Small Bathroom Gut Remodel

Full DIY plan — sequence, purchase list, costs, and install notes.

~5' × 7' (35 sq ft) 60" alcove tub Full DIY Big-box finish level St. Louis area 1929 house · 2nd floor Original plumbing Prices as of Aug 2026

First: should this be a gut at all?

This is the actual question on the table, and it deserves a straight answer before anyone buys a vanity. The goal here is not to talk anyone into demo — it's to spend one afternoon and about $60 finding out which project this really is, before committing money either direction.

What we know, and why it matters

The cast iron vanity trap has rusted through. This is the load-bearing fact. A trap that's rusted open hasn't been holding a water seal, which means two things have been true for a while: sewer gas has had a path into the room, and every drop from that sink has been going into the floor cavity instead of down the drain. That water lands where the vanity meets the wall — over a joist bay, next to a bottom plate. Highest-probability rot location in the room, with a steady supply.
The toilet doesn't flush, and a new flapper didn't fix it. That rules out the cheapest cause and leaves two very different ones: a fault inside the toilet, or a restriction in the drain below it. These lead to opposite actions and wildly different costs, so settle it before buying anything — see Diagnosing the toilet in the next section.
Cast iron doesn't fail in one spot. It scales and rusts from the inside out at a rate set by water chemistry and the age of the pour. If the trap is gone, the branch arm it ties into and the closet bend under the toilet are the same vintage sitting in the same conditions.
1929 with original plumbing means the galvanized supply is decades past its service life. Galvanized steel closes up with rust from the inside; typical useful life is 40–70 years. At 97 years it isn't a question of whether it gets replaced, only whether it's replaced on your schedule or on its own.
It's on the second floor. This cuts both ways. It removes the free diagnostic (see below) — but it also means a future failure doesn't just damage this bathroom, it comes down through the ceiling of the first-floor bathroom that's already been redone.

The second-floor wrinkleOn a first floor over a basement, you walk downstairs and look up at the joists for free. You don't have that here. But you are not stuck — see the inspection plan below. Do not let the lack of a basement view become a reason to skip looking.

The afternoon that settles it — ~$60, mostly reversible

None of this is demo. Every step is either something you have to do anyway or something that patches in under an hour.

Buy a borescope / inspection camera. $35–50 for a USB or wifi one that runs to a phone. This is the single best money in the whole project.
Pull the toilet. Thirty minutes, no cost, fully reversible — and you have to pull it regardless to diagnose the flush. You immediately see the flange condition, whether the closet bend is cast iron or lead, and whether the subfloor around it is soft. Probe the wood with a screwdriver: if it sinks in, that's rot, not stain. Stuff a rag in the open drain.
Pull the vanity. Not optional — the failed trap is getting replaced no matter which path you take. Look hard at the floor beneath it and the base of the wall behind it.
Run the camera through the openings you just made. The toilet flange hole and the vanity drain penetration both open into the joist bay. You can see joist tops, the underside of the subfloor, and the condition of the drain lines without cutting anything new.
If that's not conclusive, cut one 4" hole in the first-floor ceiling below. A 4" hole is a ten-minute patch with a scrap of drywall and a setting compound — genuinely less work than repainting a wall. If the bathroom below sits directly under this one, that's your view of the joists. If it doesn't, put the hole in whatever room does.
Snake or scope the drain before buying a toilet, so you learn whether the flush problem is the fixture or the pipe.
Check the supply pressure. Open the tub spout full and watch it. Weak flow that gets worse when another fixture runs is galvanized closing up.

Then pick a path — the decision rule

Path A — Minimal scope

roughly $700–1,400

Legitimate if: joists probe solid, subfloor damage is a localized patch, and the drain lines are serviceable iron with no active leaks.

Replace the vanity trap and drain arm out to good pipe
Cut out and patch the damaged subfloor locally, sister a joist if one spot is soft
Repair or replace the toilet; new flange and wax if needed
New vanity and faucet
Paint — last

This is a real outcome, not a consolation prize. If the inspection supports it, take it.

Path B — The full plan below

roughly $4,900–6,300

Required if: joist tops are soft or punky, rot extends past one bay, the drain is failing in more than the trap, or the supply is visibly scaled shut.

