Changing from double to triple crankset

Can anyone give me an advice as to what parts need to be replaced when changing from a double to triple cranksets?

I currently have a double (53/39) with a 12-27 rear Shimano Ultegra drivetrains. Thanks!

you need the crankset and longer BB spindle,and front deralier. Your rear derailier works,but because of chain wrap limitations,you won't be able to use some of the smaller cogs when in the granny ring. Not a big deal if you are just using the granny as a bailout.

Thanks!