Hidden among the crowded lanes and expensive streets of South Melbourne lies three remarkable tiny houses.

But they're not the kind being lauded in modern-day design magazines or snapped up by hip young couples trying to get a foot in an out-of-reach property market.

In fact, these three homes are among the first permanent buildings in Melbourne, having been shipped from England in packing crates and rebuilt here to solve a housing crisis from another era.

The history of the original kit homes

In the 1850s Melbourne's population was booming. Prospectors were flocking in from around the globe en route to the goldfields.

The gold rush created a chronic housing shortage and also an exodus of skilled tradesmen from the city.

Enter kit homes — kind of like flat-pack furniture only for entire houses.

These prefabricated homes were built overseas then dismantled, every component labelled, loaded into packing crates, shipped and reassembled in all corners of the British Empire.

The Abercrombie house is transported from North Melbourne to South Melbourne. ( Supplied: National Trust )

Most were made of timber; about half came from Britain, and almost as many came from its colonies including Singapore.

A substantial number also came from the United States.

Some, including those still standing at 399 Coventry Street, South Melbourne, were made of iron.

Nearly all of these came from Britain, which at the time was in the grips of the Industrial Revolution.

National Trust assets coordinator Alyce McCue said it might seem like an inefficient process, but at the time it was the best way to erect mass housing in the new settlement.

"A lot of the ironwork that would have been produced in the UK couldn't have been done here," Ms McCue said.

"We didn't have the manufacturing industry present in order to do this, so it was a simple solution to get a complete packaged house."

The iron homes were freezing in winter and stifling in summer but they arrived at a time when most people in South Melbourne were living in tents.

They were the first type of semi-permanent housing in Melbourne.

The buildings may be rudimental but are an important part of Melbourne's history. ( ABC News: Nicole Mills )

Ms McCue said these basic homes, ordered from a catalogue, were part of a push to improve housing standards in the city.

In their day, they would have been considered quite luxurious.

"The sort of people that lived here, even though it seems a bit primitive to us now, they would have probably been middle class, so your administrative types, your clerks," Ms McCue said.

"This would have been quite a good way of living back in those times."

Escaping slum clearances, finding refuge

Only one of the three prefabricated homes still standing in South Melbourne was built on site.

The building facing the street is the original, which was built by Robert Patterson.

The other two, which are placed behind the Patterson house, were relocated to South Melbourne around the time of the slum clearances.

Portable iron houses in Patterson Place, South Melbourne, in 1966. ( Supplied: National Trust of Australia )

"They were brought over by the National Trust to save them from demolition in the 1960s and '70s period when we had slum clearances across many inner-Melbourne suburbs," Ms McCue said.

"They wouldn't have survived without the National Trust."

The Abercrombie house came from North Melbourne and the Bellhouse building was moved from Fitzroy.

Why bother saving these tiny, basic homes?

Ms McCue said the buildings might be rudimental but were an important part of Melbourne's development story.

"We're not just about looking after grand buildings, we're about looking after what's considered important or significant.

"It's two parts of [Melbourne's] development life: the gold rush period when you've got a great amount of people coming into Melbourne, and then also the slum clearance time when there's a lot of change in Melbourne as well, so it's representative of multiple periods."

The buildings themselves are also rare — the Bellhouse cottage is believed to be one of only two iron homes built by the manufacturer remaining in the world.

The other is at the royal estate at Balmoral in Scotland.

"That's of international significance," Ms McCue said.

National Trust Victoria chief executive Simon Ambrose said the houses were significant because they provided a glimpse of what early housing was like for many Victorians.

"They also demonstrate early prefabrication methods developed as a result of the Industrial Revolution that dramatically streamlined the process of building construction throughout Australia and the world," he said.

The Patterson house is in the best condition of the three iron houses. ( ABC News: Nicole Mills )

Volunteer property manager Justin Croft dedicates many hours to preserving and opening the buildings to the public.

He said they told a story of the earliest British occupation of the area known as Emerald Hill, which was later renamed South Melbourne.

"This important heritage place helps tell complex stories of the area, empire, political systems, global commerce, communication, industrial and transport networks, dispossession of the first peoples of the land, migrants and their aspirations.

"The iron houses are an intrinsically valuable place for all Victorians, but they also make an important contribution to the cultural life of inner-city Melbourne and the place is demonstrative of Melbourne's unique aesthetic architectural characteristics."

The need for repair

The three iron homes are in varying condition.

The Patterson house is in reasonable shape and is kitted out with simple furniture including beds in the two second-floor rooms, which are accessed by a steep and narrow wooden staircase.

The Bell house, which has been stripped back to its bare bones inside, needs some repairs, while the Abercrombie house is in dire need of work.

Alyce McCue says the Abercrombie house will undergo repairs later this year. ( ABC News: Nicole Mills )

Mr Ambrose said a Living Heritage Grant would allow the National Trust to complete conservation work both inside and outside the building.

The works will include exterior cladding repairs, treatment of corrosion, restumping, replacing the verandah floor and pinning back peeling wallpaper.

As part of the Australian Heritage Festival the homes will be open to the public on May 6 from 11:00am to 4:00pm. Entry fees apply.