Designers Circle Feature

Skip the Lightweight Concrete Topping with a Thicker All-Wood Floor System

Meet acoustic and fire performance standards, avoid delays


All-Wood Floor System

Lightweight concrete and gypcrete toppings are routinely used as a component of fire-rated floor assemblies to provide both fire and acoustic performance in multifamily and commercial construction. This extra step can be eliminated, however: All-wood floor systems can meet fire and acoustic performance requirements and speed up construction by eliminating delays associated with the installation of lightweight concrete or gypcrete topping.

In supporting the development of all-wood floor systems without lightweight gypcrete or concrete topping, APA – The Engineered Wood Association conducted a series of acoustic tests for code compliance based on sound transmission class (STC) and impact insulation class (IIC) ratings. The 2015 International Building Code (IBC) specifies a minimum STC rating of 50 for walls, partitions, and floor-ceiling assemblies between adjacent dwelling units, sleeping units, and adjacent public areas and a minimum IIC rating of 50. The floor assemblies tested by APA had STC and IIC ratings that met or exceeded IBC standards for multifamily residential and nonresidential buildings.

These thicker all-wood floors are stiffer than conventional light-frame floors. While typical light-frame floor construction employs a single layer of 23/32 Performance Category floor sheathing, the thicker all-wood floor systems use thick subfloor sheathing, such as a single layer of 1-1/8 Performance Category panel, or double layers, with a 19/32 Performance Category top layer over a 23/32 Performance Category base layer. The resulting floor is an enhanced assembly that performs above the code requirements satisfied by the typical light-frame assembly. Multiple assemblies were tested with different finish flooring, including cushioned vinyl, vinyl tile, quarry tile, hardwood flooring, and carpet and pad.

“In my region, the apartment market is very strong. I am also seeing more and more wood-framed hotels,” said Warren Hamrick, Engineered Wood Specialist. Hamrick has shared the all-wood systems with multiple large developers and design firms and notes that feedback has been largely positive, with this floor assembly making a good option for certain projects. "Having documented testing results showing the acoustic performance of this assembly with multiple floor coverings as well as the assembly’s fire rating has been key when presenting the information to the interested parties."

Warren Hamrick

For more details on the floor assemblies and their test performance, download Technical Note: Acoustic Performance of All-Wood Floor Systems, Form T230

Warren Hamrick is an Engineered Wood Specialist for APA – The Engineered Wood Association, serving the southeastern United States. Warren conducts workshops and consults with designers, code officials, and other building professionals on best practices for specification, selection, and application of engineered wood products. Warren graduated from North Carolina State University with a Bachelor of Science in civil engineering. Prior to joining APA, he worked as a project manager for a structural engineering firm that specialized in commercial construction.