Knob-and-tube and aluminum: what inspectors flag in pre-1975 homes.

Two wiring types turn up in pre-1975 Sunnyvale homes that make inspectors write notes and insurers ask questions. Here is what they look like and what we do about them.

Knob-and-tube (before about 1950)

Single conductors on porcelain knobs, passing through porcelain tubes in the joists. No ground, cloth insulation that crumbles, and it must not be buried in attic insulation. Common near the Heritage District and in the older blocks west of Sunnyvale Avenue. It is replaced, not repaired: we fish new copper from the attic and crawlspace, room by room, and open drywall only where a run cannot be fished.

Aluminum branch wiring (1965–1973)

Looks like modern cable, but the conductors are silver. Aluminum expands and contracts more than copper, loosens at terminals, and that is where the heat starts. Two fixes: a full copper rewire, or COPALUM / AlumiConn connectors at every device, which insurers accept. Which one depends on the house; we tell you on the walk.

Eichler conduit (1950s–60s)

Not a hazard, but a constraint: slab floors, no attic, every run in conduit through the roof deck. Rewiring an Eichler means pulling new conductors through the existing conduit, and planning every new fixture around it. We have done enough of them to know where the pull points are.

What the inspector looks for

• Knob-and-tube under insulation, or spliced to modern cable outside a box.
• Aluminum on devices not rated CO/ALR.
• Missing grounds on three-prong receptacles.
• Open splices in the attic, the most common find of all.