On outside wall? I have seen them cut on inside load bearing walls for cold air returns 16" and more. This is not a problem if a 2x4 is supporting the joist above.
John,
When my plumbers or HVAC boys have to notch deeper than 50% I make them “strap” both sides on load bearing walls.On occasion they’ve had to cut all the way through and I have them “strap” both sides in those instances as well.
On exterior walls we would only strap the inside as the outside is held in line by the sheathing which is already in place .Rarely ,though ,have I ever built a home that required a hole that big on an exterior wall.
On interior load bearing walls if the ceiling joists,(single storey)or floor joists are joined together properly over the bearing wall this will also help keep the wall in line.In addition when the floor joists,(if present) above are sheathed this will prevent movement as well.
I will say that when it comes to a plumbing related notch I won’t use straps at all but rather a Bocca plate ( nail guard).They are heavier guage and better than a strap.If I can’t get one from a store I have them made by a welder.
Right or wrong I don’t know but the codes inspectors haven’t questioned it in any instance.
Safe thing to do is ask you local codes admin.
Yes I understand that a metal strap can be added
to the top plate. But it seems odd that a huge
notch would be allowed without limitation in the IRC.
Imagine a 3"x3" notch on an outside wall top plate.
That would only leave half an inch of wood left
after the notch was taken out (because the top
plate is only 3.5" on a 2x4 wall).
Just seems odd that the code does not address
how deep the notch can be … it just says to
add a metal strap if over 50%. Hmmm.
I will tell you what the ONTARIO BUILDING CODE states.
9.23.5.4.[1] TOP PLATES IN WALLS SHALL NOT BE NOTCHED,DRILLED OR OTHERWISE WEAKEND TO REDUCE THE UNDAMAGED WIDTH TO LESS THAN 50mm [2"] UNLESS THE WEAKENED PLATES ARE SUITABLY REINFORCED.
Like I said you can cut the entire top plate with no problem as long as you reinforce the top plate that a joist is resting on. on either side]I will try and post a picture of what I’m talking about.
We also have the 2/3 rule if a stud or 2x4 is load bearing [vertical]