In our January 2021 issue, Frank Woeste and Don Bender wrote, “Hybrid Lumber" Grade Stamps Require Special Attention. This article provided information on how to recognize hybrid grade marks and how to calculate hybrid lumber values for truss design. Included was this caution:
A hybrid product grade mark indicates a mixture of species groupings and/or regions, requiring careful consideration of design values. For each design value, the lowest of the mixture must be used. This includes strength and stiffness values, along with the specific gravity. Specific gravity is especially important as it influences truss plate gripping values, unit shear capacities for diaphragms and shear walls, and hold-down capacities for shear walls.
In our May 2021 issue, we were pleased to provide an update on the situation, made available by the American Wood Council (AWC), New Table 4G in NDS Supplement – Multi-Species and Country Grademarked Lumber. This included the following from AWC’s WoodPost:
To help designers and code officials navigate this relatively new approach to grade marking, the lumber grading agencies, working with the American Lumber Standards Committee and AWC staff, have developed a new table of design values for multi-species lumber grade marks. This new table, entitled Table 4G, Reference Design Values for Multi-Species and Country Grademarked Visually Graded Dimension Lumber (2"-4" thick), has been approved and included as an addendum to AWC’s 2018 NDS Supplement. For an extensive number of multi-species grade stamps from various countries, including some North American multi-species groupings, the table provides the lowest design values among the combined species for each design property (and therefore the appropriate single set of design values to be used with the grade stamp). Users of this table will no longer have to check the design values for each included species indicated by a multi-species grade stamp to determine the minimum values for each design property. The new Table 4G can be viewed and downloaded here.
On June 15, the use of European lumber came in question in North Carolina following a press release by the NC Dept. of Insurance (NCDOI): N.C. Building Code Council warns of the use of European lumber in North Carolina. That statement was met with responses by AWC and the Pacific Lumber Inspection Bureau—both of which are included on the following pages.
It is expected that NCDOI will be issuing a revision to its opinion, which we hope will further clarify the proper use of this non-typical lumber.
AWC Responds to NCDOI Press Release
LEESBURG, VA. – June 18, 2021 – On June 11, the North Carolina Department of Insurance (NCDOI) issued a news release warning of the use of European lumber in North Carolina. The news release identified several potential use issues given the building community’s lack of familiarity with European lumber and served to alert suppliers, designers, builders, and regulators that lumber should be used in accordance with applicable codes and standards; however, there were several statements that need to be clarified or corrected. The Pacific Lumber Inspection Bureau has prepared a detailed response to the NCDOI new release.
Prescriptive provisions in the building codes that cover wood-frame construction are primarily based on the four major commercial species combinations: Douglas Fir-Larch, Hem-Fir, Southern pine, and Spruce-Pine-Fir (SPF) from Canada. These prescriptive provisions provide species- and grade-specific span tables for common loading conditions for the four major species combinations or the requirements are based on the minimum properties for certain grades of the four major species combinations. However, the building code allows the use AWC’s Span Tables for Joists and Rafters (STJR) for other grades and species of lumber and for other loading conditions. The span tables in STJR are species independent and only require the user to know the adjusted design values for the grade and species of lumber. Where European lumber has the same or higher design values than North American lumber, the material can be directly substituted.
In areas where the basic wind speeds are 130 mph or less (in some locations less than 140 mph), prescriptive provisions in the building codes that address wall studs and connection requirements have been considered to be independent of the lumber species. However, in areas where the basic wind speeds are greater than 130 mph, including coastal areas of North Carolina, the prescriptive provisions of the building codes don’t typically apply and the user is directed to use the pre-engineered wood-frame construction provisions in AWC’s Wood Frame Construction Manual for One- and Two-Family Dwellings (WFCM) or ICC’s Standard for Residential Construction in High-Wind Regions (ICC 600) or to design the structure in accordance with the loads in ASCE’s Minimum Design Loads for Buildings and Other Structures (ASCE 7). When designing to the wind loads in ASCE 7, AWC’s National Design Specification® for Wood Construction (NDS®) is used, which includes design values for all North American and non-North American species approved by the American Lumber Standards Committee, including European lumber species. Adequate resources exist for use by plans examiners, builders, and designers to accommodate the use of European lumber with these standards.
Due to the rapid increase in use of and lack of familiarity with lumber species other than the four major species, prescriptive design provisions for these other species are lagging, but are being developed. The Pacific Lumber Inspection Bureau is working to develop species-specific span tables for use with the prescriptive provisions in the building codes based on the NDS and has already developed exterior wall stud tables in accordance with provisions of the WFCM for use in high wind areas and can be located at the following link: TR-5-Max-Stud-Length-Tables-for-European-Species-1.pdf (plib.org).
