Let’s face it. Showers are the bathing choice of just about
everyone. So if your bathroom has become a family
bottleneck because you don’t have enough shower stalls
or the one you have is leaking, read on. We’ll show you
how to replace a leaky base, replace a tub with a shower
only or install an additional shower to handle demand.
Preformed shower bases have vastly simplified
the installation process. They’re virtually leakproof
and are vastly easier to install than
traditional solid mortar bases.
Still, setting a base can be challenging, especially when you’re remodeling
older plumbing. In this article, we’ll show you how to rip out an old
tub and replace it with a one-piece fiberglass shower base. We’ll walk
you through the tricky parts, first how to relocate the drain just right,
then the necessary venting. Next, we’ll show how to set a
rock-solid base—one that won’t crack or leak down the road. Our step-by-
step instructions will take you right up to the point where the walls
are ready to finish. But we won’t go into those finish details here.
This is mostly a plumbing project. To take it on, you should
be familiar with basic pipe joining techniques. Mostly this involves
cutting and cementing plastic pipes and fittings. Don’t worry if you
make mistakes. The materials are inexpensive and corrections are easily
made by cutting out sections and installing new fittings and pipes.
Completing this job—getting the old tub out, reworking the plumbing
and installing the new base—will take a Saturday at least, a weekend
at most. If you have to run a drain line through joists or studs, we
recommend that you rent a 1/2-in. right-angle drill and a 2-in. hole
saw (or bit; Photo 6). Otherwise basic plumbing tools and hand tools
are all you’ll need. Be sure to apply for a plumbing permit and have
an inspection done at the rough-in stage (when everything is still
exposed) and after everything is complete (wall surfaces finished, final hardware installed).
Planning the job
Start by deciding on the size of the shower
base and ordering it. Delivery can take
weeks, so don’t rip anything apart until
the new one is in hand. If you’re replacing
an existing base, simply get one the same
size. If you’re replacing a tub with a shower
as we did, there are more details to consider.
You’ll have the fewest problems if you
match the new base to the old tub’s width
(the front of the tub to the wall). Go wider
if you like, but you may have to replace
flooring. Or you may overstep required
minimum distances from toilets and
sinks. You might have to shift the supply
valve as well. Keeping the same tub footprint
(or smaller) minimizes the hassles.
We replaced a 5-ft. tub with a fairly
spacious 4-ft. base the same width as the
tub. (See “Selecting a Shower Base,” below.) We framed a 1-ft.-wide
filler wall at the end, which is a nice place
to build recessed niches and shelves for
Now’s a good time to buy a new shower
valve too, especially if your old one doesn’t
have scald protection, as all new ones do.
It’s a big project to replace a valve that fails
after tile or wall panels are installed.
You’ll need an assortment of pipes and
fittings for installing the new drain and
for reworking water lines. Pick them up
after you open up the floor and walls. At
that point you can see what you need, plan
the new drain and water supply runs and
make a list of supplies. Make a sketch like Figure A to help you keep track of parts.
Shower base and drain details
Figure A: Shower Base/Drain Details
Make a sketch of the project that includes the waste, vent and water supply. Drawing the details will help avoid potential problems and also reduce the number of trips to the hardware store.
Remove the old surround and tub
1 of 3
Photo 1: Remove the wall
Remove the faucet valve handles and escutcheons. Cut through the drywall that surrounds the tile with a utility
knife and pull chunks from the wall.
2 of 3
Photo 2: Disconnect the plumbing
Shut off the main water supply valve. Cut out the water supply lines and install ball valves if you don't already have them.
3 of 3
Photo 3: Remove the tub
Disconnect the trap from the tub drain, then lift the tub free from the wall and carry it out.
First unscrew the showerhead and the
bathtub spout. Most styles will unscrew,
but some will need persuasion with a pipe
wrench. If you want to reuse any parts,
wrap the tool jaws with cloth to prevent
damage. Then remove the handle and
mixing valve escutcheon cover. Most handles
have a little plastic cap that pops off
to expose a screw. Remove the screws and
pull off the handle and the escutcheon.
Next, strip off the tub surround. Begin
by cutting completely through the drywall
around the perimeter with a utility knife.
If you have cement board behind the tile,
simply cut through the tape joint at the
ceiling and strip the entire wall. Rip off
the tile and drywall together in big chunks (Photo 1). If you have a fiberglass surround
with a flange behind the drywall,
cut 2 in. outside of the enclosure and pry
the sections free one at a time.
With the wall open, disconnect the
plumbing. Usually you can access the
trap from an access panel in the room
behind the tub or from an unfinished
basement. If you don’t have access, you’ll
have to cut a hole in the wall from
behind the tub base. If your shutoff
valves are in good shape, cut off the
water lines above them. If they’re missing,
stuck or corroded, shut off the main
supply valve, cut off the water lines and
install two compression fitting–style ball
valves and leave them in the closed position
so you can turn the water back on
to the rest of the house (Photo 2). Cover
the ends with tape to keep out debris.