Everything in the phased plan that follows
Plus the branch re-pipe adds in the table below

Choosing this after looking is a decision. Choosing it before looking is a guess, and guessing costs $3,500 more than the camera does.

The honest bet: before looking, I'd put money on finding rot. Two confirmed cast iron failures plus a century of original plumbing plus years of unintended irrigation into a floor cavity is not usually a story that ends with sound framing. But that's a bet, not a diagnosis — and it costs $60 and one afternoon to replace the bet with a fact. Nobody should be arguing about scope until after step 4 above.

Diagnosing the toilet — branch by test result

The flapper is already replaced, so the free fix is spent. Everything below is a test with a defined action attached to each outcome. Work them in order and stop as soon as one is conclusive — do not buy a toilet before Test 1 comes back.

Test 1 · free · two minutes · do this first

The bucket test

Fill a 2-gallon bucket and dump it into the bowl in one fast pour — not a trickle, you want it to go in all at once. This bypasses the tank entirely and lets gravity do what the tank normally does, which separates "the toilet isn't delivering water properly" from "the water has nowhere to go."

Clears fast and pulls hardThe drain below is fine. The fault is inside the toilet — take the left column.

Rises, crawls down, or gurglesThe toilet is innocent. The restriction is downstream — take the right column.

Branch A — It's the toilet

$0–99 · does not change the remodel scope

Check the tank water level.free It should sit about 1" below the top of the overflow tube. Low level means low volume and low head, and no flapper fixes that. Adjust the fill valve up and re-test.
Watch a flush with the lid off.free The new flapper should stay open until the tank is nearly empty. If it drops early, it's the wrong spec for that flush valve — common when a modern flapper goes into an older toilet. Adjustable flappers have a dial on them.
Inspect the rim jets and siphon jet.~$5 Top suspect in a house on century-old galvanized supply. Hold a mirror under the bowl rim and look at the small holes; check the larger jet at the bottom of the bowl. Scale closes them and you get a lazy swirl with no pull. Pour a few cups of white vinegar down the overflow tube, leave it overnight, then poke each hole clear with a bent wire or small allen key.
Run a closet auger through the bowl.~$25 Clears an object or a scale chunk lodged in the toilet's own internal trapway.
Check what toilet it actually is.free A first-generation 1.6 gpf model (roughly 1992–1997) is a 3.5 gpf design choked down and flushes badly by design — no repair fixes it. Same verdict if it's the original 1929 fixture. In either case, replace it and stop spending time.

Outcome: the flush problem is closed out for under $100 and tells you nothing bad about the floor. It does not clear the vanity trap issue — that inspection still happens.

Branch B — It's the plumbing beneath

$0–2,500 · likely pushes toward Path B scope

Test 2 — narrow down how far down it is. Run the tub, then the sink, and watch both while someone flushes.

Tub or sink also slow, or they gurgle when the toilet flushes.free to find Shared branch problem, and gurgling specifically points at a venting fault. Worth knowing the rusted-out vanity trap may be the same root cause if that branch was wet-vented. This is a re-plumb, not a snaking job.
Only the toilet is slow, tub and sink drain normally.free to find The restriction is local to the closet bend. In 1929 cast iron that's usually decades of scale narrowing the bore; sometimes a lead bend that has sagged out of pitch.
Snake it before concluding anything.$25 rental A soft blockage clears and you're done cheap. If it clears and then returns within weeks, the pipe interior is the problem, not the clog.
Pull the toilet and scope the bend.$35–50 camera You're pulling it anyway for the floor inspection. Heavy scale, a cracked hub, or a soft lead bend you can dent with a thumbnail all mean replacement back to the stack.
If it's a re-pipe: add $400–900 in DIY materials, or $1,200–2,500 with a plumber. Both figures are already in the add-ons table below.

Outcome: the floor is coming open at the toilet regardless, which means the marginal cost of doing the full plan drops a lot. Re-read the Path A / Path B rule with that in mind.

