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 2×6 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?
Best Answer
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.)