Duntryleague Mansion Foundation chair John Cook said the Heritage Council had objected to the design of a new lift and a planned extension to the rear of the building.

"We were disappointed, to say that is an understatement," he said.

"The main sticking point was the extension of the lift through the roof. It is at the rear so I didn't think anyone would see that."

Mr Cook said the foundation needed to get a DA approved so they could seek funding for the project which aims to make Duntryleague more functional for staff and more accessible for guests to stay there.

He said the plans had the backing of Orange City Council and heritage architects after about five years of work by volunteers but it had still been refused.

"The council was very disappointed it didn't go through as planned," he said.

"The whole idea is to ensure we preserve the building and also the accessibility of the building not only for guests but for staff."

Mr Cook said a lift would aid staff carrying laundry baskets and equipment and help guests access the top floors. Currently they all have to use the stairs.

He said the lift would not impact on the heritage appearance of the interior.

Mr Cook said it would be based in an old toilet area on the ground floor, was in a store room on the first floor and in a bedroom on the top floor.

He said the rear of the building needed refurbishment to repair work done years ago.

"We were also going to bring the old verandah back that was out there. We found the original posts," he said.

Mr Cook said they were now looking for ways to resolve the situation and were preparing preliminary drawings for changes they hoped would satisfy heritage requirements.

"We've spent a lot of money on the project," he said.

"We've sent some draft plans down."

However, he said they needed to keep a check on spending so they would be submitting "some rough sketches" before getting new plans drawn up.

The plans were unveiled at a fundraising lunch at Duntryleague last August by leading heritage architect Ian Stapleton and heritage expert Maisy Stapleton.

Mr Stapleton's work in Sydney has included the re-design of the Sydney GPO and the Woolloomooloo finger wharf.

He said Duntryleague's heritage character would not be impacted by bringing the building up to date.

"We can get the lift in without spoiling anything original," he said.

"The lift makes it more attractive for people to stay. While people like to walk on the stairs, when you arrive and leave you need a lift for the luggage."