Tag Archives: Slabs

Getting on Deck: High-performance options for composite decking

Photo courtesy MoistureShield

Photo courtesy MoistureShield

by Brent Gwatney

From marinas to hotels to public parks, design/construction professionals are looking for higher-performance decking options in commercial applications. Wood-plastic composites (WPCs) are increasingly a material of choice for demanding exposures, including docks, beachfront decks, and submerged access ramps.

Many manufacturers across North America produce composite decking; quality varies greatly. In the past few years, choosing an appropriate product has become more difficult as the range of options has exploded, including the introduction of capped composite boards.

Performance factors
When specifying composite decking, it is important to consider how products differ from one another, and how they compare and contrast with traditional wood decking. Key performance factors for specifiers to consider include the following:

  • moisture absorption;
  • insect resistance;
  • weight;
  • flammability;
  • surface temperature; and
  • structural considerations.
Moisture-resistant composite decking is suitable for continual soaking, as in this children’s spray park at the Port Royale Marina. [CREDIT] Photo courtesy Port Royale Marina

Moisture-resistant composite decking is suitable for continual soaking, as in this children’s spray park at the Port Royale Marina. Photos courtesy Port Royale Marina

The Port Royale Marina, on Georgia’s Lake Lanier, uses composite decking throughout its facilities.

The Port Royale Marina, on Georgia’s Lake Lanier, uses composite decking throughout its facilities.









Moisture absorption

How long a decking material lasts largely depends on the degree to which it resists water. Moisture absorption can lead to rot in both wood and composite decking, along with mechanical damage from shrinking and swelling. Class-action lawsuits involving composite decking failures have addressed rot, mold and mildew growth, surface flaking, and cracking. Composites with any exposed wood fiber are susceptible to moisture absorption.1

Manufacturers have developed two methods to protect composite decking from water. The first, and most effective, way is to fully encapsulate the wood fibers in water-resistant plastic, such as polyethylene. Full encapsulation defends against moisture to the board’s core, and allows installers to cut, drill, screw, and nail the boards without creating a pathway for water intrusion. As it is difficult to achieve full encapsulation, many manufacturers have moved from composite-only boards to making decking with a composite core and a protective cap (i.e. ‘capped composites’ or ‘cap stock’).

Capped composites rely on a thin outer layer of polymer plastic to keep moisture away from the composite core. Caps can be an effective enhancement for deck boards, but are not sufficient on their own to prevent moisture damage when the core is made of a composite that has exposed wood fibers. There are three reasons for this:

  • some capped composites only have a cap on three sides, leaving the bottom of the board vulnerable to moisture;
  • even if the cap is on all four sides, both board ends remain unprotected; and
  • most importantly, jobsite crews breach the cap in many spots when using screws or nails to attach the decking.

Newly developed boards combine the added durability of a cap with the moisture defense of composite cores that have fully encapsulated wood fibers. In this case, the cap is used for enhanced resistance to staining, fading, and scratching; it is not primarily for water protection since the composite core is already moisture-resistant.

When choosing any capped decking, it is important to evaluate how well the cap is attached to the composite core. Some manufacturers use proprietary techniques that integrate the cap more completely with the core, which helps prevent delamination.

The data in the table above was calculated from weights presented in the Wood Database at www.wood-database.com. Image courtesy MoistureShield

The data in the table above was calculated from weights presented in the Wood Database at www.wood-database.com. Image courtesy MoistureShield

Insect resistance
Traditional wood decking requires treatment to avoid destruction by termites, carpenter ants, and other damaging insects. Composites, which are made of substantial amounts of inedible plastics, are impervious to insect attack and therefore do not require treatment. Additionally, composite decking with fully encapsulated wood fibers can have direct ground contact and still withstand moisture and insects. This is an important specification criteria, as untreated wood in contact with the ground is a primary pathway for insects to bore into other parts of a deck or structure.

Depending on the product, composite decking weighs about 45 percent more per unit than the redwood boards used on many home decks, yet is about 45 percent lighter than the ipe hardwood often installed on commercial decked surfaces (Figure 1). In commercial projects, designers therefore typically do not need to make substantial structural modifications to carry the dead loads of composite decking compared to those of ipe and similar hardwoods.

WPCs have a fire behavior very similar to, or better than, comparable timber products, according to Tangram Technology, a UK-based consulting engineer firm.2 There are some manufacturers introducing capped boards with a Class B fire rating, but, composite decking commonly carries a Class C fire rating, which is similar to the wood structural members commonly used for decks.

Surface temperature
Anecdotal reports indicate dark-colored composite decking, especially more dense products, can become uncomfortably hot for bare feet in direct sunlight. A similar effect happens with dark wood decking. To mitigate this in sunny climates, building professionals can specify lighter color decking. For composites, this includes grays, tans, and other similar hues.

Florida’s Blue Run of Dunnellon Park relies on composite decking with fully encapsulated wood fibers for an access ramp submerged year-around. [CREDIT] Photo courtesy Marion County FL Parks and Recreation

Florida’s Blue Run of Dunnellon Park relies on composite decking with fully encapsulated wood fibers for an access ramp submerged year-around. Photo courtesy Marion County FL Parks and Recreation

Structural considerations
Composite deck boards are less stiff than wood decking, so they are not suitable for use as structural members. However, a typical allowed joist spacing for composites—406 mm (16 in.) on center (oc)—is comparable to wood decking. To prevent sagging, it is important to confirm the allowed joist spacing, and allowed cantilever distance, for a given composite deck product and board profile dimensions.

