Here’s a general overview of the correct way to do things when installing new bathtub fixtures. First, there are a few things that are absolutely essential for you to remember:

- Never take building codes as “suggestions.” Follow them. They’re there for a reason.
- Don’t forget to make sure your fixtures are level as you install them.
- Don’t forget to make sure there’s an air gap filling space when you put the fixtures in.
- Always correctly align tubing when placing them into any stop valves or fittings, because if you don’t, you’re going to cause a leak.

Beginning Installation

Before you get started, check to make sure your new bathtub fixture doesn’t need support framing. Think about the tub when it’s filled with water, and then think about yourself in the tub – it can get fairly heavy, and that’s a lot of strain on your flooring.

If there is another room beneath the bathroom, you might actually need to open the ceiling and add in some extra support. Building codes will tell you what you need to do and how much support is necessary to hold the weight. Make sure you follow them.

In advance of actually setting your new bathtub fixture in place, have all the necessary piping installed.

Placing Your New Fixture

When you’re placing the tub, make sure the wall studs are continuous with the flange, and resting on 2x4 supports. You can use 1x4 if you want, though that’s somewhat less stable. Use nail or screws through the flanges and into the stubs to ensure your tub is anchored to the bathtub enclosure.

Next, connect the drain overflow with the tub’s overflow by putting the drain connections above the trap. Don’t connect them beyond the trap, or else the drain won’t actually work. Traps come with compression fittings that you should be able to screw securely over the overflow assembly arm.

Have the hot and cold water lines sweated onto the hot and cold mix valve ports, and these will run directly to the tub mix valve, which is where they should be directly attached. If you were planning on adding a shower fixture to the bathtub enclosure, you’ll also need to run a pipe up the wall to hold onto the showerhead. You can then sweat a brass female threaded winged fitting directly onto the top of the pipe. Make sure this fitting is securely fastened into some part of the support frame.

Securing & Checking

To get the small details of the new fixtures in place, make a tub spout with a piece of half-inch pipe. A male threaded fitting will need to be sweated onto the end of the pipe, or if you have a half-inch cap, you can combine this with a brass nipple to complete the spout. Be sure to double-check your length measurements for each step.

Next, you’ll have to call in a professional plumbing inspector to ensure that everything you’ve done so far is up to code. It may seem like a hassle, but if it means not having to rip everything out and start again down the road, it’ll be worth it. He’ll check the drain connection for leaks, and also make sure your water pressure is providing water to the supply pipes at the correct gauge.

Final Fixture Details

Once you have your new bathtub fixture installed and in place, there are just a few minor details to take care of. Of course, you’ll have to put the wall back up with moisture-resistant drywall, and use silicone caulking to protect the tub and wall joints from water damage.

Then you can install the tub spout, the showerhead, and the tap handles. That task should take you all of about ten minutes, since these things often screw right onto the fixtures themselves. However, clean your pipe threads and apply new joint compound for pipes before installing the pieces, just to be sure that you’re avoiding potential leaks.