Most bathroom remodels are planned backwards. The tile is chosen, the vanity is ordered, the tub is on a truck, and then someone asks where the drain goes. By that point the plumbing has to bend around the design, and bending plumbing after the fact is where remodel budgets break and timelines slip by weeks. The fix is not complicated: make the plumbing decisions first, in the order below, and let the finishes follow them.
The order is not arbitrary. It follows how a bathroom is actually built. Rough-in plumbing happens before the walls and floor close. Once tile is on, every change costs several times what it would have cost a week earlier, and some changes stop being possible at all.
Decision 1: Is anything moving?
The single biggest cost driver in a bathroom remodel is whether the toilet, the shower drain or the sink move from where they are now. Keeping fixtures in their current positions means the existing drains, vents and supply stubs stay. Moving them means new pipe, and in most Houston homes the floor is a concrete slab. Moving a toilet 18 inches means cutting the slab, rerouting a 3- or 4-inch drain underneath with the correct fall, tying into the vent, and pouring the concrete back. That is a different project from a cosmetic refit, with a permit, an inspection and a jackhammer.
Decide this before the design is drawn. If the layout genuinely needs to change, budget for slab work and accept the timeline. If it does not, tell the designer the drains are fixed points and design around them. Many bathrooms that feel cramped are fixed with a wall-hung vanity, a glass enclosure instead of a curtain, and better lighting, without a single pipe moving.
One check belongs here regardless of the answer: what is under the floor now. In a house built before the mid 1970s the drains under the slab are usually cast iron, and cast iron of that age may be channelled, scaled or cracked. Closing a new floor over a failing drain is the most expensive mistake a remodel can make. A sewer camera inspection through the existing drains before demolition costs an hour and shows exactly what you are building on. If the camera finds a problem, you fix it while the floor is already open, not two years later through new tile.
Decision 2: Tub, shower, or both
A freestanding tub looks effortless in photographs. Underneath it is a floor drain in one specific spot, a filler that may need its own floor-mounted supply lines, and enough floor structure to carry the tub, the water and a person: a cast iron soaking tub full of water can exceed 700 pounds. A walk-in shower needs a floor sloped a quarter inch per foot to a drain, a waterproofed pan, and a drain sized for what you plan to put above it.
That last point surprises people. A standard shower drain handles a standard showerhead. A rain head plus a handheld plus body sprays can push more water than a 2-inch drain clears, and the result is a new shower with water pooling at your feet. If the design includes multiple outlets, the drain size and the pan slope are decided now, with the fixture list in hand.
| Fixture choice | What it decides underneath | When it must be settled |
| Freestanding tub | Drain location away from the wall, floor-mounted filler supply, floor loading | Before the slab or subfloor is touched |
| Alcove tub-shower | Standard drain at one end, single valve height, surround type | Before rough-in |
| Curbless or walk-in shower | Pan recess, slope, linear or center drain, waterproofing method | Before the floor is poured or framed |
| Multiple shower outlets | Drain size, valve type and count, hot water demand | Before the valve is bought |
Decision 3: The valve behind the wall
The shower valve is the one component you cannot change later without opening the tile. Every trim kit you see in a showroom is a cover for a valve body that goes into the wall during rough-in. Choose the valve family first, then the finish.
Three things to settle with the plumber:
- Pressure-balance or thermostatic. A pressure-balance valve keeps the mix steady when a toilet flushes elsewhere in the house, which is the anti-scald protection most codes require. A thermostatic valve holds an exact temperature and allows separate volume control; it costs more and needs more wall depth. Either is fine. Mixing them up after the wall is closed is not.
- Number of outlets. One showerhead, a handheld, a rain head and body sprays each need a diverter, a separate valve, or a combination valve with multiple ports. The count decides which valve body is roughed in.
- Valve and head heights. The typical shower valve center sits around 48 inches from the finished floor, with a tub-shower valve lower, around 28 inches, so it can be reached from the tub. A showerhead is usually set at 80 inches or higher. A tall household may want the head higher and the valve at a comfortable reach. Write the heights on the framing before the plumber arrives, because nobody can move them once the tile is set.
A small detail with a large payoff: ask for the valve body to be installed with the trim’s plaster guard in place and the finished wall thickness known. A valve set too deep or too shallow for the tile buildup leaves trim that does not seat, and the only fix is opening the wall.
Decision 4: Where the water comes from, and where it goes
Every drain needs a vent, and the vent has to run up through a wall to the roof or tie into an existing vent within a distance set by code. Moving a sink to an exterior wall or an island-style vanity can make venting difficult, and difficult venting is why some remodeled bathrooms gurgle and drain slowly. Older Houston homes often have vents that were already marginal; a remodel is when they get corrected.
