How to Install a Bathtub
Credit: Opensource

Installing a bathtub is not complicated but it does require some plumbing, carpentry and tiling skills. Before installing a tub, review everything that you are going to do in the bathroom and determine whether you have the skills to complete the job or if it is best left to a professional. If you decide to go ahead with the job on your own, check with local codes and get any necessary permits. You will definitely need one for the plumbing since you are altering it, but others may also apply.

Next, measure the width of the bathroom, the doors and passageways within the room. You need to know if you can actually remove an old tub (if necessary) or how big of a new tub you can get into the doorway. Typically, this type of job goes better when done by two people.

Before you begin installing a new bathtub you will need to remove the old one and any sheetrock or other materials on the wall. It is best to start from scratch and for this discussion, we will install a bathtub with tiled walls and assume the bathroom area has already been gutted down to the wall studs. Afterall, the only instructions you need for demo work is to wear safety goggles and do not smash any pipes or electric work.

Therefore starting out, you should be looking at wall studs with the plumbing already roughed in. Before you start any work on the new project, you should go pick up a few supplies and materials that you will need for the job.

How to Install a Bathtub
Credit: Opensource

Framing the Walls for the Supply Lines

How to Install a BathtubCredit: OpensourceFrame the walls so that the opening is just large enough to slide the new tub into place with about an 1/8 of an inch at each end.

Install the plumbing for the risers, faucet and shower head securing each assembly with 2x4 blocking for support in between wall studs.

If you removed an existing tub, the drain pipe and P trap should already be in place.

Build Up a Base for the Tub

How to Install a Bathtub
Credit: Opensource

Tubs made of enamel, steel, acrylics, fiberglass and other similar types of material will flex when water is put inside them so before you slide the tub into place, you need to build up a bed of soft support under the tub.

Typically you can use something like a sand mix according to the manufacturer’s directions and pour it on the floor where the tub will rest. Cover the wet sand mix with 6 mil. plastic sheeting to prevent any reaction with the tub.

Now carefully lift the tub into place with a helper and rest it on the base you just created and check for level using a 48” level.  It is a good idea at this point to lay newspaper or old carpet down inside the tub to prevent any damage while you are working inside it.

Once you have leveled it out, mark the top of the nailing flange at each wall stud.  If you are installing a fiberglass or acrylic tubs, a ledger board is required. Measure the distance from the top of the nailing flange you just created to the underside of the tub rim inset. Subtract that figure (somewhere around an inch) from the marks on the wall studs you made earlier and mark the ledger board mounting height with a pencil.

Connecting the Drain and Overflow

To connect the drain assembly you will need to pull the tub out from the alcove so that you can work at the head of it in the drain area. Following the instructions provided by the manufacturer, assemble the drain system so that you can measure the trim and drain tailpiece to connect with the P trap below.  The drain pipe will slide into the pressure fitting on the P-trap but you will probably have to trim it to fit.

Next, connect the overflow drain to the tub.

Installing Ledger Boards and Setting the Tub

Each ledger board to support the tub should be cut to fit all three sides of the alcove. Use wood galvanized screws (exterior screws resistant to moisture) to attach each ledger load to the studs using the marks in made earlier. Install the boards in sections if necessary to make room for any structural braces at the ends of the tub. Make sure that each board you install for support is level.

Now that all of your support ledgers are in place, set the tub (using a helper) back in place on the bed you made earlier and rest its lip on the support ledger. The tub must sit firmly on the ledger strips and the drain must be flush with the P-trap.

Assuming everything is correct, nail galvanized nails through the predrill holes into the wall studs to secure the bathtub in place.

Connecting the Drain and Faucet Assembly

How to Install a Bathtub
Credit: Opensource

Now that the bathtub is secured to the wall, install the drain assembly through the overflow opening in the tub. This can be tricky because you are trying to feed it through a small opening.

Attach the overflow cover plate to the mounting flange with screws. Test everything for leaks by pouring water into the tub. Be sure to check areas under the drain in the floor, either in areas directly under the bathroom on the first floor, or down in a crawl space under the bathroom.

Now is the time to call local officials for an inspection before you close up any walls.  Once the inspector signs off on your work, connect the rest of the faucet handles and tub spout.

Use silicone caulk to seal around the handles and apply a bead around the edge of the bathtub. Turn on the faucets and check for leaks once again before proceeding to finishing the walls.

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Finishing the Walls

Most people like to finish walls in the bathroom with tile, however, there are other options such as shower surrounds that are installed in panels with built-in shampoo and soap caddies. For the purposes of this discussion, we will assume that you are finishing up the walls with a tile base.

First, since tiles are heavy and you will need a moisture resistant surface, Durock cement fiberboard is the best choice for walls in the bathtub or shower.

At this point it is best to install an access panel behind the faucets and supply lines so if there is an issue in the future, you will not have to break the wall to work on either of them. Within this access panel should be shutoff valves to isolate the plumbing to the bathtub from the rest of the plumbing in the house.

Piece the wall with backerboard, then using a key hole saw, cutout the shower outlet. Apply fiberglass tape to all of the gaps, then apply thinset mortar to cover the tape. After it dries, the walls are ready to be tiled.

Final Thoughts

Install a Bathtub
Credit: Ian McKellar via Wikimedia Commons

If working with copper pipes or fitting drain assemblies seems beyond your expertise, consider hiring a professional. However, if the plumbing has already been roughed in, or you are going to be using your existing plumbing and drain setup, the job of installing a bathtub is not that difficult.

The basic steps are measuring the area where the tub will be placed, providing a solid base of support with a bed of sand mix or related material, building a ledger board system and nailing the tub in place. 

Don’t forget to call for a city inspection before you start closing up walls because the last thing you want to do is open things back up just to let someone glance at it to make sure you did it right.