Selecting the right subfloor and underlayment combination is one of the most important decisions in floor construction. Engineered wood panels like APA Rated Sturd-I-Floor® and APA Rated Sheathing provide a stable, durable base for virtually any finish floor. Understanding the differences between these products, and how they work with your finish floor choice, ensures your floor system performs as intended from the ground up.
Whether you’re building with a single-layer APA Sturd-I-Floor system or a two-layer subfloor and underlayment assembly, engineered wood panels offer proven advantages that make them the go-to choice for floor construction.
APA Rated Sturd-I-Floor is a combination subfloor-underlayment product designed for single-layer floor construction beneath carpet and pad. These panels are produced from plywood or OSB and feature a built-in underlayment that allows the convenience of using only Sturd-I-Floor under certain finish flooring, especially carpet and pad. Some finish floorings, like vinyl or ceramic tile, also require the addition of an underlayment over the Sturd-I-Floor.
APA Rated Sheathing panels are an all-around construction workhorse intended for roof, wall and subfloor applications. These panels are produced from either plywood or OSB. When used as a subfloor, APA Rated Sheathing typically requires installation of an additional layer of underlayment on top of it before finish flooring can be applied.
Underlayment is a special grade of APA rated plywood that is attached on top of the subfloor to provide a durable and resistant layer under finish flooring. It has a special face and inner-ply construction that resists dents and punctures from concentrated loads. Underlayment is recommended for use with APA Rated Sheathing, but can be skipped if the floor system uses Sturd-I-Floor under carpet and pad.
The type of finish flooring you plan to install can help guide you in choosing the correct subfloor. APA Rated Sheathing or Sturd-I-Floor may be used with an underlayment for vinyl, ceramic tile or fully adhered carpet.
Underlayment is optional for APA Rated Sheathing or Sturd-I-Floor when used with hardwood. When using carpet and pad, the best option is Sturd-I-Floor, which does not require installation of underlayment.
Underlayment can have a solid, touch-sanded or fully sanded face, depending on the finish flooring. For example, underlayment with sanded face is recommended as a base for resilient floor coverings.
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 and increase floor stiffness. Sturd-I-Floor can be manufactured with square edges or with tongue-and-groove edges. Using tongue-and-groove panels eliminates the need for installation of blocking along long panel edges, speeding up the floor construction process.
The system components are specifically designed for carpet and pad installation to help keep the floor quiet, making Sturd-I-Floor an ideal solution for multifamily buildings.
Span rating is the maximum recommended center-to-center spacing in inches of the supports, such as I-joists, that floor panels will be attached to. The most common span ratings for Sturd-I-Floor are 20, 24 and 48 o.c.
APA Rated Sheathing has a different system for span ratings, due to its wide variety of applications. On APA Rated Sheathing, the first number is the maximum center-to-center spacing of supports in inches for roofs, and the second number gives the maximum center-to-center spacing of supports in inches for subflooring. The most common span ratings for APA Rated Sheathing are 24/0, 24/16, 40/20 and 48/24.
Cost and time savings: Sturd-I-Floor’s combined subfloor-underlayment design eliminates the need for a separate underlayment layer, saving both material costs and installation time.
Versatility: Both APA Rated Sheathing and Sturd-I-Floor work with a wide range of finish flooring types, including carpet and pad, vinyl, ceramic tile and hardwood, providing builders with a variety of options.
Quieter floors: When installed using the APA Glued Floor System, Sturd-I-Floor reduces noise underfoot, making it an ideal choice for multifamily buildings.
Structural performance: The APA Glued Floor System combines adhesive with nails to eliminate squeaks and pops, thereby increasing overall floor stiffness.
Engineered wood panel floor systems offer a proven combination of performance, versatility and value that is hard to match with alternative materials. With clear span ratings, tested installation methods and APA’s comprehensive technical resources, builders and designers have everything they need to specify and build a floor system that performs.
Technical Note - T350
This publication discusses how to minimize the risk of future wood flooring problems when moisture at the jobsite is an issue
Excerpt - E30X-FC
This publication is an excerpt from the APA Engineered Wood Construction Guide, providing information about floor framing and wood structural panel products
Technical Note - T230
This publication describes single- and double-layer all-wood floor assemblies for acoustic performance and includes both construction details and acoustic ratings
Specification Guide - SP-1102
This publication provides an overview of the APA trademark and includes a sample specification for APA Rated Sturd-I-Floor (OSB).
Specification Guide - SP-1102
This publication provides an overview of the APA trademark and includes a sample specification for APA Rated Sturd-I-Floor (Plywood).
Specification Guide - SP-1103
This publication provides an overview of the APA trademark and includes a sample specification for APA Rated Sheathing.
Optimizing Floor System Performance with Engineered Wood Products
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Quality Floors from Start to Finish: Choosing and Preparing Wood Subfloors for Finish Floorings
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Construct a Solid, Squeak-Free Floor System
This publication describes how to prevent floor complaints and callbacks with proper floor sheathing installation
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Proper Selection and Installation of APA Plywood Underlayment
This publication provides an overview of selection, handling, installation and fastening of APA plywood underlayment.
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Always use a plywood underlayment when installing a thin resilient finish floor product. See Table 2 in APA’s Data File: Selection, Installation and Preparation of Plywood Underlayment, Form L335 for typical panel floor specification based on finished floor installation.
An APA plywood underlayment is a special grade of plywood that has enhanced resistance to face veneer punctures. Underlayment as thin as 1/4 to 11/32 inch resist dents and punctures from concentrated loads. A touch-sanded underlayment is ideal for carpet and pad installations while resilient floor coverings should be installed over a fully sanded Underlayment. Refer to APA’s Data File: Selection, Installation and Preparation of Plywood Underlayment, Form L335 for more information.
Plywood Sturd-I-Floor is a span rated underlayment that can be used for direct application of carpet and pad. It includes a floor span rating which allows it to be used as a structural panel for spanning floor systems. Refer to Table 15 in APA’s Engineered Wood Construction Guide, Form E30 for more information.