PEX vs. Copper Pipes: The Freeze-Thaw War
Quick Answer
When building a new home or repiping a historic Des Moines property, the material you choose dictates whether your basement floods during the next polar vortex.
For generations, the only acceptable residential plumbing material was rigid copper. It was universally trusted, heavy, and practically indestructible—unless the water chemistry was wrong, or worse, the temperature dropped too low.
Over the last 20 years, a revolution in material science introduced Cross-linked polyethylene (PEX). Today, PEX is the undisputed king of residential repiping and new construction in the Midwest. Here is a granular, contractor-level look at why Copper was dethroned.
Copper: The Rigid Traditionalist
Copper pipes have a proven track record lasting over 50 years under ideal conditions. It is naturally biostatic, meaning bacteria cannot grow inside the metal, keeping drinking water extremely safe and clean. It is highly resistant to UV light and won't melt if exposed to open flames.
The Copper Drawbacks:
- Astronomical Cost: Copper is a commodity traded globally. The raw material cost to repipe a standard home in copper is easily triple the cost of plastic.
- Aggressive Water Chemistry: Copper requires a neutral pH. If your city water or well water is highly acidic, or if a water softener is tuned too aggressively, the water will slowly eat the copper from the inside out, causing "pinhole leaks."
- Labor Intensive: Because it is rigid, turning a corner requires cutting the pipe and using a blowtorch to solder a 90-degree elbow fitting. An entire house requires hundreds of soldered joints, which demands intense labor hours and presents a severe fire hazard inside old, dry wooden stud cavities.
PEX: The Flexible Modern Marvel
PEX is a highly engineered, braided plastic polymer. Because it is flexible, it arrives on massive 100-foot spools. A plumber can run it continuously from the basement mechanical room all the way to a second-story bathroom, bending it around corners inside the walls without needing a single joint or fitting.
The Freeze Advantage (Crucial for Iowa)
This is the ultimate reason PEX dominates the Midwest. When arctic air infiltrates a wall cavity and freezes the water inside a pipe, the water expands by 9%. Rigid copper cannot expand. It violently bursts. When the ice thaws, 500 gallons of water per hour flood the home. PEX, however, is a flexible polymer. The plastic pipe simply expands like a balloon to accommodate the ice. When the home warms up, the PEX shrinks perfectly back to its original shape.
While PEX shouldn't be intentionally frozen, it provides a massive, built-in safety net that saves homeowners tens of thousands of dollars in insurance claims.
The PEX Achilles Heel: UV Light and Mice
- Sunlight Degradation: Unlike copper, PEX cannot be exposed to UV light. Even a few weeks lying outside in the sun before installation will chemically break down the plastic, making it brittle. It must remain strictly inside dark wall cavities.
- Rodents: It is rare, but if a home has a severe pest infestation, mice and rats have been known to occasionally chew through the plastic surface seeking the sound of running water on the other side. This is physically impossible with copper.
- Direct Heater Connections: PEX cannot be connected directly to a water heater. Plumbers must legally solder 18 inches of rigid copper piping moving away from the heater before transitioning the line to plastic PEX, ensuring the plastic isn't exposed to excessive, concentrated heat.