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I am installing a exhaust fan duct in my 1st floor kitchen. I had planned to go under 2nd story joists/above kitchen cabinet, thru the wall. Unfortunately, the desired location on the wall would split--half above and half below the soffitt line.

I can either try to go up 3" or down 3". To go up 3" will require cutting the double top plate. I should mention the wall is 2x6 construction and the exhaust is at the corner of the exterior wall (load bearing). To go down 3", will require cutting 6" holes in the kitchen cabinet top/shelves and installing 2 elbows--one down into the cabinet, then one to return to a horizontal path and then thru the wall. Hate the idea of hacking cabinets and losing that storage space, but cutting the double top plate scares me--structurally speaking.

Advice?

  • To some extent the doubled top plates act as a beam for carrying roof trusses. It's probably a code violation to remove part of them, but whether it's an actual problem depends on what rests on the plates between the studs in that same bay. Are you able to determine the details of that situation? – isherwood Aug 27 at 14:40
  • nothing is resting on the area that would be cut. rafters are aligned to the studs. the roof load here is small (about 8' horizontal with 5/12 pitch). Roof load is standing seam metal, not asphault plus 1/2" plywood. Really concerned about this being the area between the actual corner and the 1st stud of the wall. – peinal Aug 27 at 14:56
  • There's no additional concern, then. The roof sheathing and framing really have the wall locked into place. – isherwood Aug 27 at 15:01
  • There are always ways to "box in" cutouts, similar to the headers required around windows. As always, check local code before deciding to do this to the top plate. One must ask: how full are your cabinets right now, and could you get rid of lots of junk? – Carl Witthoft Aug 27 at 18:27
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    cabinets are full. I could get rid of lots of junk if I wanted my wife to leave me. The more I think about it, the better the cabinet mod sounds. – peinal Aug 27 at 19:09
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Do not cut the double top plate.

A double top plate acts as part of a giant horizontal beam that resists wind and seismic loading. Cutting the top plate is the same as notching a regular beam holding a floor up.

Having it in the corner of your house is good, but I wouldn’t do it until a professional could check it out.

Btw, the Code requires continuous double top plates lapped at the corners and lapped a minimum of 48” elsewhere with a minimum of 8- 16d into each side. of the joint. (See ICC 2308.5.3.2.)

  • That is code where you live; these things vary greatly by location and by country. – Carl Witthoft Aug 27 at 18:24
  • @CarlWitthoft But structural concepts don’t... – Lee Sam Aug 27 at 18:35
  • @CarlWitthoft Read the whole answer. The Code reference was a Btw... – Lee Sam Aug 27 at 18:37

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