Why the order mattersIf the fault is downstream, a new toilet does nothing — you'd set a $99 fixture in fresh wax, watch it behave exactly like the old one, and be out the money and the afternoon. Two gallons of water in a bucket prevents that. Given that a trap on the same branch has already rusted through, Branch B is the way to bet before testing.

Making the case for looking first

The reasonable version of the "let's not do a bunch of demo" position is let's not do unnecessary demo — and that's correct. Nothing above commits anyone to a gut. But three points are worth putting on the table:

Cosmetic-first is the one path that can cost the most. If a new toilet, new vanity, and fresh paint go in over rotted framing, and it surfaces in two years, the demo happens anyway — and the new fixtures and paint come out with it. That's the full scope plus the wasted cosmetic round.
A second-floor leak isn't contained to the second floor. A failure here lands in the ceiling of the first-floor bathroom that's already been redone. The downside isn't "we redo this room again," it's "we redo this room and repair the finished one below it."
The trap work is happening either way. A rusted-open trap is a live sewer gas path into the house right now. That's not a someday item and it's not a preference — it's the one thing on this whole list that shouldn't wait for a decision about scope.

Framed that way, the ask isn't "let's gut the bathroom." It's "let's spend one afternoon and $60 so we're choosing instead of hoping." That's a much easier conversation, and if the floor comes back sound, Path A is a genuinely good result.

What a 1929 house specifically hands you

Drum trap at the vanity or tub. A cylindrical iron canister with a screw-off cleanout cap, standard in the 1920s. It can't be replaced like-for-like — they're no longer code-compliant, so you re-plumb to a proper P-trap. That usually means opening floor or wall regardless of which path you pick.
Lead closet bend at the toilet. Common through the 1930s. A soft grey pipe that dents with a thumbnail. Replacing it means going back to the cast iron hub with a no-hub band.
Galvanized supply. Expect ⅜" of effective bore left in a ½" pipe. It also tends to crumble at the threads the moment you put a wrench on it, which is how a small repair becomes a branch re-pipe.
Knob-and-tube wiring. 1929 is squarely in the era. You cannot legally extend it, so any circuit that touches it goes back to the panel as a new home run.
Plaster and lath on the walls and ceiling, likely over rough-sawn framing that isn't a true 16" on center and isn't plumb. Measure every bay rather than assuming.
Lead paint, essentially guaranteed. Test before disturbing anything painted.
Undersized floor framing by modern standards, and a century of notching by previous plumbers. Look specifically for joists that have been notched deeply for the old drain — that's a common find and a common reason a floor needs sistering even without rot.

If the inspection goes badly — likely add-ons

These are on top of the $4,052 materials budget below, and they're the reason the contingency in that table is set at 25% rather than the 20% I'd use on a generic older house. If several of these land at once, treat the high end as the real number.

Re-pipe the branch supply in PEX back to a live main	$200–500
Replace cast iron drain / lead bend back to the stack (DIY materials)	$400–900
Same, if a plumber does it	$1,200–2,500
Sister 2–3 joists and replace full subfloor	$150–350
New home run circuit if knob-and-tube is in the path	$120–250
Repair the first-floor ceiling below if it's already water-damaged	$150–400
Realistic all-in if most of these land	$5,500–6,300

Before you swing a hammer — five things specific to your bathroom

The radiator is the schedule driver. You cannot demo around it. If it's hot water, you drain the zone, break the unions, and lift it out. If it's one-pipe steam (single big pipe, air vent on the side), it must go back at a 1" per foot pitch back toward the supply valve or you'll get banging forever. Photograph the pitch and the valve orientation before you touch it. A 5-column cast iron rad runs 250–400 lbs — two people and a hand truck, minimum.
Assume plaster and lath, not drywall. Old plaster walls are ~7/8" thick. New 1/2" drywall will sit recessed unless you fur the studs out with 1/4" or 3/8" strips, or use 5/8" board plus shims. Decide this before you buy sheets.
Test for lead and asbestos first. Pre-1978 paint and old sheet-vinyl / 9"×9" tile mastic are the usual suspects. You're exempt from EPA RRP certification in your own home, but the dust is the same either way.
Open the floor before you buy the tub. Old St. Louis baths often have a cast-iron closet bend with a lead bend at the toilet, and galvanized supply that crumbles when disturbed. Budget the 25% contingency below for exactly this.
The heated fan probably needs its own circuit. A fan/heater pulls ~1,400 W. That's ~12 A on its own — it cannot share the 20 A bathroom receptacle circuit with anything else. Plan two home runs to the panel.

