Roughing In the Kitchen Sink Drain and Supplies in Florida.

What the Rough-In Fixes

The plumbing rough-in is the stage that locates the drain, the hot and cold supplies, and the dishwasher branch inside the sink base before cabinets, counter, or finished floor go in. On a Florida slab-on-grade home it carries extra weight: the drain leaves the cabinet through a hole saw-cut in the concrete, so its position is effectively permanent once the slab is patched.

Because the penetration is hard to move later, the rough-in is where the whole assembly is decided — heights, the drain size, the trap the sink and dishwasher will share, and the backflow method the local inspector expects. Get those four right on paper and the connection at trim-out is routine. Miss one and the fix often means reopening the slab.

Why the slab changes the math

In a stick-framed home over a crawlspace, a plumber can shift a drain by reworking pipe under the floor. Florida's prevailing slab-on-grade construction removes that freedom: the drain and its trap arm run inside or beneath a poured slab, and the stub that rises into the cabinet is fixed by the saw cut. That single constraint is why this article treats the rough-in as a measured plan, not a field guess.

The four numbers that travel together

• Drain centerline height — where the DWV stub exits the wall or floor of the base.
• Supply stub heights — where the hot and cold stop valves sit relative to the drain.
• Trap and trap-arm size — the 1-1/2 in minimum and the run to the vent.
• Backflow method — air gap or high loop for the dishwasher discharge.

None of these stands alone. A deep sink and a disposer drop the drain; a lower drain pulls the supplies down with it; the trap arm has to reach a vent within code length; and the backflow choice sets what hardware lands on the counter. Plan them as one system.

Drain Rough-In Height

The kitchen sink drain stub-out is roughed in near the back wall of the sink base, most commonly in the 12-18 in band above the finished floor. The exact centerline is driven by sink depth and whether a food-waste disposer is in the plan — a disposer hangs below the bowl and forces the drain lower so the P-trap clears it.

How sink depth and a disposer move the line

A standard-depth bowl with no disposer can sit toward the higher end of that range, leaving room for a clean trap. Add a deep single-bowl sink or a disposer and the tailpiece drops several inches; the drain stub has to come down with it or the trap ends up cramped against the cabinet floor. Set the height to the bowl and disposer you are actually installing, not a generic number.

Center it, then leave room for the trap

The drain is usually centered behind the bowl, but the controlling check is vertical: there must be enough fall from the tailpiece, through the trap, into the stub to keep water moving without the trap bottoming out. On a disposer build, that clearance is the number that sets the final stub height.

Supply Line Height

The hot and cold supply stub-outs land a few inches above the drain centerline — in practice most Florida sink bases put the stops in the 20-24 in band off the finished floor, set roughly 4 in to each side of the drain so the angle stops and supply tubes clear the trap and disposer.

Spacing the hot and cold stops

Convention puts hot on the left and cold on the right as you face the sink, with the two stub-outs spread far enough apart that two angle stops and braided supplies do not crowd each other or the disposer. Keeping them above the drain also keeps the valves accessible at the front of the cabinet instead of buried behind the trap.

Leave the valves reachable

Shut-off access matters more in a humid climate where a slow supply drip can feed mold inside a closed cabinet. Roughing the stops high and to the sides means a homeowner can reach them fast, and a service tech can swap a faucet without dismantling the drain. The faucet you choose at sink installation rarely changes these stub locations.

Drain Size and the Shared Trap

The minimum drain pipe size for a kitchen sink is 1-1/2 in at the trap and trap arm, and under FBC-R P2717.2 that single 1-1/2 in trap is allowed to serve a one- or two-compartment sink together with the dishwasher, with or without a food-waste disposer. One trap, one penetration — by code, not by shortcut.

Can a dishwasher and sink share one trap?

Yes. FBC-R P2717.2 states the combined discharge from a dishwasher and a one- or two-compartment sink, with or without a disposer, is served by a trap of not less than 1-1/2 in outside diameter. The dishwasher drain hose must rise to the underside of the counter and be fastened there before it connects to the head of the disposer or to a wye fitting in the sink tailpiece. That rise is not optional — it is part of the backflow protection the code requires.

