June 16, 2021

Professional Tool Reviews for Pros

How to Do a Plumbing Rough-In

How to Do a Plumbing Rough-In

For those of you considering entering the trades as a career, first of all, congratulations! You’re looking at the potential of high income, the ability to one day run your business, and enjoy the tangible results of a hard day’s work. As a plumber, I’m hoping you’ll follow my path. To help you understand what the job of a plumber is like, let me walk you through how to do a plumbing rough-in.

How to do a Plumbing Rough-In

Get There Early

Typically my apprentice and I get to the site bright and early in the morning. The first thing we do is curse the cold weather, as nobody likes being cold. Hey, we’re in Canada, not Central Florida like Clint DeBoer and Kenny Koehler. The first thing you do on any new job is check for power. If you have it, you’ll roll out the extension cords you need to cover your area. If not, you’ll pull our the generator and get her cranked up.

Pro Tip: If you have to use a generator, be sure you have enough fuel for the day. Breaks to run out for gas or other items you don’t have on-site take time – and time is money.

In the last year however, I have decided to make the move to cordless for all my tools in order to leave the generator in the van to collect dust, to cut down on the amount of time a job takes me, and to never have another corded tool unplug itself when I get to the top of a ladder because it got caught on something on the way up. Cordless tools are more expensive thanks to the batteries, but I haven’t had to use my generator in over a year now.

Plumbing Rough In

Failing to Plan is Planning to Fail

The first and sometimes the more annoying part is the planning stage. This is where you take your blueprints, walk around the house and mark where you want your drainage and venting to run.

Pro Tip: Visually marking each hole helps ensure you don’t miss any when you go back on your final walk-through.

The Bathroom Takes Priority

Setting the tubs comes next. At first, you’ll need to physically set and level each tub and mark where the drain to the waste portion goes. Once you do this enough times, you’ll get to know your measurements by heart and be able to place cut the hole needed without placing the tub first. The best tool for creating the hole is a high-torque drill, like a Hole Hawg or Stud & Joist Drill.

How to Do a Plumbing Rough-In

Pro Tip: Before you drill that hole, check to make sure you’re directly over a joist. Your boss won’t be happy about a back charge bill for a new joist to be put in.

If you happen to be over a floor joist on the tub drain, all you need to do is to offset your waste and overflow beside the joist. However, if there is a joist on the center of a shower drain, then it’s time to call back the framers to do their job properly! But not before you check the rest of the house for framing issues.

Once you cut the holes, you can bring the tub back, re-level it, and set it with at least 2″ screws.

I’m sure every plumber has their own system but what I like to do is once the tub/shower is in place is to mark and drill out the water closet holes (toilet holes for y’all in the US). Believe me when I say that if you come across a joist under the toilet, there will be a few choice words exiting your mouth that may or may not be directed towards the individuals that framed the house.

Pro Tip: It’s important to know what kind of toilet is being installed as you can then check the manufacturer’s shop drawings to make sure you drill your hole in the proper location.

If the finishes have not been chosen, I will usually measure 13″ off the back wall and then – if the fixture is directly off the tub – I’ll measure 15″ off it. That being said, there are times that the home builder you are working with will spec a specific measurement, which you will have to verify and then duplicate. Typically a 4-1/2″ hole saw will do the trick when drilling out for a toilet.

Drains and Vents

Plumbing Rough InNow it’s time to drill out the holes for drainage and venting. If you weren’t already using a Hole Hawg style drill, you will really want one at this stage. Usually what I do upstairs is pop all my vents up into the ceiling. Once all that has been done, I get up into the attic to connect the appropriate vents and then terminate them to outside air through the use of a roof increaser.

One very important thing in the plumbing trades are the following words: drainage MUST grade. For everything up to 3” pipe, the grade must be set to ¼” per foot and 4″ pipe must be set to 1/8 per foot.

Pro Tip: Be considerate and realize when other tradesmen will be installing around your work. For example, in a ceiling, HVAC needs to pound tin up through the same areas, so stay either high or low in the joist spaces. Leaving them space is not only considerate, it makes you look like even more of a Pro.

Making the Connection

When gluing fittings together in a new build, there is no such thing as too much glue. With your application brush, coat the pipe as well as the hub of your fitting with a generous serving of glue, then when it comes time to put your fitting on and grade it, push on and rotate left then right before setting your grade. The reason we do this is to ensure that there are no bare spots inside the glue joint. Then once the fitting is in place, wipe off the excess glue.

Water Lines and More Hole Drilling

Now that we’re done with the drainage and venting into the basement, what next? If you have an apprentice, you will probably let him or her focus on running water lines to the upstairs for the fixtures. In new builds, the only type of PEX (cross-linked polyethylene) my company uses is PEX A (specifically Uponor) and the connections are made via expansion PEX.

Plumbing Rough In

I find that the best way to run water lines in residential plumbing is to run with 3/4″ as close to where you have a bathroom group or other fixture that requires water lines (a fridge line, washing machine, or kitchen sink). Then put a header up and reduce the 3/4″ water line and to run 1/2″ water line to each individual fixture. The goal here is to keep the 1/2″ lines as short and straight as possible, which cuts down on wasted water. It is imperative that you do not accidentally kink any of the waterlines. However, with PEX A, you can simply use a heat gun or a torch to take a kink out.