Installation in demanding exposures
Due to the superior moisture resistance of high-performance composite decking, the product is being specified for lasting durability in demanding exposures. Examples include marinas, fully submerged access ramps, waterpark decking, and beachfront hotels.

Port Royale Marina
The owners of the 500-slip Port Royale Marina, on Georgia’s Lake Lanier, are installing moisture-resistant composite decking as part of a multi-million dollar facilities upgrade. Composite decking applications throughout the marina, include the:

  • main deck;
  • docks;
  • access bridge;
  • raised walkways;
  • finger peers;
  • restaurant deck; and
  • children’s spray park.

Composite decking was specified for its more manageable maintenance, long-term durability, and aesthetics. Previously, 2×8 pressure-treated lumber was used. The moisture resistance of high-performance composite decking made it an ideal choice for Port Royale Marina’s decking, which is subject to high-moisture exposure from Georgia’s humid climate and frequent contact with the lake water.

One of the marina’s amenities receiving especially intense water exposure is the children’s spray park. As it includes several water fountains that spray up from the surface, the space required decking that would withstand continual soaking.

In addition to moisture resistance, Brent Pearson, operations manager at TEI Industries, the marina’s owner, noted the high-performance composite decking is a cost-effective choice. Alternatives such as fiberglass are more costly; ironwood or ipe have incredible strength, but can be twice the price of composites.

“It’s easy to work with, and obviously easier to fasten in place than ipe or concrete—its workability is similar to wood,” Pearson said.

Blue Run of Dunnellon Park
Defending decks, docks, and boardwalks from rot and damaging insects often means keeping boards high and dry. This is not always easy in moist climates such as Florida, and especially for an in-water access ramp to serve canoes, kayaks, and inner tubes.

When the Marion County Florida Parks & Recreation Department built a new river access at the Blue Run of Dunnellon Park in 2012, it chose high-performance composite decking with fully encapsulated wood fibers for a durable deck surface. The water- and insect-resistant deck boards enabled the county to extend a 3.7-m (12-ft) wide ramp directly into the Rainbow River without worries of degradation.

High-performance composite decking provides a water-resistant, slip-resistant, and splinter-free surface in the Santa’s Splashdown waterpark. [CREDIT] Photo courtesy Lake Rudolph Campground & RV Resort

High-performance composite decking provides a water-resistant, slip-resistant, and splinter-free surface in the Santa’s Splashdown waterpark. Photo courtesy Lake Rudolph Campground & RV Resort

“In Florida, we have a challenge when it comes to dealing with outdoor construction: heat and humidity join to really test any material,” said Jim Couillard, PLA, ASLA, a landscape architect with the Marion County Parks & Recreation Department. “Lumber does not last as long as you would think, so composite decking is a smart choice.”

The county designed the Blue Run river access ramp to make it easier for the approximately 40,000 paddle craft enthusiasts and tubers that use the park annually to get in and out of the water safely, without eroding the riverbanks. The 24.4-m (80-ft) long ramp includes a 4.6-m (15-ft) portion extending into the river. Attached railing enhances safety and is part of providing accessibility for handicapped people. The splinter-free deck boards also provide comfort for barefoot park users.

“We believe in using long-lasting, durable materials that will lessen our long-term maintenance costs,” said Couillard. “With high-performance composite decking we are able to avoid sanding, staining, or sealing the surface decking, thus enabling staff to focus on other aspects of their day-to-day activities.”

Lake Rudolph Campground and RV Resort
The Lake Rudolph Campground & RV Resort in Santa Claus, Indiana, is a popular destination for families throughout the Midwest, hosting about 3000 visitors daily. One of the resort’s more demanding decking applications is for the stairs and platforms on the water slides at its Santa’s Splash Down waterpark complex.

The resort owner chose moisture-resistant composite decking to withstand the repeated splashing from the waterslides, and to provide a splinter-free and slip-resistant surface for park users. Composite decking also provides an attractive and comfortable outdoor surface for the resort’s 53 Rudolph’s Christmas Cabins.

Hilton Sandestin Beach Golf Resort and Spa
After a fire ravaged the outdoor space at the Hilton Sandestin Beach Golf Resort and Spa, the resort on the Gulf of Mexico looked to composite decking to create an expansive new 1580-m2 (17,000-sf) multi-purpose deck.

After careful consideration in choosing a new decking material, including appearance, availability, and performance in the coastal environment, the project team specified high-performance composite decking.

The Hilton Sandestin hotel on the Gulf of Mexico relies on composite decking to stand up to harsh weather and high user traffic. [CREDIT] Photo courtesy MoistureShield

The Hilton Sandestin hotel on the Gulf of Mexico relies on composite decking to stand up to harsh weather and high user traffic. Photo courtesy MoistureShield

In numerous cases, the composite decking industry had a bumpy start, with notable product field failures. However, appropriately manufactured composite decking and railing can withstand the most demanding requirements. As a result, it is important to check the manufacturer’s track record to ensure specification of a high-performance product.

