If you clip their flight feathers on one wing, not so high. Having said that, today one of my EEs, wing clipped, easily cleared a 4-foot fence to get to her rooster, who had accidentally gotten out and was calling his hens. I would'na believed it if I hadn't seen it with my own eyes. She cleared it with a good foot and a half to spare. Barring this incident, they NEVER get out! 
