I had posted this a while back but didn't cover an important question.

I'm going to add ducting between first and second story for hood vent. Joists run proper direction to make a run out. I don't know what to expect as I try and get out of the siding? Will I likely find two layers of wood? Are these headers?

Can I cut 3.25 x 10" for a boot without impacting integrity?

Thanks in advance.

Depends if you're going into only the bottom plank of siding or the bottom 2.
You just have an extra board of siding instead of the water table lap in the profile below.
You're drilling through one 2x_ on the end, possibly a layer of sheathing (but sometimes it doesn't cover the 2x_), vapor barrier, and a layer of siding.

A 10" penetration in just about any member is going to be a no without reinforcement. If I recall, 3.25" is the max hole size for a 2x12 at center.

Right, but is an exterior plate? Header? Supporting weight like a joist across a span? I don't think so.

I found a post online of someone asking a similar question.

"The hole cutting rule does not apply to rim joists since they rest CONTINUOUSLY on an exterior wall. They do not carry weight like a regular joist, their main purpose is to align and hold vertical the joists that are fixed to them, and provide a solid continuous nailer for the subfloor, and wall plate above."

evan_aggie said:

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"The hole cutting rule does not apply to rim joists since they rest CONTINUOUSLY on an exterior wall. They do not carry weight like a regular joist, their main purpose is to align and hold vertical the joists that are fixed to them, and provide a solid continuous nailer for the subfloor, and wall plate above."

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Agree with this. The blocking and the end joist aren't supporting anything. Since you'll be mostly removing one of the blocking pieces and putting a hole in the ceiling anyway, I'd add another blocking piece behind/upstream of where your vent goes into the ceiling just to be safe.

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Made a little progress today.

Technically, the band or rim joist is a supporting member. It transfers loads vertically from the floor joists as well as from the wall of the second story.

You're probably fine making a penetration, but I would do it in the top third of the band board limiting damage to the bottom half where any deflection may occur (not much should occur because it is resting on the top plate of the wall). It may also be a good idea to provide a 2x along the bottom of the band board between the two floor joists to reinforce the bottom half.

Now the drywall...

If I remember correctly you can remove something crazy like 50% of the web out of the TJI's without any structural implications. As long as you don't damage the top and bottom LVL's you should be fine.

AggieArchitect04 said:

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Technically, the band or rim joist is a supporting member. It transfers loads vertically from the floor joists as well as from the wall of the second story.

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Do the floor joists not transfer loads vertically by way of sitting on the wall? I would think the only think the rim joist picks up is the wall above, and that is spread over the entire length of the wall.

Perhaps there are different ways to build "rim joists".

I didn't show a photo but there was an internal plywood lvl nailed between the joists. Honestly this was probably just to square out the end. There were 2x8d between the joists laying flat (also for spacing I assume).


I don't think the part I cut was carrying any real load.

ABATTBQ11 said:

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AggieArchitect04 said:

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Technically, the band or rim joist is a supporting member. It transfers loads vertically from the floor joists as well as from the wall of the second story.

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Do the floor joists not transfer loads vertically by way of sitting on the wall? I would think the only think the rim joist picks up is the wall above, and that is spread over the entire length of the wall.

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Rim joists are used in platform framing. I misspoke about it transferring loads vertically. It's primary function is lateral support for the floors and joists. It gives rigidity to the joist system. Loads from interior bearing walls are transferred to the floor joists and then distributed and pushed out to the rim joist and exterior walls. A single hole in the rim joist is probably okay, but if you had several along it's length (or had a rotten or damaged rim joist) then there is potential for problems. Since the rim joist is part of a system with the floor joists and decking, I would agree that the rim joist does accept some of the load from the wall above.

https://www.hunker.com/13720287/what-is-a-rim-joist