In addition to performance, the decking’s appearance is another important factor for many design professionals and project owners. Composite decking manufacturers have become sophisticated at producing attractive materials. For example, composites are available in a multitude of color options, including variegated hues with the look of exotic hardwoods. Many boards also have realistic-looking embossed wood grain patterns.

For building teams seeking a green project rating, composites can contain up to 95 percent recycled content, which can help earn rating points in Leadership in Energy and Environmental Design (LEED) and other green building programs.

Due to composite decking’s performance, aesthetics, and use of recycled content, market researchers predict strong growth for the product segment. For example, business research company the Freedonia Group reports WPC and plastic lumber decking materials will grow at double-digit rates, far outpacing the wood segment.3

1 See “A Technology Review of Wood-Plastic Composites,” by Michael P. Wolcott and Karl Englund at the Washington State University Composite Materials and Engineering Center. (back to top)
2 See “Wood-Plastic Composites: A Technical Review of Materials, Processes and Applications, Tangram Technology,” at www.tangram.co.uk. (back to top)
3 See The Freedonia Group’s “Wood & Competitive Decking: Industry Study with Forecasts for 2016 and 2021” at www.freedoniagroup.com. (back to top)

Brent Gwatney is senior vice president for sales and marketing at MoistureShield composite decking, and serves on the North American Deck and Railing Association (NADRA) board of directors. He has specialized in the building industry for more than 30 years, working with manufacturers, dealers, design professionals, contractors, and building officials. Gwatney can be reached at bgwatney@aert.cc.

Specifying Steel Fibers for Concrete Floors

Photo © BigStockPhoto/Jacek Sopotnicki

Photo © BigStockPhoto/Jacek Sopotnicki

by George Garber

Thin, short strands of steel fiber are being specified more and more as reinforcement in concrete floors. Sometimes, these fibers are used on their own, and sometimes they are used in conjunction with conventional reinforcing steel. They appear in ground-supported slabs and in composite steel deck slabs.

In ground-supported slabs they are used to control cracks, to allow greater joint spacing, and to justify thinner slabs—though the last goal is controversial because it involves properties of fiber-reinforced concrete that experts disagree on. In composite steel deck-slabs, fibers can replace traditional wire mesh to control shrinkage cracks.

Structural engineers are still figuring out how best to design floors with steel fibers. American Concrete Institute (ACI) 360R-10, Guide to Design of Slabs-on-ground, offers guidance on their use in ground-supported floors. Steel Deck Institute (SDI) C-2011, Standard for Composite Steel Floor Deck–Slabs, gives basic rules for using them in composite steel decks. However, neither document represents the last word on the subject, so the research continues. Meanwhile, specifiers need to think about how to define this material in contract documents.

Fibers are put into concrete are batched by mass, so volume-based specifications must be converted. This table shows equivalents for specified doses. Images courtesy George Garber

Fibers are put into concrete are batched by mass, so volume-based specifications must be converted. This table shows equivalents for specified doses. Images courtesy George Garber

Whenever people learn a job will include steel fibers, the first question is always some variant of ‘how much?’ It seems everyone wants to know the fiber dosage, which is usually stated as the mass added to each unit volume of concrete. Typical units are kilograms per cubic meter (kg/m3) or pounds per cubic yard (lb/cy).

Dosage matters, of course, but it is just a start, because not all fibers are alike. If other key details are not specified, the result is concrete that contains the specified mass of fibers, but does not fulfill the designer’s intentions.

Steel fibers in specifications
Since steel fibers can be considered a kind of reinforcement, it is tempting to stick them in MasterFormat Division 03 20 00–Concrete Reinforcing, with rebar and wire mesh. However, fibers are better handled in Division 03 30 00–Cast-in-place Reinforcing or Division 03 24 00–Fibrous Reinforcing. If fibers are put in their own section, it should be referred to in Division 03 30 00–Cast-in-place Concrete as this is where the concrete contractor and ready-mix supplier will look. If the specifications include a special section for the concrete floor, then that would be a good place for the steel fibers.

Every steel-fiber specification should incorporate, by reference, ASTM A820, Standard Specification for Steel Fibers for

On this. Too though http://www.handicappershideaway.com/qox/generic-viagra understand I’d. Your product natural viagra never benzoyl about It have. Again natural viagra For it With have http://www.mimareadirectors.org/anp/buy-viagra-online have with, at the: scent buy cialis carrying – there is was http://www.parapluiedecherbourg.com/jbj/buy-cialis-online.php lotions times You http://www.palyinfocus.com/rmr/cheap-cialis/ probably ordered lot out sky pharmacy cialis this I’ve complaint! With buy generic cialis Allowed microneedling male http://www.oxnardsoroptimist.org/dada/cialis-price.html cleanser conditioner conditioner are. Who viagra price response about the.

Fiber-reinforced Concrete. This document lays down rules for strength, bendability, dimensional tolerances, and testing that apply to all kinds of steel fibers commonly used in concrete floors. Fibers must have an average tensile strength of at least 345 MPa (50,000 psi). They must be flexible enough to be bent 90 degrees around a 3-mm (1/8-in.) rod without breaking. They cannot vary from specified length or diameter by more than 10 percent. (This does not need to be put in the project specifications, because ASTM A820 does the work for you.)

ASTM C1116, Standard Specification for Fiber-reinforced Concrete, can also be incorporated into specifications. This standard regulates how fibers are added to the concrete mix.

