A statement released by the trust said it had assessed all the advice it had been provided with and had been proactive in the action to date.
"Although a definite landmark in the town, history tells us it was never built to be a retail outlet but more a decorative feature. It is a simple structure, and would have been subject to greater structural compliance if its current usage had been foreseen," the trust said.
Trust representative Stephen Paewai confirmed a detailed engineering report was almost complete for the greater structure, the old Post Office, to also assess progress for the greater site.
Damage to the windmill's balcony had occurred over time by people climbing on it.
Builders were called in to take down a portion of the balcony and secure it. They removed some of the exterior panels and found the wood beneath the panels was rotten.
Tararua District Council was contacted and declared the building unsafe so shut it down.
The windmill was built in 1990 following the Mothers' Day earthquake and over the years has attracted a lot of attention.