Where the dishwasher branch ties in

Two legal tie-in points exist: the dishwasher inlet on the side of a food-waste disposer, or a directional wye on the sink tailpiece when there is no disposer. Either way the hose climbs to the counter first. The branch itself is the small 3/4 in dishwasher drain connection; it does not need its own trap because it discharges into the sink's trap downstream of that high point.

Read the table as one chain rather than six rows: the drain height sets the trap position, the trap size sets what the sink and dishwasher can share, and the trap-arm length governs how far that drain can travel to reach a vent. Change one value and the others follow.

Air Gap vs High Loop

For the dishwasher, Florida's FBC-R (built on the IRC) accepts either a high loop or an above-counter air gap, but some local jurisdictions and any Uniform Plumbing Code adoption require the air gap fitting. Which one passes is decided by the local authority having jurisdiction, so it belongs in the rough-in plan, not in a trim-out argument with the inspector.

What each method actually does

High loop

The dishwasher drain hose is fastened to the underside of the counter so it rises above the sink flood rim before dropping to the disposer or tailpiece. It is simple and hidden, and it is the method the IRC and FBC-R accept by default.

Air gap

A small fitting mounted on the counter or sink deck that physically breaks the drain line open to atmosphere, certified to ASME A112.1.3. It cannot siphon under any condition, which is why air-gap jurisdictions treat it as the only true backflow break.

Why the distinction matters in a humid kitchen

Backflow here means dirty sink water siphoning back into the dishwasher. A high loop relies on the loop height to break siphon; an air gap breaks the line physically. In a Florida kitchen with a disposer and frequent dishwasher cycles, confirming the accepted method up front avoids a failed inspection and a counter that has to be drilled late for an air-gap cap.

The decision tree resolves to one habit: ask the authority having jurisdiction during planning. The hardware is cheap and the loop is free; the expensive part is discovering at final inspection that your county wanted the other one.

Venting on a Slab

Every kitchen sink trap needs a vent, and on a slab home the vent path is part of the rough-in puzzle. The trap arm — the pipe from the trap weir to the vent connection — must stay within the developed length IRC Table P3105.1 allows, roughly 6 ft for a 1-1/2 in arm, and the vent must not connect below the trap weir.

Trap-arm length and slope

The trap arm runs at a gentle slope toward the drain, conventionally about a quarter inch per foot, and it cannot run so far that the fixture self-siphons before reaching the vent. On a slab, where the drain leaves through concrete and turns toward a wet wall, that length budget is real — a sink stranded too far from a vent wall will not pass.

• Wet-wall vent — the standard path, taking the vent up an adjacent wall to tie into the home's vent stack.
• Island (loop) vent — a code-recognized loop under the counter for a sink with no wall behind it.
• Air admittance valve — a one-way vent under the cabinet, allowed only where the local authority accepts it.

The first option is the default and the simplest; the other two exist for island and peninsula sinks where a wall vent is not available, and only the local code tells you whether the valve is on the table.

Island sinks and the vent problem

An island sink has no wall behind it to carry a vent up through the roof, which is the classic Florida slab headache. The fix is an island (loop) vent or, where the local code permits it, an air admittance valve under the cabinet. We plan this with the cabinet layout, the same way we route power for an island sink and outlets on a slab.

Setting the Slab Penetration

Because the drain exits through concrete, the sink-base rough-in on a Florida slab follows a fixed order: confirm the layout and the backflow method, mark the penetration, cut and rough the drain and supplies, then connect at trim-out. Skipping the confirmation step is what turns a one-day rough-in into a slab repair.

That sequence is why the planning stage carries so much weight on a slab: by the time the trap goes together, every decision that needed concrete has already been made. A whole-kitchen scope folds this into the larger schedule, which is how we run a full kitchen remodel and any layout change that moves the sink in an open-concept plan.