What is the minimum height required for vertical/trees in a UC?

There are numerous factors you have to take into consideration, strain, UC bucket size (8 or 13 Gallon) veg time. If you have a low low room you have to be able to cool it well, you will also need extra room in case your strain stretches really bad. I would say at minimum a 9' ceiling. You would also need to keep your veg time down and make them into wide bushes. Your bulbs hang right into the canopy so it really depends on how big you let them get. Some people let their strain veg too long and end up using cinder block to raise their light racks and what not.

If you veg them to like 2'f above the bucket and flower you should be okay in like an 8' ceiling. Anything lower and you need to limit your height. Just do what you can work with and flower them smaller then you really want to just to be safe. Once you know what that strain does in its stretch you can adjust accordingly. Its pretty much common sense, just be sure you got ample room man, keep them proportionately smaller according to your room size. Its better to find you have extra room at the end then them hitting your ceiling and fucking them up.
Thanks Jimmy
I plan on running Bubba Kush,have 8' ceilings (skipping the tent due to height) and will be averaging 3K vertical per plant.
Since I'm short on room, I plan on picking them up during their veg right at round 20", putting them in the UC and flipping right at 24"

Does this sound doable? Not positive, but this should be safe with BK as they don't go to crazy.