Copper tubing used in interior plumbing is usually joined with which type of joints, and copper that is buried is usually joined with which type?

• A. interior solder joints; buried flare/compression
• B. interior flare/compression; buried solder joints
• C. interior solder joints; buried solder joints
• D. interior compression; buried flare

Answer: (A)

The idea is to use joining methods that fit the environment and accessibility of the piping. Inside a building, copper tubing is typically joined with solder (sweat) joints because this method provides a tight, durable seal in a dry, controllable space and allows the installer to carefully manage heat and cleanliness.

For buried copper piping, solder joints are avoided because soil moisture, movement, and the difficulty of repairing or reworking underground can compromise a heated solder connection. Instead, mechanical joints—flare or compression fittings—are used. They seal reliably without needing to heat the pipe underground and can accommodate minor movement and soil conditions, making installation and future maintenance more practical.

So, interior copper is commonly joined by solder joints, while buried copper uses flare or compression fittings.