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Bath Project Notes · Glossary
Bathroom remodeling terms, and how to use them when reading a proposal
The terms on this page are the ones that separate a complete bathroom proposal from a vague one: the waterproofing membrane, pre-slope, flood test, linear drain, blocking, valve type, fan CFM and allowance. Knowing them lets you check what a bid includes, compare two bids line by line, and ask the specific questions that reveal whether the shower assembly underneath the tile is built to last.
12 terms you will see in bathroom remodeling proposals
- Allowance
- A placeholder dollar amount in a proposal for an item not yet selected, such as tile or a faucet. Spending above it is a change order; unspent allowance should come back to you as a credit.
- Blocking
- Solid lumber fastened between studs behind the wall finish so grab bars, shower seats and heavy fixtures can be anchored anywhere along it. It must be installed before drywall or backer board.
- Cement backer board
- A rigid, moisture-stable panel used as the substrate for tile in wet areas in place of drywall. It is not waterproof by itself and still needs a membrane in a shower.
- Comfort-height toilet
- A toilet with a bowl rim about 17 to 19 inches from the floor, versus 14 to 15 inches on a standard model, easing sitting and standing for taller and older users.
- Curbless (zero-threshold) shower
- A shower with no raised curb, so the floor runs continuously into it. It needs the shower floor recessed or the surrounding floor raised to keep the slope, plus a waterproofing plan that extends beyond the shower.
- Exhaust fan CFM
- The cubic feet per minute a bathroom fan moves. Sizing commonly follows one CFM per square foot of floor with a 50 CFM minimum, and the fan must duct to the outdoors, not into the attic.
- Flood test
- Plugging the drain and filling the shower pan with water for 24 hours before tile to confirm the membrane holds. Ask for it in the proposal and ask to see the water level before it is drained.
- Linear drain
- A long, narrow drain set along one wall or the entry of a shower, letting the floor slope in one plane. It makes large-format tile and curbless entries practical.
- Pre-slope
- The sloped layer under a traditional shower pan liner that directs water reaching the liner toward the drain's weep holes. A flat liner traps water and grows mold; a pre-slope is the fix.
- Pressure-balance vs. thermostatic valve
- A pressure-balance shower valve keeps temperature steady when another fixture draws water; a thermostatic valve holds a set temperature and controls volume separately. Thermostatic costs more and suits multi-head showers.
- Waterproofing membrane
- The continuous sheet or liquid-applied layer behind or on top of the shower substrate that keeps water out of the framing. Tile and grout are not waterproof; the membrane is. Common systems are bonded sheet membranes and liquid membranes rated to ANSI A118.10.
- Wet room
- A bathroom in which the entire floor is waterproofed and sloped to a drain, so the shower area is not separated from the rest of the room by a curb or full enclosure.
Bathroom proposals are written in trade shorthand, and most of the words describe things you will never see once the tile is up. That is exactly why they matter. Houzz found 84% of bathroom renovators hired a professional and 45% a general contractor, which means most homeowners are reading someone else's description of the work rather than doing it. The definitions below the guidance on this page are short; the sections explain how to put them to work when a proposal arrives.
Each term links back to a decision covered elsewhere on the site. The membrane and flood test are explained in context on the walk-in shower page, blocking and comfort height on the accessible remodeling page, and allowances in the 2026 cost guide.
How should you use these terms when a proposal arrives?
Read the proposal once for the total and once with this list beside it. For each wet area, look for the membrane system by name, the drain type and size, whether a pre-slope or a sloped foam tray is used, and whether a flood test is listed. For the walls, look for the substrate: cement backer board, foam board or a waterproof panel, and what covers the seams. For the valve, look for pressure-balance or thermostatic. For the fan, look for a CFM rating and a duct to the exterior.
Anything missing is a question, not an assumption. A proposal that says tile shower with no membrane named may include one or may not; a proposal that lists a fan with no CFM may reuse an undersized unit. Houzz found 37% of renovators went over budget in 2025, and vague line items are where the overruns begin. Asking for the missing terms in writing costs nothing and makes every later change order easier to judge.
Which terms do homeowners and bidders most often confuse?
Waterproof and water-resistant are the first pair. Cement backer board is water-resistant and stable when wet, but water passes through it; it needs a membrane on or behind it to be waterproof. Green drywall is neither. A second pair is pre-slope and shower pan: in a traditional build, the pre-slope sits under the pan liner so water that reaches the liner still drains, while a bonded membrane goes on top of a sloped bed. Bids that mix these words may be describing different systems.
Curbless and low-curb are a third pair, and the cost difference is thousands of dollars because curbless changes the floor structure; Houzz found 44% of renovators chose a low curb and 20% went curbless. Pressure-balance and thermostatic valves both prevent scalding in different ways and at different prices. An allowance is a placeholder for an unselected item, not a fixed price, and a contingency is a reserve for unknown conditions; they are not interchangeable. The entry comparison and the valve entries below explain each difference.
