Is zakat obligatory on money saved for building a house, knowing that paying zakat would prevent the completion of the amount required for building?

Zakat (definition) is obligatory on saved money if it reaches the nisab (definition) and a full year has passed, whether it is invested or saved, because it is considered as growing wealth. The saved money can be invested or used to start building a house, in which case zakat will not be obligatory on the portion spent on construction before the year is complete. Zakat is obligatory on each partner's share individually if it reaches the nisab.