This article was originally published in The Construction Specifier, October 2014 issue, pg 62- 70.
A childhood treehouse, a place to hang a swing, or the support for a hammock in the cool shade—many of us can think back to these valuable memories that reflect the utility of trees in urban and suburban spaces. What if there were additional memories to be gained from the death and removal of those same trees? In a growing number of cities in the United States, urban forests are being recognized as a valuable, renewable resource for furnishings, paneling, flooring, or trim for residential or commercial spaces.
However, this transformation is neither straight forward nor simple. The process does not call for clear-cutting local parks—it involves the removal of trees that are diseased, storm-damaged, at the end of their natural lives, or need to be removed to make way for new development and street repairs.
Urban forestry is an industry resulting from the infestation of the emerald ash borer (EAB) that began in Michigan in 2002 and has now spread as far as Colorado, Georgia, and northeastern Canada. There are an estimated eight billion ash trees in the United States, and approximately 150 to 200 million have already died as a result of this invasive species.1 However, urban forestry is not limited to ash trees. In Milwaukee, the city cuts down and transports Norway maples, elms, honey locusts, basswood, and poplar—all of which are sent to a local mill for processing and are available for sale.
Urban versus wilderness
Milwaukee is somewhat unique in that its department of forestry is responsible for cutting and trimming all city trees. The department can uniformly instruct the workers how to cut down the trees. The city also has a unique relationship with a local sawmill (Kettle Moraine Hardwoods), whose owner, Bob Wesp, has personally taught the workers how to look at a tree and keep in mind its usability as urban-cut lumber.
This might sound simple, but it is important to keep in mind the average city’s municipal employee is not a lumberjack from the Pacific Northwest with the skill and knowledge of how a mill will cut the tree into 1-by planks. For urban forestry, the first thing that needs to be done is to tell the workers the logs need to be as long as possible. Typically, tree service companies cut down trees into 915 to 1220-mm (3 to 4-ft) long logs that are small enough to fit into a Bobcat skip loader so they can be taken to the corporation yard where they will be ground into wood mulch. However, carpenters want trim that is at least 2.4 m (8 ft) long—preferably 3.1 to 3.7 m (10 to 12 ft) to eliminate mid-wall joints. Additionally, mills want a trunk or branch to be at least 254 to 305 mm (10 to 12 in.) in diameter for efficient sawing.
Urban foresters should take this into account by cutting too high up on the trunk or too close to the crotch of a pair of branches they may unintentionally lose some really rich graining that will add a great deal of character to the planks. This is particularly the case for wood selected for furnishings where a unique grain pattern or coloration can make all the difference between just a piece of furniture and that special chair or table that can garner a higher price.
In regular forest-harvesting, the logs are placed on a 15 to 21-m (50 to 75-ft) tractor trailer. In urban forestry, a 25-m2 (30-cy) dumpster is the typical means of carrying the logs from the site to the mill, which means a log’s length is limited to a maximum length of about 7 m (21 ft) due to the dumpster’s length. The urban forester also needs a lift large enough to safely handle a 58 to 76-mm (20 to 30-in.) log that is 6.9 m (20 ft) long. Once the dumpster is full, it is transported to the mill.
Meet the beetles
Photo credit: organicplantcarellc.com
One of the first cities to undertake such efforts was Ann Arbor, Michigan, which was badly hit by the emerald ash borer. It is estimated that 7000 ash trees that lined its streets and yards were lost, and another 3000 were removed from the parks and surrounding nature areas, at a cost of at least $2 million. It is further estimated southeast Michigan lost upward of 30 million ash trees.2
EAB is believed to have come to the United States from Asia via packing crates and pallets. The beetle kills a tree by burrowing under the bark and depositing its larvae in the Cambrian layer, disrupting the tree’s ability to transport water from the roots to the leaves. Fortunately, the larvae do not damage the wood—this means if the tree is healthy and solid without rot or large splits, its lumber will be fine for higher-value uses.
The first method of EAB control was to clear cut areas within 405 m (1320 ft) of the infested tree. Now, this radical surgery-management style is giving way to a controlled cut system such as that employed by Milwaukee in which insecticide is used to slow the EAB from destroying entire neighborhoods of trees, thereby giving the forestry department time to extend the devastation and tree replacement process out over a decade or more. The loss of so many trees within such a short time produced a significant volume of wood. Traditionally, such lumber was ground up for mulch, processed for bio-mass energy generation, or just sent to the landfill.
