Watch Moisture Content in Wood Building Studs
Wood builders have known the value of wood moisture content assessment for generations. However, these times carry new emphasis on measuring the moisture content of wood studs. Regulatory jurisdictions are expanding in cross-referenced ways to include moisture content measurement of building studs, long ignored by regulations as a safety hazard in wood structures. Times change. But these times have produced what can appear to be a perplexing puzzle of crossed regulatory boundaries on wood moisture content test procedures.
International Code Council
The International Code Council is a member-focused association dedicated to helping the building safety community and construction industry provide safe, sustainable and affordable construction through the development of codes and standards used in the design, build and compliance process. Most U.S. communities and many global markets choose the International Codes.
Effective August 1, 2009, the evaluation service of the International Code Council (ICC) published Acceptance Criteria for Wood-Based Studs. “Test Performance and Analysis,” Section 3.0, contains clauses related to moisture content control:
Clause 3.1.3: Moisture content and specific gravity shall be measured and reported for specimens tested in the qualification program. Measurements for moisture content shall be in accordance with ASTM D 4442, and measurements for specific gravity shall be in accordance with ASTM D 2395. Density measurements may be used as an alternative to specific gravity measurements.
Clause 3.1.4: The wood-based stud material shall meet all applicable requirements in AC47 and ASTM D 5456, in addition to the requirements in this criteria
The ICC references several standards authored by the American Society for Testing and Materials (ASTM). While state building code regulators may have their own moisture content rules for wood studs, ASTM industry standards can be linked directly with their International Code Council counterparts. Therefore, wood builders are advised to confirm if their state standards are also linked with moisture content wood stud measurement rules from the ICC and the ASTM.
ASTM International, formerly known as the American Society for Testing and Materials (ASTM), is a globally recognized leader in the development and delivery of international voluntary consensus standards. Today, some 12,000 ASTM standards are used around the world to improve product quality, enhance safety, facilitate market access and trade, and build consumer confidence.
The ASTM also provides industry-wide wood moisture content measurement procedures. These procedures largely apply to production levels for timber processing and not as job-site assessments. But it is worth knowing their general intent.
ASTM D4442 “Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials” covers four methods for assessing the moisture content in wood:
- Method A- Primary Oven-Drying Method
- Method B- Secondary Oven-Drying Method
- Method C- Distillation (Secondary) Method
- Method D- Other Secondary Methods
ASTM D2395 “Standard Test Methods for Specific Gravity of Wood and Wood-Based Materials” states the following:
It may be desirable to know the specific gravity of a living tree, a structural member already in place, a log cross section, a segment of a research element, or the earlywood or latewood layer. The specimen thus may be large or small, regular or irregular, and at a variety of moisture contents.” These test methods give procedures that include all of these variables and provides for calculation of specific gravity values to degrees of accuracy generally needed.
Standard Specification for Evaluation of Structural Composite Lumber Products” recognizes the complexity of structural glued products. This specification, or parts thereof, shall be applicable to structural composite lumber portions of manufactured structural components.
“Tests shall be performed to determine the properties of the material in accordance to the following test methods: moisture content measurement; bending; tension parallel to grain; compression parallel to grain; compression perpendicular to grain; longitudinal shear; connections; bond quality; product durability; edgewise bending durability; lateral edge nail durability; thickness swell; and density gradient through the thickness.
Role of the Wood Moisture Meter
Builders who use a wood moisture meter for moisture content measurements and assessments in wood flooring and other wood products of a project design now also need to apply them to wood studs (and are wise to do so). As always, the key is to utilize the most accurate wood moisture content meter in the process.
Pinless moisture meters, such as Wagner Meters MMI1100 “Data Collection” meter, provides cost-effective quality control moisture content measurements for meeting regulatory specifications and/or guidelines.
Using wood moisture meters like the MMI1100 is an efficient and quick way to scan large amounts of stud lumber prior to installation. The MMI1100 detects moisture contents between 5-30%. Users simply turn on the wood moisture meter, program it for the correct species and run it along the stud surface to obtain moisture content measurements up to three-quarters-inch deep. It also carries an industry-leading seven-year warranty.
Wood studs provide the crucial framework for many building projects. A quality wood moisture meter is just as crucial to meeting performance standards.
International Classification for Standards, 2005. Sixth Ed. (PDF).
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