Three separate inspections usually bracket the work. A rough plumbing inspection<\/strong> happens once pipes are in and before anything is covered. A final inspection<\/strong> comes after fixtures are set and working. In between sits the rest of the build, which is exactly the problem.<\/p>\n What that means practically is that the rough-in inspection is your last chance to change anything for free. After drywall and tile, every correction means opening a finished wall, so the cost of a two-inch error grows by an order of magnitude in about a week.<\/p>\n Because layout and fixture choice feed directly into this stage, it is worth settling those before the plumber starts rather than during. The decisions that interact most are covered in bathroom layout and fixtures<\/a>.<\/p>\n The single most consequential number in a bathroom rough-in is the toilet rough-in: the distance from the finished wall<\/strong> behind the toilet to the center of the drain flange in the floor.<\/p>\n Three sizes cover nearly all residential work. Twelve inches is the standard and what most toilets are built for. Ten and fourteen inches exist because of how older bathrooms were framed, and you will find them in houses built before the mid-1950s.<\/p>\n The finished wall is the trap. Rough-ins are set to the surface you will actually see, which means tile, backer board, and any wall panel all push the finished surface forward and shrink your usable depth. Add half an inch of backer board and tile and a nominal 12-inch rough-in drops to roughly 11.5 inches effective.<\/p>\n When measuring an existing bathroom, hook the tape on the wall surface above the baseboard rather than on the trim. A baseboard or tile cove will read a quarter inch long and send you looking for a fixture you do not need.<\/p>\n Two more numbers travel with it. Code typically requires at least 15 inches from the flange centerline to any side obstruction, which is about 30 inches of clear width for the whole toilet zone, and about 21 inches of clear floor space in front of the bowl. Accessibility guidance prefers 18 inches on each side instead of the 15-inch minimum.<\/p>\n Then set the height. The top of the flange should finish flush with the finished floor or a quarter inch above it, and that is the detail most worth watching on a remodel, because a thicker tile floor can eat a flange you set correctly.<\/p>\n Moving a flange after the fact is possible with an offset closet flange<\/strong>, but it shifts the drain a couple of inches at most and most jurisdictions will not accept the result. Measuring before framing is much cheaper than arguing with an inspector afterward.<\/p>\n A tub and shower valve is anchored to blocking between the studs, and its height is not a matter of taste. The usual reference is about 48 inches from the finished floor for a shower valve, with tub filler height running nearer 28 inches.<\/p>\n Those figures are measured from the finished floor<\/strong> to the finished wall<\/strong>, which is the same two reference points that trip people up on the toilet. Measure to bare studs and add your tile thickness and backer board afterward, or the finished head will end up lower than planned.<\/p>\n The valve also dictates what happens around it. A pressure-balanced or thermostatic mixing valve<\/strong> is required for showers in most jurisdictions, and it has to sit on solid blocking rather than being screwed to a stud face, because the body is heavy and the trim gets handled constantly.<\/p>\n That anti-scald requirement is worth understanding. These valves limit delivered water to about 120 degrees Fahrenheit, which is the temperature at which a brief exposure burns skin. An older valve without that mechanism is not just a comfort issue in a house with kids.<\/p>\n The spout is set separately from the valve. Its pipe length is determined by the valve model<\/strong> and the wall thickness, which is one more reason the wall finish gets decided before the plumbing does.<\/p>\n Tub and shower plumbing runs through the same stages as the rest of the room, and the drain side of it is covered in how a drain vent system actually works<\/a>.<\/p>\n Drain, waste, and vent lines are graded rather than run level. The near-universal minimum fall is a quarter inch per foot<\/strong>, and there is a practical reason for it beyond the code number. Drainage depends on a thin moving film of water, and a pipe that is too flat leaves solids behind to form a blockage you will pay to clear later.<\/p>\n Slope is also why the subfloor<\/strong> and the joist layout constrain a bathroom remodel. Getting the required grade through an existing joist bay sometimes means notching, which weakens structure, or relocating the drain entirely.<\/p>\n Venting is the part people find least intuitive. A drain needs air moving through a vent to keep the trap seal intact, which is why you see a vent rising through the roof. That vent stack is a constraint on where the bathroom can sit in the plan.<\/p>\n Before anything is covered, the system gets tested. Common methods include standing water head, typically ten feet of column held for fifteen minutes, or a low-pressure air test around five psi for a similar interval. Supply lines are capped and pressure tested separately.<\/p>\n Ask who performs the test and what they record of it. A photograph of the completed rough-in with a tape measure in frame is worth more than a promise, because it captures valve heights and drain locations that nobody can verify once drywall is up.<\/p>\n Hot and cold supply lines run inside the walls to every fixture, and the material decision matters more here than in most of the house. The tradeoffs between the common options are laid out in PEX versus copper piping<\/a>.<\/p>\n Two details are easy to leave out and expensive to add later. First, each fixture needs its own accessible shutoff valve<\/strong> at the fixture rather than relying on the main to isolate one sink. The differences between those valve types are worth knowing, and covered in the guide to plumbing shutoff valve types<\/a>.<\/p>\n Second, the tub and shower supply should be sized so that a pressure-balancing valve performs correctly when another fixture draws water. Undersized supply creates a pressure drop that makes the valve hunt between temperatures, which is a common and confusing complaint in new bathrooms.<\/p>\n Leak protection is the part that pays for itself. Walls get opened for plumbing in a bathroom, so this is one of the few rooms where the plumbing sits directly behind tile and is effectively permanent. Before the walls close, it is worth confirming the rough inspection<\/strong> passed, and budgeting for what a failure means after tile is up, which is set out in what a bathroom renovation costs end to end<\/a>.<\/p>\n You do not need to be a licensed plumber to ask these questions. You need them answered before the wallboard is ordered, not after it is hung.<\/p>\n If the answer to the inspection question is anything other than before, that is the one to resolve on site today. It is the only item on this list where being a day late costs the whole wall.<\/p>\n The rest of the work, once the wall is closed, is finish work. What happens on the other side of the waterproofing and tile stages is worth reading before you commit to a finish schedule.<\/p>\n","protected":false},"excerpt":{"rendered":" The walls go up, the tile goes on, and the shower valve is four inches lower than you wanted. Rough-in is the stage where bathroom plumbing gets set, and it is the last moment any of those positions can change. Once drywall covers the framing, every dimension you chose becomes expensive to undo. Most people […]<\/p>\n","protected":false},"author":2,"featured_media":1097,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1098","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-tips"],"_links":{"self":[{"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/posts\/1098","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/comments?post=1098"}],"version-history":[{"count":0,"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/posts\/1098\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/media\/1097"}],"wp:attachment":[{"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/media?parent=1098"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/categories?post=1098"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.skala8.com\/blog\/wp-json\/wp\/v2\/tags?post=1098"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}The Toilet Rough-In Is Measured to the Finished Wall, Not the Studs<\/h2>\n
Shower and Tub Valves Are Set by Height, and Tile Moves the Wall<\/h2>\n
![\"Exposed](\"\/blog\/wp-content\/uploads\/bathroom-plumbing-rough-in-guide.jpg\")
Drain Slope and the Test That Has to Pass Before the Wall Closes<\/h2>\n
Water Supply, Shutoffs, and Where Leaks Will Find You<\/h2>\n
The Rough-In Checklist to Walk the Site With<\/h2>\n
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