Remodel a Small Bathroom: Project Walkthrough

1. Demolish and size the container on what a bathroom actually contains

Run the dumpster size calculator for the old tile, backer board or greenboard, any cast-iron tub, and old fixtures coming out — see estimating demolition debris for converting a small room's material into the weight and volume figures the calculator wants. A bathroom's demolition weight is disproportionate to its square footage compared with almost any other room: old mortar-bed tile floors and cast-iron tubs are dense in a way that a similarly sized bedroom's drywall and carpet never approach.

2. Rough-in plumbing and electrical while the walls and floor are open

Move or add supply lines, drain lines, and any new outlets or switches now, while framing is exposed — a bathroom remodel is the one practical window to relocate a drain or add a dedicated circuit without opening a finished wall later. Confirm the shower or tub drain's rough height and the toilet flange's position before closing anything up, since both of those fixed points are what the floor buildup in the next step has to be measured against.

3. Build the floor from the subfloor up, at the thickness the tile actually needs

Run the backer board calculator for the floor and any tiled walls, deciding board thickness and whether a thinset bedding layer goes under the board — a bedding layer adds real height on top of the board's own thickness, and it's worth using specifically where the subfloor has minor unevenness the board alone won't bridge. Then run the tile calculator and grout and thinset calculator once the tile itself is chosen, since floor tile thickness varies meaningfully by material and finish.

This is the step with the strongest early-changes-later relationship on the whole page, worked through with real numbers below — the total floor buildup this step produces has to land at a specific finished height, not just a reasonable one.

4. Plan the fan duct route while the ceiling is still open

Run the bathroom fan CFM calculator for the room's size and fixture count, then plan the actual duct run — the shortest practical path to an exterior wall or roof vent, with the fewest elbows, since every elbow adds resistance the fan has to work against. This has to be decided while the ceiling is open for the plumbing and electrical rough-in in step 2, because cutting a new duct path through a finished ceiling later means patching drywall that's already been mudded, sanded, and possibly painted.

5. Cost the labor once the real scope is known

Run the labor cost calculator after steps 1 through 4 are settled, not before — a small bathroom's labor hours per square foot run far higher than a larger room's because of the trade density in step 1's intro, and a production-rate estimate borrowed from a bigger tile job elsewhere in the house will understate a bathroom's actual hours by a meaningful margin.

Why the tile chosen last reaches back and changes the backer board bought first

Trade practice generally wants a toilet flange's top sitting at or slightly above the finished floor, not recessed meaningfully below it — a flange left more than about a quarter inch below the finished floor after tile goes down is enough of a gap to compromise the wax ring seal, which is exactly the kind of problem a flange extender kit exists to fix, but only as a second trip after the fact. That finished floor height is the sum of every layer stacked on the subfloor: backer board thickness, an optional thinset bedding layer under the board, the tile-setting thinset on top of it, and the tile itself.

The two floor buildups, and why a quarter inch of tile changes the flange decision

A common lighter buildup — quarter-inch backer board with no bedding layer, standard tile-setting thinset around three-sixteenths of an inch, and a three-eighths-inch ceramic floor tile — lands at roughly seven-eighths of an inch total above the subfloor. If the plumber set the flange to that figure during rough-in in step 2, everything lines up.

Choose a heavier natural stone or large-format porcelain tile later — five-eighths of an inch is a realistic figure for stone — and add a half-inch backer board instead of quarter-inch for the extra rigidity that thicker, heavier tile generally wants, and the same buildup comes out closer to an inch and a half: half an inch of board, three-sixteenths of thinset under it if bedding was used, three-sixteenths of setting thinset, and five-eighths of tile. That's roughly five-eighths of an inch taller than the flange was set for — well past the point where a flange extender becomes necessary, and the toilet can't simply be reset onto the original rough-in without one. The tile decision, made at the end of material selection, reaches all the way back to a plumbing rough-in height set in step 2, which is why the tile has to at least be tentatively chosen before that flange gets set, not picked out afterward at the tile showroom.

What goes wrong when the floor gets built before the tile is chosen

Set backer board at a generic quarter-inch thickness and leave the tile decision for later, and a subsequent switch to a heavier stone or large-format tile can mean pulling that board back up — thinner backer board is a poor substrate for a heavier tile regardless of the height mismatch, since large-format and natural stone both want more rigidity underneath them than a quarter-inch board over standard joist spacing reliably provides. Both problems — the wrong board thickness and the wrong flange height — trace back to the same root cause: the floor was built to a generic assumption instead of to the tile that ended up going down.

The same ordering mistake shows up with the fan duct in step 4: patch and paint the ceiling before finalizing the fan's actual CFM requirement and duct path, and a later change to a higher-capacity fan needing a shorter, straighter run means reopening a ceiling that was already finished, rather than routing it correctly while everything overhead was still exposed.