Can chickens climb?

I am buildina a hen house that's around 3.5 feet off the ground. How steep/long should the laddered ramp thingy be for then to easily climb inside?

Is there a reason for it to be so high ? If you aim to let the chickens shelter underneath 2ft high should be enough if its a small coop. The higher you make it off the ground the more the rain will blow under it.
Kev

Mine climb and jump. One has decided she likes goosebery bushes so much she has stripped the bottom layer completly. And now jumps for the higher branches. Very comical!