# Can I bore a 4inch hole through my ceiling joists?

I need to install a bathroom ceiling fan for a new bathroom I'm adding to my house. The only issue is that the floor joists are running perpendicular to where I need to run the 4'' aluminum duct pipe.

My question is do I just bore a 4'' hole through the joists?

Based on this answer from StackOverflow and this one it seems I can bore a hole 1/3 the depth of my joists (which are 11'') as long it's a joist (and not a beam) and the hole is no closer than 2inch from each edge... is that correct?

Follow-up Note: This room is on the first floor, and there is a room above it (so venting through the attic isn't a possibility - as far as I know)

• 4 x 3 =12 so 1/3 of 11 is less then 4" Commented Jan 16, 2021 at 21:02
• @AlaskaMan - Yea, I was wondering about that too. 1/3 of 11 = ~3.667inches. Being a diy n00b, I didn't know if that was close-enough.. or I was being too precise. Looks like the consensus though is DONT DO IT haha Commented Jan 17, 2021 at 0:03
• Isn’t the 1/3 guidance only for I-joists? I don’t think you can cut anything nearly that large in standard dimensional lumber. It doesn’t mention which type of floor joists they are. Commented Jan 17, 2021 at 4:59
• it depends where you are some places don't even allow 2" holes. Commented Jan 17, 2021 at 5:32
• A 4" duct takes a 4 1/4" hole to get it to pass through. It may possibly with a 4 1/8" hole, but it will be really tight.
– Jack
Commented Jan 17, 2021 at 7:44