APA Designers Circle News & Features

April 2017

Highlights from this Month's e-Newsletter


Rated Sturd-I-Floor® versus Rated Sheathing: What’s the Difference?


“Sheathing” is a somewhat generic term for either plywood or OSB panels that are used to construct roofs, floors, and walls. But the differences between Rated Sheathing and Rated Sturd-I-Floor® can be unclear, especially when their uses are similar or even interchangeable. Basically, Rated Sheathing refers to OSB and plywood panels that are qualified for roof, wall, and subfloor applications, while Rated Sturd-I-Floor panels are a special panel intended for single-floor applications.
Let’s dive into more specifics.

What is Sturd-I-Floor?

Sturd-I-Floor is a combination subfloor-underlayment produced from OSB or plywood. These panels feature a built-in underlayment that allows the convenience of using only Sturd-I-Floor under certain finish flooring, especially carpet and pad. This single layer construction is a cost-saving and time-saving solution that works especially well with multifamily buildings, because Sturd-I-Floor is quieter underfoot when installed using the APA Glued Floor System.

A word of caution: While Sturd-I-Floor is manufactured as a combination subfloor-underlayment that can be used without an additional layer under carpet and pad, some finish floorings, like vinyl or ceramic tile, also require the addition of an underlayment over the Sturd-I-Floor.

What is APA Rated Sheathing?

Typical sheathing trademarksAPA Rated Sheathing panels are an all-around construction workhorse intended for roof, wall, and subfloor applications. Like Sturd-I-Floor, Rated Sheathing may be plywood or OSB. When used as a subfloor, Rated Sheathing typically requires installation of an additional layer of underlayment on top of it before finish flooring can be applied. The underlayment requirements vary depending on the finish flooring.

What is Underlayment?

Underlayment is a special grade of APA plywood that is attached on top of the subfloor to provide a durable and resistant layer under finish flooring. Underlayment’s special face and inner-ply construction resists dents and punctures from concentrated loads. Underlayment is recommended for use with Rated Sheathing, but can be skipped if the floor system uses Sturd-I-Floor under carpet and pad.

Basic Floor Construction Considerations

Finish Flooring

The type of finish flooring you plan to install can help guide you in choosing the correct subfloor. Rated Sheathing or Sturd-I-Floor may be used with an underlayment for vinyl, ceramic tile or fully adhered carpet. An underlayment is optional for Rated Sheathing or Sturd-I-Floor when used with hardwood. When using carpet and pad, the best option is Sturd-I-Floor, which allows for completely bypassing installation of underlayment.

Underlayment can have a solid, touch-sanded, or fully sanded face; its choice depends on the finish flooring. For example, underlayment with sanded face is recommended as a base for resilient floor coverings. 

A visual comparison of typical floor assemblies:

Sturd-I-Floor versus Rated Sheathing + Underlayment

Sturd-I-Floor Application

Sturd-I-Floor is designed to be used with the APA Glued Floor System, which uses an adhesive in addition to nails to help eliminate squeaks and nail popping, as well as increase floor stiffness. Sturd-I-Floor can be manufactured with square edges or with tongue-and-groove edges. Because use of tongue-and-groove panels eliminates the need for installation of blocking along long panel edges, floor construction goes more quickly. The system components are specifically designed for carpet and pad installation to help keep the floor quiet, making Sturd-I-Floor the perfect solution for multifamily buildings.

Joist Spacing and Span Ratings

Span Rating is the maximum recommended center-to-center spacing in inches of the supports, such as I-joists, that the panels will be attached to. The most common Span Ratings for Sturd-I-Floor are 20 oc (on center), 24 oc, and 48 oc.

Due to the wide variety of applications for Rated Sheathing, it has a different system for Span Ratings. Rated Sheathing’s first number is the maximum span in inches for roofs, and the second number gives the maximum span on center for subflooring. The most common Span Ratings for Rated Sheathing are 24/0, 24/16, 32/16, 40/20, and 48/24.

For More Information

To learn more about the building requirements for floors and specific uses of APA-rated products, as well as the APA Glued Floor System, refer to the “Floor Construction” section of the Engineered Wood Construction Guide. Sturd-I-Floor may be also used for other applications, such as roofs; this use of Sturd-I-Floor is covered in the “Roof Construction” section of the Engineered Wood Construction Guide. For general information regarding engineered wood products, their specifications, and their applications, contact the specialists at the APA Help Desk.

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Project Spotlight

Quebec's Mistissini Bridge Reflects Community Values and Sustainability

Mistissini Bridge

The Mistissini Bridge, completed in June 2014, is one of Canada’s most significant wooden bridges.

Mistissini Bridge

The 160-meter-long glulam bridge crosses the Uupaachikus Pass, west of Mistissini, Quebec, creating an access point for residential expansion, permitting gravel to be sourced from a quarry, and expanding economic opportunities for the Cree Nation of Mistissini. Designed by Stantec, the bridge was constructed using laminated wood in a series of semi-continuous arches and glulam girders.

The Mistissini Bridge designers faced significant challenges. The bridge not only needed to provide an environmentally sustainable option with a negative carbon footprint, but it also needed to withstand the severe weather conditions of Northern Quebec. To address these challenges, laminated wood was chosen.

The bridge features locally sourced cross-laminated timber panels and glulam girders and panels. It has a steel guardrail and a steel plate with Bimagrip covering the wood walkway. A bituminous coating, several sheets of membrane, and marine plywood protect the bridge deck from water damage.

Using glulam beams made it possible to eliminate expansion joints on the bridge, giving the structure durability. All of the bridge bearings are fixed, which distributes the seismic effects over all foundation units, and reduces cost. “The bridge reflects nature around Mistissini,” said Denis Lefebvre, a senior associate and director of expertise, bridges and works of art out of the Stantec office in Longueuil, Quebec. “Constructing a wood bridge is more symbolic to the community than other kinds of bridges, such as steel or concrete.”

Inside the Circle

Connection Design Solutions for Wood-Frame Structures—Northwest Wood Solutions Fair

Jared Hensley

Come see APA's Jared Hensley on April 25 at the Northwest Wood Solutions Fair in Seattle, Washington. His topic of discussion will be Connection Design Solutions for Wood-Frame Structures. The course agenda will include common fastener types and their design values, the orthotropic nature of wood and its role in connection design, commodity and specialty connectors, the use of steel connectors in wood-frame construction, and the best practices for wood connection detailing.

Jared holds a Bachelor of Science in Architectural Engineering with an emphasis in structural design from the University of Wyoming. An expert on residential and commercial design with engineered wood products, Jared spent eight years as a Professional Engineer in Colorado, Wyoming and Washington. His design and construction management experience includes structural design for new and renovated buildings incorporating steel, masonry, timber and concrete, as well as acting as a consulting engineer on structural design and rough framing inspections for several large residential and commercial builders in the greater Denver area. Jared joined APA in the spring of 2015 and covers the Pacific Northwest territory.

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Outside the Circle