How to Fish Wire Through Insulation

How to Fish Wire Through Insulation

Fishing wire through insulation-filled walls requires careful technique to avoid displacing insulation, damaging existing wires, or creating fire hazards. When attic access is available, the approach is to remove insulation above the wall cavity, drill through the top plate, and drop the wire down the wall using a fish tape or drill bit extension. Without attic access, fishing through the wall itself requires a drill bit extension, a fish tape, and often a stiff wire guide to navigate around insulation.

Methods Based on Wall Access

• From the attic: expose the top plate, drill through it, and feed wire down using a fish tape or weighted string
• Through the wall cavity: use a long flexible drill bit or drill bit extension to bore through blocking, feed fish tape down from above or up from below
• Blow-in insulation: fishing is harder as blown cellulose or fiberglass fills the cavity; a heated fish tape helps cut through dense fill
• Fiberglass batt insulation: batts can compress and bind the fish tape; use a lighted fish tape or pull fish tape and wire simultaneously

Important Safety Notes

Insulation in contact with wiring creates heat buildup if the wiring is undersized or if connections are loose. Never compress insulation tightly around cables — the Canadian Electrical Code requires clearance around wiring in certain applications. If the wall contains knob-and-tube wiring, insulation cannot be added above it without first replacing the wiring, as knob-and-tube requires air circulation for cooling. Fishing wire into walls with existing knob-and-tube is work for a Licensed Electrical Contractor familiar with the specific code requirements.

EZSMART runs new circuits and fishes wire through finished walls across Ontario with all required permits. Contact us for a quote on adding circuits to your home without opening walls.

Amir Azimipour

Electrician Since 2008 Journeyman Electrician Designated Master Electrician at EZSMART Corp