- Water-resistant board versus waterproof membrane
- Pre-slope under a liner versus a sloped bed under a bonded membrane
- Low curb versus curbless (zero-threshold)
- Pressure-balance versus thermostatic valve
- Allowance versus contingency
What questions do the terms let you ask?
Which membrane system are you using, and will you use that manufacturer's matching drain and seam tape? Is there a flood test, and how long is it held? What size is the drain, and does it move? Where will blocking go, and does it run continuously so bars can be placed later? What CFM is the fan, where does the duct terminate, and is it on a humidity sensor or timer? What is the allowance for tile, and what happens if my selection costs more or less?
The answers do more than fill gaps. A pro who answers these quickly and specifically is showing how they build; one who is vague about the membrane or dismissive of the flood test is also telling you something. NKBA found 89% of designers now want fewer or no grout lines, which puts more weight on the substrate and membrane beneath large tiles, so the questions matter more for modern finishes, not less.
Which terms change the price the most?
Curbless, linear drain and wet room are the terms that move a bid by thousands, because each changes the floor structure or the waterproofed area; Houzz found 16% of bathroom renovators created a wet room. Thermostatic valve and frameless glass move it by hundreds to low thousands. Blocking, flood test and a correctly sized fan move it very little but carry most of the long-term value. HomeAdvisor's estimate that labor is 40% to 65% of a bathroom bill explains why structural terms cost more than finish terms: they are hours of skilled work.
When two bids differ by more than a few thousand dollars, look for these terms first. The calculator models the big ones as toggles, and the base comparison shows how the floor system choice alone can swing a shower budget.
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Glossary questions
Do I need to know these terms to hire a good pro?
Not in depth, but knowing a handful lets you read proposals on equal terms. Membrane, flood test, drain size, blocking, fan CFM and allowance cover most of what separates a thorough bid from a thin one. You do not need to specify the system yourself; you need to see it named and ask why if it is missing.
Is a waterproofing membrane the same thing as a shower pan?
Not exactly. A shower pan is the waterproof floor of the shower, which may be a prefab base, a traditional liner over a pre-slope, or a bonded membrane over a sloped bed. The membrane is the waterproof layer itself, and in a tiled shower it should continue up the walls as well. A proposal should name both the floor method and the wall waterproofing.
What does it mean when a proposal says 'per manufacturer specifications'?
It means the installer intends to follow the membrane or product maker's instructions, which is good, but it tells you little unless the product is named. Ask which manufacturer and system, then you can check that the drain, seam treatment and cure times match. It also matters for warranties, since most system warranties require matched components.
Why do some bids list a pre-slope and others do not?
Because they use different floor systems. A traditional mortar build with a PVC or CPE liner needs a pre-slope under the liner; a bonded membrane system over a sloped mortar bed or a foam tray does not. Neither is wrong. The problem is a traditional liner with no pre-slope, which leaves water sitting on the liner under the tile.
How is fan CFM chosen for a bathroom?
A common rule is one CFM per square foot of floor for bathrooms up to about 100 square feet, with higher figures for larger rooms or separate enclosed showers. Long or bent duct runs reduce real airflow, so the rating on the box overstates what a poorly ducted fan delivers. Ask for the rated CFM and the duct route to the outside.
What should an allowance line include?
The item it covers, the dollar amount, whether it covers material only or material and labor, and what happens to the difference if your choice costs more or less. Tile, vanity, lighting and plumbing fixtures are common allowance items. An allowance set well below realistic prices makes a bid look cheaper than it will end up.
Where can I see how these terms affect my own budget?
The calculator treats the terms that move price most, such as curbless entry, frameless glass and heated floors, as options you can switch on and off. The polls show which choices other planners are making, and each service page explains the assembly behind the terms in more detail.
See the terms in context
Service guideComplete Bathroom RenovationA complete bathroom renovation rebuilds the bathing area, vanity, toilet, floor, wall finishes, lighting and ventilation together, and may move drains, walls or the door.
Service guideWalk-In Shower InstallationA walk-in shower installation rebuilds the bathing area from the subfloor up: a sloped base, a drain bonded to a waterproofing membrane, wall board and membrane, a valve, tile or panels, and an enclosure with a defined entry.
Service guideTub & Shower ConversionsA tub-to-shower conversion removes the bathtub and builds a shower in its alcove, usually with a new drain, a rebuilt substrate, a waterproofing membrane, new walls and an enclosure.
Service guideAccessible Bathroom RemodelingAccessible bathroom remodeling plans the room around a specific person's transfers, reach, mobility aid and likely future needs: turning space, a curbless shower, blocking and grab bars, a comfort-height toilet, a reachable vanity, nonslip surfaces and a wider door.
Free planning tools
Free toolBathroom remodel cost calculatorSize, material tier and complexity in, a realistic budget range out.
Free toolBathroom comparisons: the five decisions that change the assemblySide-by-side tables for the decisions that change the price most.
Free toolBathroom remodel quiz: find your scope and check the numbers10 questions that show what you already know and what to check next.
Free toolBathroom remodel polls: see what other homeowners are choosingSee what other planners chose and add your vote.
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