Glued Laminated Timber Appearance Classifications for Construction Applications

TECHNICAL NOTE Glued Laminated Timber Appearance Classifications For Construction Applications

Number EWS Y110 a Premium appearance classification may desired finished member appearance for August 2003 be specified based on the presumption any layup combination. However, the that the member will have better structural structural properties assigned for the characteristics than an Architectural or specified layup combination (or struc- This Technical Note clarifies the Industrial classification when, in fact, all tural grade) are not affected by these distinction between appearance consider- three classifications will have identical cosmetic modifications that are made to ations and structural properties of glued strength characteristics if manufactured to change the finished member’s appear- laminated timber (glulam) members. In the same layup combination. To minimize ance. (See EWS Technical Note Y117 for addition, it describes practical buyer- this confusion, Engineered Wood Systems a more detailed discussion of allowable seller appearance classifications of (EWS) identifies these different appear- design properties for glulam.) glulam members as they are commonly ance characteristics as appearance used in residential and commercial con- “classifications” rather than “grades.” Commentary on struction applications. Appearance Classes Appearance Characteristics vs. It is important to understand that the Introduction Structural Properties of Glulam individual laminations used in the manu- Industry recommendations for the Structural properties of glulam are facture of any glulam product may pos- finished appearance of glued laminated established by industry manufacturing sess the natural growth characteristics timber have traditionally identified three specifications and/or building code permitted for the lumber grade specified, “grades:” Premium, Architectural and research approvals. Lumber species and regardless of finished member appear- Industrial. All of these appearance grades are specified for glulam in various ance classification. This is the basic “grades” permit the individual lamina- layup combinations that in turn establish premise for defining the appearance tions used in the glulam layup to possess specific design properties for the classifications that follow. the natural growth characteristics of the given member. Premium Appearance (PREM) – The laminating lumber grades specified. In A typical layup combination (or structural highest appearance classification for use order to account for the visual impact grade) would have a designation such as when appearance is the primary design of these natural growth characteristics, 24F-V4 (DF) or 24F-V5 (SP) depending consideration. Specific characteristics of cosmetic repairs may be made to the on species and end use requirements. this classification are: finished member as required to meet These layup combinations require that a In exposed surfaces, all knot holes and other the desired finished appearance. certain species of lumber be used and voids shall be filled with a wood-tone filler or However, the use of the term appearance that specific grades of lumber be posi- with clear inserts selected for similarity with “grades” associated with these non-struc- tioned throughout the depth of the mem- the grain and color of the adjacent wood. tural cosmetic classifications often leads to ber in accordance with their individual The wide face of laminations exposed to view confusion in the marketplace. Specifiers strength characteristics. shall be selected for appearance and shall be and users often think of appearance Lumber grade characteristics, such as free of loose knots with the knot sizes limited “grades” in terms of structural distinctions open knots or other voids, and the to 20% of the net face width of the lamination. when in fact structural properties for a appearance considerations inherent in Not over two maximum size knots or their given glulam layup are independent of the glulam manufacturing process itself equivalent shall occur in a 6-foot length. appearance considerations. As an example, may be cosmetically altered based on the

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©2003 APA – The Engineered Wood Association All voids shall be filled in exposed surfaces. The wide face of laminations exposed to view Loose knots and knot holes appearing on the Voids greater than 1/16 inch wide created by shall be free of loose knots and open knot wide face of the laminations exposed to view edge joints appearing on the wide face of the holes shall be filled. shall be filled. lamination exposed to view shall be filled. Knot holes shall not exceed 3/4 inch when Members are required to be surfaced on Exposed surfaces shall be surfaced smooth measured in the direction of the lamination two sides only and the appearance require- with no misses permitted. length with the exception that a void may be ments apply only to these sides. longer than 3/4 inch if its area is not greater The corners of the wide faces exposed to view Occasional misses, low laminations or wane than 1/2 in.2 shall be eased. (limited to a maximum of 1/4 inch measured Voids greater than 1/16 inch wide created by across the width) are permitted on a cumula- Commentary – This is perhaps the most edge joints appearing on the wide face of the tive basis, not to exceed 10% of the width of misunderstood classification. Because of lamination exposed to view shall be filled. the member at any glueline. The frequency of its name, specifiers and end users often

