Full list of all 14 Outlast achievements. It takes around 8-10 hours to unlock all of the achievements in the base game on Windows.
The base game contains 8 achievements, and there is 1 DLC pack containing 6 achievements.
Turn off the gas
Turn off the electricity
Finish the Whistleblower DLC
Finish the DLC in Insane mode
Collect all documents
Complete all recordings