Wood Preservatives: New Report Explores Directions and Possibilities

A new report has just been published: Wood Protection Research Council, Research Priorities 2013

In this report, authors Carol A. Clausen, Frederick Green III, Grant T. Kirker, and Stan T. Lebow report on findings and recommendations from the Wood Protection Research Council.

Why wouldn’t a homeowner want to build with wood? Sometimes homeowners do not select wood as a building material because of its vulnerability to biodeterioration by fungi and insects under certain conditions of storage and use. These limitations are also a prime cause of user dissatisfaction. Therefore, efforts to protect wood from biological degradation are among the earliest research at the Forest Products Laboratory. This research has successfully reduced the demand for lumber from our National Forests by reducing the need to repeatedly replace existing wood products.

WPRC-cover-art

The cycle of wood harvest, research, and use protects our natural resources.

Wood protection has undergone dynamic changes since the industry voluntarily withdrew chromated copper arsenate (CCA) from most residential uses and new products were introduced to the marketplace. According to the Environmental Protection Agency (EPA), “CCA is a chemical wood preservative containing chromium, copper and arsenic. CCA is used in pressure treated wood to protect wood from rotting due to insects and microbial agents. EPA has classified CCA as a restricted use product, for use only by certified pesticide applicators.”

Obviously, alternatives for wood protection are needed. However, to bring a new preservative to the marketplace, a considerable amount of performance data needs to be obtained. Current laboratory methodologies to determine the durability of test specimens are insufficient, and long-term field testing is required to ensure that a treatment is effective.

Improved accelerated test methods to predict performance would reduce the time needed for the development and acceptance of new preservatives. Potential improvements for accelerated testing may include selection of test fungi, techniques to detect incipient stages of fungal decay, methods to properly assess durability of wood plastic composites use of rapid laboratory bioassays for screening, and field tests that could measure loss in mechanical properties and statistical analysis.

Possibilities and research opportunities abound. For instance, protection systems could be targeted to specific problems. With nanotechnology at the forefront, novel advances in wood protection could replace the broad spectrum biocides traditionally used to inhibit decay fungi. The most logical approach to develop targeted biocides is to take advantage of unique physiological attributes of decay fungi, such as their ability to sequester metals through production of oxalic acid or natural tolerance to preservatives. Discerning and describing these mechanisms may enable us to design specific, targeted inhibitors to control decay and circumvent preservative tolerances that are common in brown-rot basidiomycetes.

This report summarizes presentations and comments from the inaugural Wood Protection Research Council meeting. Research needs for the wood protection industry were iden­tified and prioritized. Methods for successfully addressing research needs were discussed by industry, academia, and association representatives.

 

 

 

Direct Application of Shakes and Shingles: More Techniques for the Homeowner

According to the publication Installation, Care, and Maintenance of Wood Shake and Shingle Siding, for direct application, shakes or shingles are applied directly over properly installed and flashed Type 30 felt (or house wrap as approved by local codes). Shakes and shingles may be single-coursed, stagger-coursed, or double-coursed. The double-course application permits the use of a lower grade for the first layer and a greater exposure of the higher quality second layer of shake or shingle. Pressure-impregnated preservative-treated products can be used in these applications.

With some knowledge and skill, shakes can also be applied over existing siding.

overbrick

Rain screen technique over brick. Used with permission
from Cedar Shake and Shingle Bureau Exterior and Interior Wall Manual.

 

Shakes and shingles may be used to cover existing wood beveled siding, masonry, or stucco. The shakes or shingles can be applied directly over the existing siding; however, rain screen application is necessary over brick, stucco, and foam sheathing. If applied directly over composite wood siding products such as hardboard siding, use longer fasteners and nail through the siding to the underlying sheathing. The brick molding around windows and doors will have to be extended, so it may be better to increase the wall thickness even more and use the rain-screen application. Fasten vertical furring strips to the underlying wallstuds, fasten horizontal boards to the vertical strips, and nail the shakes or shingles to the horizontal nailing strips.

