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I have an attached garage with no living quarters above the ceiling. The firewall separating the attic from the garage is finished with drywall up to the roof line.

This drywall seems to be mounted to 1x4 strips (indicated in blue) which are attached to the engineered roof trusses (indicated in red) on the attic side.

We would like to pass an HVAC vent through one of the cavities in the roof truss which would require cutting the 1x4 and relocating it ~6" to either side. Proposed passage in green.

I know the modification of any engineered truss is not permitted without engineering oversight, but this 1x4 does not seem structural to the truss, and merely serves to support the drywall. I dont see the 1x4s in place on any other truss member in the garage or attic trusses.

Is it ok to modify this 1x4 support as described?

Picture below is from inside attic facing toward the backside of the firewall.

enter image description here

isherwood
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nathan_jr
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2 Answers2

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Garages are to be separated from single family residences by 1/2” gypsum board on garage side ONLY, provided the garage does not open into a sleeping room. (See ICC Table R302.6.) (R309.1)

The Code does not mention the required size of the studs or their spacing of the wood supports for 1/2” drywall between garage and house.

Ducts passing through the wall shall be 26 ga. Minimum. (See ICC R309.1.1)

Lee Sam
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Yes, you an modify those. They're just to support the drywall and are not structural. Sometimes you'll see a special truss there with ribs installed on 24" centers already.

Just be sure that the firewall is still supported well (typically at least every 24" with all seams blocked), and that any penetrations meet code for that situation.

isherwood
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