The Southeast Michigan Resource Conservation and Development Council (SEMIRCD) received a grant from the U.S. Department of Agriculture (USDA) to show there could be an economic benefit from the EAB problem and demonstrate markets for removed lumber.3 Through their efforts, numerous new markets for urban wood have been developed. For instance, an American Institute of Architects (AIA) Michigan award-winning project (Ann Arbor’s Traverwood Library) used reclaimed ash for flooring, wall panels, and ceilings. Structural columns utilized trees that were simply stripped and sealed leaving the scarred, rune-like patterns left by the chewing beetles.4 Similar efforts are now being employed in other cities, including Milwaukee.
From mill to shop
Once at the mill, a log may be set aside to dry, but because there might not be enough lumber to make up a pallet of one type, logs may have to wait until an adequate amount has accumulated. Unless there is a specific order for pieces of a specific size, a tree will be cut as ‘log-run,’ which is approximately 25 mm (1 in.)—or 4/4—thickness by random widths. This can be milled to 18-mm (3/4-in.) material that in turn can be used for most siding, flooring, and trim. Stair treads, mantels, and other special pieces need to be identified early so wider pieces with particularly good character can be cut at the same time. As this is log-run material, a pallet of lumber is not sorted or graded and the planks from a set of trees can range from FAS to No. 2 Common as defined by the National Hardwood Lumber Association (NHLA).
Another issue for urban lumber that is much more of a challenge is the greater likelihood that nails, wire, or bolts have been embedded in the tree. This means each log has to be magnetically scanned and cleared. Hitting even a small nail can ruin a blade, endanger workers, and result in downtime to make repairs. The mill operator in Milwaukee reported that from 30 to 35 percent of the urban trees it receives contain metal versus about two percent for trees coming from a standard forest preserve. They then have to pull those trees aside and search for the metal, and then remove it. If they cannot find the metal (or if there is too much of it), the tree may have to be discarded.
Once cut, hardwoods can take as long as 200 days to achieve 20 percent moisture content (MC) when just stacked with stickers (wood strips) between the planks. This is still a long way from the six to eight percent needed for interior use, so the wood must be put in a kiln, which takes two to four weeks to bring the wood to the desired moisture content. Then, the board can be shipped to a cabinet shop for fabrication.
If an owner or designer wants to use a particular stand of trees, the required time to turn those living trees into usable lumber for a carpenter or furniture-maker would be two to three months from the date of hewing the trees to have lumber stock ready to be milled into flooring, paneling, or trim. Most mills will have cut and dried urban lumber, but it is necessary to check to find out how much lumber is on hand so as not to delay the project.
Due to the need for a city to have a clear process to deliver its trees, most cities will probably have just one mill do the processing. Contractors and designers must connect with this firm, or work with another organization that has established a relationship with the mill to facilitate ordering and delivery. Groups such as Southeast Michigan Resource Conservation and Development Council in Michigan and Wudeward Urban Forest Products in southeast Wisconsin promote urban lumber use though education to the design and construction industry. More can be found on a state-by-state basis as businesses and cities look for an ecologically sound response to the losses in urban forests.
Once the lumber arrives at a cabinet shop, the real beauty of the wood emerges as the rough-sawn planks are trimmed, edged, and shaped into usable pieces. The hidden benefit of urban lumber starts to be realized at this time as richer colors and grain patterns emerge. However, since log-run lumber is not graded or sorted, splits, warping, and snapping at loose knots can easily claim upward of 50 percent of the lumber delivered from a pallet, adding to the cost to the fabricator in lost materials and time. The designer and owner may want to schedule a visit to the shop at this time to verify the design intent for the wood is being realized, especially when the piece is a feature element such as an entry wall or reception desk.
The green forest
Another clear benefit of using urban lumber is the ability to gain credits from sustainability programs. With the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design (LEED) program, credits can be easily claimed for Materials and Resources (MR) Credit 5, Regional Material Use.
MR Credit 7, Certified Wood, is a more problematic credit to obtain. The difficulty arises in the lack of an established recognition by the Forest Stewardship Council (FSC) of urban wood. At press time, FSC had announced there will be a motion offered at its General Assembly to be held in Seville, Spain, in the fall to ‘capture’ urban wood as part of the supply stream. Many issues will have to be resolved to establish the type of recognition, but this is a positive event that was not expected by many in the urban wood community for at least another three years.