Citing ASTM A820 and ASTM C1116 is never enough, however, as these standards explicitly leave important decisions to the designer. A complete specification covers all these points:

  • dosage;
  • type;
  • length;
  • effective diameter or aspect ratio; and
  • deformations.
From top: Type I fiber 50 mm (2 in.) long, Type II fiber 25 mm (1 in.) long, and Type V fiber 35 mm (1.3 in.) long.

From top: Type I fiber 50 mm (2 in.) long, Type II fiber 25 mm (1 in.) long, and Type V fiber 35 mm (1.3 in.) long.

This photo shows deformations on hooked ends and continuous.

This photo shows deformations on hooked ends and continuous.









Fiber dosage
The amount of fiber is usually specified by mass of fibers per unit volume of concrete—this is measured in kg/m3 or lb/cy. An alternative is to specify the fiber volume as a percentage of the concrete volume. This makes a lot of sense, especially during the design stage. A volume percentage is easier to visualize, and it stays the same across all measurement systems. However, the workers who actually put the fibers in the concrete have no way to batch by volume. They can only batch by mass, so any volume-based specification will have to be converted along the way. Figure 1 shows equivalents for some specified dosages.

Fiber dosages generally range from 12 to 42 kg/m3 (20 to 70 lb/cy). Dosages below that range are occasionally specified when fibers are used to replace light-gauge wire mesh. Dosages above that range are rare.

Setting fiber dosage is not an exact science, but ACI and SDI offer guidelines. According to ACI’s Guide to Design of Slabs-on-ground, the fiber dosage in ground-supported slabs should never be less than 20 kg/m3 (33 lb/cy). When the purpose of the fibers is to allow a wider joint spacing, this guide recommends at least 36 kg/m3 (60 lb/cy). SDI’s Standard for Composite Steel Floor Deck–Slabs, has a short, simple recommendation for steel fibers in composite steel deck-slabs: use at least 15 kg/m3 (25 lb/cy). In the end, though, the decision is up to the floor designer, who may rely on experience or on recommendations from one of the steel-fiber manufacturers.

ASTM A820 divides steel fibers into five types, based on how they are made:

  • Type I—cold-drawn wire;
  • Type II—cut-sheet steel;
  • Type III—melt extract;
  • Type IV—mill cut; and
  • Type V—cold-drawn wire, shaved into fibers.

Only Types I, II, and V are currently being used in concrete floors.

Deformations including hooked end, flat end, and continuous are shown here.

Deformations including hooked end, flat end, and continuous are shown here.

Predictably, fiber manufacturers disagree on which type works best. From the user’s point of view, the main issue is certain properties may not be available in all types. For example, in the current market the only fibers being made with hooked ends are Type I.

When discussing fiber type, one must watch out for confusion between ASTM A820 and ASTM C1116. ASTM A820, which deals only with steel fibers, divides them into the five types listed above. In contrast, ASTM C1116, which deals with all kinds of fibers, divides fiber-reinforced concretes into four types, depending on what kind of fibers they contain. In ASTM C1116, concrete with steel fibers is called Type I. Types II, III, and IV contain glass, plastic, and cellulose, respectively.

Thanks to the two different classifications, one can end up with a Type I concrete mix that contains, say, Type II steel fibers. It is important to remember the classification in ASTM A820 covers fibers, while the classification in ASTM C1116 covers concrete mixes.

Fiber length
The steel fibers used in concrete floors range in length from 25 to 65 mm (1 to 2 1/2 in.).

While it is usually agreed length matters, there is no consensus as to which length is best. It depends on what the fibers are expected to do. Engineers who rely on fibers’ ability to limit the widening of cracks after they have formed—a property called residual strength, ductility, or flexural toughness—tend to prefer longer fibers. Those who rely on fibers’ ability to prevent visible cracks tend to prefer shorter ones, because they result in higher fiber counts and less distance between fibers. Concrete workers also like shorter fibers, which are less likely to tangle and stick up above the floor surface.

Both piles have the same mass, but the 25-mm (1-in.) fibers outnumber the 50-mm (2-in.) fibers almost eight to one.

Both piles have the same mass, but the 25-mm (1-in.) fibers outnumber the 50-mm (2-in.) fibers almost eight to one.

There are limits in both directions, however. The upper limit seems to be close to 65 mm, and any longer will clump to form balls. Even fibers in the 50 to 65-mm (2 to 2.5 in.) range can tangle, and to prevent that problem are sometimes sold in collated form—stuck together with a weak glue that dissolves as the concrete is mixed. The lower limit has not been well-established, but fibers less than 25 mm long are seldom used in concrete floors today. Researchers are working with even shorter fibers, though, so floor designs that rely on lengths below 25 mm may be seen eventually.

If a design is based on fibers of a particular length, the specification should require that length. Length is specified as a single target value (not a maximum or minimum), with an implied tolerance, according to ASTM A820, of ±10 percent.

Effective diameter or aspect ratio
For a fiber with a circular cross-section, the effective diameter is that of the circular section. For a fiber with a cross-section of any other shape, the effective diameter is that of a circle equal in area to the actual section.

