How to Choose a Rough-In Valve for Your Shower

What is the Purpose of a Rough-In Valve?

In plumbing, the term “rough-in” refers to the essential component that connects to the water supply lines and acts as a core for various fixtures, such as showers and tubs. "Rough-in" indicates that the valve is installed during the initial construction phase of the building before finishing touches like tiling and fixture installations take place. The rough-in valve is typically concealed within the wall or under the floor, providing a secure mounting point for the intended fixtures while keeping the pipes and connections out of sight.

The main purpose of a shower mixer rough-in valve is for water regulation and diverter function, essentially controlling water volume, temperature, and sometimes diverter function. A shower mixer rough-in valve has two inlets, one for hot and one for cold water, and two outlets, one for the shower head and one for the spout, in order to regulate water best.  

Water Regulation: The rough-in valve is responsible for controlling the flow of water to the showerhead or tub spout. It allows you to turn the water on or off and adjust the water temperature and pressure to your liking.

Diverter Function (Optional): In some cases, the rough-in valve may be for  a diverter, which enables you to switch the water flow between various shower components like a handheld showerhead, overhead rain shower, or bathtub spout.

Types of Rough-In Shower Valves: Pressure Balance Valve vs. Thermostatic Valve

Pressure Balance Valve: Pressure balance valves are designed to maintain a consistent water temperature, even if there are fluctuations in hot or cold water supply lines. They provide protection against sudden temperature changes regardless of changes in water pressure. You’ll be safe from scalding water if a toilet is flushed or another faucet is used. Another option with more functions included is our Thermostatic tub and shower valve with volume control.

Thermostatic Valve: Thermostatic tub and shower valves offer precise temperature control by maintaining a stable water temperature regardless of hot and cold water supply changes. They are particularly beneficial for families with young children or the elderly, as they reduce the risk of scalding. Check out our Thermostatic Valves Related Items: 

Thermostatic shower valve sleeve

Thermostatic cartridge

How Pressure Balance Valves Work

A pressure balance valve usually has a single handle that controls the water's volume and temperature. When you turn the handle to adjust the temperature, the valve will modulate the flow of hot and cold water to maintain the desired temperature ratio, regardless of any changes in pressure.

It's important to note that a pressure balance valve does not regulate the overall water pressure; it only balances the ratio of hot and cold water to maintain temperature stability. If you want to control the overall water pressure in your shower or tub, you would typically need a separate pressure regulator or a thermostatic mixing valve.

How Thermostatic Valves Regulate Water Temperature with Precision

Thermostatic valves represent a sophisticated advancement in plumbing technology, specifically designed to deliver precise and consistent water temperature control during showers and baths. Unlike pressure balance valves, which adjust the mix of hot and cold water to maintain temperature, thermostatic valves have built-in thermostats that actively regulate the water temperature to your preferred setting. This means that even if there are significant fluctuations in the hot and cold water supply, the thermostatic valve will compensate to maintain the precise temperature you've set. They are particularly well-suited for households where different users have varying temperature preferences or for those who appreciate the convenience of having a pre-set temperature for every shower.

The inner workings of a thermostatic valve are more complex than those of a pressure balance valve, featuring an internal thermal element or a wax capsule that senses the water temperature. When you turn on the shower and set your desired temperature, the thermal element expands or contracts in response to the incoming water temperature. If the water is too hot, the valve will reduce the hot water flow; if it's too cold, it will increase the flow of hot water until the desired temperature is reached.

Depth of Installation for Tiled and Untiled Bathroom Walls

If the rough-in valve is installed too shallow, it may not be adequately supported, leading to potential leaks, rattling noises, and compromised water flow. On the other hand, if the valve is installed too deep within the wall, it may be challenging to connect the fixtures securely, and the finished result may not align correctly.

Use this general measurement formula to figure out the recommended installation depth for your specific wall and valve configuration:

First, figure out the wall thickness, which is the thickness of your tile, backer board, float, waterproofing membrane, and thin-set combined.

Wall Thickness = tiles + backer board + float + waterproofing membrane + thin set

Next, measure the depth of the rough-in valve (from front to back,) and subtract the wall thickness. This will determine where to install your backer board (where the rough-in valve will be mounted). We advocate for great DIY projects, but consulting a professional or referring to the valve’s manufacturer manual is recommended for the best final result. 

Choosing Your Valve

Before choosing a rough-in valve, determine the water pressure and flow rate in your bathroom. Low water pressure may require a valve that compensates for the lack of pressure to maintain a consistent water flow. On the other hand, high water pressure might call for a valve that can handle the increased force. To assess water pressure, you can use a pressure gauge or consult a plumber who can test the pressure in your plumbing system.

If you already have a specific shower trim or plan to use a particular type in the future, ensure that the rough-in valve is compatible with that shower trim. Generally each Valve rough-in is designed to fit specific trim and usually not interchangeable.