How close can garage overhead storage be to fire sprinklers?
You should not store any items within 18" of the ceiling near a sprinkler head. The items can obstruct the water flow of the sprinkler if it goes off.


  NFPA 13 (2013), Clearance to Storage, has a requirement in 8.5.6.1,
  which states, "Unless the requirements of 8.5.6.2, 8.5.6.3, 8.5.6.4, or
  8.5.6.5 are met, the clearance between the deflector and the top
  of storage or contents of the room shall be 18 in. (457 mm) or
  greater."
  
  OSHA  29 CFR 1910.159(c)(10) in part states, "The minimum vertical
  clearance between sprinklers and material below shall be 18-inches
  (457 mm).
  
  The 18" should be considered a minimum vertical clearance. All items
  in the storage area must fall below this plane