Understanding Rough-In Plumbing
Rough-in plumbing is literally the foundation of running water supply lines, drain lines, vents, and pipeline connections after framing is done and before a final layer of finish. There are a few things you can do before pouring the concrete slab that pertains to plumbing rough-in. When this core infrastructure has been installed and passed by a building inspector, the project will move on to finish plumbing.
What Is Rough-In Plumbing?
Rough-in plumbing is the installation of all these essential components — vents, waste lines, and water supply lines. This is when the basic framing has been done, but no outlets, lights, etc. have been installed. It’s an important step before any walls are enclosed. Rough-in begins with breaking ground to run underground pipes from utility sources into main structures. This can involve running pipes in wall cavities, routing vent stacks out the roof, and connecting drain lines to sewer or septic systems. Pipeline connections are made, and water lines are connected to the main supply valve. After the rough-in plumbing is completed, the project enters the finish plumbing phase.
Rough-In vs. Finish Plumbing
A rough-in plumbing refers to the early stage of building (including installation) in a new outlet or addition, where cables are uncovered and run before the walls are sealed. After this, the plumber completes the finish plumbing, installing faucets, under-sink drain assemblies (trap), water system valves, and other fixtures.
Typically, rough-in plumbing is performed by a licensed professional plumber, which includes excavating the yard to lay underground water and drain lines and drilling holes in the home for water, waste pipes, and vent stacks. The plumber then runs supply lines, drains, and vents through the wall cavities to connect to the required lines.
Finish plumbing work, on the other hand, can be done by a talented DIYer or professional plumber. Fixtures are installed, and caps are removed from the drain and water supply lines. The plumber installs under-sink drain assemblies, water system valves, and tests each connection to ensure they are leak-proof.
How to Perform Rough-In Plumbing
DIY rough-in plumbing is generally very difficult to perform, and it is not recommended unless you have professional experience and up-to-date knowledge of current building codes and inspection requirements. If you have some experience, you might be able to handle rough-in plumbing for new bathrooms, kitchens, or laundry rooms in existing homes. Before starting the finish phase of plumbing, rough-in functions need to be inspected.
Here are a few things to consider when rough-in plumbing:
- Gravity: Drain lines should be sloped downward, as gravity is the driving force of any drainage system.
- Horizontal Drains: Avoid long horizontal drain line runs whenever possible.
- Venting: Proper venting of the wastewater system is crucial to prevent plumbing problems in the future.
Steps for Rough-In Plumbing
- Dig Out and Lay Main Water and Drain Lines
Excavate to install water lines and drain lines from utility connections to the building. You can either do these connections yourself if you have the expertise or hire a good plumber to run the main water line and the main drain line from your utility connections to your building.
- Measure and Drill Tub and Toilet Drains
After laying the main water and drain lines, turn your attention to the bathrooms.
- Bathtub: Test-fit the tub, then level and plumb it before marking the drain location. Remove the tub and drill a hole for the drain, ensuring not to drill over a floor joist. Move the tub back into place and screw in a 2-inch screw.
- Toilet: Measure a standard 13 inches from a back wall and 15 inches on both sides. Use a hole saw to create the hole for the toilet drain.
- Drill Holes for Drainage and Venting
Use a hole saw to create holes through studs for drainage and venting circuits. When gluing a drain fitting, use a brush to coat both the pipe and the fitting well. Insert the pipe inside the connection, twisting it back and forth to cover as many visible areas as possible within the glue joint. Quickly wipe off any remaining glue before it dries.
- Add Water Lines
After the drain and vent lines are in place, install water lines. Use 3/4-inch pipes close to the bathroom, kitchen, or water-using appliances (refrigerator, washing machine, dishwasher), then step down to 1/2-inch lines for each fixture. Keep 1/2-inch pipes straight and short. Drill holes on the exterior of your home for hose bibs. In winter months, hose bib lines should be angled upward to prevent freezing.
- Exterior Venting Plumbing Equipment
Drill vent holes for any external plumbing equipment like sump pumps, water heaters, and boilers. Check your blueprints to determine where these installations are located, then drill the necessary holes.
- Finish Water, Drain, and Vent Tie-Ins
Bring down major hot and cold water lines in the basement, drop the main 3-inch drain stack, and run the central vent stack. Connect the main water lines and tie the hot and cold lines together. Tie the drain lines into a 3-inch main drain stack, fasten the vent lines to the main vent stack, and attend to the drain lines in half-bathrooms.
- Connect the Water Supply System
Connect the incoming service to the water lines using a main shut-off valve. Seal or cap the water lines, then turn on the water to test for leaks.
Remember, rough-in plumbing is just the beginning. Correct any issues before covering the plumbing with drywall.
The rough-in plumbing phase is critical for having a reliable and efficient plumbing system. Careful planning and installation of water, drain, and vent lines set the stage for a smoother finish plumbing phase. Follow local building codes and best practices, and schedule regular inspections to diagnose any issues early. A solid rough-in plumbing foundation ensures long-lasting performance and comfort in your home.
