Replace All Plumbing Systems
A whole home remodel is the perfect time to replace aging plumbing with modern materials. New supply lines using PEX, updated drain-waste-vent systems, and proper fixture rough-ins will serve your home reliably for decades.
Quick Summary
Typical Cost
$10,000 - $30,000
Complete supply and DWV replacement
Time Required
1 - 2 weeks
Rough-in before drywall
Difficulty Level
Professional Required
Licensed plumber
Why This Matters
Plumbing systems are typically designed to last 40-80 years, but many older homes have systems well past their prime. Galvanized steel supply lines corrode from the inside, reducing water flow and eventually failing. Cast iron drains develop internal rust and can crack. Polybutylene pipes (common in the 1980s-90s) are prone to sudden failure. A whole home remodel provides the ideal opportunity to replace these aging systems.
Modern plumbing materials offer significant advantages. PEX supply lines resist corrosion, handle freezing better than rigid pipes, and install faster with fewer fittings. ABS and PVC drain pipes will never rust and resist chemical damage. These materials will outlast the next owners of your home.
Beyond materials, remodeling allows you to optimize your plumbing layout. You can add fixtures, relocate pipes away from exterior walls, install proper venting for better drainage, and add convenient features like instant hot water recirculation. This is your chance to create a plumbing system that truly meets your needs.
Step-by-Step Guide
Step 1: Evaluate Existing Plumbing
Understanding your current system helps plan the replacement effectively. Have a licensed plumber assess all visible plumbing.
- Identify supply line material: galvanized, copper, PEX, polybutylene
- Determine drain pipe material: cast iron, ABS, PVC, lead
- Check water pressure and flow at multiple fixtures
- Note any existing leaks, corrosion, or slow drains
- Locate main shutoff, water heater, and water meter
- Identify sewer line material and connection point
Step 2: Design New Plumbing Layout
Create a comprehensive plan for the new plumbing system that accounts for all fixtures and meets code requirements.
- Mark all fixture locations on floor plans
- Plan drain routing to maintain proper slope throughout
- Design vent stack locations and connections
- Plan supply line routing from water entry point
- Consider manifold system vs. trunk-and-branch for supplies
- Include cleanout access points per code requirements
Step 3: Pull Plumbing Permits
Plumbing work requires permits and inspections in all jurisdictions. This protects you and ensures code compliance.
- Submit plumbing plans showing fixture locations and pipe routing
- Include fixture count and pipe sizing calculations
- Show connection to municipal sewer or septic system
- Pay permit fees (typically based on number of fixtures)
- Schedule inspections: rough-in and final
- Post permit on site during construction
Step 4: Remove Existing Plumbing
With walls open, remove old plumbing to prepare for new installation. Work carefully to avoid damaging framing.
- Shut off water at main and drain all lines
- Remove all fixtures being replaced
- Cut out old supply lines, saving valves if reusable
- Remove accessible drain pipes, capping connections temporarily
- Test for lead in old pipes and handle appropriately
- Dispose of old materials properly (recycling copper)
Step 5: Install Main Drain and Vent Stack
Start with the main drain line and primary vent stack, as these establish the foundation for the entire DWV system.
- Install main drain from sewer connection through foundation
- Maintain proper slope: 1/4 inch per foot for pipes under 4 inches
- Install main vent stack, typically 3-4 inches through roof
- Use proper fittings: no 90-degree fittings on horizontal drains
- Install cleanouts at required locations
- Support pipes at required intervals (typically every 4 feet)
Step 6: Run Branch Drains to Fixtures
Connect all fixture drains to the main system, maintaining proper slope and using correct fittings throughout.
- Install toilet flanges at proper height for finish floor
- Run drain lines for sinks, tubs, and showers with proper trap arms
- Size pipes correctly: 3-inch for toilets, 1.5-2 inch for sinks
- Install trap arm with proper length (within developed length limits)
- Protect pipes from nails with nail plates where required
- Fire-stop all penetrations through rated assemblies
Step 7: Install Vent Connections
Every fixture drain requires venting to function properly. Connect all fixtures to the vent system.
- Connect individual vents or use wet venting where allowed
- Maintain proper vent sizing based on fixture units
- Install vents rising vertically before any horizontal runs
- Connect vent branches to main vent stack above highest fixture
- Extend vent through roof with proper flashing
- Consider air admittance valves where code allows
Step 8: Install Water Supply System
Run new supply lines from the water entry point to all fixtures. Modern homes typically use PEX for interior runs.
- Install main shutoff valve at water entry point
- Consider manifold system for individual fixture control
- Run separate hot and cold lines to each fixture location
- Support pipes at required intervals (every 32 inches for PEX)
- Install shutoff valves at each fixture location
- Protect pipes in exterior walls from freezing
Step 9: Rough-In Water Heater and Specialties
Install connections for water heater and any specialty systems like recirculation loops or water treatment.
- Run supply lines to water heater location
- Install expansion tank if required by code
- Plan recirculation loop for instant hot water if desired
- Install whole-house filter or softener connections
- Run lines for outdoor fixtures, hose bibs, irrigation
- Install gas line for water heater if applicable
Step 10: Test and Inspect
Before closing walls, pressure test all systems and schedule the rough-in inspection.
- Pressure test supply lines at 50-100 PSI for 15-30 minutes
- Test DWV system with water or air pressure test
- Check all connections for leaks during testing
- Verify proper slope on all drain lines with level
- Confirm all fixtures are roughed in at correct heights
- Schedule and pass rough-in plumbing inspection
Pipe Material Comparison
PEX Supply Lines
The most popular choice for residential water supply, offering flexibility and freeze resistance.
