Centuries ago, tulip bulbs were so precious that they were more expensive than houses. And while today the ‘tulip mania’ is nothing more but a historical anecdote, the delicate nature of flower bulbs still requires special growing and storing conditions. Royal de Ree Holland is a leading Dutch producer of flower bulbs whose giant factory building in Lisserbroek needed a thorough roof makeover to ensure optimal interior conditions. The plan also included fully embracing sustainability by going carbon-neutral and energetically independent.