Why builders used it
When copper prices spiked in the mid-1960s, many builders switched to aluminum for the branch circuits that feed outlets and lights. It carries electricity well, but it behaves differently from copper.
Where the risk is
Aluminum expands and contracts more than copper, oxidizes where it's connected, and can loosen at outlets, switches, and splices over time. Loose connections run hot, which is why the concern is concentrated at the connections, not along the wire itself.
The fixes
The U.S. Consumer Product Safety Commission recognizes two permanent repairs short of rewiring: COPALUM crimp connectors and AlumiConn connectors. Both join a short copper pigtail to the aluminum wire at every connection in the home.
A full rewire to copper is the other option. We'll compare the cost and disruption of each for your home.
What doesn't work
Twist-on connectors that aren't rated for aluminum can make things worse. Swapping in outlets marked for aluminum is not a substitute for a proper repair at every connection.