- Cost: $0.50-1.50 per linear foot
- Lifespan: 50+ years
- Pros: Easy install, freeze resistant, corrosion-free
- Cons: Not UV resistant, some taste concerns
- Best for: In-wall supply runs
Copper Supply Lines
Traditional choice with proven longevity, preferred for exposed locations.
- Cost: $2-5 per linear foot
- Lifespan: 50-70 years
- Pros: Proven reliability, looks professional, recyclable
- Cons: Expensive, requires soldering, can corrode
- Best for: Exposed runs, water heater connections
ABS Drain Pipe
Black plastic pipe common in residential DWV systems, easy to work with.
- Cost: $0.50-2 per linear foot
- Lifespan: 50+ years
- Pros: Single-step gluing, good in cold temps
- Cons: May not be code-approved everywhere
- Best for: Residential DWV systems
PVC Drain Pipe
White plastic pipe widely used for DWV and available in many sizes.
- Cost: $0.50-2 per linear foot
- Lifespan: 50+ years
- Pros: Wide availability, chemical resistant
- Cons: Requires primer, brittle in extreme cold
- Best for: Residential DWV, underground
Cost Breakdown
Pro Tips
Consider a Manifold System
A home-run manifold system runs individual PEX lines to each fixture from a central manifold. This provides individual shutoffs, eliminates hidden fittings in walls, and allows quick hot water delivery. The added material cost is offset by easier installation and long-term benefits.
Install Cleanout Access
Put cleanouts where you can actually access them. A cleanout behind drywall is useless. Install accessible cleanouts at direction changes and before connections to the main sewer. Consider cleanouts in vanity cabinets or utility rooms where access is easy.
Plan for Hot Water Recirculation
Nothing wastes more water than waiting for hot water. Plan a recirculation loop now even if you install the pump later. Running the return line while walls are open costs almost nothing. Retrofit later would cost thousands.
Camera the Sewer Line
Before connecting your beautiful new plumbing to the old sewer line, have it video-inspected. Root intrusion, bellies, and deteriorating pipe are common in older lines. Better to know now and include repairs in the project than to discover problems after move-in.
Use Expansion PEX (PEX-A)
PEX-A with expansion fittings creates the strongest joints and maintains full flow through fittings (unlike crimp fittings that reduce internal diameter). It is also the most flexible, making installation easier. The slightly higher cost is worth it for a whole-home replumb.
Document Everything
Photograph all plumbing before closing walls. Document where pipes run through framing, especially supply lines that could be hit by nails or screws. This saves future contractors from causing leaks and helps with any future modifications.
Common Mistakes to Avoid
Improper Drain Slope
Drains that are too flat drain slowly and clog frequently. Drains that are too steep allow water to outrun solids, leaving debris behind. Maintain 1/4 inch per foot for most drains. Use a level and measure carefully throughout the entire run.
Inadequate Venting
Improperly vented drains gurgle, drain slowly, and can allow sewer gas into your home. Every fixture needs proper venting within the code-allowed developed length. Do not rely on air admittance valves where code requires true vents. Proper venting is not optional.
Wrong Pipe Sizes
Undersized drains overflow and clog. Undersized supply lines create low water pressure. Oversized drains do not develop enough velocity to clear waste. Use proper sizing: 3-inch for toilets, 2-inch for showers, 1.5-inch for sinks. Size supplies based on fixture count and run length.
Using Wrong Fittings on Drains
Standard 90-degree elbows create turbulence and potential clogs on horizontal drains. Use long-sweep 90s or two 45s for direction changes. Never use a tee on its back for drainage - use a wye and 45. Proper fittings prevent chronic clogging problems.
Pipes in Exterior Walls
Water pipes in exterior walls are at risk of freezing, even in moderate climates. During a remodel, relocate supply lines to interior walls whenever possible. If exterior wall routing is unavoidable, insulate behind the pipe (toward the cold side) and consider heat trace cable.
Frequently Asked Questions
Should I use PEX or copper for supply lines?
PEX has become the preferred choice for most residential remodels. It is less expensive than copper, easier to install, resistant to freezing and corrosion, and requires fewer fittings. Copper remains excellent for exposed locations where appearance matters and offers proven longevity. Many plumbers use a hybrid approach: copper where visible and PEX for in-wall runs. PEX comes in PEX-A (most flexible), PEX-B (most common), and PEX-C varieties.
What pipe should I use for drains?
ABS (black) and PVC (white) are the standard choices for residential drain-waste-vent systems. ABS is slightly easier to work with in cold weather and requires only one-step gluing. PVC requires primer before cement but is available in more sizes and fittings. Cast iron is occasionally used for its sound-deadening properties under bedrooms or in high-end homes. Local codes may specify which material is allowed in your area.
How much does a whole house re-plumb cost?
A complete re-plumb for a typical 2,000 square foot home costs $8,000-$15,000 for supply lines and $5,000-$12,000 for the drain-waste-vent system. Factors affecting cost include number of fixtures, accessibility (open walls vs. retrofit), material choice, and local labor rates. A whole home remodel with walls open is the most cost-effective time to replace plumbing, as labor costs are significantly lower than retrofit work.
What is the proper slope for drain pipes?
Drain pipes must slope toward the sewer or septic at 1/4 inch per foot for pipes 3 inches and smaller, and 1/8 inch per foot for 4-inch and larger pipes. Too little slope causes slow drainage and potential clogs; too much slope can cause liquids to outrun solids, also leading to clogs. Maintaining consistent slope throughout the run is essential for proper drainage.
Why do I need a plumbing vent?
Plumbing vents serve two critical functions: they allow air into the drain system so water flows freely (like removing your thumb from a straw), and they allow sewer gases to escape above the roofline rather than entering your home. Every fixture must be vented, either directly or through a wet vent. Improperly vented drains gurgle, drain slowly, and can allow dangerous sewer gases into living spaces.