Curbless showers look great, but how much work is required to have one? Does one just cut the floor joists to make that happen?
How do you recess a subfloor for a curbless shower? This post answers these questions and more.
Estimated reading time: 6 minutes
The Floor in the Shower Area Needs to be Lowered
In the past, I’ve heard comments such as “Why does a curbless shower cost more when it’s literally LESS?”
The reason is that if you want a curbless shower, additional work is needed to lower the shower area to the same height as the neighboring flooring.
Otherwise, it naturally would sit higher.
Since the shower floor needs to slope to the drain, the easiest way to accomplish this is to build the outsides up and slope them to the center of the floor. But you may never have noticed the additional height because a curb typically hides the sides.
Now that we’ve established the need to lower the floor, here are three ways to recess a wood subfloor for a curbless shower.
1. Notching the floor joists to recess a wood subfloor
This method seems simple, but it’s anything but.
The idea is that a shower floor usually needs to be lowered 2-4 inches so that a mortar bed shower floor can be sloped to the drain.
Consequently, one would pull up the plywood subfloor, cut the joists down to the appropriate width, and reinstall plywood across the now lowered shower area.
However, if you do this without consulting an engineer, you have likely ruined your home.
Floor Joist Spans
The widths, thickness, and spans of the floor joists were determined when the home was first built. You can’t just alter those and think there will be no structural consequences.
A structural engineer with knowledge of your local codes is required so they can tell you exactly if and how your floor can be reinforced so that you are not compromising what is likely your most important investment.
Advantages
- This method allows for the most options as far as shower floor size, shape, and drain location
- Costs may be quite reasonable if absorbed into a new build or addition
Disadvantages
- Requires an engineer and, oftentimes, a building permit
- Quite expensive if one is renovating an existing home
2. Recess only the plywood subfloor
Thanks to the invention of foam shower pan systems, you no longer have to cut the floor joists to create a curbless shower.
Many tile shower system manufacturers are making their foam shower pans thin enough so that they are slightly thicker than the plywood subfloor. The Wedi Ligno shower is one example.
This allows them to be incorporated into a curbless shower by only cutting out the subfloor in the shower area.
Only the subflooring needs to be recessed
To accomplish this, the plywood or OSB subfloor in the shower is removed and reinstalled between the floor joists, so that it’s flush with the tops of the joists.
This means that you will recess your wood subfloor by about 3/4 inch. That’s all you need for most preformed shower pans.
Blocking and cleats for a recessed wood subfloor
Installing plywood so that it’s the same height as the floor joists means that you need to create supports for it to sit on.
Consequently, you’ll have to cut some different-sized lumber to use for blocking and attach them to the joists.
Yes, this can get tricky when you are dealing with pipes and possibly wires or HVAC running through the area.
That’s where this next option can help.
Advantages
- Don’t require cutting any joists
- Allow for DIY’ers to install curbless showers without calling in experts
- May not require building permits (consult your local building department)
Disadvantages
- They are limited to more standard-sized shower systems.
- Requires manufactured shower system, which can be costly
- Installing blocking and supporting subfloor can be challenging and unclear
3. Subfloor Lowering Kit
Subfloor lowering kits accomplish the exact same thing as above: they turn preformed tile shower systems into curbless showers.
Additionally, they do it the exact same way that is covered in Option #2, above. They lower the plywood subfloor part of the shower without cutting into any floor joists.
So, why use them?
They take the guesswork out of installing supports for the subfloor. How big does the blocking need to be? How many fasteners are needed? What types of fasteners?
Additionally, because they are made of steel, they are not as bulky as wood blocking and they can fit more nimbly around the plumbing and other obstacles.
Advantages
- Take the guesswork out of how to support the subfloor
- Engineered to hold the weight
- Different kits allow for different types of drains and locations, center drains, linear drains, drains at one end of the shower, etc.
Disadvantages
- They are limited to more standard-sized shower systems
- Requires manufactured shower system, which can be costly
- The recess subfloor kit is more costly than wood blocks and screws
Conclusion
When it comes to wood subfloors, you now have more options if you want a curbless shower.
You no longer have to hire an engineer and go through the building permit process. Rather, there are options for DIYing your own curbless shower enclosure.
Are you planning on building a curbless shower? Here are 6 pitfalls you want to avoid! Additionally, do you ever wonder just how strong your floor structure needs to be for tile?
Many curbless showers use what we call ‘bonding flange drains’. These are the 4 best.
Finally, only one waterproofing method is approved for curbless shower installations. Do you know which one it is?