The work, in order

Plan, test, permit

1–2 weeks of lead time — start here while the bathroom is still usable

Measure and lock the layout. Confirm tub alcove is a true 60" (old ones run 59½"–60½"). Measure toilet rough-in: wall to the center of the closet bolts — 12" is standard, 10" and 14" exist in old homes and require a specific toilet.
Test for lead and asbestos. Swab painted trim with a 3M LeadCheck. For flooring, cut a quarter-size chip through all layers, bag it, and mail it to a lab (~$40/sample, 3-day turnaround). Do not sand or dry-scrape anything until results are back.
Pull permits. City of St. Louis issues separate permits per trade — building, plumbing, electrical, mechanical. Homeowners can pull their own on an owner-occupied residence. Doing this now avoids a stop-work order and a re-inspection fee later.
Order the long-lead items. Tub and vanity are frequently ship-to-store. Get them on site before demo day.
Set up the second bathroom or a plan B. Realistically this bath is out of service 2–4 weekends of DIY work.

Demo to the studs and joists

1–2 days · the messiest part of the whole job

Kill the utilities. Breaker off and verified dead with a tester. Water off at the fixture stops or the main. Drain the heating zone at the boiler drain before opening the radiator unions — do this on a day the heat is off.
Pull the radiator. Back off the union nuts at the valve, break it free, walk it out on a hand truck, cap the open pipes. Set it somewhere it won't get chipped — you're reusing it.
Toilet: shut the stop, flush, sponge the tank and bowl dry, disconnect the supply, pull the closet bolt caps and nuts, rock and lift. Stuff a rag in the open drain so sewer gas doesn't fill the house.
Vanity: shut both stops, disconnect supplies and the P-trap into a bucket, cut the caulk bead at the wall, unscrew from the studs, lift out.
Tub and surround: cut the wall material 6" above the tub flange first so you can see the fasteners. Cut the drain and overflow free from below or from the access panel. A cast iron tub can be broken up with a sledge under a moving blanket — wear a face shield. A steel or acrylic tub comes out whole but usually needs to be cut in half with a recip saw to clear the door.
Walls and ceiling to the framing. Score plaster in grids and pull it in sheets; a flat bar under the lath pops it off fast. Bag as you go instead of at the end.
Subfloor up. Set the recip saw or circular saw depth to exactly the subfloor thickness so you don't nick joists, wiring, or pipes below. Cut back to the center of a joist on each edge so the new panel has bearing.
Vacuum with a HEPA shop vac, then look hard at what you uncovered — joists, drain, supply, wiring — before you order anything else.

Watch forRot around the toilet flange and the tub drain is extremely common and is the #1 source of scope creep on this job. If a joist is soft, sister a new 2×8 alongside it, glued and bolted, spanning at least 3 feet past the damage in both directions.

Framing repairs and blocking

Half a day

Sister any damaged joists and replace rotted subfloor bearing. Everything structural gets fixed now.
Add blocking between studs at: 33–36" for a future grab bar in the tub, behind the vanity mounting rail, behind the toilet paper holder and towel bar, and at the ceiling for the fan housing. Scrap 2×6 blocks — costs nothing now, impossible later.
Check the tub alcove walls for plumb and the ledger height. Shim studs flat before anything gets covered; a bowed stud shows through an acrylic surround badly.

Plumbing rough-in

1 day · leave everything exposed for inspection

Set the shower valve. Delta MultiChoice body screws to a 2×4 cross-brace between studs. The plaster guard on the body tells you the depth — set it so the finished wall surface lands inside the marked range, or the trim won't seat.
Run supplies in PEX. ½" PEX-B with crimp rings is the cheapest reliable DIY path. Transition from existing copper or galvanized with a threaded or push-fit adapter. Support every 32" and keep it out of stud edges or use nail plates.
Drain and vent. Tub drain gets a 1½" P-trap; toilet is 3"; lavatory is 1¼"–1½". Maintain ¼" per foot fall on horizontal drain runs. If you're tying into cast iron, a no-hub band coupling is your friend.
New quarter-turn stops at the toilet and both vanity supplies. Never reuse a 60-year-old multi-turn stop.
Pressure test before you cover anything: cap the ends, bring the water back on, and leave it under pressure overnight with paper towels wrapped at every joint.