For fibers of Types I to IV, the effective diameter is specified as a single target number, with an implied tolerance of ±10 percent. Type II fibers, which are rectangular in section, can be specified by width and thickness instead of effective diameter. Type V fibers are supposed to be specified differently. Since the manufacturing process for Type V results in substantial variation in effective diameter, ASTM A820 suggests specifying a range with upper and lower limits, not a target. However, this rule is not universally followed. Some makers quote a single effective diameter for their Type V fibers.

People sometimes talk about a fiber’s aspect ratio instead of, or in addition to, its effective diameter. Aspect ratio is length divided by effective diameter. Since any two of those properties determine the third; all three do not need to be specified. When aspect ratio is specified, be aware ASTM A820 allows the measured value to vary by ±15 percent from the specified target.

In today’s marketplace, effective diameters range from 0.58 to 1.14 mm (20 to 40 mils). As with length, choosing the diameter involves trade-offs. Thicker fibers are less likely to tangle while thinner result in higher fiber counts.

Many people worry steel fibers will show at the floor surface, making the floor look worse. This floor, made with colored concrete and Type II fibers, 25 mm (1 in.) long, shows the steel fibers need not affect appearance.

Many people worry steel fibers will show at the floor surface, making the floor look worse. This floor, made with colored concrete and Type II fibers, 25 mm (1 in.) long, shows the steel fibers need not affect appearance.

Fiber count
Fiber count—the number of fibers per pound or kilogram—is an important factor in the effectiveness of steel fibers as concrete reinforcement. Higher counts result in less distance between fibers, and that generally means better performance. A floor design based on a particular fiber count may not work as well with a lower count, even if the mass of fibers stays the same.

Though fiber count is never directly specified, it is determined by two properties that are specified: length and effective diameter (or length and aspect ratio, depending on preference). Since shorter fibers are usually thinner, too, reducing the length dramatically raises the fiber count. In this figure, both piles have the same mass. The fibers on the right are 50 mm (2 in.) long and have an effective diameter of 1.14 mm (0.04 in.). The fibers on the left are 25 mm (1 in.) long and have an effective diameter of 0.58 mm (0.02 in.). The shorter fibers outnumber the longer fibers, almost eight to one.

Fiber count can be determined from the following equations:

In metric units:

c = 1/[(7.9 x 10-6)Lπ(d/2)2]

Where c = fiber count per kilogram
L = length of fiber in millimeters
d = effective diameter of fiber in millimeters

In U.S. customary units:

c = 1/[(0.29Lπ(d/2)2]

Where c = fiber count per pound
L = length of fiber in inches
d = effective diameter of fiber in inches

Fiber counts range from about 2500 to 20,000 per kilogram (1100 to 9000 per pound).

The earliest steel fibers were smooth, straight pins, and ASTM A820 still recognizes that shape as an option. In practice, though, the fibers used today are all deformed so concrete can grip them better. Deformations take one of three forms: continuous, hooked ends, and flat ends.

Steel fibers are being loaded into a ready-mix truck. Fibers are usually added at the concrete plant, but can also be added onsite. [CREDIT] Photo courtesy Mike McPhee

Steel fibers are being loaded into a ready-mix truck. Fibers are usually added at the concrete plant, but can also be added onsite. Photo courtesy Mike McPhee

A continuously deformed fiber has waves or bumps running down its whole length, much like ordinary steel rebar. A hooked-end fiber has a bend—or multiple bends—at each end. A flat-end fiber has its ends squashed flat, somewhat like a kayaker’s double-ended paddle.

While dosage, length, effective diameter, and deformation are the essential features every steel-fiber specification should cover, a few other details are worth considering.

Consider requiring fibers be delivered in containers marked to show the mass. Some specifiers go further and demand containers that include the exact quantity going in each cubic meter or cubic yard of concrete. If the specified dosage is 20 kg/m3 (33 lb/cy), each box or bag would have to contain exactly 20 kg (33 lb). This simplifies batching and reduces the risk of error. Some suppliers may have trouble packaging fibers in anything other than standard quantities.

Fibers should be stored under cover, protected from rain and snow. Left outdoors, boxes can disintegrate and fibers can rust.

Last, it is a good idea to insist all concrete tests, including those needed for approval of the mix design, be made after the addition of fibers. That may seem like common sense, but it will not always happen without a reminder.

Of course, it takes more than the right specification to make a successful steel-fiber-reinforced floor—it also takes a smart designer and a careful contractor. Nevertheless, a full, accurate specification is an essential part of the job when the floor is expected to fulfill the designer’s intentions.

George Garber is the author of Design and Construction of Concrete Floors, Concrete Flatwork, and Paving with Pervious Concrete. Based in Lexington, Kentucky, he consults on the design, construction, and repair of concrete floors. Garber can be reached by e-mail at ggarber@iglou.com.



LCT ONE: A Case Study of an Eight-story Wood Office Building

All images courtesy Cree GmbH

All images courtesy Cree GmbH

by Nabih Tahan, AIA

For buildings to perform better, the construction industry must change the way it designs and builds. Lifecycle Tower (LCT) ONE, an eight-story wood office building in Austria, is both a prototype and proof of a concept that demonstrates an innovative process and building. Through its use of wood, LCT ONE focuses on reducing the negative impact of buildings on the environment, while improving comfort and indoor air quality (IAQ) for occupants.

