Same diameter, different walls
Copper water pipe is made in several types that share the same outside diameter but have different wall thicknesses. Type K is the thickest and is often used underground. Type L is a common middle choice. Type M is thinner and has been widely used for interior residential lines.
A thicker wall means more metal between the water and the outside of the pipe. Owners who have been through pinhole leaks often ask about wall thickness for that reason. Your plumber can explain what code allows for your house and what they recommend.
Copper types at a glance
| Type | Wall | Typical marking color | Common use |
|---|---|---|---|
| K | Thickest | Green | Underground and service lines |
| L | Medium | Blue | Interior and some underground use |
| M | Thinnest | Red | Interior residential supply lines |
How to read existing pipe
- Look for a printed stripe or stamp along the pipe in exposed areas.
- Check near the water heater, under sinks and in the garage.
- Markings fade over time, so a missing stripe does not tell you the type.
- Keep a cut piece from any repair; a plumber can measure the wall.
Joining methods
Soldered (sweated) joints
- Traditional method using heat, flux and solder.
- Requires open flame in walls and attic, so fire precautions matter.
- Widely understood by plumbers.
Press fittings
- Joints made with a pressing tool and sealed fittings.
- No open flame needed.
- Fittings themselves differ from solder fittings.
Questions for a copper repipe
- Which type of copper will you use, and is it written on the estimate?
- Will joints be soldered or pressed?
- How will pipe be supported and insulated where it runs through the attic?
- How will you isolate copper from contact with other metals?
Common questions
Is Type L always required?
Requirements depend on code and the application. Ask your plumber what the code calls for and what they recommend for your house.
Does thicker copper prevent pinhole leaks?
A thicker wall adds margin, but corrosion depends on several factors. Ask a plumber what they expect for your water and layout.
Should attic copper be insulated?
Insulation can reduce heat loss on hot lines and condensation on cold ones. Ask what the plan is for your attic.
General information for Yorba Linda, not a quote or professional advice. In an emergency, call 911.