Electrical rough-in

Half to a full day

Home run #1 — 20 A, 12/2, for receptacles. Bathroom receptacles must be on a dedicated 20 A circuit that serves no other room (NEC 210.11(C)(3)). At least one receptacle within 36" of the outside edge of the sink basin, and it must be GFCI protected.
Home run #2 — 20 A, 12/2, for the fan/heater. The heater element alone is the reason. Wire the fan, light, and heat as separate switch legs (12/3 or 12/4 from the switch box up to the housing, per the unit's diagram).
Use dual-function AFCI/GFCI breakers at the panel for both. That satisfies GFCI and arc-fault in one device and is cleaner than stacking a GFCI receptacle downstream.
Vanity light on the receptacle circuit is fine. Box it at ~78–80" above finished floor for an over-mirror fixture, or 66" for sconces flanking the mirror.
Mount the fan housing to the ceiling joists now, flush with what the finished ceiling plane will be. Nothing about a fan is fixable after drywall.
Label the circuits in the panel directory while you remember what they are.

Stop — inspection hold pointPlumbing, electrical, and mechanical rough-in inspections all happen now, with the walls open. Do not hang a single sheet of drywall until they're signed off. Covering unapproved work means tearing it back open.

Ventilation and insulation

Half a day

Duct the fan to the outside — through the wall rim or the roof, never into the attic or a soffit. Use 4" insulated flex (uninsulated duct in a cold attic condenses and drips back down through the fan). Keep the run short, slope it slightly downhill to the exterior cap, and seal every joint with foil tape plus a clamp.
Install a damper-equipped exterior cap and caulk the flange to the siding.
Insulate exterior-wall stud bays while they're open. R-13 or R-15 unfaced batts with a vapor retarder toward the interior for our climate zone.

Subfloor, tub set, wall board

1–2 days

New subfloor: ¾" plywood (not OSB in a wet room). Run panels perpendicular to the joists, leave a ⅛" gap at the walls and between sheets, bead construction adhesive on every joist, and screw with 2" deck screws at 6" on edges / 8" in the field.
Set the tub. Dry-fit it first. Then spread a 1–2" bed of mortar mix in the footprint, drop the tub in, seat it dead level side-to-side and along the length, connect the waste and overflow from below before the mortar cures, then screw or nail the flange to the studs through the pre-punched holes. The mortar bed is what stops the flex-and-creak in a light acrylic tub — don't skip it.
Protect the tub with cardboard and a drop cloth for the rest of the job.
Wall board: moisture-resistant drywall on the general walls and ceiling; cement board on the wet wall stud bays behind and beside the tub. The board must land on top of the tub flange, with a ¼" gap above the tub deck that gets filled with silicone, never with mud.
Ceiling first, then walls, top sheet then bottom, screws dimpled but not torn through the paper.

Tub surround, tape, prime, paint

3–4 days, mostly waiting on compound and paint to dry

Dry-fit the surround panels and mark every cut — valve, spout, showerhead — with a template or careful measurements. Cut the holes ⅛" oversize with a hole saw so the escutcheons cover the edges.
Glue up in order: back panel first, then the two end panels, then the corner/shelf pieces. Use only the adhesive the manufacturer specifies (solvent-based construction adhesive will melt the panel). Press and roll from the center outward, brace with 1×2s wedged against the opposite wall overnight.
Tape and mud the drywall — three coats, feathering wider each time, sanding lightly between. Corner bead at the outside corners.
Prime everything with a stain-blocking primer, then two coats of a bathroom-rated (mildew-resistant) satin or semi-gloss. Ceiling gets flat.
Repaint the radiator now, while it's out of the room and you can hit all the fins. Use a brush-on rust-inhibiting enamel; skip metallic paint, which cuts heat output.

