How to Handle a Retrofit Rough-In

Here are tips for tackling plumbing rough-in work on a home remodel

How to Handle a Retrofit Rough-In

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Ask any finish guy how difficult “trim-out” or “finish” work can be and the answer will be: “Depends on how the rough-in crew did its job.” You may or may not do new construction, but for plumbers who don’t do rough-ins on a daily basis, here are some tips.

The Details are Important

When working with a homeowner on a remodel, it is imperative to understand the variables that come with a new fixture setup. Never assume that the new vanity will have the same rough-in dimensions as the old model. The old rough-in may work, but proper is proper for a reason. Never forget that the goal of a great rough-in is to make the piping perfect so that the fixture will easily attach. An accurate rough-in saves time, material, and makes the fixture operate efficiently.

First, get the cut sheet and/or rough-in dimensions and stick to them. Never eye-ball the rough-ins. You will be sorry when the end product looks terrible because you were off 2 inches on a measurement. Larger manufacturing companies used to provide plumbers with annual cut-books that had all of their fixtures’ rough-in dimensions. Today these books are hard to come by — and even harder at times to find online. Some units come with a cut-sheet in the box but most don’t. At times it will be worth a call to the manufacturer to have the cut-sheet emailed to you, which they will usually do. 

Lay Out and Design

Start out by making a sketch of the fixture locations. This will get your mind thinking about what difficulties you are going to run into during the re-rough piping process. If you know how to make a “to scale” drawing, do so. If you don’t know how, ask one of the masters or journeymen you work with. They would be happy to show you. A good plumber will even sketch the plank and beam locations using dotted lines to help further the thinking process in regards to obstacles.

Now take your drawing and physically lay it out. Laying out new bathroom fixtures in an old bathroom can be frustrating. The space you’re working in may not be up to code to begin with, and more than likely the homeowner (or God forbid a designer) has picked out vanities and units that are larger than the old ones. Space will be tight. I suggest cutting cardboard in rectangles to the length and width of the fixtures being put in place so that they can easily be moved around. For objects larger than cardboard, use some 2-by-4s or painter’s tape. It is a quick way to lay out the room and get some distance measurements. Remember to take into account any drywall or tile that will push out your measurements.

Once you get things laid out, your plumber Jedi mind will take over and find problems that you might run into once the actual units are installed. It is also a good way to show the homeowner your spacing concerns and get their stamp of approval.

Once you have the layout done, start thinking about where the piping is currently versus where the rough-in piping needs to be. Do you need to run any new waterlines? Are you adding a re-circ line or a new fixture location? Is the homeowner putting in a shower where the tub used to be? If that is the case, you need 2-inch pipe instead of 1 1/2-inch. Does it currently have proper venting? Will the tile floor have to be removed to get the tub out? Do they have a big enough waterline to handle the new gpm produced by the shower? Think it all out and make notes.

Marking the Existing Walls

If you are lucky enough to re-rough with the wall completely open and exposed, take care to leave the structure as strong and secure as possible. Try to limit your cuts and holes to one pass and always follow the local rules for cutting into beams and joists. If you have to do a re-rough with finished walls, use a deep scan stud finding tool and mark the walls with tape and pencil marks the best you can. Instead of using your sawzall right off the bat, consider taking a small sample of drywall out with a keyhole saw (or jab saw). Have a feel around to see what’s lurking behind the wall before you cut. If you know for certain the coast is clear, consider one of those super tiny sawzall blades. Better yet, take the time with an oscillating saw to make your cuts and make them square to bracing. Have your helper (if you have one handy) hold the shop-vac near the saw while cutting to keep the area clean and clear. 

Work Area

Cleanliness and order is king of the rough-in — more important than any other step. Any trash gets thrown directly into a receptacle. Don’t set anything up against the wall. Don’t unpack everything in the same room you are working in and lose all the screws. Don’t lose the installation manuals. Have a staging room away from the room you are working in that is also kept clean and organized. Remove everything you can from your work room. Plastic and tape off everything you can including the floor. Cardboard and tape every inch of the tub or shower pan and curbs. Plug the drains so material doesn’t fall into them. Make sure all fire alarms and smoke detectors are shut off.

These small things add up to not only a gigantic time savings, but also provide a professional appearance and installation that shows the customer how much of a professional you truly are.

Finishing the Rough-In

Hit your spots. The difference between you and a hack is hitting your marks. Make sure the drain piping and water piping is secure and coming out of the walls right on the money and perfectly straight. Secure, straight, and plumb. Don’t be that guy who leaves PEX stub-outs willy-nilly. If you must run PEX, run it to a PEX X FIP Lug ear elbow, screw it to a 2-by-4 in the wall and come out with capped rough nipples until the drywallers are complete. Some old-timers would give the water piping under the floor pitch so that it was easy to drain the building if necessary during winter months when families would travel out of town.

The drainage piping is probably the most important. Make sure and follow the DWV codes, especially with venting and line sizing. The last thing you want to do is take the easy route and install an S-Trap just because it’s easier than going into the wall. You don’t need a siphoning trap in the second floor’s brand-new bathroom. Even though you will be running the drain and vent on an outside wall more than likely, do not install the water in the outside wall. Come up through the bottom of the vanity in this semi-conditioned space.

Put blocking in for anything that requires blocking. If this remodel requires a brand-new stack, then put one in. This is not the time to let the customer scrimp. Lastly, you should of course test your work before the walls go up.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 22 years of experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College. 


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