I modified a KIWI to drive 12 foot posts by fabricating and attaching a 24 inch extention on the foot. It worked OK, but the controls were 7 1/2 feet off the ground. I tried just raising it off the ground to drive longer posts, but it wouldn't hold it's plumb. Some drivers have a plate that sits atop the post and keeps it steady while hammer drops, but the KIWI doesn't--just an open chamber. The guy I bought it from said he drove 14 foot posts using the KIWI by just picking it up in the air with his LULL, but the controls would have been 9 feet in the air, so I would have to have seen that one to believe it.