What you're talking about here is a compound adjective. The rules regarding hyphens in compound adjectives are these:
If the compound adjective is right before the noun, use a hyphen:
- Built-in types
- A well-educated student
- The fast-moving river
If the compound adjective directly follows a linking verb, don't use a hyphen:
- The types are built in.
- The student is well educated.
- The river is fast moving.
However, if an adverb in a compound adjective ends in "y," don't use a hyphen regardless of where the compound adjective is:
- A quickly moving river
- The river is quickly moving.
- A finely tuned watch
- My watch is finely tuned.
Then there are some compound adjectives that are always hyphenated.
- A state-of-the-art sound system
- This sound system is state-of-the-art.
So in your example, you would not use a hyphen: "You can use the types [that are] built in to the library."