Fire Separation Wall — Garage to Living.

The short version.

What you can actually pick.

• 1-hour wall (5/8 Type-X each side)

  Pros — Code-minimum for attached ADU, well-understood assembly, predictable cost.

  Cons — Requires demo of existing finishes to install correctly.

  $45–$75 / linear ft50+ years

• 1-hour wall + STC-50 acoustic

  Pros — Fire + acoustic in one assembly — neighbors and family don't hear each other.

  Cons — Adds resilient channel and double layer of gypsum, ~25% more cost.

  $70–$110 / linear ft50+ years

• Fire-rated door upgrade

  Pros — 20-minute rated door at the dwelling opening (if interior connection retained).

  Cons — Self-closing hardware adds cost and slightly heavier door operation.

  $650–$1,400 per door20+ years

What we deliver.

• ▸Demo existing garage wall finishes to expose framing
• ▸Inspect framing for fire-blocking and draft-stop continuity
• ▸Add fire-stops at top and bottom plates per CBC §718
• ▸Install mineral wool or fiberglass cavity insulation (R-15 minimum)
• ▸5/8 in Type-X gypsum board, both sides, taped and finished
• ▸Fire-stop putty / sealant at all electrical, plumbing, and HVAC penetrations
• ▸Self-closing 20-minute rated door at any retained dwelling-side opening
• ▸Continuous draft-stop at wall-to-roof / wall-to-attic intersection
• ▸Inspection of completed assembly before drywall close-up
• ▸Documentation photos for inspector and final permit close-out

The code parts most owners miss.

• §CRC §R302.6 establishes the baseline garage-to-dwelling separation; ADU conversions follow CBC §711.2.4 for 1-hour rated assemblies.
• §Gypsum must be Type-X (fire-rated, 5/8 in minimum) — regular 1/2 in gypsum does not satisfy the 1-hour rating.
• §Penetrations (outlets, switches, conduits) must be either fire-stopped with listed putty/sealant or use a fire-rated electrical box.
• §Self-closing door hardware is mandatory at any opening; solid wood 1-3/8 in or 20-minute labeled rated door.
• §Draft-stopping at the wall-to-roof line is required by CBC §718 — most-missed inspection item.

Why getting this right pays off.

What goes wrong — and how to avoid it.

• ✕Using 1/2 in regular gypsum instead of 5/8 in Type-X — fails fire rating
• ✕Skipping draft-stop at the wall-to-roof line — most-common inspection failure
• ✕Standard electrical boxes without fire-stop putty — fails penetration test
• ✕Hollow-core door at the dwelling opening — must be solid 1-3/8 in or 20-minute rated
• ✕Forgetting self-closing hinges on the rated door — fails final
• ✕Not photographing the assembly before drywall close-up — inspector requires re-opening

After we hand you the keys.

• ▸Confirm self-closing door operates fully and latches monthly
• ▸Check fire-stop sealant at penetrations every few years for shrinkage
• ▸Don't drill new penetrations through the rated wall without re-sealing
• ▸Re-paint with intumescent paint only — standard latex over rated gypsum is fine

In short.

When do I need a 1-hour fire wall in a garage conversion?

Whenever the converted space shares a wall, ceiling, or roof structure with the main house. Detached garages with a 4 ft+ separation from the main house don't need a fire wall on the house-facing side — but they may need fire-rated exterior siding if within 5 ft of a property line.

What's the difference between 1/2 in gypsum and 5/8 in Type-X?

1/2 in regular gypsum is the code minimum for typical garages but does not satisfy the 1-hour rating required for an ADU. 5/8 in Type-X gypsum has fiberglass reinforcement that maintains structural integrity in a fire test — required for the rated assembly.

How much does fire separation cost?

$3,000–$9,000 for a typical attached-garage ADU conversion, depending on linear feet of wall and ceiling. Wall: $45–$110/linear ft. Fire-rated door: $650–$1,400 per opening.

Can I keep the interior door between the garage ADU and the house?

Yes, if it's a 20-minute rated or solid wood 1-3/8 in door with self-closing hardware. Most owners installing an ADU for rental seal this opening permanently for privacy.

Do I need fire separation if the garage is detached?

Not from the main house, but the side facing a property line within 5 ft may need fire-rated exterior siding (1-hour rated wall, no openings or limited openings).

What's draft-stopping and why does it matter?

Draft-stopping (CBC §718) is continuous fire-blocking at the wall-to-roof intersection that prevents fire from spreading laterally through the attic. It's invisible after drywall close-up — and the most-missed item on garage conversion final inspections.

Can the same wall serve as both fire and acoustic separation?

Yes — the 5/8 Type-X gypsum + cavity insulation that satisfies fire code also drops sound transmission by 35–45 dB. Adding resilient channel and a second gypsum layer pushes it to STC-50, the threshold where neighbors stop hearing each other.

Will the inspector look behind the drywall?

Yes — they inspect the framing, fire-stopping, and draft-stopping before drywall close-up. Photo documentation is helpful for the final close-out but doesn't replace the in-person inspection.

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