Tub Spout Rough In: An Installation Guide for Beginners

The most daunting aspect of plumbing is having to do the rough-in. If you can get this step right, you’ve got a majority of the project already completed.

It’s not as complicated as it seems when you consider that there are standard measurements that you can use for various sections of the bathroom, like toilets, tubs, and sinks. 

Additionally, the product’s manufacturers offer outlined instructions according to their fixture.

Before you begin the tub spout rough-in process, check to see that the specs you have in mind will work with what the manufacturer has provided. 

Without further Ado, here’s the essential information you should know before attempting to rough-in a tub spout.

Tub Rough-In Valves

Are you planning on installing a bathtub? You need to get a tub rough-in. A rough-in valve is a critical part of the bathroom. It’s necessary to make the faucet function correctly. You’ll connect the rough-in to the tub spout for an easier installation. 

Role of the Rough-In Valve

The rough-in valve is the key to the plumbing system in the bathroom. Located behind the wall, it connects the tub spout to the entire piping system. 

The rough-in valve delivers cold and hot water to the faucet, so that’s what you’re adjusting when setting the water to the perfect temperature before you hop in for a bubble bath. 

How To Select the Correct Tub Rough-Ins

Even though it seems as simple as grabbing a valve, there are a few factors you need to consider as you’re getting ready to rough in the tub spout. The list can get quite exhaustive, so we’ll narrow it down to two things you should keep in mind. 

Features

A tub spout rough-in has similar features from one to the next. However, some components, like the type of piping, differ. For example, some valves function better with copper pipe; others only work when using galvanized piping. You’ll want to assess which is best for your setup. 

You can watch here to see the installation process and pick up tips on how to make it seamless. 

You’ll notice that some tub spout rough-ins have integral check stops built-in. That allows you to repair the valve whenever necessary without shutting the water off in the house. 

Always examine what you need beforehand, so you don’t have to reinstall at a later date. It might be a small part, but it’s worth taking the time to research and get the right rough-in. 

Brand

Matching brands is a thing with rough-ins. So, if you have a Moen spout, you should probably purchase a Moen rough-in. The individual brands’ components match each other well, and buying them together can often save you headaches down the road. 

That’s not to say that you’ll always have to do it this way, but this general guideline is safe for most people who perform DIY rough-ins. 

Some rough-in valves for the rib are universal, so they fit any faucet. Ask a customer service representative for assistance if you’re unsure which route to take between matching the brand or choosing a universal rough-in. 

Standard Tub Spout Rough-In Dimensions 

Here are a few basic dimensions that work for most tub spout rough-in applications:

Vertical Tub Supply

You should place the tub spout valve 20-22″ higher than the floor. Situate the spout horizontally to the left or right of the center. The tub spout should be about four inches higher than the rim.

Discharge Hole (Back Wall)

Put the drain directly on the centerline. You can offset the drain access anywhere between 10-14″ from the framing and six to eight inches wide.

Place the drain at floor height for the vertical discharge hole—the distance is zero.

Fixture

The fixture for a side-to-side, or a front buffer, needs at least 18″.

Sizing the Pipes for the Water Supply

Both the hot and cold water supply supplies for a shower or run faucet need about a ½” diameter for the pipe supplying the water. This measurement is standard across all rough-ins. 

If you use a PEX pipe, however, be attentive to sizing because it’s slightly different. They are flexible and easy to manipulate when installing, but they can be tricky. 

When you compare it to a copper pipe, the interior diameter is smaller, so you have to regulate the size of the pipes with where you’re using the water supply. You’ll need a PEX pipe with a larger diameter if you’ll be using it near the shower.  

Having a pipe with a bigger diameter helps to provide a stronger water stream further from the water source. 

Drain Pipe Size

Shower and tub setups require a P-trap and at least a one ½” diameter drain pipe. However, it’s better to have a two-inch pipe instead. Units that have showers only need a P-trap and a two-inch drain.

The drain will need an angle of fall of a ¼” per linear foot or a horizontal drop. You will also need to install a vent pipe and connect it to the drain pipe.

Additional Tub Spout Rough-In Installation Details

Ensure that you install the nipple for the spout at a max of 3/4″ and a min of 3/8″ to past the finished wall. You can screw a pipe adapter onto the nipple.

A spout slides over the adaptor, and you can lock it in place with a set screw at the bottom. That will allow the spout to be correctly aligned.

The size of the whole of the tile and the backboard should measure approximately 1/4″ to 1/2″ bigger than the diameter of the nipple. That gives a 1/8″ to 1/4″ gap between the tile and the nipple.

You should have installation instructions concerning the diverter valve that details the vertical location of the valve as it relates to the spout and the setback distance in the wall.

Typically there’s plastic placed over the diverter valve that you have to set flush with the finished wall. This covering has the opening that is necessary for the valve. 

Frequently Asked Questions 

Below are the answers to the most commonly asked questions concerning a tub spout rough-in:

How far should the tub spout be from the wall?

Typically the spout is offset by 1/2 inch or more from the wall. If the gap is wider, you may have to fill in the gap with caulk. Regardless it’s a good idea to caulk the base of the spout and the perimeter to allow the trim plate to seal out water.

How far should the pipe stick out for the tub spout?

Make sure that the pipe coming from the wall is the right size. Slip-on tub slots require a minimum of 1″ and a maximum of 2-7/8″ in length, with the kind of tub spout serving as the determining factor.

How high do you rough in a tub spout?

A faucet valve should be 20 to 22 inches above the floor. Faucets go 4 inches to the right/left of the centerline, and the tub spout 4 inches horizontally above the tub rim.

Conclusion

It’s reasonably simple to install a tub spout rough-in. You just have to know which one to pick and follow the correct measurements so that everything fits snugly. 

Watching videos helps to give you a better idea of how things should look from one step to the next. Always keep in mind that the manufacturer’s specs are the best route.

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