ORIZED BY EWS IS PROHIBITED BY THE U.S. COPYRIGHT LAWS. THE U.S. EWS IS PROHIBITED BY ORIZED BY occurrence shall not exceed one in ten pieces equate this to what the glulam industry Exposed surfaces shall be surfaced smooth of lumber used. The maximum area of low refers to as a “furniture grade,” i.e. the with no misses permitted. laminations shall not exceed 5% of the sur- customer expects the finished glulam to The corners of the wide faces exposed to view face area of a side and no more than two low approach the appearance of high quality shall be eased. laminations shall be adjacent to one another. furniture. Unfortunately, this is not possi- Commentary – This is perhaps the most Permissible wane in accordance with the ble and although all voids will be filled, versatile and widely specified appearance provisions of the layup combination is not the finished glulam will still exhibit the classification because it is compatible limited in length. natural visual characteristics of lumber with a wide range of building designs. Industrial-L Appearance (IND-L) – This such as knots. Also, this appearance class Most of the voids associated with the appearance classification is a sub-classifi- is often specified based on the misunder- natural characteristics of the laminating cation of the Industrial appearance classi- standing that it will impart higher strength lumber are filled for an Architectural fication. The “L” indicates that laminated properties to the member, when in fact, it appearance classification. This classifica- veneer lumber (LVL) has been used for does not. tion is suitable for a variety of construc- the outer laminations. All other character- Premium appearance should only be tion applications where glulam members istics remain the same as those listed for specified when the highest available visual are exposed in the finished structure the Industrial appearance classification. characteristics of glulam are required and such as in residences, office buildings, where exposed glulam members must restaurants, schools and a myriad of Commentary – Industrial appearance is have smooth surfaces suitable for staining other similar uses where finished appear- just what its name says, an appearance and painting. The use of glulam as the ance is of importance but is not the classification that is suitable for most structural framing members in religious overriding consideration. industrial applications such as roof beams in warehouses or manufacturing structures is just one example where this Most “stock beams” inventoried by dis- facilities where the appearance of the appearance classification is typically speci- tributors and dealers for residential and exposed glulam is not of primary impor- fied. The specifier is cautioned that light commercial uses are Architectural tance. These are also typically used when Premium appearance glulam is not a appearance. This permits the contractor the members will be concealed by sus- stock item and longer lead times are to use them in an exposed application if pended ceilings or other coverings, required to obtain this type of product. required, while also effectively using regardless of the type of construction. Architectural Appearance (ARCH) – A them in concealed applications such as high quality appearance suitable for appli- headers and floor beams. Framing Appearance (FRAMING) – The Framing appearance classification is a • ALL RIGHTS RESERVED. • ANY COPYING, MODIFICATION, DISTRIBUTION OR OTHER USE OF THIS PUBLICATION OTHER THAN AS EXPRESSLY AUTH THAN AS EXPRESSLY OTHER USE OF THIS PUBLICATION DISTRIBUTION OR OTHER MODIFICATION, • ANY COPYING, • ALL RIGHTS RESERVED. cations where appearance is an important Industrial Appearance (IND) – The classification introduced by the industry but not overriding consideration. Specific minimal appearance classification nor- to accommodate home building and characteristics of this classification are: mally suitable for use in industrial plants, other construction markets where glulam In exposed surfaces, all knot holes and voids warehouses and other similar structures is used in combination with dimension measuring over 3/4" shall be filled with a and for concealed applications where lumber in roof, wall and floor framing. To wood-tone filler or clear wood inserts selected appearance is not of primary concern. be compatible with the conventional ENGINEERED WOOD SYSTEMS for similarity with the grain and color of the Specific characteristics of this grade are: framing lumber sizes without the need adjacent wood. ©2003 Voids appearing on the edges of laminations for furring or other specialized framing, need not be filled. glulam is supplied in 3-1/2, 5-1/2 and 7-1/4-inch widths. 2 Glulam members manufactured to be compatible with these dimensions are FIGURE 1 finished to what are referred to in the MANUFACTURING IRREGULARITIES PERMITTED industry as “hit or miss” surfacing. Since IN FRAMING APPEARANCE CLASSIFICATION none of the previously described appear- ance classifications have this minimal level of surfacing, the new Framing Wane void classification was introduced. Surface characteristics of glulam members finished to this classification include: Glue squeezeout Manufacturing characteristics including low laminations, end joint offsets and glueline squeezeout are permitted. Lumber characteristics permitted for the “Low lamination” areas given layup combination may include knot holes, splits and wane. Dimension Finished lumber glulam Voids appearing on the edge of laminations width width need not be filled. Loose knots and knot holes appearing on the wide face of the laminations exposed to view appearance member widths are Special Appearance Considerations need not be filled. surfaced to net sizes (3-1/2 inches and In addition to the appearance Members are required to be surfaced “hit or 5-1/2 inches) which permit width com- classifications described in this Technical miss” on two sides only and the appearance patibility with dimension lumber sizes Note, additional appearance require- requirements apply only to these sides. used in conventional 2x4 and 2x6 fram- ments for glulam members may be speci- The accumulative depth of hit and miss and ing systems. Figure 1 above illustrates fied based on buyer-seller agreement in wane shall not exceed 15% of the width of the some of the manufacturing and lumber accordance with project specifications. member in any glueline. The maximum area characteristics that would be permitted Such special appearances may include of low laminations or wane occurrence shall in the Framing appearance classification rough sawn surface texturing, plant appli- not exceed 25% of the surface area of a side. when glulam is surfaced to match cation of stains or other surface finishing. Permissible wane in accordance with the dimension lumber widths. The specifier or buyer are urged to con- provisions of the layup combination is not As indicated, glulam surfaced to net tact their supplier before specifying any limited in length. dimension lumber widths will typically special appearances. Framing-L Appearance (FRAMING-L) – result in areas of low laminations and This appearance classification is a sub- voids due to the presence of wane lumber Further Information that may not be surfaced away as shown classification of the Framing appearance For further information on any aspect in the illustration. Glue squeezeout along classification. The “L” indicates that lami- of designing with glued laminated gluelines in low lamination and wane nated veneer lumber (LVL) has been used timber, contact: for the outer laminations. All other char- areas may also be visible in the finished width of the Framing classification. This APA EWS acteristics remain the same as those listed 7011 So. 19th St. for the Framing appearance classification. appearance class should be used only when the member will be concealed from Tacoma, WA 98466 Commentary – The surface irregularities view in suspended ceilings, headers, or Tel: 253-565-6600 common to the glulam manufacturing other applications where appearance is Fax: 253-565-7265 process are typically removed by surfac- not important. ing to standard glulam widths of 3 inches or 3-1/8 inches for nominal 4-inch mem- The Framing appearance classification is bers, and to 5 inches or 5-1/8 inches for also applicable to resawn glulam beams nominal 6-inch members, depending on that have a sawn surface on one vertical species used. As noted, the Framing face.

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Form No. EWS Y110B Revised August 2003/0100

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