Fiberglass and steel tubs are fairly
light; you can just tip them up and carry
them away (Photo 3). If framing makes
it difficult to pull out, cut out more drywall
along the plumbing wall. Then you
can pull the tub away from the wall
before you tip it up. Cast iron tubs, on
the other hand, are extremely heavy, and
we recommend just busting them up with a sledgehammer and carrying out
the pieces. (Lay an old blanket over the
tub to catch flying shards, and wear safety glasses for this!)
Mark the exact drain location and open up the floor
1 of 2
Photo 4: Mark the new drain
Set the shower base in place
and mark the drain hole.
2 of 2
Photo 5: Cut an access slot
Mark and cut an access slot in the subfloor for roughing in the new P-trap and drain line. Cut over the center of
joists where possible.
Snug the new shower base up to the wall
studs and mark the drain hole (Photo
4). Then pull it aside and draw an access
slot on the subfloor (Photo 5). Make
the slot about a foot wide and extend it
just beyond the new drain location.
Keep the edges of the slot over the middle
of joists wherever you can to make
patching easier later. Make reference
marks on the floor outside the slot so
you can relocate the center of the drain
once you remove the flooring (Photo
6). Pull any nails that fall within the cutting
lines. Then set your blade depth to
cut just through the subfloor, make the cut and pry it free (Photo 5).
Rough in the drain and vent lines
1 of 4
Photo 6: Cut a path for the drain
Drill 2-in. holes through the floor joists for the new drain line. Reference marks help you find the
drain center later.
2 of 4
Photo 7: Install the sanitary tee
Cement 6-in.-long nipples to both ends of a 3 x 1-1/2-in. sanitary tee, then mark and cut the main stack. Join
it to the stack with transition couplings.
3 of 4
Photo 8: Run the vent
Drill 2-in. holes through the studs, sloping away from the tee 1/4 in. for every 1 ft. of run.
4 of 4
Photo 9: Dry-fit the waste and vent
Dry-fit the new vent
line and drain line
fittings, working your
way toward the P-trap.
Use reference marks on
the subfloor to fine-tune the location of the drain.
With the floor and wall open, you can
plan your new drain and vent lines. Reworking drain and vent lines will be
slightly different with every bathroom,
but our photos and Figure A will give you
the general idea along with a look at the
various fittings you may need.
If your tub didn’t have a vent, you’ll
probably have to add one. A local plumbing
inspector will tell you the rules (usually
within 42 in. of the shower P-trap)
when you apply for a permit. The new
vent must join the main vent at least 6 in.
above any “spill lines” (that usually means
sink rims) that share the vent. You’ll
probably have to open a wall to get it in
(Photos 7 and 8).
The two keys for adding a drain are to
make sure the horizontal lines slope
1/4 in. for every running foot and that the
P-trap opening falls directly below the
shower drain hole. Start by measuring the
height of the center of the existing drain
line and the distance to the new drain. Cut
off the old P-trap, then run the drain line
to the new drain location (Photos 6 and
9). Remember to allow 1/4-in.-per-foot
slope when you drill holes in joists. Drill
2-in. holes to leave some room to move
the 1-1/2-in. pipe up or down to get the
necessary slope. But don’t drill in the
lower or upper 2 in. of any joist. Most
shower drains are designed to receive 2-in.
piping, while most existing tub drains are
1-1/2 in. The plumbing code calls for the
transition to be made with a reducer
directly below the shower (Photo 10),
To run the new vent, mark a section of
main stack for removal using the 3 x
1-1/2-in. tee (with 6-in.-long nipples) as a
guide (Photos 7 and 8 and Figure A). If
your main stack will be plastic, cutting it is
easy with a hand or reciprocating saw with
an 8-in. blade. If you have cast iron, you’ll
have to rent a pipe snapper to make the
cut. Slip the fitting into the opening and
secure it with transition couplings. Then
run the vent line down to the drain, cutting
holes in the framing as needed.
Horizontal sections should also follow the
1/4-in.-slope rule, running downhill
toward the drain. Cut all the pipes and
dry-fit them one at a time to the fittings,
then double-check the drain line slopes
and final drain position. Set the shower
base in place to double-check the final
placement of the P-trap, inserting a short, temporary tailpiece (Photo 9). When
you set the shower base permanently,
measure and cut a permanent tailpiece
and cement it into place.
Starting at the main vent and working
toward the P-trap, begin cementing the
parts together. If you’re using PVC, hold
the parts together for about 20 seconds
after cementing. Otherwise, the parts
will “squirt” apart before the solvent
cures. Save the P-trap-to-drain-line connection
for last. Cement it together, and
quickly plumb the P-trap with a 6-in. level before the joint sets (Photo 9).
Your building inspector will want to see
the drain and vent (and possibly the
water supply rough-in; Photo 11) before you close up the floor.
