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.

Soft?Story Woodframe Buildings: What are They and How Do We Protect Them from Earthquakes?

In a new paper in the Proceedings for the American Society of Civil Engineers (ASCE) 2014 Structures Congress, FPL’s Douglas Rammer discusses wood work pertinent to earthquake-prone areas of the world. In the recently published paper, Overview of the NEES?Soft Experimental Program for Seismic Risk Reduction of Soft?Story Woodframe Buildings, Rammer states that the existence of thousands of soft-story woodframe buildings in California is considered a disaster preparedness problem, which has resulted in mitigation efforts throughout the state.

A soft-story building is a building that has one or more stories with significantly less stiffness (and strength) than the stories above or below. This condition usually occurs at the bottom story of a multi-story building and is often the result of large openings that are used for main building entrances, store fronts, or parking garages. These buildings were generally built before 1970 and many as early as the 1920s, which means that the contractors used construction practices not considered acceptable by today’s codified standards. The wall lengths available to resist lateral loads, in general, are too short at the bottom story, thereby resulting in a soft-story.

The considerable presence of these large multi-family buildings in San Francisco prompted the city to mandate their retrofitting over the next seven years. The NEES-Soft project is a five-university multi-industry three-year project that has many facets including improved nonlinear numerical modeling, outreach, retrofit methodology development, and full-scale system-level experimental validation of soft-story retrofit techniques.

In 2013, two full-scale buildings were tested within NEES-Soft. A hybrid test of a three-story building consisting of a one story numerical substructure and a two-story physical structure above at the University at Buffalo, and a shake table test of a four-story building at the University of California-San Diego. A series of retrofits, based on methodologies ranging from FEMA P-807 to performance-based seismic retrofits developed as part of the project, were tested at both sites. Collapse testing for both building specimens was also conducted at the end of each test program. This paper presents a summary of selected test results for these full-scale building tests within the NEES-Soft project.

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.

Looking into the Future of Wood Preservation

Carol Clausen and her group are serious about wood as a sustainable and versatile building material. Here Amy Blodgett, Rachel Arango, and Bessie Woodword check soil block samples in their ongoing research.

Amy-B--Rachel-A--Bessie-W(1)

Members of the Durability and Wood Protection Research Unit check soil block samples.

The soil block decay test method determines the minimum amount of preservative that is effective in preventing decay of selected species of wood by selected fungi under optimum laboratory conditions. Conditioned blocks of wood are impregnated with solutions, emulsions, or dispersions of a preservative in water or suitable organic solvent to form one or more series of retentions of the preservative in the blocks. After periods of conditioning or weathering, the impregnated blocks are exposed to recognized destructive species of both brown-rot and white-rot wood-destroying fungi.

Speaking about her work, Clausen says that wood’s “increased use in construction minimizes life-cycle impacts of a structure while maximizing carbon storage for the life of the structure.” An upcoming report by Clausen, Frederick Green III, Grant Kirker, and Stan Lebow summarizes presentations and comments from the inaugural Wood Protection Research Council meeting, where research needs for the wood protection industry were identified and prioritized.

As a part of that conversation, Clausen states that chemicals used to protect wood from deterioration by fungi and insects have generally been broad-spectrum biocides that have been discovered by the traditional screening approach. However, a more logical approach is to develop selective and targeted biocides by defining the target first, characterizing that target, and then designing inhibitors based on the mechanism of action of the defined biotarget.

Despite substantial progress in explaining the biochemistry of wood degradation, biochemical targets for fungal inhibition have seldom been described. Discovering the mechanism of preservative tolerance(s) in economically important fungi and insects will enable researchers to design preservative systems that neutralize, block, prevent, and eliminate the preservative tolerance. Development of a genetic database of microbial activity during the process of wood deterioration will offer a better understanding of precisely how and when decay or insect attack begins. A molecular database would provide myriad of capabilities to the wood preservation community. For example, researchers could characterize decay risks for a particular location, define the prevalence of tolerant fungi on a national and international basis, and determine the influence of preservative exposure on the ecology at test plots.

The next generation of novel wood protection methods may incorporate nanotechnology for design or controlled delivery of biocides for improved durability of building materials, with an emphasis on engineered composites. Nanotechnology may also play a vital role in the development of water-resistant coatings and treatments for the prevention of fire. Results from basic research on genetic analysis, biochemical processes, nanotechnology, and characterization of biotargets will lead to technological developments that extend the service life of wood and wood-based materials in all major end uses emphasizing environmentally friendly methods.

 

Installing Wood Shingles: The Skinny on Spacing

The spacing between shakes and shingles depends on the grain angle, width of the shake or shingle, and moisture content at the time of installation. Flat-grained shakes and shingles shrink and swell almost twice as much as vertical grained ones and require more space between them to avoid buckling.buckled-siding

These shingles were installed with an insufficient gap and have therefore buckled.

Wide shingles require more space than narrow shingles. If the moisture content is low (5%–6%), leave a little extra space; if it is high (above 20%), decrease the spacing slightly. As a general rule for shingles equilibrated to ambient conditions (about 12% moisture content), shingles should be installed about 1/8 to 1/4 in. (3 to 6 mm) apart whereas shakes should be spaced about 3/8 in. (9.52 mm) apart and not more than 1/2 in. (13 mm) apart. Adjacent courses should be offset at least 1 1/2 in. (38 mm). Shakes and shingles siding may be attached to exterior walls in a variety of ways.