Under the Model Regulations 2017, a heavier decision (article 56.5) can only be taken if at least two thirds of all votes are present or represented. If not, a second meeting is called (article 56.6).
That second meeting is held no earlier than fifteen days and no later than six weeks after the first. The notice must state that it is such a second meeting. There, the same items can be decided by two thirds of the votes cast, regardless of how many votes are present. With a sub-division the periods are doubled.
Practical tip: for important proposals, plan a possible date for the second meeting straight away, and ask owners who cannot attend for a proxy. Check whether your regulations have the same arrangement.
See also: Quorum, Qualified majority, Meeting notice (oproeping), Proxy (volmacht)
Read more: Quorum and majorities in a VvE
Legal basis: Modelreglement 2017, art. 56.5–56.6