Open concept bathrooms are coveted for their sleek design and functionality. Curbless showers
are appreciated at any stage of life, but are especially useful for those who wish to
age in place. With Schluter®-Systems offering various solutions,
creating curbless showers is easier than ever to achieve!
Before you begin, you’ll need to decide if you are going to build up the bathroom
floor outside the shower area, or recess the floor within the shower area.
A recessed shower floor allows for the installation of a sloped mortar bed or a prefabricated
shower tray that is flush with the surrounding bathroom floor.
Let’s take a look at one way to recess a wood subfloor. Please refer to detail K-SHCR
for all requirements. Graphic/Title: Recessing the bathroom floor
must be done in a way that preserves the structural integrity and safety of the construction.
This may require the services of a qualified design professional such as an architect or
an engineer. Verify with the local inspector or authority having jurisdiction (AHJ).
This installation method is only applicable to dimensional lumber assemblies. Recommendations
for blocking other wood construction assemblies such as those that use I-joists or trusses
should be made by the framing manufacturer or a design professional.
Determine the area that will be recessed. Remove the plywood from this area, making
sure not to damage the floor joists or adjacent subfloor panels. The floor joists should never
be compromised or altered in any way. Because the edge of the shower tray lands
in the middle of a joist bay the plywood is also removed from the remainder of the joist
bay. It will be replaced later in the process. We were very careful when planning our shower
installation to ensure that the plumbing outlet did not align with a floor joist.
As you can see, our joists are spaced at 16 inches on-center. The maximum allowable joist
spacing for this application is 19.2 inches on-center.
It is critical to provide support to the shower assembly and surrounding subfloor. We do this
by installing wood blocking and ledgers. First, the blocking is installed. We used
2 by 6’s for this since they were readily available.
Dimensional lumber can’t be ripped and maintain the manufacturer’s load ratings. Therefore
blocking lumber must be selected to fit the assembly without such modification.
The blocking must be pre-drilled and installed flush with the top of the joists.
Next we begin work on the recessed ledgers, which will support the recessed plywood subfloor.
One option is to pre-assemble the recessed ledgers and install them into the joist bay
as a unit. We used 2 by 4’s for this as they were readily
available in our area. Another option is to install the recessed
ledgers individually. The recessed ledgers have been pre-drilled
and are fastened to the joists such that the plywood will be flush with the tops of the
framing members. We used suitable wood screws in this application,
but nails could be used as well. Fastener type to be selected based on construction
methods used in your area. Complete the installation of the recessed
ledgers. Now that all of our blocking and recessed
ledgers are properly installed, we can re-install the recessed plywood in the shower area.
We determined where our drain outlet will be located and cut the opening in the appropriate
location. The final step in this example is to reinstall
plywood over the remaining open joist bay(s) such that it overlaps the recessed area up
to the perimeter of the shower tray. The face grain of the plywood, or strength
axis of OSB, must run perpendicular to the framing. The leading edge of the panel must
be gapped from the existing subfloor and fastened to the floor joist in accordance with building
code requirements. Where the panel overlaps the recessed plywood,
it is fastened as though it is an underlayment. The maximum on-center fastener spacing is
6 inches along panel edges and 6 inches in the field. Refer to the Wood Underlayment
guidelines in the Schluter®-DITRA Installation Handbook for complete specifications.
The preparation of the recessed subfloor is now complete, ensuring proper support in the
shower area. As you can see in this cutaway, the KERDI-SHOWER-TT
trays are ideal for installations in curbless shower applications because they are relatively
thin at the perimeter. Let’s get started with the tray installation.
Make sure the area is clean. The shower tray is installed using any of
our Schluter thin-set mortars or an unmodified thin-set mortar.
A one-quarter inch by three-eighths inch square or U-notched trowel is used to apply the mortar.
Apply a thin layer of mortar to the subfloor with the flat side of the trowel and then
comb additional mortar using the notched side of the trowel.
Place the shower tray and solidly embed in the mortar, using cardboard to protect the
tray while embedding. Next we will install the KERDI-DRAIN.
Fill the step in the shower tray and the area surrounding the hole in the subfloor completely
with thin-set mortar. Press the KERDI-DRAIN firmly into the mortar
for full support of the bonding flange. Clean excess mortar from the bonding flange
to prepare for the KERDI collar installation A 1/4 inch x 3/16 inch V-notched trowel or
the Schluter-KERDI-TROWEL, which features a 1/8 inch x 1/8 inch square-notched design,
is used to apply the mortar. Using the flat side of the trowel apply thin-set
mortar over the bonding flange and within the recessed area of the shower tray surrounding
the drain. Then comb additional mortar using the notched side of the trowel.
Center the included KERDI collar over the KERDI-DRAIN and embed using the flat side
of the trowel or a dry wall taping knife. Make sure this connection is secure. Clean
the excess mortar from the step in the bonding flange.
We are installing the DITRA-XL uncoupling membrane on the bathroom floor to achieve
a flush transition to the shower tray. The DITRA-HEAT-DUO uncoupling membrane could be
used for this purpose as well and would allow quick and easy integration of floor warming
in the application. Apply the mortar to the substrate using the
DITRA-HEAT/DITRA-XL trowel, or a 1/4" x 1/4" (6 mm x 6 mm) square-notched trowel.
The membrane is installed using Schluter ALL-SET®, Schluter FAST-SET® or a modified thin-set
mortar. Solidly embed the membrane in the mortar using
a wood float or a roller. We have achieved a flush transition between
the shower area and the bathroom floor. When recessing the floor is not an option,
the KERDI-SHOWER-SR ramp can facilitate a sloped transition to the shower area from
the bathroom floor. Alternatively, you can raise the elevation
of the bathroom floor to meet the shower area. For example, installing a 5/8? or 3/4? -thick
underlayment and DITRA-XL or DITRA-HEAT membrane over the bathroom floor will result in an
even transition to the KERDI-SHOWER-TT thin shower tray.
When raising the floor, check the transition to the adjacent room before beginning the
installation.
The transition will typically be manageable when the adjacent floor covering is relatively
thick, such as a carpet with pad or three-quarter inch thick hardwood.
Now that the installation of the shower tray and DITRA-XL is complete, we can continue
with waterproofing. Using the same technique as shown previously,
install the KERDI-KERECK corners and KERDI-BAND waterproofing strips to seal the shower tray
to the walls and adjacent floor. Make sure that 2 inch overlaps are maintained
at all seams and transitions to ensure a waterproof assembly is achieved.
Schluter®-Systems strongly recommends water testing before setting tile to verify a successful
installation. Refer to the Water Test for Curbless Showers
video for more details on how to perform a water test for curbless applications.
The Schluter®-Shower System ensures a waterproof, vapor tight assembly and makes curbless shower
installations easier than ever, allowing you to create a spa-like retreat with sleek design
and consummate functionality.