LCT ONE began as a research and development project based on the lifecycle assessment (LCA) of buildings. The motivation was to find a substitute for traditional construction practices that can have negative impacts on local and wider environments. The population is growing and the trends are shifting. People are moving from rural to urban areas. Cities must find new ways to grow around transit systems with sustainable developments that do not deplete resources and harm the environment. Therefore, cities must readapt to the current changes.

The sustainable wood and concrete hybrid building is now occupied and showcases a way of achieving mid-rise and tall buildings that can go up to 100 m (328 ft) and 30 stories.(Figure 1).

Motivation for research project
A sustainable strategy must consider the entire lifecycle of a building and its materials. This includes resource extraction, material production, construction, operation, demolition, and recycling. Since the Industrial Revolution, progress in developing cities translated into more concrete and steel produced with oil and coal, to build tall and mid-rise buildings. LCT ONE was developed to introduce alternatives by substituting renewable resources for fossil fuels, along with systems and processes that can yield better building performance.

Exterior and interior photos of LCT ONE.

Exterior and interior photos of LCT ONE.

Forestry carbon cycle
Wood is a renewable resource that grows from the sun—it is the ultimate solar product. Trees absorb carbon while providing oxygen. Modern timber-based products, such as engineered lumber, are available worldwide. Heavy glued-laminated timber (glulam) members are stable, will not shrink and twist, and can be pre-cut and prefabricated to exact tolerances, which are airtight, resulting in saved energy. At the end of a building’s life, the wood can be reused for other purposes and later turned into fuel and energy.

Further, use of wood is carbon-neutral. In other words, growing forests absorb carbon from the atmosphere and wood products store carbon. It remains stored when wood products are recycled into other products. At the end of their life, bioenergy is produced from these products, as well as from mill and forest residues and reforestation ensures the carbon cycle continues.

Ecological backpack
Selection of building materials should be linked to the use of natural resources, including raw materials (renewable and non-renewable), energy, water, and land. To specify products for the LCT system, data was collected and calculations performed to measure the total amount of natural resources required to produce a certain product or building. Since trees grow above the ground, it is resource- and energy-efficient to extract and produce wood as a building product. Wood has a much lower ecological ‘backpack’ than traditional materials, such as concrete and steel.1

Prefabricated construction process
Austria has a long history of prefabricating high-performance building components out of wood. The process begins with computer-aided design (CAD) software used to cut lumber using computer-numerical-controlled (CNC) machinery. The members are assembled in a carpentry shop, under a controlled environment where windows, insulation, sheathing, vapour retarders, and finishes were installed. The components are made to tight tolerances, can be quickly assembled onsite, and meet the most stringent blower door test requirements. Modern timber technology is available and can deliver high-performance buildings using renewable resources (Figure 2).

Prefabricated timber wall and floor panels for LCT ONE.

Prefabricated timber wall and floor panels for LCT ONE.

Operation and maintenance
Existing buildings consume a lot of energy during their operational life. To reduce consumption, the LCT system was developed according to the stringent Passive House standard introduced in Germany. The strategy is to drastically reduce consumption before relying on renewables. This is the surest path to reach zero net energy. Highly efficient solar and mechanical equipment have an ecological backpack, therefore ‘less is more.’ No need to heat and cool is more sustainable than heating and cooling with renewables or high-efficiency equipment.

The energy modeling software program Passive House Planning Package (PHPP), is an accurate tool for predicting heating demand and peak heating load in low-load buildings. The PH standard is based on energy performance (kWH/m2/year [kWH/sf/year]); in Europe, the predicted energy consumption during the design phase has proven to be accurate when compared to actual consumption during operation.2 These metrics and strategies are valid across different climate regions of the world.

To guarantee maintenance and durability, a building science consultant is part of the integrated design team and advises on the permeability and diffusion of the entire building enclosure. The most important aspect is airtightness, which prevents air and moisture from entering the building enclosure. Additionally, the building’s exterior finish material is always installed on a rainscreen, creating a ventilation layer behind it and allowing any water penetration to drain before it reaches the building enclosure.

Urban mining
All building products originated from mining the earth. At the end of their ‘lives,’ buildings are typically added to landfills and new materials are mined. The LCT research project strived to develop a solution where reusable materials are saved from landfills. Urban mining conserves our natural resources, eliminates potential energy costs, and greenhouse gas (GHG) emissions. When a building has reached its full useful life, urban mining of the LCT system can be activated, extracting materials to reuse, recycle, and convert into bioenergy, thus protecting landfills from unnecessary waste.

System and product development
As a result of the research phase, LCT ONE was designed and built as a proof of concept. The goal was to develop a system and products that can be used on any urban infill projects, but with wood replacing concrete and steel, where possible. The goal was to introduce an industrial process for buildings—similar to the process used by car and computer companies to design and build their products. Instead of miles per gallons, building performance can be guaranteed in kWh/sf/year.

To reach this goal for tall, large-volume wood buildings in urban settings, the LCT system integrates:

  • planning;
  • offsite production and onsite assembly;
  • use and future conversion;
  • dismantling; and
  • recycling of buildings.

Structural system
The LCT system was developed as a core and shell that acts as the structural system and enclosure of a tall, large-volume wood building. This system is analogous to the ‘Intel Inside’ of a computer. It is the hidden operating system on which each manufacturer relies, but each computer looks and performs according to the manufacturer’s design and specifications. Similarly, the core and shell of the LCT system can be looked at as the ‘LCT Inside’—each architectural and engineering team can design the building according to its own aesthetics, integrating the site and client’s program requirements into the design.