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The American Wood Council (AWC) is the voice of North American wood products manufacturing, an industry that represents provides over 450,000 men and women in the United States with family-wage jobs. AWC represents 86 percent of the structural wood products industry, and members make products that are essential to everyday life from a renewable resource that absorbs and sequesters carbon. Staff experts develop state-of-the-art engineering data, technology, and standards for wood products to assure their safe and efficient design, as well as provide information on wood design, green building, and environmental regulations. AWC also advocates for balanced government policies that affect wood products.
Pacific Lumber Inspection Bureau —
Response to N.C. DOI News Release on European Lumber in North Carolina
June 17, 2021
On June 11, the North Carolina Department of Insurance, issued a news release warning of the use of European lumber in North Carolina. PLIB believes that additional information related to some of the statements will be helpful to those who may have questions about the notice.
Statement:
“The council has determined European lumber, which is being imported to help with the nation’s lumber shortage, does not meet N.C. building code requirements and, in some cases, could cause catastrophic failures in wall, floor and roof framing.”
Response:
While it is true that there has been an increase in the amount of European lumber imported to the U.S. as a result of the nation’s lumber shortage, European lumber has been accepted and used in the U.S. and in North Carolina for decades. PLIB is unaware of any catastrophic failures in wall, floor, or roof framing applications. The prescriptive portions of the N.C. code are based on four major species commonly used in the U.S.: Douglas fir (U.S.), Hem-Fir (U.S.), Southern Yellow Pine (U.S.) and Spruce-Pine-Fir aka SPF (Canada). Alternative species (from North America or Europe) can be used with the prescriptive code if their design properties are equal or greater to the lowest value of these four major species. If a critical design property is found to be lower, alternative species can still be used with supporting documentation (such as span tables) and/or engineering evaluation.
Statement:
“A primary concern is the specific gravity or wood density that affects the performance of fastening devices, such as nails, screws or gusset plates. A lower specific gravity may result in a decreased resistance capacity of a shear wall designed to withstand wind and seismic loads, lower gripping strength of a truss metal plate, or lower bending strength that could affect wall height.”
Response:
The prescriptive portion of the North Carolina building code is based on an assumed minimum specific gravity value of 0.42. All European species with one exception have a specific gravity value or 0.42 or greater.
Statement:
“There are also concerns with the differences between U.S. and imported lumber milling processes.”
Response:
It is difficult to pinpoint what is meant by this statement but lumber produced in Europe that has the grade stamp of an ALSC accredited agency is manufactured, graded, and held to the same quality standards and quality audit requirements as North American lumber. This means the size requirements and tolerances are the same, the grade specifications are the same, the inspection requirements are the same, etc. All structural dimension lumber, regardless of the country of origin, that is graded and grade stamped under the supervision of an ALSC accredited agency follow the same quality standards as outlined in Product Standard 20 published by NIST and enforced by the ALSC.
Statement:
“I urge builders to know the difference between imported and domestic ‘No. 2’ stamped lumber so they don’t mistakenly use the wood in an unsafe manner that does not meet code.”
Response:
Lumber that is stamped No. 2 (or any other NGR grade) with an ALSC accredited agency stamp, whether imported or domestic, has been manufactured using the exact same grade rules. In other words, No. 2 produced in Europe uses the same grade rule as No. 2 produced in North America. Differences in design values are not due to different rules being applied for domestic versus imported lumber. Each species, be it U.S., Canadian or European, has its own set of design values.
Statement:
“As a result of these significant issues, the N.C. Building Code Council has issued an advisory that European lumber can only be used as an alternate material that must be reviewed by the code enforcement official before it is used.”
Response:
There are also many North American species that are commonly used in North Carolina that are not one of the four major species that the code is based on. These may not meet the prescriptive code requirements and must also be reviewed by the code official before being used.
Statement:
“Code enforcement officials must ensure the documentation includes the testing or evaluation performed on the lumber to support compliance with the building code requirements. Without the documentation, the use of European lumber products will require an engineering analysis and subsequent seal to verify code compliance.“
Response:
It is not clear what is meant by “...testing or evaluation performed on the lumber...” but allowable design values for all European species have been approved by the ALS Board of Review and published by PLIB. These design values also appear in the American Wood Council’s National Design Specification (NDS) Supplement. Generic span tables for joists and rafters are published in AWC’s Span Tables for Joists and Rafters (STJR). These span tables can be used with the published design values to determine appropriate spans for European species. In addition, PLIB’s website includes a span calculator that can be used with domestic and European species. PLIB has also published Technical Report No. 5 Maximum Allowable Stud Length Tables for European Species and Countries in High Wind Zones. Additional tables for girders, headers and jack studs are being produced to further assist the engineer and code enforcement official. These will be made available on PLIB’s website www.plib.org/resources.