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We just had a new AC air handler installed, and it's much taller than the old one. Due to an error on my part, it's actually too tall for the space. And it is deeper than the space between the trusses.

I need to cut a truss chord so that I can make an alcove in the ceiling around the air handler. My plan is run another 2x4 above the existing chord, then use 3/4" plywood on the face of the existing struts and chord with a notch cut out where I need to cut out the chord.

Here is a picture of what I am thinking of doing (red is new 2x4, blue is plywood, black is chord material to be removed):

enter image description here

Is this a good plan? Should I attach the new 2x4 to the existing chord somehow? What should I use to attach the plywood?

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    Do you have a plan B? Altering an engineered truss is an extremely poor idea without actual engineering support.
    – Aloysius Defenestrate
    Jun 1, 2015 at 14:26
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    The 2x4 you have identified is not a joist, it's the bottom chord of a truss. Truss members are not subject to bending the same way a beam or joist is. That member is probably under tension, and if you cut it the whole truss will sag.
    – Hank
    Jun 1, 2015 at 15:20

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Absolutely not. You CANNOT cut a truss in this way. They are not engineered with a huge amount of wiggle room. You risk having your roof collapse. The saner solution would be to lower the platform that the unit sits on to create some more room.

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  • Lowering the platform is not a great option either. Concrete slab in the way. Oh well. I was hoping there was some kind of accepted method of modifying an engineered truss in this way.
    – longneck
    Jun 1, 2015 at 16:14
  • If the slab is above grade level, you can always demo it. Otherwise, I guess you'll have to return the air handler and get a smaller one. Measure twice, cut once... Alternatively, you may be able to get a structural engineer to sign off on some kind of modification plan, but I doubt that would be cheaper than your other options.
    – iLikeDirt
    Jun 1, 2015 at 16:46
  • What you have to realize is that a member under load has sagged a bit (deflected) from its original location in order to absorb that load. If you patch in a new member and remove the old one, the whole system will again sag to the point where the new member is bearing the load. That is bad! You have to externally support the system into a pre-sag state to do the surgery and then let it sag into load bearing position.
    – lordadmira
    Dec 22, 2020 at 3:02

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