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Designing Millwork: What Architects Should Know
By Jim McBryar
Architectural millwork is often the first thing that someone sees upon entering a space. Carefully used, architectural millwork can be a primary tool to communicate design intent and produce the atmosphere that the designer is seeking to achieve. At the same time, the potential exists for millwork to become a bland but expensive disappointment. Worse yet, if millwork is not properly designed and constructed it can lead to expensive errors which diminish function or even damage the millwork or other surfaces. Fortunately, a few simple tools and approaches to millwork design and specification can help designers avoid some of the most common sources of problems and disappointment.
First and foremost, any design professional who will be designing and specifying millwork should familiarize themselves with the quality standards established for architectural millwork by the Architectural Woodwork Institute (AWI). AWI is a non-profit trade association with over 4,000 members from manufacturing, supply and design firms. The quality standards for architectural millwork established by AWI are the industry standard for the design, construction, and installation of millwork of the highest quality. The standards speak to every aspect of millwork production including technical specifications for materials, joinery, finishing, and installation of a wide range of millwork products such as cabinets, doors, windows, trim etc.
These standards are published by AWI in Architectural Woodwork Quality Standards Illustrated. Because the production of architectural millwork is highly technical the AWI standards provide a reliable way for design professionals to be certain that the millwork that is part of their projects will be properly constructed and installed without having to become technical experts in wood product manufacturing. AWI has established three quality grades: economy, custom and premium. Economy grade is rarely specified in commercial millwork and the majority of work performed to AWI standards is either custom or premium grade. Premium grade standard is the best grade for use in commercial applications where millwork receives the most wear and tear.
By specifying millwork be compliant with the AWI quality standards, the designer can save time that would otherwise be spent on construction details and verify compliance by checking shop drawings. This approach frees time to be proactive in the specification of critical materials like veneers or LEED certified products.
The proper specification of veneers for architectural millwork is one of the most important things a designer can do to insure a beautiful end result and a satisfied client. Veneer specifications should take into account the unique qualities of wood as a natural material and the wide variation this creates is the quality and price of different flitches of veneer. (The complete set of thin individual pieces of veneer called leaves that are sliced from an individual log are referred to collectively as a flitch, thus, each flitch comes from only a single log.) Just as each tree looks different from every other tree on the outside, so each individual log looks different from every other on the inside. The four most important visual elements of each flitch are its color, grain, figure and size. Grain refers to the long lines formed by the tree’s annual growth rings which generally run parallel along the length of the flitch. Figure refers to patterns of lighter and darker wood that are the result of natural patterns of growth or sometimes biological “defects” in the wood. Common forms of figure include curl, flame, fiddle back, burl, bird’s eye, and bee’s wing. Because veneer is a product from a living organism the color, grain figure and size of each flitch vary not only from each other but between each leaf in the flitch and even within each individual leaf, as the log varies from one end to the other
The price of each flitch is determined by the overall appearance of the log, with logs having the most figure and most beautiful and consistent color fetching higher prices. Some figures like bird’s eye that are the result of defects in the wood commonly occur in only portions of the log, so flitches with the figure throughout are rare and therefore very expensive. Because the trees from which the flitches are sliced can also vary greatly in diameter, the width of flitches can vary widely as well, even within the same species of wood. This great variation in individual flitches means there is also great variation in the price of veneer. The selling price of the material alone may be as little as six to eight dollars a square foot for veneer laid up from plain narrow flitches of common domestic hardwoods or as high as 30 to 35 dollars a square foot and more for veneer laid up from wide, highly-figured flitches of tropical hardwoods. It also means that different flitches of the same species may or may not be a good match for any given millwork design. A narrow flitch may have a stunningly beautiful figure but produce an unattractive striped effect if used on broad expanses of wide wall panels. Similarly, a wide flitch applied to a narrow element like a pilaster or corridor portal may be wasted or even look odd.
These issues are most likely to arise when there is a minimal specification of veneer. Faced with a specification like “cherry to match architect’s sample,” millworkers and veneer suppliers are faced with a difficult dilemma. Manufacturers and suppliers are most likely to quote middle of the road to less expensive materials when faced with vague specs. Once work is awarded, submittals of veneer samples still require a great deal of guess work when the designer’s intentions are not clearly communicated with a precise veneer specification. These realities may lead to disappointing multiple rounds of material submittals or worse.
