Replacing a bathtub costs $1,500 to $5,500 for a standard alcove tub with no plumbing changes. The same replacement with a premium freestanding tub and floor-mounted faucet costs $4,000 to $10,000. The cost difference between a project that goes smoothly and one that spirals into unexpected expenses is almost never the tub itself. It is what the contractor finds when the old tub comes out: rotted subfloor, mold behind the surround, plumbing that is not to code and must be updated before the new tub can be connected. The planning phase — ordering the tub, verifying the floor can support it, locking in the plumbing rough-in location — prevents these surprises from becoming emergencies. An emergency is a $5,000 project that becomes $12,000 because the subfloor was rotted and nobody budgeted for it. A plan is a $5,000 project that becomes $7,500 because a 20% contingency covered the subfloor repair and the project stayed on schedule.
The sequence of a bathtub replacement is fixed. You cannot set the tub before the plumbing rough-in is complete. You cannot install the wall surround before the tub is set and level. You cannot tile before the waterproofing cures. The planning phase is where every decision with a lead time gets locked in — the tub material and dimensions, the faucet type and valve rough-in, the surround material, the waterproofing system — before demolition begins. The six planning steps below organize the 15 to 20 decisions into the correct order, with the measurements, lead times, and code requirements that prevent the most common and expensive mistakes.
Step 1: Measure the Existing Tub and the Bathroom — Before You Order Anything
The standard alcove tub opening is 60 inches wide by 30 to 32 inches deep. An existing tub in a 60-inch alcove may actually measure 59-1/2 to 60-1/4 inches, and the difference between the rough opening and the tub flange is covered by the wall surround. The new tub must fit within the existing rough opening or the wall must be moved, moving a wall is a bathroom remodel, not a tub replacement, and the cost difference is $3,000 to $8,000.
Measure the width of the alcove at the back wall, at the front, and at the midpoint. The narrowest measurement is the one that matters. If the alcove is 59-1/2 inches, a standard 60-inch tub will not fit without notching the studs or furring out the wall. A 59-inch tub exists but is harder to find and has fewer style options. The depth of the alcove, the distance from the back wall to the front edge of the tub deck, determines whether the new tub will sit flush with the existing flooring or require the floor to be patched. A standard tub is 30 to 32 inches deep. If the existing tub is 32 inches and the new tub is 30 inches, there will be a 2-inch gap at the front that must be filled with a deck extension or flooring patch.
Measure the drain location. A standard tub drain is centered on the width of the tub and located at the end opposite the faucet. The rough-in drain pipe should be centered 14 to 16 inches from the back wall and positioned at the head or foot end depending on the tub orientation. Moving a tub drain, cutting into the subfloor and rerouting the waste pipe to a new location, costs $500 to $1,500. The tub you order should match the existing drain location unless the bathroom floor plan is changing and the drain move is part of the plan.
Step 2: Choose the Tub Material and Type, Acrylic, Cast Iron, or Stone Resin
The tub material determines the weight, the heat retention, the durability, and whether the existing floor can support the new tub without reinforcement. An acrylic tub weighs 75 to 150 pounds. A cast iron tub weighs 300 to 500 pounds. A stone resin tub weighs 200 to 400 pounds. A standard wood-framed bathroom floor can support an acrylic tub without modification. A cast iron or stone resin tub on an upper floor may require joist reinforcement, sistering additional joists or adding blocking between existing joists, at a cost of $500 to $1,500 before the tub is installed.
Acrylic is the most practical material for most bathroom replacements. It is lightweight, non-porous, waterproof by nature, and costs $500 to $2,000 for the tub alone. It holds heat moderately well, water stays warm for 15 to 20 minutes. Cast iron is the most durable, 50-plus years, and holds heat excellently, but the weight limits which bathrooms can accommodate it. Stone resin offers cast-iron-like heat retention at roughly two-thirds the weight, with a warm-to-the-touch surface and a premium price tag of $1,800 to $5,000. Fiberglass is the budget option at $200 to $800, but the gel coat finish dulls and crazes within 5 to 8 years of regular use. Fiberglass is right for a rental or a budget flip. It is wrong for a primary bathroom used daily.
According to ENERGY STAR, pairing a bathtub replacement with WaterSense-labeled bathroom faucets can reduce water consumption by 20% or more compared to standard models, a consideration worth factoring into the fixture selection during the planning phase since the faucet rough-in happens at the same time as the tub installation.
Step 3: Choose the Faucet and Valve, Before the Wall Is Closed
The tub faucet type determines the valve rough-in that must be installed in the wall before the tub is set. A standard tub spout with a shower diverter requires a valve at the standard height, roughly 28 to 32 inches above the floor for the spout, with the valve centered on the tub width. A freestanding tub filler, a floor-mounted faucet that rises from the floor next to the tub, requires the hot and cold supply lines to be roughed into the floor at the exact location of the filler base, with the drain and overflow in a different location than an alcove tub. Moving from a wall-mount faucet to a freestanding filler is a plumbing rough-in change that must be planned before the floor is closed. The cost to move the supply lines from the wall to the floor is $500 to $1,000.
