Any framers out there - need to cut a ceiling joist

It will be fine if you do as I understood your intention of bridging (double 2X6) at the cut ends of the joists. And putting them 90 degrees to the joists. No problem. Doing it from below is not only easier, it is cooler.

I would cut a larger square opening then run a 2×6 braces to the other joists to support the cut joist. It will require patching the drywall, which means repainting at least that area, if you have the same paint.

Strengthening the other joists is not the issue, as you’re not adding any weight to them. It’s the one you cut that you need to keep from sagging. Running braces to the uncut joists so the drywall isn’t supporting the cut joist. I’m better with pictures than with words… I’ll be right back….

I’m back.. header joists is the term I was looking for. This is the proper way to do it.

-- I'll grow up when ketchup bottle farts stop being funny.

Also, if you cut the drywall carefully and pry it out without breaking it you’ll be able to reuse the piece you cut out.

Use joist hangers to attach to the uncut joists, and face nail into the cut ends of the middle joist.

Also, you have to make sure the joists, and header joists, are a few inches away from the duct. Check local building code for the minimal allowance.

-- I'll grow up when ketchup bottle farts stop being funny.

TedW-
Your diagram is what I’m intending. The headers on the cut joist will be doubled and attached to the uncut joists on either side. I would add additional blocking to the left and right of the circle on your diagram (parallel to the uncut joists but in closer to the circle …. duct…) These additional blocking pieces would be part of the support system for the range hood and might add some stiffness assuming I get them in there nice and tight.

I already have lots of patching holes to do (sparky just finished today) and the whole room will get painted so painting the ceiling is just another step at this point. I might get done by Christmas at this rate. :)

And it’s gyprock with a hard plaster skim coat. So there’s no carefully prying it out. It’ll need patching. :)

A 1960 ranch? Is the ceiling drywall? i hung a lot of rocklath and plaster in the late 60’s early 70”s didnt see much drywall untill late 70’s but that was in south florida, making a bigger hole in drywall is a lot easier then in lath and plaster.

-- My theroy in wood working will be. If I'm not enjoying doing it i won't do it.

Ahh.. okay.. I misread your post and thought you intended to just cut a round hole.

I use a carbide grit blade on my reciprocating saw to cut through rock-lath plaster. It’s the least dustiest way I know how and gives a nice clean edge for patching.. but you’re probably way ahead of me on that one too. :)

Now I get the question, right there at the bottom of your post as plain as day (I always miss the obvious). I don’t see any need to beef up the uncut joists for just that one. I wouldn’t even double anything for that little space, but doing so doesn’t hurt anything either.

You’ll probably have to do the same with the rafters, unless there’s room to angle the duct around the rafter above the joist. That will be the fun part. :)

-- I'll grow up when ketchup bottle farts stop being funny.

Yeah, amazingly this ceiling has no discernible sag despite the fact that they used 2×6s at about the maximum span. Looks like #2 doug fir but could possible be YP which has a longer span rating. Because of the size of the hole I’m going to need in the ceiling to get this done, it would also be possible to “gusset” the cut ends to the roof rafters. At the one end the bottom of the roof rafter is only about 4 inches away from the top of the ceiling joist. At the other end it’s more like 8 to 10 inches.
Just checked…. the roof rafters are 2×6 as well. That’s a heck of a span for a 2×6. I’m probably over-thinking this with the gusset idea (I am the king of over-thinking, stressing and then overbuilding). It’s 1 joist to cut. The thought behind the gusseting was that the range hood could weight 50 pounds (or 80) and I don’t want to induce sag over time by hanging something that heavy from the ceiling. I wish they’d used 2×8s, but that’s out of my control at this point. The gussets would have the roof rafters sharing the load.
I think I just talked myself out of the gusset idea :)

OK, here’s another thing I should plan for somehow. The roof cap and what happens during a roof replacement. If I install a roof cap just about directly above this range hood, and a couple years from now I have to replace the roof (which I will), am I going to have to open the ceiling again to reconnect it? (that would suck). If that’s the case I think I’m going to design a decorative “medallion” to surround the ceiling penetration that we can remove to have access to the connection. Because I KNOW we’ll be replacing the roof within the next 2 to 5 years and it will be a tear-off as there are at least 2 roofing layers up there now.

I would probably add a couple triangles of plywood between the cut ceiling joist and chord above it. Not sure if I would do so to prevent roof sagging or prevent ceiling sag – just to be safe.

-- "I dream of a world where a chicken can cross the road and no one questions its motive"' - Anne Nonny Mouse

There’s know reason you should have to open up the roof or ceiling to replace your roof cap or roof. Caps(aka boots)
have rubber gaskets on them . Just make sure when you install your vent pipe that you use some self taping screws to anchor you vent pipe to your fan so the pipe is not pulled out when the try to remove your fan cap when it’s time to re roof.

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/

I’ve never seen a rubber boot on a range hood vent cap.

I wouldent cut the joist at all.I would make a plywood box (flue) that straddles the joist and the roof rafter. attach it to the joist to hold it in place. Caulk the seames and use it for the flue connector . cut a hole in the roof and install a vent cap. Attach the vent to the plywood flue box, Your hole in the celing can be 16” square.

-- Nils, So. Central MI. Wood is honest.Take the effort to understand what it has to tell you before you try to change it.

your right charlie it’s a metal sleeve and cap or a roof top vent ,but it will still be fine if you screw down the vent pipe

-- W James Brokenbourgh Custom furniture maker http://artisticwoodstudio.com/

Bridging the cut rafter sounds like it would probably meet code. The only other suggestion I would make would be to make a bulkhead above the range (cooktop?) just big enough to offset your vent pipe.

-- When questioned about using glue on a garbage bin I responded, "Wood working is about good technique and lots of glue........I have the glue part down."

Ceilings are 7’-8” from floor. That’s part of the problem. All of the island hoods seem to assume everyone has 8 ft ceilings as a minimum. There’s a minimum distance the manufacturers want you to have from the cooktop. Then there’s a measurement of exactly how short you can make the entire assembly. Most are around 31 inches. If I have a range hood hanging 31 inches from the ceiling, then according to the manufacturer, it’s too close to the cooktop. The bottom of the range hood would be at my chin. Sounds like a head banger to me. I know on many of them I can shorten the stack by cutting the legs of the support tower and taking the stainless duct covers to a metal fabricating shop to have them shortened. But…. seriously?

Anyways, I found a brand new one from Kobe that has both a short duct AND would meet the clearance-from-cooktop requirements of the manufacturer and ME. We’re going to open the ceiling either way, but there’s a scuttle in the garage that accesses the space. “Access” is a tricky term here as there’s only 18 inches of headroom at the peak and the range hood is only about 5 or 6 feet from the eaves. Anyways, I’m going to try to slide some 6 inch duct over the top of the insulation to get from the scuttle to the range hood. About 12 feet. The idea is that if I have to penetrate the roof, I’d rather do it over the garage AND in a place where I have access to inspect/maintain if necessary. If I have to penetrate directly over the range hood, there’s a possibility I’d have to open the ceiling again if there are any issues at all (a leak, re-roof makes it need reconnect, whatever)

The issues with this are: #1 Can I feed a 4 ft section of 6 inch duct through the scuttle. (I think I can, but I’ve been wrong before.) – if yes, great. If no, this whole idea stops and I have to penetrate over the range hood. #2 will an INSULATED 6 inch duct fit into that “pinch” space where the ceiling joist and roof rafter are closing in on each other. If I can slide the duct without insulation over to the hole in the kitchen ceiling, then I’d pull it back to the scuttle and start sliding an insulation sleeve over it and push it back to the hole.