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The Home Depot

How to Install a Bathtub

Pro Referral > Home Guides > Handyman > How to Install a Bathtub
How to Install a Bathtub

Anyone with young children knows just how essential the bathtub is. Those too that enjoy a little luxury will herald the value of a good whirlpool or soaker tub.


When we talk bathtubs, we might immediately think of the classic claw foot. But day-to-day, we're probably a little more familiar with the drop-in or built-in types. The fact is that bathtubs come in a variety of forms (with many different options), and the style we choose may not only dictate the steps needed to install, but may even say a little something about our lifestyle choices.


Let’s break it down: a bathtub is installed in one of two ways. A bathtub can be placed either as a stand-alone fixture, where there are no enclosing walls, or it can be incorporated in a pre-designed wall cavity, or alcove, often in conjunction with a shower. In this second case, you'll typically find three walls enclosing the tub.


This article will focus on the second type of installation, because the tub/shower combination is the most common. Many of the techniques described, however, may carry over to other types of installations.

Materials Skill Level Estimated Time
• Pry bar Intermediate to Advanced 2 to 5 days
• Hammer
• Drill driver
• Screwdrivers
• Levels (2' and 4')
• Pencil
• Tape measure
• Pipe wrench
• Channel locks
• Hacksaw
• Circular Saw
• Tub drain (removal) wrench
• Chalk box (optional)
• Caulk gun
• Tub
• Drain and overflow assembly
• Plumber's putty
• Thread sealant (if gaskets are not provided with the drain kit)
• 2 x 4 x 12 (at minimum--lumber load varies according to installation)
• 1x3 or 1x4 (scrap for cross bracing of supply line plumbing and to ease installation)
• Cedar shims
• Roofing nails (1 1/8" to 2 1/2")
• Deck screws (1 3/4" to 4")
• Fiberglass batt insulation (optional)
• Dry set mortar or (high strength) cement mix + related tools
• Thirty pound roofing felt (tar paper)
• Roof-rated aluminum flashing
• Silicone caulk

Plan Your Bathtub Installation

  1. 1. Selecting a Tub

    Traditional materials have included cast iron or steel. Today, tubs are lined with enamel, replacing the more historic porcelain. In recent decades, the industry has transitioned to lighter weight options like acrylic or fiberglass (A big win in and of itself for ease of installation). The most common tub color by far is white, but there are certainly "statement" and coordinating colors available (at a premium cost).


    When selecting a tub for a tub/shower installation, you will need to determine whether a left-handed or a right-handed tub is needed. To identify a tub's handedness, simply stand in front of your intended tub location and ask yourself, "Is the plumbing on my left or is it on my right?" If it's on the left, you'll need a left-handed tub; if it’s on the right, a right-handed tub. Cut-outs for drains as well as the tub's "apron" will be located on the indicated side of the tub.


    Standard apron tubs are 60" or five-feet long (smaller sizes are available). Alcoves should be framed at a fraction larger, and this should be verified prior to beginning installation. Always ensure that you are working within local plumbing codes and allow for around 30" of free space immediately in front of the tub after it is installed.

  2. 2. Removing an Old Tub

    Whether you choose to get into a more substantial remodel, which could include a refresh of wall surfaces or an update of tub/shower faucet(s), at minimum 6" of wall surface will need to be cut back to allow access to an existing tub for removal and replacement. To remove an old tub:

    • A. Grab a nifty tub drain removal tool, and following its instructions, disconnect the existing tub drain from the tub.
    • B. Cut back any caulking and remove any existing fasteners holding the tub in place.
    • C. Lift up on the tub, perhaps using a pry bar, and slide the tub from its opening. Note: Place a piece of cardboard under the tub's front lip in order to protect existing finished floor surfaces.

Prep the Location for the new Tub

  1. 3. Preparing to Prepare

    While overall steps can change significantly depending on your selected tub type, the amount of prep needed will depend in part on a few simple factors:

    • A. Is the plumbing where you need it?
    • B. Is your tub location structurally sound?
    • C. Will the new tub sit on an exterior wall?

    How you answer these questions and how you address the given situations, may require more advanced techniques and perhaps the assistance of a licensed professional.


    Thoroughly read the plumbing specifications for your tub. If you are plumbing a new bath, doing significant re-working in an old bath, or just making tweaks to an existing tub drain, you may enlist the help of a licensed plumber.


    Important! Before setting a new tub, ensure that the structure, i.e. the floor system, can support the weight of a new tub. This is especially important in old houses where framing may be undersized, or when replacing say a "builder grade" fiberglass tub with a heavier option. This may require a look from a licensed contractor or from a local building inspector, but in general framing should be larger than 2x10s and should be spaced no more than 16" apart.

Unboxing the New Tub and Prepping for Installation

  1. 4. Unbox the Tub

    In many cases, a new tub will be wrapped with a protective film (or other material). When unboxing, try not to disturb this material as it will help protect your tub as you install it. Break down your new tub's box and set it aside, later we'll use it to line the interior of the tub to further protect it as we work.

  2. 5. Mounting the Drain Kit with Overflow to the Tub

    Install your drain-waste-overflow kit prior to installing your new tub. Best practice would have you elevate your new tub in some manner, e.g. resting on a set of 2x4s. Alternatively, a tub can be tipped gently onto its side. Follow manufacturer recommendations for installing your drain and overflow kit, as these products too may vary.


    Note: Varying requirements in tub height and depth will require adjustments more than likely in the drain/overflow's tailpipe. Threaded fittings will not require but can receive thread sealant (aka pipe dope) and coordinating slip nuts can be tightened using a pipe wrench or an appropriate sized set of channel locks. Warning: Do not overtighten.