The supply side has its own list. If the home still has galvanized steel supply lines, which were common into the 1960s, the remodel is the moment to replace the runs feeding the bathroom with copper or PEX, because the walls are open and the rusted pipe is already restricting flow. The small shutoff valves under the sink and behind the toilet should be replaced with quarter-turn valves whatever the pipe is; a new faucet on a seized 30-year-old valve is a future emergency. And if the bathroom shares a wall with the kitchen, the same contractor should look at both sides, since kitchen and bathroom plumbing in a slab home usually shares a drain line and a vent stack, and a change on one side affects the other.
Decision 5: Hot water for the new bathroom
Spa bathrooms are built around hot water the house may not have. A 66-gallon soaking tub takes most of a 40-gallon tank’s usable hot water. Two showerheads running together at two and a half gallons a minute each can empty a small tank in a few minutes. If the remodel adds capacity, the water heater question has to be answered before the finishes are ordered, not after the first cold bath.
| Household and fixtures | Heater that usually fits | What to check |
| One or two people, one shower, no large tub | 40-gallon tank or a mid-size tankless | Recovery rate; tankless flow at winter inlet temperature |
| Family of four, two bathrooms, standard tub | 50-gallon tank, or tankless sized for two fixtures at once | Simultaneous use in the morning hour |
| Large soaking tub or multi-outlet shower | 75-gallon tank, or a large tankless unit, sometimes two | Gas line size and venting for a bigger unit |
| Far bathroom, long wait for hot water | Any of the above plus a recirculation line | Pump placement and a return line or crossover valve |
A plumber who does water heater installation in Houston regularly will count the fixtures, check the gas line and the venting, and tell you which option the house can actually support before the tub is bought. Buying the fixture first and then discovering the gas line is undersized for the heater it needs is the most common way a bathroom project doubles its plumbing cost.
Decision 6: Water quality and the finish you chose
Houston water is hard. Matte black and brushed brass finishes show mineral spotting faster than chrome and nickel, and the cartridge inside every faucet and valve scales up over time whatever the finish. If the remodel budget stretches to a whole-house softener, this is the moment to add it, because the plumber is already in the walls and the main line is accessible. If not, choose finishes that tolerate spotting, specify PVD finishes rather than painted ones, and plan on wiping fixtures down.
Decision 7: Permits, inspections and who does what
In Houston, moving plumbing or adding fixtures needs a permit, and a licensed plumber’s name goes on it. Replacing a faucet or a toilet in the same location does not. Decide early which side of that line the project falls on, because it changes the sequence: permit, rough-in, inspection with the walls open, then drywall, waterproofing, tile and trim.
The permit is not red tape to route around. The rough-in inspection is the last time anyone will see the drains, vents and valve bodies before they disappear for twenty years. An inspector catching a missing vent or a drain with no fall is the cheapest correction in the whole job.
The order of work, once the decisions are made
- Demolition and discovery. Walls and floor open. The plumber confirms what is actually there: pipe materials, vent routes, the condition of the drains. This is where the camera inspection from Decision 1 pays off.
- Rough-in plumbing. Drains, vents, supply lines, the valve bodies, any slab work. Pressure test on the supply, water test on the drains. Inspection if permitted.
- Electrical, then drywall, then waterproofing. Cement board and a waterproofing membrane in the wet areas. The shower pan is tested by plugging the drain and filling it overnight; a pan that leaks now is a pan that leaks forever.
- Tile and flooring.
- Trim plumbing. The faucets, the shower trim, the toilet on a new wax ring, the vanity and sink, the tub filler. Supply lines and shutoffs connected.
- Final test. Every fixture run, every drain flushed, the floor around the toilet checked dry after several flushes.
Two plumber visits is the minimum for a real remodel: rough-in and trim. A third visit, a short inspection before demolition, is the cheapest money in the whole project because it tells you which of the seven decisions above have already been made for you by what is in the walls.
Five mistakes that cost the most
- Ordering the tub before checking the drain and the floor. Freestanding tubs in particular have fixed drain positions and real weight.
- Buying the shower trim before the valve body. The trim has to match the body; the body has to match the wall thickness.
- Skipping the pan test. Waterproofing failures show up as a stain on the ceiling below, months later, under new tile.
- Reusing old shutoff valves and supply lines. They are the same age as everything you just replaced.
- Adding a multi-outlet shower to a 40-gallon tank. The shower is beautiful for six minutes.
A note from the trade
The remodels that come in on budget are the ones where the homeowner and the designer sat down with a plumber before anything was ordered. Royal Flush Affordable Plumbing, a Houston company that has handled remodel rough-ins and fixture installations since 2007, puts it simply: the drains decide the layout, the valve decides the shower, and the water heater decides whether you enjoy any of it. Settle those three first, and the rest of the bathroom is decoration.