The valve must be ordered with the tub. The lead time for a specialty faucet can be 4 to 8 weeks, and the plumber cannot rough in the valve without the valve body on site. The trim, the handle, escutcheon, and spout, can arrive later, but the valve body must be on the job before the rough-in inspection. Order the faucet when you order the tub. The two components are installed by the same plumber on the same day, and their lead times should be synchronized.
Step 4: Specify the Waterproofing System, Before the Surround Goes Up
The tub surround, the walls above the tub, must be waterproofed before tile, acrylic panels, or any finish material is installed. The tub flange, the raised lip around the perimeter of the tub, must overlap with the wall waterproofing so that any water that runs down the wall drains into the tub, not behind it. The waterproofing material, sheet membrane, liquid membrane, or a factory-installed acrylic wall system, must be specified in the contract with the specific product name. “Waterproofed shower walls” is not a specification. “Schluter-Kerdi membrane over cement board, Kerdi-Band at seams and corners, membrane overlapping tub flange by 1/4 inch” is a specification.
The most common waterproofing failure on a tub replacement is the seam between the tub flange and the wall waterproofing. If the waterproofing stops above the flange instead of overlapping it, water wicks into the gap and saturates the wall cavity. The damage is hidden behind the tile for years until the grout cracks at the tub line and water visibly leaks onto the floor. By then the wall studs are rotted. The fix is to specify the flange overlap in the contract and verify it before the tile goes up.
Step 5: Order Materials Before Demolition, Lead Times Control the Timeline
A custom tub can take 6 to 12 weeks from order to delivery. Specialty tile can take 4 to 8 weeks. A cast iron tub from a manufacturer with limited production runs can take 8 to 12 weeks. The most common bathtub replacement delay is waiting for materials ordered after demolition instead of before. The bathroom sits empty for 2 months while the tub is being manufactured. The contractor moves to another job.
Order the tub, the faucet and valve, the surround material, the tile, and the grout before demolition. Store everything in the garage or a spare room. When the old tub is removed and the rough-in is complete, the materials are on site and the installer can work without interruption. The planning window is not about indecision. It is about lead times. Use it.
Step 6: The Construction Sequence, What Happens After Demolition
The construction sequence after the old tub is removed is fixed. Any contractor who deviates from this order is either cutting a corner or does not understand waterproofing.
1. Subfloor inspection and repair. Before the new tub goes in, the subfloor under the old tub must be inspected for water damage, rot, and structural integrity. This is the 15-minute step that prevents the $3,000 surprise. Budget for 1 to 2 sheets of subfloor replacement, roughly $200 to $400 in materials and labor, as a contingency.
2. Plumbing rough-in. Move the drain if the new tub requires a different location. Rough in the valve. Run the supply lines to the valve location or the freestanding filler location. This is the only window to change the plumbing configuration.
3. Tub setting. Set the tub in place. Level it with shims. Secure it to the studs through the flange with roofing nails or screws, not through the tub deck. Screws through the tub deck crack the acrylic and void the warranty. Connect the drain and overflow. Fill the tub with water and check for leaks before the surround goes up. A leak at the drain connection that is discovered after the tile is installed requires removing tile to access the connection.
4. Wall substrate and waterproofing. Install cement board or mold-resistant drywall. Apply the waterproofing membrane. Tape and seal all seams and corners. Overlap the tub flange.
5. Surround installation. Tile, acrylic panels, or solid surface. The finish material goes up after the waterproofing cures.
6. Trim and faucet installation. Install the faucet trim, spout, and showerhead. Connect the supply lines. Test the valve for leaks and proper operation.
7. Final inspection. If a permit was pulled, required for any plumbing drain change, the inspector verifies the work before the project is closed.
Frequently Asked Questions
Tub liner vs. full replacement, which is better?
A tub liner, an acrylic shell custom-fitted over the existing tub, costs $1,000 to $3,000 and installs in one day with no demolition. It covers surface damage and updates the appearance. A full replacement costs $1,500 to $5,500 and addresses structural problems, a flexing tub floor, a rusted-out drain connection, water damage to the subfloor. A liner is the right choice when the existing tub is structurally sound but cosmetically unacceptable. A full replacement is necessary when the tub flexes, leaks, or has rusted through. A liner installed over a structurally failing tub will crack at the flex point within 2 to 3 years because the liner mirrors the movement of the tub underneath. If the old tub moves, the liner moves with it and eventually fails at the same point.
Do I need a permit to replace a bathtub?
Replacing a tub with a new tub of the same size in the same location, with no plumbing drain changes, does not require a permit in most jurisdictions. Moving the drain, changing the valve configuration, or converting a tub to a shower requires a permit. When in doubt, call your local building department. The phone call is free. Unpermitted plumbing work discovered during a home sale costs thousands.