    Working (but not standing) inside the tub:

    • A. Apply a ring of plumber's putty to the underside of the drain flange (and to gasket if one is included).
    • B. Line up the drain pipe from underneath, include any provided gaskets, and tighten the drain flange down to the drain. Being careful here not to mar your new "trim," a tub drain wrench may work well here.
    • C. Remove any excess plumber’s putty.
    • D. Connect the overflow coverplate to the provided flange of the overflow pipe using a hand held screwdriver.

    Materials for Drain-Waste-Overflow kits typically range from Brass to PVC.

Leveling and Setting the Tub

  1. 6. Preparing to Set the New Tub

    If you are installing new faucets and the walls are open, it may make sense to complete required supply-side "stubs" prior to beginning the process of actually setting the tub. Before setting the tub make sure that your tub's drain is trimmed to an appropriate height (with a hacksaw).


    At this point, slide your new tub into place (perhaps working with a partner), and do a quick check of level--both side to side and back to front. Shims may be used to make small adjustments to the tub's level. If the the tub is level, trace the top edge of the tub. Your new tub will have a nailing flange; mark at each stud location around the entire perimeter of the tub.


    Remove your new tub carefully. Measure the distance from the nailing flange to the top of the tub's rim, the underside of the tub within the tub's frame.


    Subtract that difference and, using the marks you already made on your studs, make a second level line. This is best done using either a four-inch level or by snapping a chalk line with a chalk box. (Check your tub manufacturer's instructions as it may provide additional guidance here.)

  2. 7. Install a Cleat/Stringer for Your Tub

    Your new tub will rest on a ledger that should wrap the entire tub. (Make sure to leave room for plumbing connections.) Taking your 2x4s, measure and cut to length. These are best installed using exterior-rated (deck) screws and a drill driver. The top edge of your 2x4s should meet the top edge of your bottom line.

  3. 8. Create a Mortar Bed

    Just when you think you are ready to install your tub, apply a layer of dry-set mortar to the area immediately below your tub (providing a build-up at the area below the "bowl" of your tub). If you had employed shims in leveling earlier, do not disturb them.


    It may be best practice to cut a section of roofing felt and place it (unfastened) on the subfloor prior to installing your mud set. To avoid disturbing this mortar bed (or your drain assembly for that matter), place 1x4 "runners," pitching them if possible from the back wall's bottom framing plate. With the help of a friend, slide your tub carefully back into place, lift up slightly, and remove your runners.

  4. 9. Nail your Tub to Framing

    While some tubs come pre-drilled, many do not. Your tub will be nailed to framing using Roofing Nails. It probably goes without saying that you need to take care when nailing your tub into place. Do not overdrive nails. Nail heads should be absolutely flush to the nailing flange (as to avoid an opportunity for water penetration). Nail at each available stud around the perimeter. Once nailed, and if water is available at this point, fill the tub with water and allow the mortar to set up four to six hours or more.

  5. 10. Flash over the Nailing Flange

    Because we are in fact at a wet location (even more so if your tub it combined with a shower), we want to provide some level of flashing that will lap the tub's nailing flange. The purpose of this flash is to catch any water that may get behind your wall surface.


    Flashing can be achieved successfully in a number of different ways. In its most traditional form, simply use a flat aluminum coil flashing stock (four to six inches tall), and installing in this manner:

    • A. Cut to size.
    • B. Bent and overlap at corners.
    • C. This too will be nailed to wall studs. It should overlap the nail flange but should be held up from the tub itself (by about a ½ inch) to allow for some expansion and contraction of materials.

Making the Final Plumbing Connections

  1. 11. Connecting the Drain

    Since the drain with its overflow is already attached to the tub, it is often only a matter of extending the drain's tailpipe (an extension actually of the overflow) down to the plumbing's p-trap (roughed in earlier and sitting below the floor plane).

    • A. Trim drain further using a hacksaw if needed.
    • B. Connect using the supplied slip nut.
    • C. Tighten with a pipe wrench or appropriately-sized set of channel locks, taking care not to overtighten.

    Important! With existing finished rooms, it may make sense (or be necessary) to cut an access on the opposite side wall behind/outside the tub's wet wall (if possible), usually in an adjacent room.

Complete the Install

Installing or replacing a tub will almost certainly be done in conjunction with work on the "tub surround." Because the walls surrounding a tub will be addressed and, in most cases are opened, it of course is an opportune time to replace your tub/shower faucet.

  1. 12. Caulking at your Tub

    Regardless of whether you choose to do more significant remodeling with your tub install, your tub needs to be caulked to ensure water tightness. This should be your final step in the installation process. Caulking is done with a caulk gun.


    Important! Cut your caulk tip to the exact size of the bead of caulk you will need. Work slowly around the perimeter of your tub smoothing as you go. Allow caulk (based on manufacturer recommendations) to dry a minimum of three hours before using your new tub.


    Finish around the outside of your tub with caulk or trim as needed.

Level of Difficulty

This guide focuses on installing a lightweight, alcove bathtub. While there are many steps involved, it is likely the easiest of all tub installations. While the process of installing the tub itself is an intermediate project, especially for individuals with basic plumbing and carpentry skill, difficulty can increase (as mentioned above) based on related factors such as rough plumbing and framing needs/issues. Installing a new bathtub may also be done in conjunction with installing new wall surfaces and bath faucet(s), which can further extend the complexity of the project. Good luck.

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