Yes, often. The usual approach is to keep the joists intact and create the shower recess by lowering or reframing the subfloor between the joists. Other possibilities include a low-profile foam tray, a thin mortar bed, or raising the bathroom floor outside the shower. Do not cut, notch, or drill structural joists to make room for the shower without a design from a qualified structural professional. The final plan must also accommodate the drain, waste piping, waterproofing system, finished tile, and any locally adopted plumbing or building requirements.
How a curbless shower fits without cutting joists
A curbless shower needs enough vertical space for a sloped shower floor, drain connection, waterproofing, setting materials, and tile. If the existing bathroom floor is not lowered, the shower assembly may sit higher than the surrounding floor and create a step. Keeping the joists intact means finding that vertical space somewhere else.
In most projects, the options are to recess the shower floor between the joists, use a low-profile tray, form a shallow mortar bed, raise the rest of the bathroom floor, or combine two or more approaches. The best choice depends on the joist direction, joist depth, drain location, subfloor construction, and the available ceiling-to-floor height below.
A true zero-height appearance is not always possible. A small transition may be necessary when the structural depth or plumbing layout does not allow the shower floor to align exactly with the adjacent finished floor. The goal is a safe, durable, properly waterproofed transition, not simply the removal of a curb.
Option 1: Recess the shower floor between the joists
Recessed framing creates a lower platform for the shower assembly while leaving the primary joists intact. Depending on the existing construction, a contractor may remove the subfloor in the shower footprint, install engineered headers and blocking, and support a lower subfloor or shower base between the joists.
This method can provide the greatest amount of usable depth, especially when the shower needs a longer run to a drain or a larger sloped area. It is often the most flexible approach for a bathroom renovation over a framed floor, but it is not a simple matter of cutting out a rectangle and adding a few boards.
The framing must transfer loads around the opening and maintain support for the surrounding subfloor. Joist spacing, span, species, grade, engineered-joist design, bearing points, and the location of walls below all matter. The recessed floor framing approach for a curbless shower should be reviewed before demolition begins.
Solid-sawn joists and engineered I-joists have different allowable modifications. An I-joist manufacturer may limit or prohibit field-cutting of flanges and webs, and a structural engineer or other qualified design professional may be needed for changes to load-bearing framing. A building department may also require permit review, depending on the scope and local rules.
Option 2: Use a foam tray or low-profile shower base
A pre-sloped foam tray can reduce the amount of floor buildup compared with a conventional site-built shower floor. Many trays taper from a higher perimeter to a lower drain area, allowing the installer to place tile over the waterproofed assembly without forming the entire slope from scratch.
A foam tray does not eliminate structural planning. It still needs a flat, adequately supported substrate, enough room for its perimeter and drain, and compatibility with the selected waterproofing system. The tray must be installed according to the product instructions, including the required drain body, mortar or adhesive, seams, and waterproofing connections.
Tray dimensions also affect the transition. A larger shower usually requires more horizontal distance for the floor to slope toward the drain. A small tray may fit over the existing subfloor, while a larger tray or a drain near one end may require a recess or a raised bathroom floor to keep the entry low.
Some low-profile systems are designed for a linear drain at one edge, while others use a center or offset drain. Do not assume that a tray can be trimmed or rearranged without checking the manufacturer instructions. Cutting a tray may change its slope, drain position, support, or waterproofing details.
How much floor buildup does the shower need?
The required depth is the total thickness of every layer between the structural support and the finished shower surface. Depending on the system, that may include a recessed subfloor, pre-sloped tray or mortar bed, bonding material, waterproofing layer, tile, and grout. The exact thickness is product-specific, so the installer should create a section drawing using actual materials before framing or ordering the drain.
| Layer or condition | Why it affects the design | What to verify |
|---|---|---|
| Structural recess | Provides space below the shower assembly without cutting the main joists. | Framing support, load path, joist type, and inspection requirements. |
| Shower tray or mortar bed | Creates the slope needed to move water to the drain. | System thickness, minimum support, slope, and allowable drain locations. |
| Drain body and waste piping | May require space below the floor and a route to the branch drain. | Outlet size, trap position, pipe slope, access, and plumbing rules. |
| Waterproofing assembly | Must connect the floor, walls, drain, and corners into one continuous system. | Membrane type, seams, drain connection, and manufacturer instructions. |
| Tile and setting materials | Determine the final finished elevation at the shower entry. | Actual tile thickness, mortar thickness, and transition detail. |
The phrase “drop” refers to the elevation difference needed from the shower perimeter or entry toward the drain. The actual drop depends on the shower dimensions, drain location, and slope selected by the system. For a deeper explanation of planning this elevation, see how much drop a curbless shower floor needs.
Do not measure only from the top of the subfloor to the top of the drain. The drain flange, waterproofing connection, tile, and setting bed all affect the finished surface. A section drawing should show the adjacent bathroom tile, shower tile, waterproofing layer, drain assembly, and the floor framing below.
Structural limitations you cannot ignore
The joists are part of the building's load path. Cutting or notching them to lower a shower floor can weaken the floor system, cause deflection, damage utilities, or create problems that are hidden after the shower is tiled. This is especially important with engineered wood, post-tensioned concrete, trusses, and floors containing embedded or concealed services.