Flooring

Half a day

Let the LVP acclimate in the room 48 hours before install.
Undercut the door casing with a jamb saw so the plank slides underneath instead of being scribed around.
Float the click-lock planks starting from the longest wall, ¼" expansion gap at every wall and at the tub apron, staggering end joints at least 8". Do not fasten LVP down and do not run it under the toilet flange.
Cut the toilet flange opening to fit around the flange, not under it. If the new floor raised the height, add a flange extender ring so the flange sits on top of the finished floor.

Fixture and trim out

1 day · the fun one

Vanity: level and shim, screw through the back rail into the blocking you added, then set the top and connect the faucet, drain, P-trap, and supplies. Silicone the top to the wall, not the cabinet to the floor.
Toilet: new wax ring (or a waxless seal, which is far more forgiving of a second attempt), set straight down without rocking, snug the nuts alternately and gently — over-torquing cracks the china. Connect the supply, fill, check for leaks, then caulk the base leaving a gap at the back so a future leak is visible.
Shower trim, spout, and showerhead. Teflon tape on threads, plumber's putty or the supplied gasket under the escutcheon.
Reinstall the radiator — new union gaskets and pipe dope on the threads, reset the pitch you photographed, then refill the system slowly and bleed the air out at the radiator vent. Watch the boiler pressure gauge as it fills.
Electrical devices: GFCI receptacle, switches, vanity light, fan grille and heater cover. Trip-test the GFCI and the breaker.
Baseboard and quarter round, caulked at the top and painted.
Caulk with 100% silicone (not latex) at the tub-to-surround seam, tub-to-floor, and around the vanity top. Fill the tub with water before caulking the tub perimeter so the joint is at its widest — then let it cure before draining.
Mirror, towel bar, TP holder, curtain rod.
Call for final inspection.

Purchase list & budget

Materials & permits

$4,052

57 line items

Contingency (25%)