The designer’s role through this process is that of educator and facilitator. They need to ensure the contractor (and the related subcontractors) are aware of this special product and that additional care may be required during bidding and fabrication. They also need to make certain owners are aware this unique, sustainable resource is available and can be an asset to the completed project. As mentioned, the designer needs to be much more hands-on to facilitate the proper use of the urban lumber. It is akin to working with a fine marble slab—the goal is to capture as much of the intrinsic drama and beauty possible from a natural and non-uniform material.
Specifications
Specifiers have a key role in that urban lumber correctly specified and incorporated in the project. Typical sections that would be used are MasterFormat 06 20 00–Finish Carpentry, 06 41 00–Architectural Casework, and 09 64 00–Wood Flooring. A small but important addition to a standard master specification should be a brief definition such as:
Urban Lumber: Wood that is obtained from trees located in cities, towns or suburbs not harvested for their timber value, but removed because of insect, disease or circumstance.
This will help clarify the material, distinguishing it from salvaged lumber, which may be collected from an existing building, or from rivers and lakes.
Other key areas should be inserted into a specification section depending on the level of desired aesthetic control. They include:
- samples of adequate size and length to show the range of acceptable color, grain, and acceptable flaws;
- pre-fabrication meeting, where the designer, owner, contractor, and millworker meet to establish the quality of the finish work;
- mockup approval of casework, paneling, or flooring to verify the desired quality level;
- list of approved mills or suppliers that deal with urban wood near the project; and
- clarification of the grade (or lack thereof) provided by the mill or supplier for the urban wood—NHLA grades are probably the best source for these, but there is no recognized grade for log-run material (it should be listed to give the cabinet shop an idea of what to expect).
Another important provision, especially for casework or stairs, is to use (AWI/AWMAC/WI) standards to define the expected quality standard of the completed work. These standards control the amount of grain and color-matching between members to ensure a uniform appearance is achieved (or not achieved, depending on the designer’s intent). This is especially the case when using wood such as ash that can have a broad variety of color and grain pattern within the same board.
When the designer is aware of the possibilities, a truly remarkable piece of casework or paneling can be achieved. By utilizing urban lumber, owners can attach a great story and add a unique component to any building.
Conclusion
From the disaster of emerald ash borer infestation emerges new opportunities to enrich urban spaces and provide new memories from city trees. Architects, contractors, and owners have the ability to use and promote this unique resource, but as with any ‘new product,’ the various parameters must be understood for its correct use to achieve the best results for all involved.
Provided design/construction professionals and urban forestry workers know the ideal criteria for board length, importance of identifying special cuts early, and the need to sort or grade material prior to delivery to fabricators to minimize waste results, urban lumber has great opportunity for richer character in the wood, making for a unique finish with a great back story.
Notes
1 This comes from Therese Poland and Deborah Therese’s April/May 2006 article in Journal of Forestry, “Emerald Ash Borer: Invasion of the Urban Forest and the Threat to North America’s Ash Resource.”
2 See Marianne Rzepka’s August 22, 2010 article in the Ann Arbor Chronicle, “Seeds and Stems.”
3 For more information, visit www.semircd.org.
4 The project was profiled in Bradford McKee’s October 6, 2009 article, “Traverwood Branch Library,” which appeared in Architect.
Additional Information
Author
- Gerard Capell, FCSI, AIA, CCS, is principal of Capell Design Associates in Milwaukee, Wisconsin, providing architectural design and specification writing services. His experience has broadly evolved from his work in California, Wisconsin, and Florence, Italy; this includes work as a rough and finish carpenter, architect, and specification writer on healthcare, education, civic, residential, senior living, retail, and industrial projects. Capell has served on CSI’s Certification Committee and Board, along with positions at the region and chapter level over his 28 years as a member. He can be reached at jgcapell@wi.rr.com
Abstract
In the wake of the devastation caused by the emerald ash borer, urban lumber harvesting has emerged as a response in the United States and Canada. Instead of grinding the wood into mulch, the urban wood movement promotes using urban forests to provide distinctive finishes for built spaces while also connecting those spaces to a piece of history. Designers, contractors, specifiers, and related professionals wishing to use urban wood must be aware of special considerations if they wish to take advantage of this unique resource