Patch the floor
1 of 1
Photo 10: Close the floor
Add blocking to
shore up the subfloor
and screw a patch to
the framing with 1-5/8-in.
screws. Add a second
layer of 1/2-in. subfloor
if your finished floor covering will permit it.
Add blocking to bolster unsupported plywood edges and screw a patch to the framing with 1-5/8-in. screws (Photo 10). We added a second layer of 1/2-in. underlayment under the entire shower for a sturdier floor and to better match the finished floor height (1/2-in. backer board and tile). If you need to preserve the original floor height, skip the second layer, but add blocking under the single-layer
patch to fully support the shower base.
Selecting a Shower Base
You won’t be able to enter a home center and walk out with a 4-ft.-long
shower base like the one we show. Ask to go through the plumbing fixture
books there to special-order one that suits your bath decor and budget.
Some come with drain adapters, as ours did. You’ll have to check, and purchase a separate shower drain kit if needed. The manufacturer’s directions will help you choose the right one.
There is another (but more costly) option if you’d like to skip all of the
extra venting and drain work. Select a shower base that has the drain
located at one end, right or left, chosen to match your old tub drain.
Select one the same length as the tub and you won’t even need to add
filler walls. Since the drain position roughly matches the tub drain, you
may not have to add a separate vent, cut out and patch the floor, or reroute the drain line.
Mount the mixing valve and redo the supply lines
1 of 1
Photo 11: Run new supply lines
Mount a new mixing valve and run new CPVC or copper tubing from the ball valve to the mixing valve and showerhead. Cap the tub spout outlet on the underside of the mixing valve. Turn on the water
and check for leaks.
Unless you’re planning to reuse all of the
existing supply lines and valves, simply cut
out and remove everything and start fresh.
Use a hacksaw or a reciprocating saw.
If you’ve chosen a shower base that’s
wider than the tub, center the new mixing
valve and showerhead over the base.
Choose a valve height that’s comfortable
to reach and clears any obstacles, and
make sure the showerhead lands either
above or below the top edge of the shower
enclosure or tile. Mount the mixing
valve first, following the manufacturer’s
instructions, and then fill in the pipes and
fittings to and from it (Photo 11). You’ll
need to add blocking to support it.
There may be a threaded nipple or hole
in the bottom of the mixing valve for a tub
spout. Be sure to cap that. After everything
is together, shut off the mixing valve, turn on the water and check for leaks.
Level the base and mark the studs
1 of 2
Photo 12: Position the base
Level the shower base on all four edges, shimming where needed. Mark the lip where it abuts studs. Measure, cut and cement the final
tailpiece to the P-trap.
2 of 2
Photo 13: Set the base in mortar
Spread mortar under the base. Push the base into the mortar until it rests on the shims and aligns with
the stud marks. Let the mortar harden.
Photo 12 shows you how to dry-fit, level
and shim the shower base. Take your time.
Getting the base level is critical for good
drainage. Mark the lip height on the studs
and outline the shim locations so you can
lift out the base and return it to the exact
position. Some bases require that you fit it
over a tailpiece when you set it in mortar.
To set the base, mix up about half a
60-lb. bag of mortar with water to a
creamy consistency. Avoid concrete mix;
stones in the mix will hold the base away
from the floor. Spread the mortar over the
floor under the base, about 1 in. or so
thick. Then lower the base into the wet
mix, forcing it down to the shims and the
stud marks. Make sure to push it against
the wall. Let it cure overnight. Don’t use
the base as a work platform until the next
day or you’ll disturb the mortar before it
cures. Clamp the base lip to each stud if
clamps are included with the unit.
Otherwise, clamp it with fender washers
and 2-in. screws. Avoid drilling through
the lip and screwing the base directly to
the studs. The base might crack and leak.
Attach the drain and frame the end wall
1 of 3
Photo 14: Complete the drain hookup
Anchor the base to the studs with screws and washers. Push the rubber gasket into place and seat it with
a nut driver.
2 of 3
Attach the drain cover to the drain opening.
3 of 3
Photo 15: Complete the framing
Frame the end wall at least 80 in. high for shower doors
and curtain rods.
The base will have directions to guide you
through the final drain hookup; your
drain system may vary from ours. Cut the
tailpiece and cement it at the right height.
If your drain has a thick rubber gasket,
wet it with soapy water and then work it
around the tailpiece pipe. Finish seating it
by driving it down with a blunt tool.
Our base was shorter than the old tub,
leaving a void between the wall and the
base. We filled in the space with a 2x4 wall. Add backing where the new walls
meet existing ones to make the connection
solid and for anchoring backer
board. And if you leave it short of the ceiling
as we did, you can add a convenient built-in shelf.
Copper to CPVC transition
Copper vs. CPVC
If you're comfortable working with and soldering copper, by all means go ahead and use it for your water supply lines. We show CPVC plastic fittings because the installation is as simple as cutting and cementing plastic fittings, just as you do with plastic drain and vent lines. To make the transition from copper to CPVC, use compression fittings as shown. You'll find all the CPVC fittings and pipes you need at any hardware store or home center.