$1,013

Raised for a 1929 house

Realistic total

$5,065

Your labor at $0

Same job, GC bid

$14–22k

For comparison

Item	Notes	Cost
Permits & testing
Building permit (City of St. Louis)	Homeowner may self-permit owner-occupied	$175
Plumbing permit	Base fee, separate trade permit	$90
Electrical permit	Base fee, separate trade permit	$85
Mechanical permit	Covers the vent fan	$30
Lead test swabs (3-pack)	3M LeadCheck or equivalent	$20
Asbestos lab analysis, 2 samples	Flooring + mastic; mail-in	$80
Subtotal		$480
Demo & disposal
Bagster bag + pickup	Cheaper than a dumpster at this volume	$215
6-mil poly, zip pole, tape	Dust barrier at the door	$60
P100 respirators, goggles, gloves	Non-negotiable with old plaster	$70
Contractor bags, 42 gal (20 ct)	Double-bag plaster	$25
Recip saw rental + demo blades	2 days; skip if you own one	$80
Subtotal		$450
Framing & subfloor
2×4 studs and blocking (12)	Grab bar, vanity, fixture blocking	$60
2×8 sister joist stock (2)	Assume you'll need it	$50
Structural screws, hanger nails	GRK or equivalent	$40
¾" plywood 4×8 (2 sheets)	~$41/sheet; plywood over OSB in a bath	$82
Subfloor adhesive (3) + 2" screws	Glue and screw every joist	$45
Subtotal		$277
Plumbing & fixtures
Delta MultiChoice valve body	Universal rough-in; trim swaps later	$53
Delta Classic tub/shower trim kit	Chrome; T13420 family	$61
Bootz Aloha 60×30 alcove tub	Cheapest reliable acrylic; L or R drain	$229
Tub waste & overflow kit	Match to your drain rough-in	$45
½" PEX-B 100 ft + fittings	Plus transition adapters to existing	$110
PEX crimp tool	Buy — cheaper than two rentals	$60
PVC drain fittings, trap, primer/glue	Add a no-hub band if tying to cast iron	$70
Quarter-turn stops (3) + supply lines	Never reuse old stops	$40
Glacier Bay 2-pc toilet, seat included	1.28 GPF, 12" rough-in	$99
Wax ring, closet bolts, flange extender	Buy two wax rings	$25
Vanity faucet + pop-up drain	Single-hole or 4" centerset	$79
P-trap + tailpiece	Chrome or PVC	$25
Subtotal		$896
Electrical
12/2 NM-B romex, 100 ft	Two home runs to the panel	$95
Dual-function AFCI/GFCI 20 A breakers (2)	Must match your panel brand	$110
20 A GFCI receptacle + plate	Within 36" of the basin edge	$28
Boxes — device, ceiling fan-rated	Old work and new work	$35
Vanity light fixture	Damp-location rated	$65
Connectors, staples, nail plates	Nail plates are a code item	$30
Non-contact tester + fish tape	Buy the tester regardless	$45
Subtotal		$408
Ventilation & heat
Broan fan / heater / light unit	Reuse yours if it's sound; Panasonic WhisperWarm is the ~$404 upgrade	$185
4" insulated flex duct, wall cap, clamps	Must terminate outside	$75
Radiator valve, union, gaskets, dope	Rebuild the connection while it's open	$70
Rust-inhibiting radiator enamel + brush	Not metallic paint	$30
Subtotal		$360
Walls & surround
Delta Pro-Series 5-piece tub surround	60"W × 57"H glue-up; $289 for the tall Galiant	$119
Surround adhesive (4 tubes)	Manufacturer-specified only	$40
½" moisture-resistant drywall (7 sheets)	~$18/sheet; go 5/8" if furring to plaster depth	$126
¼" cement board 3×5 (2 sheets)	USG Durock @ $12.50; wet wall bays	$27
Compound, tape, corner bead, screws	Buy more mud than you think	$80
Mortar mix (2 bags)	Tub bed	$20
Subtotal		$412
Finishes
Stain-blocking primer + bath paint	1 gal each, mildew-resistant	$85
Rollers, brushes, trays, tape, drops		$55
LifeProof LVP, 2 cases (~40 sq ft)	$2.49/sq ft; 40 sq ft covers 35 + waste	$100
Underlayment / vapor film	Only if the plank doesn't have it attached	$30
Baseboard + quarter round, 30 lf	Primed MDF or PVC in a bath	$70
Transition strip at the door		$20
100% silicone caulk (4) + gun	Silicone, not latex, at every wet joint	$45
Subtotal		$405
Vanity & accessories
Glacier Bay 25" vanity with cultured marble top	Assembled, sink and top included	$159
Medicine cabinet or mirror	Recessed needs stud bay planning	$85
Towel bar, TP holder, robe hooks	Into the blocking you added	$55
Shower curtain rod		$30
Grab bar (optional)	Blocking is already in — do it now	$35
Subtotal		$364
Materials & permits		$4,052
+ 25% contingency (1929, original plumbing)		$5,065

Where this budget breaks

Cast iron drain or a lead closet bend that has to be replaced back to the stack — add $400–900 in materials, or $1,200–2,500 if you call a plumber.
Galvanized supply lines that crumble when you disturb them. Re-piping the branch back to a live copper main: $200–500 in PEX and fittings.
Confirmed asbestos flooring — abatement runs $1,200–3,000 for a room this size. Encapsulating by floating new subfloor over it is sometimes legal and much cheaper; ask the city.
Knob-and-tube wiring anywhere in the circuit path. You cannot legally extend it, so the run goes back to the panel.
A panel with no open slots for two new breakers. Tandem breakers may work, or you're looking at a subpanel ($300+) or a service upgrade.
Steam heat with a stuck valve. If the radiator valve won't seat, you're replacing it — and on a one-pipe system that's a threaded connection into a heavy iron riser. This is the one item on the list worth calling a heating guy for.

If you hire out the two riskiest trades

A licensed plumber to set the valve, drain, and fixtures runs roughly $1,200–2,200 in the St. Louis market. A licensed electrician to run two circuits, set the fan/heater, and terminate devices runs roughly $900–1,600. That takes you to about $7,200–8,900 all-in while you keep demo, framing, drywall, flooring, paint, and trim — which is where DIY saves the most per hour anyway.