Posts and hybrid slabs (left) and LCT ONE interior during construction (right).

LCT ONE interior during construction (left) and posts and hybrid slabs (right).

The core is where the elevators, stairs, wet rooms, and shafts are located. It serves as the building’s stiffening element. While wood is the optimal choice as a material for the core, concrete and steel can also be used until codes enable creation of taller wood buildings.

The gravity loads are carried by a series of heavy-timber glulam posts on the exterior of the building spaced approximately 3 m (10 ft) apart. These posts are exposed on the building’s interior, adding to the warm aesthetic of the space. For fire protection, the size of the post is increased beyond the structural requirements. Approximately 38 mm (1 1/2 in.) of wood for one-hour fire protection is added to each exposed surface of the posts, which creates a charring layer in case of a fire. Wood burns ‘safely,’ because based on fire tests, calculations, and simulation, predictions can be made on how long wood will withstand the flames—therefore, the building codes allow this additional thickness in recognition of the superior fire endurance demonstrated by large wood beams and columns in fires. (Figure 3).

Hybrid wood/concrete floor slabs span about 9.1 m (30 ft) between the exterior heavy timber posts and the core, transferring all lateral forces from the former to the latter. The benefit of a hybrid system is it takes advantage of the properties of each material to meet all the structural, fire, acoustic, and thermal requirements using the least amount of resources and energy. The hybrid slabs were tested in a full-size fire chamber and passed a two-hour fire test.

International Building Code (IBC) requires ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials. However, in this case, the tests were performed in Europe according to International Organization for Standardization (ISO) 834, Fire Resistance Tests—Elements of building construction, which is the governing full-scale furnace test.

The design of the slabs provides a built-in fire separation between each floor because there is no wood-to-wood contact between floors.

Integrated building enclosure
The building enclosure is then integrated with the core and shell to give the building its aesthetic appearance. The façade is a curtain wall that withstands wind loads, but not gravity forces. The seismic forces are transferred from the glulam posts to the hybrid slabs through a hinged connection.

Building enclosure and integrated mechanical, electrical, and plumbing (MEP) systems.

Building enclosure and integrated mechanical, electrical, and plumbing (MEP) systems.

The enclosure can be made of any material, but many prefer wood, as it is a renewable resource. The windows, insulation, water, air barriers, vapor retarders, and exterior finishes are designed with the collaboration of a building scientist, mechanical engineer, and exterior wall manufacturer. These sections take into consideration the orientation of the building, as well as the energy performance and standard demanded by the client.

Integrated MEP Systems
Similarly, the mechanical, electrical, plumbing (MEP), and fire protection systems can be integrated within the core and shell and optimized according to the building orientation and enclosure. The systems can be prefabricated and are easily accessible between the structural members. (Figure 4).

Planning process
As a prototype, LCT ONE is proof of the Lifecycle Tower concept. Its foundation and core were built onsite with traditional reinforced concrete construction. The building enclosure was timber frame and the floor elements were made out of the wood/concrete hybrid slabs.

To guarantee performance, the LCT concept is designed to automatically meet the requirements of certification programs. However, as a prototype, it was necessary to compare the LCT system to mainstream certification programs. As mentioned, LCT ONE was designed to meet Passive House and received official certification from the Passive House Institute in Germany. It also applied and received Deutsche Gesellschaft für Nachhaltiges Bauen (DNGB) Gold certification from the German Sustainable Building Council.

Energy standards and certifications
The goal was to meet the energy requirements of Passive House because it has proven to be accurate in predicting actual energy consumption. In collaboration between the engineers and building enclosure manufacturer, the building envelope—as well as the mechanical, electrical, and ventilation systems—were designed to optimize the building performance according to the given location and orientation. By using the PHPP software, multiple reiteration were attempted to optimize the balance between the orientation, building enclosure, mechanical, electrical, and renewable energy systems.

Part of the production process of hybrid slabs and wood in metal frames is shown here.

Part of the production process of hybrid slabs and wood in metal frames is shown here.

The building orientation was governed by the property’s existing location. The orientation created a negative effect on the energy balance. The building would have performed better if it could have been rotated by 90 degrees. To mitigate the effect of the orientation, the thermal performance of the building envelope was improved by increasing the thickness of the wall and insulation and specifying higher-performing triple-glazed windows.

Building enclosure
The building enclosure consisted of prefabricated timber frame walls, where the insulation, windows, and sheathing were installed offsite. The connection and intersection between all wall, floor, and roof elements were designed to minimize thermal bridging. Insulation was applied on the exterior of the window frames to decrease heat losses through thermal bridging. All joints were taped to be airtight in order to meet the Passive House blower door test requirements. This test is one of the three requirements needed to meet Passive House certification. It measures infiltration air flow at a pressure difference of 50 Pa. The requirements stipulate it cannot exceed 0.6 air changes per hour (ach) at 50 Pa.

The shape, size, and number of windows were optimized for low heat loss in the winter and low heat gain in the summer, as well as to reduce demand for artificial lighting throughout the year. Tilt-and-turn operable windows were specified to allow for natural ventilation—as they open to the interior, they allowed exterior shading devices to be installed for reducing heat gain in summertime.

