dip galvanized steel has 1.85 ounces of zinc per square foot of metal, compared with 0.90 or 0.65 ounces per square foot for the more commonly available G-90 or G-65 coatings. Electrogalvanized fasteners, such as expansion bolts, should be rated Class 40 or higher (the electrogalvanizing Class scale ranges from a low value of 5 to high value of 110). Polymer coated screws may also acceptable. (Author's note: Simpson Strong-Tie recommends minimum Class 55 for electrogalvanized fasteners.)
• Avoid any contact between these treated lumber products and aluminum sheet metal or fasteners, as they will corrode quickly. Copper sheet metal is OK.
• Special care must be taken at locations such as mud sills, which must be preservative treated lumber, but are not normally associated with corrosion resistant fasteners. Nails at the bottom edge of the wall sheating that are driven into the mudsill, foundation anchor bolts and straps, and toenails fixing rim joists and floor joists to the mud sill are all possibly at risk of accelerated corrosion.
• Lumber is rated by end-use application. In order of increasing preservative concentration, categories are Decking, Above Ground, Ground Contact, and Permanent Wood Foundation.
• New borate based preservative forumulations, which do not rely on copper for their potency, are also coming to market. According to Fine Homebuilding, borates are not corrosive and have a low toxicity.