Plumbing Rough InOne feature you can run to the furthest header away from the hot water tank in the house is a recirculation line. This hooks up to a pump installed on the hot water tank. It keeps the hot water circulating through the house so that instant hot water may be enjoyed when you open the tap. With the new heating code up here in Canada, the entire hot line must now be insulated throughout the house, so this is not an overly popular addition in new builds anymore.

While your apprentice is working on the lines (or after you complete them), go outside to drill in the hose bibs and drill out the holes for the sump pump, the hot water tank, and any other piece of equipment that may require venting outside in the side wall of the house as laid out on the blueprint. Now, living up in Northern Canada, we must ensure that we use frost-free hose bibs and install them so they slope upwards. This is to ensure that the line doesn’t freeze up during the winter months.

If you had an apprentice to run the water lines, now is the time to inspect them.

All Tied Up At the Moment

Plumbing Rough InOnce you get into the basement, it’s time to start with tie-in’s. This usually consists of tying the half bath together, running the emergency floor drain for an upstairs laundry into the mechanical room and stubbing it down a ways to ensure it doesn’t get covered over later on in the build, and preparing the vent for your rough-in double plumbing (a fancy way of saying your basement bathroom vent). Additionally, you’ll need to drop your main 3″ stack along with a possibility of another 3″ stack depending how on you were forced to run the drainage to the upstairs.

It’s important to note that the easiest and neatest way to drop these stacks if they are relatively close to one another is to tie them in together if local codes allow for it. To do this, we run to a structural beam, drop onto the top of it and run the tie in horizontally at minimum grade while tying in anything that you run across along the way, such as another stack or a kitchen sink. When you use this method, you must make your horizontal connections by using a wye fitting with a 45° or fitting 45° elbow.

Pro Tip: I also usually put a 3″ fitting clean out at the furthest wye fitting on the horizontal branch. It’s not required by code, but it is good plumbing practice. If something clogs the horizontal piping system, rather than feeding your drain-cleaning tool from one of the above floors, all you have to do is carefully unscrew the cleanout and run your snake into the system a few feet.

Kitchen Specifics

The tie in type you use for kitchen sinks will depend on the sink placement. If the sink is going in an island that you can completely walk around, then you can simply angle the drain up with a 45° fitting and stud it through the floor roughly eight inches. The reason you don’t have to do anything else here is that you’ll use an air admittance valve (aka cheater vent).

If the sink is installed in an island that is attached to a wall, an island vent must be used (yes, I know how much we love plumbing in these puppies but they are a necessary evil).

Finally, if the sink is to be installed on an outside wall (where freezing of pipes is possible), the sink will be roughed in a flat vent. But what’s a flat vent?

A flat vent is a horizontal portion of a dry vent connecting a soil or waste pipe. Essentially a flat vent is used primarily on outside walls where there is a worry of freezing drainage. The vent runs into the cabinet, connected to the drainage pipe and run down through the floor.

Tying Up Loose Ends

Tie-ins also involve running the water lines in the basement. Do this and you’re almost home free! Just run your 3/4″ PEX to the mechanical room, adding headers along the way for any main floor or basement fixtures that have been roughed in and terminate the hot and cold lines around where the hot water tank is going.

Plumbing Rough In

Not So Fast, My Friend

So the house has now been roughed into the basement, you take a look around to admire your work and ensure that everything has been tied in properly according to code. Head upstairs with your apprentice and start plugging and connecting water lines where appropriate. You’ll also apply protection plates wherever drainage runs through a stud or through the bottom of a wall. These protection plates ensure that the drywallers can’t accidentally drive a screw into your drainage.


Now that you’re done inside the house, it’s time for groundworks. It’s tempting to let your apprentice tackle digging out the sewer line. If you want to get home in time for kickoff, you’ll want to help him. Once you hit the bottom of the sewer (the main building sewer to be exact), you need to look to see how much space you need for grade vs. how deep your sewer is coming into the house.Plumbing Rough In

This is a simple math problem. Take a tape measure and determine the distance from the base of the sewer to your furthest stack. Next, figure out what size drainage you will be running to it so you can get the grade that you’ll need to use. Using these two numbers, we can calculate the rise of the pipe using the formula Rise (or drop) = run x grade. Once you figure out how much space your drainage will need to come up, you can make a decision on whether or not you need to roll the sewer up or not.

Backwater Valves

The next step here in Alberta is to install a device called a normally open backwater valve. What it does is protect the house should the sewers back up for any reason. If this happens, a flap comes up and seals the house off from any potential dangers.

Backwater valves typically come in two styles – normally open and normally closed. The normally closed backwater valves can be used on branch drains that require protection for the fixture it is serving (i.e.: a basement laundry that needs to be tied in before the main backwater valve is installed). The reason we normally use an open backwater valve is that houses are used to vent the city plumbing system and need a constant flow of fresh air to keep things working properly.

Completing the Job

Once the groundwork is complete, the last step is to run your water service to where the prints call for it and install your water shut off. Then you can water test the house to ensure there are no leaks before drywall starts going up.

Roughing in a house for the plumbing trade is a very labor intensive job that is hard on the body but very rewarding at the same time. Now that you know how to do a plumbing rough-in, perhaps you’ll have a leg up if this is the route you choose in your career as a tradesman.

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