Keeping joists intact does not mean every recessed design is automatically acceptable. Removing subfloor panels, cutting blocking, installing headers, or changing how loads reach the supporting walls can still require structural review. A contractor should expose enough of the floor to identify joist type, direction, spacing, depth, bearing, and existing plumbing or wiring before proposing the recess.
Deflection also matters. Tile and stone assemblies need a sufficiently stiff substrate, and the shower base must be fully supported. A surface that feels solid during construction may move enough under load to crack tile, open grout, or compromise waterproofing. The appropriate stiffness criteria depend on the framing and the finish materials, so the tile system, framing professional, and local building official may all have a role.
Never rely on a thin layer of mortar or adhesive to bridge unsupported gaps. The substrate below the shower floor must be continuous and properly supported for the selected assembly.
Drain placement can determine the entire layout
The drain location affects both the slope and the amount of structural depth required. A centered point drain sends water in multiple directions. An offset drain changes the length of the slope on different sides. A linear drain at an edge can allow a single-plane slope, which may simplify the entry and reduce conflicting elevations, but it still needs a suitable waste connection and properly supported waterproofing.
A linear drain may be positioned against a wall in some systems, but the drain body, wall connection, waterproofing method, cleaning access, and manufacturer instructions must all match. Review linear drain placement against a shower wall before locating the drain based only on appearance.
Plumbing work must comply with the locally adopted plumbing code and any local amendments. The required trap, venting, pipe size, waste-pipe slope, and connection method vary with the jurisdiction and the existing plumbing layout. A plumbing inspector or local authority having jurisdiction can confirm what applies. The shower system manufacturer may also specify a compatible drain assembly that is not interchangeable with another brand.
Before framing the recess, mark the intended drain center or linear-drain line and trace the pipe route below. A drain that looks convenient on the floor plan may land directly over a joist, beam, duct, electrical run, or other obstruction.
Plan the finished transition height
The transition is the elevation relationship between the finished shower floor and the finished bathroom floor. Start with the adjacent bathroom floor height, then work backward through tile and setting materials to determine the available height at the shower entry. From there, account for the shower-floor slope toward the drain and the thickness of the waterproofing and tile assembly.
A low entry normally requires the shower perimeter to be close to the bathroom floor. If the drain is far from the entry, the required slope may raise the drain-side or perimeter-side assembly depending on the drain design. Recessing the structural support creates more room to keep these layers below the adjacent floor. A foam tray or mortar bed placed directly on the existing floor may instead require the bathroom floor to be raised outside the shower.
Do not create an abrupt lip by stopping the waterproofing at the visible transition. The waterproofing design should follow the selected system so water cannot migrate beneath the tile or into the surrounding floor. Whether the entire bathroom floor needs a membrane depends on the shower design, room layout, drainage risk, and the selected system rather than on the word “curbless” alone. The related guidance on waterproofing the bathroom floor for a curbless shower can help frame that decision.
A practical planning sequence
- Inspect the structure. Identify joist type, direction, depth, spacing, subfloor construction, bearing points, and obstructions below.
- Choose the drain concept. Select a point drain or linear drain and place it where the waste piping can be routed without compromising framing.
- Draw the finished elevations. Show the adjacent floor, shower entry, perimeter, slope, drain, waterproofing, tile, and all setting layers.
- Select the shower system. Confirm tray dimensions, drain compatibility, substrate requirements, waterproofing connections, and permitted modifications.
- Resolve structural work. Have recessed framing, headers, blocking, or other modifications reviewed by a qualified professional when required.
- Confirm plumbing and permits. Ask the local building or plumbing department which permits and inspections apply, and verify the locally adopted requirements.
- Install the supported substrate. Do not proceed until the lower floor or tray has continuous support and the surface meets the system instructions.
- Waterproof and test the assembly. Follow the membrane and drain instructions, complete any required flood test, and obtain inspection approval before covering the work where applicable.
Frequently asked questions
Can I lower a curbless shower by cutting only the subfloor?
Sometimes, but removing the subfloor alone does not create a safe recess. The opening needs properly supported framing, and the revised load path must be acceptable for the joist system. Cutting joists or engineered members without an approved design can weaken the floor.
Is a foam tray always low enough for a curbless shower?
No. A foam tray may reduce buildup, but its perimeter, drain, waterproofing, tile, and setting materials still occupy space. The tray may need a recessed substrate or a raised bathroom floor to achieve the desired transition.
Can a mortar bed replace recessed framing?
It can in some layouts, but a mortar bed still needs enough depth to form the required slope and must be fully supported. A thin bed cannot safely compensate for an unsupported or structurally inadequate floor.
Does a linear drain eliminate the need for a shower-floor drop?
No. It may simplify the slope because the floor can fall in one direction, but the shower still needs a slope to the drain and a waterproofed drain connection. The required elevation depends on the shower dimensions and system details.
Who should approve the joist modification plan?
For structural changes, use a qualified structural professional when needed and confirm local permit requirements with the authority having jurisdiction. For plumbing, verify the drain and waste-piping plan with the local plumbing department or a licensed plumbing professional where licensing rules apply.