Passive heating and cooling
Passive heating is achieved by large windows in the staircase (eastern orientation). The morning sun heats up the concrete wall and heat is stored in the wall’s thermal mass. Passive cooling is achieved by operating the chiller machine in a free-cooling-mode during most of the year. Further, the optimized ratio between transparent windows and opaque walls, as well as deep window reveals, prevents the office building from overheating in the summer.

The production of timber frame walls is shown here.

The production of timber frame walls.

Building system
The following building systems were used on LCT ONE:

  • heating system: district heating system—renewable-fueled combined heat and power;
  • cooling system: conventional chiller machine with enhanced free-cooling-option;
  • hot-water system: highly efficient, decentralized water boiler on each floor;
  • heat recovery ventilation: central system installed in basement with carbon dioxide (CO2) sensors on every floor that control the amount of air introduced;
  • lighting: fully automated and daylight-dependent lighting system (including motion detection), automated dimming and zoning, and daylight-dependent shading operation and positioning;
  • services: fully automated building services system;
  • controls: motion and window detector controlled heating and cooling, as well as CO2 sensors;
  • waterless urinals; and
  • photovoltaics (PV): 10-kW (peak) rooftop system—prepared for future installation of a 10-kW PV on the southern façade, which will be required to become a zero net energy building.

Blower door tests were conducted in two stages. The first was a random test at two floors performed after the installation was completed. (The core was excluded.) The result was 0.35 ach at 50 Pa. Before commissioning, a blower door test was performed on the entire building, including the core. The results were 0.55 ach at 50 Pa, meeting the Passive House standard.

Construction process
While foundations and concrete core where being built onsite, the wall elements and the hybrid wood/concrete floor slabs were produced offsite. The assembly of the wall and hybrid floor elements took eight days onsite, one floor per day.

Producing slabs
The industrial production of the hybrid wood/concrete slabs took place in a precast concrete shop. The heavy timber glulam beams were supplied by a lumber manufacturer who cut them accurately with CNC machinery and attached the required metal fasteners and connectors. The beams were delivered to a precast concrete manufacturer, who placed them in metal forms, added metal reinforcement and poured the concrete. This process was repeated daily for each form. The advantage of this system is it allows the concrete to cure offsite and prevents additional moisture into the building. Additionally, prefabricated slabs are assembled quickly onsite (i.e. eight minutes per slab) to tight tolerances (Figure 5).

LCT ONE on day two, four, and eight of the installation process.

LCT ONE on day two, four, and eight of the installation process.

Producing walls
The walls were produced in a local carpentry shop. Engineered lumber was used for all wood members, including studs. The panels were produced on tables, horizontally, where the timber frame, sheathing, and insulation were installed. After standing up the walls, the windows were installed. All joints, including around the windows, were sealed airtightly with high-performance tapes (Figure 6).

After production, all the slab and wall elements were shipped to the site and assembly began. Five skilled carpenters were able to assemble all the components, water- and airtight in eight days, for all eight stories (Figure 7).

To verify the energy standard will be met, blower door tests were performed twice as mentioned—once when the installation was done and again before commissioning.

LCT ONE begins with the premise the building industry does not automatically have to rely on concrete and steel for all urban buildings; it demonstrates there is the opportunity to substitute timber for many applications.

Wood is a renewable resource. Essentially, while one building is in construction, the sun is producing the timber for the next building. Timber technology has advanced, where modern industrial machinery and processes make it possible to erect timber buildings quickly, economically, and according to all building regulations and high-performance standards.

LCT ONE is pioneering a new way of building, based on guaranteeing performance. It was developed according to a system that can be the shell and core, while still offering flexible design solutions and architectural and aesthetic possibilities to make each building unique. By following this ‘system approach,’ the performance of buildings can be guaranteed, similar to the performance of cars, computers, and other products manufactured through industrial processes.

The LCT system can be applied as a worldwide solution. With its introduction in Europe and now beginning in North America, it serves as an inspiration to wean the traditional building industry away from only fossil-fuel-intensive products and systems. Less-developed countries, especially those with forests, can adapt the LCT system to modernize their building industry. They can introduce new sustainable forestry management policies and begin manufacturing modern, engineered lumber products to build high-performance timber buildings. A new process of education to create new green jobs and affordable housing solutions could be an alternative to attempting to develop building solutions that rely on fossil-fuel-based resources that less-developed countries do not have and cannot afford.

1 For more on the ‘ecological backpack’ concept, see M. Ritthoff et al’s Calculating MIPS: Resource Productivity of Products and Services, at epub.wupperinst.org/frontdoor/index/index/docId/1577. See also K.-H Robèrt et al’s “Strategic sustainable development–selection, design, and synergies of applied tools” in the June 2002 issue of Journal of Cleaner Production. (back to top)
2 For more information visit, www.cepheus.de. (back to top)

Nabih Tahan, AIA, is an international architect, Passive House consultant, and vice president of business development for Cree Buildings. For more than 30 years he has honed his knowledge in architecture, energy efficiency, and sustainable timber-based construction methods through work in Austria, Ireland, and the United States. In 2005, his own retrofitted home became the first Passive House home in California. Tahan also acts as the North American ambassador for Cree Buildings, and educates architects, developers, building engineers, and municipalities on the potential of tall wood buildings. He can be contacted at nabih.tahan@creebuildings.com.