Direct Application of Shakes and Shingles

According to Chris Hunt and his co-authors on Installation, Care, and Maintenance of Wood Shake and Shingle Siding, shakes or shingles can be applied directly over properly installed and flashed Type 30 felt (or house  wrap as approved by local codes). Shakes and shingles may be single-coursed,

stagger-course

Single-coursed application of shingles. Used with permission from Cedar Shake and Shingle Bureau Exterior and Interior Wall Manual.

stagger-coursed,

Stagger-course

Stagger-course application. Used with permission from
Cedar Shake and Shingle Bureau Exterior and Interior Wall Manual.

or double-coursed.

Double-course

Double-course application. Used with permission from
Cedar Shake and Shingle Bureau Exterior and Interior Wall Manual.

The double-course application permits the use of a lower grade for the first layer and a  greater exposure of the higher quality second layer of shake  or shingle. Pressure-impregnated preservative-treated products can be used in these applications.

So the homeowner who wants the beauty and natural look of cedar siding can use these techniques to cover existing siding.

Rain-Screen Method for Shakes and Shingles

Today Lab Notes returns to the FPL publication Installation, Care, and Maintenance of Wood Shake and Shingle Siding and discusses a method for installation.The rain-screen method of building construction gives a secondary barrier and drainage plane for water. Sheathing is placed over the studs and a water-resistant barrier (usually Type 30 felt) is applied. Although the shakes and shingles are not nailed directly to the sheathing in rain-screen applications, most codes still require plywood sheathing. Plywood sheathing transmits moisture better than OSB; therefore, if it gets wet, it dries more quickly.

Rain-screen

Rain-screen technique.

You must request a variance to use OSB in a rain-screen application before installing the sheathing. Furring strips (nominal 1- by 2-inch dimension lumber (19 mm by 38 mm)) or nominal 2- by 2-inch dimensional lumber (38 mm by 38 mm) are placed over the building paper directly over each wall stud. The thickness of the furring strips or (2 by 2s) must be sufficient to avoid having the siding nails penetrate the felt or house wrap. Horizontal boards (usually nominal 1 by 4 inch dimensional lumber (19 mm by 89 mm)), spaced to coincide with the exposed shake or shingle length, are placed across the furring strips to give an open space between the backside of the shakes or shingle and the sheathing. The space is vented at the top and bottom and must be screened to keep out insects. The top may be vented directly into the soffit to connect the air-flow with the attic ventilation. Flashing must be installed around doors and windows just as with any siding system.

Cedar Shake and Shingle Bureau: The Rules and the Secret to the Labels

The Cedar Shake and Shingle Bureau (CSSB) is a nonprofit organization that oversees the inspection of western redcedar (Thuja plicata), Alaska yellow-cedar (Chamaecyparis nootkatensis), and redwood (Sequoia sempervirens) shakes and shingles. The CSSB publishes quality standards (grade rules) and ensures that the member mills producing shakes and shingles meet these standards through periodical third-party inspection.

Shakes and shingles with CSSB designations have been inspected to meet grade standards. A grade stamp/label (with color code for the grade) is placed on each bundle or carton of shakes or shingles and clearly shows the grade. The label contains other information such as wood species, certifying agency, building code standards, and manufacturer. This “Certi” label assures the consumer that the shake and shingle manufacturer is adhering to grading rules as prescribed by building codes.

labels

Figure 1. Information on a Certi-Label™: 1) “Certi” brand name; 2) Product grade; 3) Product type; 4) Independent third party quality control agency; 5) Compliance with total quality processes; 6) Manufacturer; 7) Industry product description; 8) Product dimensions; 9) Cedar Shake and Shingle Bureau label number; 10) Building code compliance numbers; 11) Product performance tests passed; 12) Label identification number; 13) UPC code; 14) Coverage showing the number of bundles/100 square-feet and recommended exposure; 15) Application instruction on reverse side. Used with permission from Cedar Shake and Shingle Bureau Exterior and Interior Wall Manual.