Considerations For Curbless Showers with TJI Floor Systems

Considerations For Curbless Showers

When designing a curbless shower overtop a TJI® floor joist system, there are several important factors to consider, including: structural adequacy of the floor framing, effective moisture protection, and satisfactory floor performance. Additional weight added by the installation of new finish materials, such as tile or stone must be checked to ensure that the existing or proposed joists are adequately sized to support the additional load. If not accounted for, the additional weight from a new shower installation may cause issues with maintaining waterproofing at the shower pan, excessive deflection of the floor joists, drywall cracking, and may affect the structural performance of the floor system. This article explores various factors that should be considered when designing a curbless shower with TJI® joist framing.

Existing Bathroom Renovation

When a bathroom renovation includes removal of the existing subfloor, care must be taken to ensure the renovation does not damage the TJI floor joists. Important considerations are included below.

• Sheathing is typically installed using subfloor adhesive in attachment of the panel to the top flange of the TJI® joist. If care is not taken when removing the sheathing, the top flange of the TJI® joists can be damaged from the adhesive pulling up on the joist flange when removing the subfloor. Do not use a pry bar to remove the floor sheathing.
• When preparing to cut the new opening, prevent top flange damage by locating the joists prior to removing the subfloor. Confirm the thickness of the subfloor to ensure that the saw blade depth is correctly adjusted to avoid cuts into the top flange of the TJI® floor joist. If the flange of a TJI® joist is damaged, it will impact the structural capacity of the floor joist, and may require replacement with a new, undamaged joist.

There are methods for creating the new supports for a recessed subfloor: installing 2x_ framing sistered to the existing joists or by installing the subfloor panels using a 3^rd party kit. Each of these methods will allow the sheathing to sit flush with the TJI joist top flange.

Sistered 2x_ Construction

Figure 1 provides a conceptual drawing showing the 2x_ frame sistered into a TJI® joist. Sistering a 2x_ framing member to your TJI® floor joist starts by filling out the joist web with lumber or structural sheathing. Filling the web of a TJI joist involves installing filler blocks flush to the top flange on both sides of the joist web with a 1/8-inch gap at the bottom. This framing method may not be applicable if both sides of the joist are inaccessible. Refer to page 29 of TJ-4000 or page 30 of TJ-4500 in Canada for details indicating the recommended filler block thickness to use for your specific TJI® joist. The connection from the sistered 2x_ to the joist should engage into the filler material; nailing the 2x_ into the joist flange is not recommended. Once the filler block is installed and the 2x_ attached, the dropped sheathing section can be attached directly onto the 2x_ material. Consult with your Designer of Record (DOR) for specific nail sizes and attachment.

Figure 1: Sistered 2x_ With Web Filler Connection

Floor Recessing Kits

Another option available to recess the subfloor is to use 3^rd party floor recessing kits. 3^rd party recessing kits contain metal brackets that attach to the floor joists, and either directly support the recessed sheathing or support new 2x4 framing in the joist bay (refer to Figure 2 and Figure 3). When using a recessing kit, filler blocks must be placed tight to the underside of the top flange with a 1/8-inch gap separating the filler block from the bottom flange. The floor recessing kit’s nail spacing requirements should be checked for compatibility with TJI® joist nailing requirements. Refer to TB-206 Table 1 for recommended nail spacing into TJI® joist flanges. Note: Weyerhaeuser has not evaluated the performance nor endorses any specific 3^rd party recessing kit.

Figure 2: Recessed Floor Kit with Direct Sheathing Connection

Figure 3: Recessed Floor Kit with Hanging 2x4 Framing and Web Filler

Recessed Floor Sheathing

TJI® joist span tables referenced in TJ-4000 and TJ-4500 in Canada, assume composite action through a glued and nailed subfloor connection to the top flange when calculating deflection. When the subfloor is recessed, the floor sheathing is no longer continuous across the joists at the shower location, and therefore, the glued and nailed composite action assumption is no longer valid. Further analysis may be required to ensure adequate deflection performance for the joists below the shower. A project DOR may want to consider only the I-joist stiffness to support the floor under the cut section when analyzing the joists for deflection performance.

Additionally, any hole cut into the floor sheathing must meet code requirements for diaphragm hole reinforcement to ensure structural performance. For more details, reference section 2308.8.4.1 of the 2024 IBC or your local building codes for hole reinforcement requirements. Refer to TB-206 for recommended nailing into the top flange of TJI joists.

New Construction

For new construction, the opening for the recessed floor can be designed with headers to support the floor joists below the shower onto appropriately sized beams. At the shower location, joists of a shallower depth are installed at the level needed for the recess. This method of construction will require additional analysis and materials and is best considered during the design phase of the project to ensure adequacy and performance of the floor system. Figure 4 provides a conceptual drawing of this construction. A design professional may be needed to ensure that the additional load being diverted to the members supporting the header does not exceed the design capacity of these carrying members.

Figure 4: Recessed Floor with Dropped Joists Detail

Importance of Waterproofing

Like all untreated wood products, TJI® joists must be used in a dry service condition. Wood exposed to moisture can create an environment conducive to mold growth and wood decaying organisms which can reduce the structural properties. Protection of all wood framing, including the subfloor and mechanical connections is vital to the resilience of the structure supporting the recessed shower. The waterproofing installation must be carefully detailed and managed to ensure long term performance of the shower and supporting framing.

Final Thoughts

These tips are intended to provide general guidance when recessing sheathing within a floor framed with TJI joists. However, every project is unique, and if there are any questions with detailing around the recessed shower, we recommend consulting with a local architect and/or engineer.

If you have any questions regarding framing with Trus Joist® products, please contact your Weyerhaeuser representative. Contact information can be found at our specification center or contact our technical support team at 888-453-8358 or techsupport@wy.com.