The best way to avoid these problems is to specify the actual veneer flitches to be used and design the millwork to take full advantage of what they have to offer. In short: pick a log; then design millwork. Veneer suppliers assign each flitch an individual number and will allow designers to view flitches and select them for use on their projects. The most beautiful and distinctive millwork is created in this way. By seeing the actual size, color, grain and figure of the flitch, all surprises are removed. Designing the millwork in this way acknowledges the unique qualities of wood as a natural material and results in veneer that matches and complements the design of the millwork. This approach also makes it much easier to design effectively with more than one species or figure. It also allows the designer to specify different flitches for different areas of a job. This can be useful on large jobs where a single flitch may not provide enough material to do all areas or where some areas can use lower priced veneer to meet budgetary concerns while still using higher quality veneers for areas like lobbies or board rooms.
A second important benefit of this approach is that it puts all bidders on a level playing field and lets the designer know what the flitch price is to begin with. (Keep in mind that the waste factor when laying up veneer is high because of the irregular shape of the edges of the flitch. On average it takes about three square feet of material in the raw flitch to produce one square foot of laid-up veneer.) If a particular flitch number has been specified, the designer and owner can be sure when comparing different millwork bids that a lower price isn’t lower because the bidder quoted a lower grade of veneer.
Failing this, designers should at least specify the species, cut (plain, rift or quarter sliced), and the amount of figure (none, light, moderate, heavy) to use. While this type specification is completely subjective and cannot take the place of specifying an exact flitch number, it at least gives manufacturers and suppliers a better idea what to bid and what to use for submittals.
Designing for Wood Movement
Along with the specification of veneers, another of the most common problems in millwork arises from another quality of wood as a natural material. Wood is hydroscopic, meaning it absorbs and releases moisture in response to changes in the relative humidity of its environment. As humidity goes up, the wood swells and increases in size and it shrinks when relative humidity drops. Wood also looses moisture overall and shrinks over time. The force exerted as wood expands is extremely powerful. For example, the traditional means of splitting granite was to drill rows of holes into the stone and then insert dry wooden dowels loosely into the holes. When water is poured into the holes the force of the expanding wood splits apart the solid granite to create a slab. In millwork, the force of expanding wood cannot be contained by mechanical means. Glues and fasteners cannot resist the wood movement which will cause failure of the glue, failure of the fastener or the destruction of the wood by buckling or cracking. Expanding millwork can also destroy other surfaces to which it is attached. For instance, a long run of wall panels trapped between two sheetrock sidewalls without room to expand can easily punch holes into the sidewalls. While this problem is most pronounced in solid wood, man-made composites like particle board and MDF (medium density fiberboard) also expand and contract in the same way.
The first line of defense against these problems points back to the specification of millwork to AWI standards. The AWI technical specifications for millwork construction and installation take wood movement into account and millwork constructed to them should not exhibit these kinds of problems. It also helps to take the environment the millwork will be installed in into account. New buildings with efficient HVAC systems that closely control temperature and humidity are less likely to have problems, but the designer must consider that those systems can still break down and cause problems for poorly designed millwork. In environments like older homes without air conditioning in climates with wide variation in relative humidity, it might be best to avoid designs which are more likely to trap expanding wood such as inset stile and rail doors on cabinets. At a minimum, the design should at least leave sufficient clearances around elements like doors to allow for maximum expansion and contraction. The AWI Architectural Woodwork Quality Standards Illustrated provides guidance for wood movement for woods of different species.
Wood paneling is one of the most likely places where problems with wood movement can occur. Because of the size of individual panels and length of panel runs, expansion and contraction can become a serious problem without provisions for wood movement. The most common error to avoid is the specification of butt joints in paneling. For aesthetic reasons, it may be desirable to create wide expanses of paneling without reveals, but this design will inevitably result in problems. At the least, the panels are likely to move and shrink over time leaving unsightly and uneven gaps between panels. At worst, the panels may expand, damaging the panels or the wall. The best approach is to create designs that incorporate reveals of at least ¼” into the look of the paneling. The reveals need not be simple black lines. They can be any size wider than ¼” and can be made from materials that contrast or complement the panel material. Incorporating the reveals into the design of the paneling allows panels to move individually while maintaining a uniform look. Panels should always be hung on a system that allows each individual panel to move such as z-clips and should never be face nailed or screwed in such a way as to trap the panels.
While obviously not exhaustive, these few simple steps can avoid costly but common mistakes in millwork design and specification. Using the AWI quality standards and relying on them for construction details can’t guarantee there will never be problems with millwork, but specifying them, using millwork firms that understand and habitually employ them, and checking finished millwork for compliance can go a long way towards reducing errors. Keeping the unique qualities of wood as a natural material in mind both heads off problems and allows the design of distinctive and beautiful millwork that builds reputations and repeat business.
Jim McBryar is a cost estimator for Legere Woodworking in Avon, Connecticut, the largest producer of commercial millwork in the Northeast.
Keywords: Building performance, Millwork, Architectural woodwork, Architectural wood casework, Finish carpentry, Wood paneling, Wood veneer, Article