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Torn Duct Insulation Under the House: What It Means

What damaged ducts look like, why it matters, and what it takes to fix them in California.

Published October 31, 2026 · 4 min read

GRS

GRS Service HVAC Inc.
CSLB C-20 #1154007

What damaged ducts look like

Ducts carry the air your system heats or cools to each room. When they run under the house, you may never see them. These are the signs to look for.

Gray flexible ducts in a crawl space with a torn outer jacket and yellow insulation showing — The outer jacket has torn open and the insulation shows through.

A torn outer jacket. The gray or silver layer protects the insulation underneath.
Exposed insulation. Yellow or pink insulation showing through means the jacket is no longer doing its job.
Loose tape and hanging strips. Tape that has let go often marks an old repair or a joint worth checking.

Insulated duct in a crawl space with strips of torn jacket hanging from it — Strips of torn jacket hanging from an insulated duct.

Why it matters

A crawl space is not heated or cooled. Insulation helps the air in the duct hold its temperature on the way to your rooms. Rooms that never feel right and weak airflow at some registers are common reasons to have the ducts looked at.

Close view of yellow duct insulation exposed where the outer jacket is gone — Close up: the jacket is gone and the insulation is exposed.

A torn jacket does not prove a duct leaks. Only a leakage test shows that. If someone quotes you new ducts from a photo alone, ask for the test result.

What it takes to fix

Repair and sealing. Reconnect loose runs, replace crushed sections and seal joints with duct tapes and mastics rated to UL 181, the materials the California Energy Code calls for.
Full replacement. Take out the old ducts, install a new insulated system and test it for leaks.

Duct run under floor joists with insulation showing through the torn jacket — A long run with damage along its length can point to replacement over patching.

What California requires

The 2025 California Energy Code applies to permits applied for on or after January 1, 2026. When more than 25 feet of new or replacement ducts are installed in a single-family home:

Ducts in an attic or other unconditioned space need at least R-8 insulation in our area (Climate Zones 11 and 12).
The whole duct system has to pass a leakage test checked by an independent ECC-Rater (formerly called a HERS Rater).

Large gray duct wrapped with tape in a crawl space, with torn jacket hanging nearby — Tape wrapped around a large duct, with torn jacket hanging nearby.

Questions

Yes, plan on one. Under the Energy Code, replacing a part of the system that has code requirements counts as an alteration, and ducts have their own insulation, sealing and testing rules. The Energy Commission says a permit is required when an HVAC system is replaced or altered. We get the permit for you.

Not by itself. A torn jacket shows damage to the outer layer. A leakage test shows whether the duct is losing air.

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Ductwork, Ventilation & Air Quality → HVAC rebates in our area →