LINED up in frilly hats, starched aprons and smart jackets, Frank Green’s servants look the picture of domesticity outside Treasurer’s House in 1920.

This photograph would have been consigned to the history books had Mr Green not given his house and antiques collection to the National Trust.

By the time he did so, in 1930, he had turned the “bug-ridden slum” into a magnificent house, tended by at least 12 staff.

Nothing is known about these employees – apart from their names – but they are likely to have slept in the attic rooms that will be open to the public for the first time from tomorrow.

The collection of narrow rooms and peeling, decaying walls have not been used since the 1920s, apart from as storage by the National Trust.

There is no furniture and the walls are in mid decay. Nothing has been roped off, and it is a fascinating to walk around.

“We decided to leave it as it was, as this amazing time capsule that hasn’t been touched for 80 years, taking nothing away,” says Louise Horsfield, visitor services manager.

“You can tell quite a lot about it just be being here though, it’s quite atmospheric, and there are plenty of things to see.”

Although some of the walls have been strengthened, visitors must wear hard hats in case of any dust or small bits of debris.

There are low ceilings, old fireplaces, a space where a lift would have been and also where the staircase was, which enabled staff to walk from the attic to the basement, where they usually worked, without being seen.

Among the staff who may have lived here was Monsieur Viande, the chef, who causes mirth among visitors as “Viande” means meat in French, translating literally as “Mr Meat”. Alongside him were kitchen maid Miss Smith, housekeeper Miss Jackson and Miss Cliff, who became the first custodians of Treasurer’s House when it was handed to the National Trust, and Mr Harvey, the chauffeur.

All that is left of their presence are some rusty fireplaces, an old fire extinguisher and a set of servants’ bells.

Tour guides will share stories with visitors, but just being in the attics conjures images of how life could have been.

“We don’t ham it up, we just use really good storytelling and people can use their imagination to think what it must have been like,” says Jane Whitehead, property manager. “We don’t know much about the staff, but generally they will have worked in the basement and slept in the attic.

“They probably won’t have married, and they will have been quite poorly paid.”

From what the National Trust knows about Frank Green, however, his staff were well looked after.

Mr Green was a bachelor whose family made their fortune in a factory in Wakefield.

Accounts suggest he was a kind and generous man, whose forward thinking saw him installing fire protection units around his house and paying meticulous attention to detail to protect his house and collection. He even imposed a condition when the National Trust took over, that it maintain the fire equipment and check it each year.

He was extremely particular, too.

“Frank Green had particular ways about him,” said Jane. “He wrote notes all over the house about how workmen must wear slippers and about shutting the door.

“He was a very dapper man, too, and had his laundry done in London. It wasn’t enough to have it done here in York.”

He was a gentleman of leisure, and spent his time hunting and entertaining guests and sourcing antiques for his collection.

Documentation about the attic is scarce, bar a plan from a Royal Visit in 1900, which shows where Prince Edward’s entourage slept.

There are some things visitors can gauge for themselves, however.

Walking up the steps and across the walking parapet on the roof to the attic is a tight squeeze; the doorways are low and the walkway is high.

An old fire extinguisher on the wall and some central heating pipes indicate that Mr Green looked after his staff well, says Jane.

He at least wanted them to be safe and warm. They would probably have had simple furniture and not much of it. Some rooms would have been more like a dormitory.

We stand in one of the partitions – which Mr Green probably built to ensure his staff more privacy – examining the row of faces on the photograph; Mr Green in a smart coat and bowler hat, and his loyal servants. Then we take a look out of the window at the magnificent view of York Minster.

“A lot of our work is about piecing information together and we are always doing that,” says Jane. “But if I was a servant and lived here and had a room overlooking a view like that, I would have been quite happy.”

•Treasurer’s House is open daily, apart from Fridays, between 11am and 4.30pm and admission charges apply. Tours will be taken around the attic daily, last between 45 and 50 minutes and cost £3.20. It is unsuitable for children aged ten and under and visitors will have to wear hard hats. Other new attractions include an exhibition on rugs, wall hangings, cushions, bags and brooches, created by the Ebor Rag Ruggers. There will be rag-rugging demonstrations too. For more information, phone 01904 624247 or log on to nationaltrust.org.uk/main/w-treasurershouseyork