Running out of space in your home? Solve it with a flat pack “instant” addition of a home studio, extra room, sleepout or granny flat.

A Sydney architect has come up with an easy-to-assemble “IMBY” – In My Back Yard – a prefabricated plywood cabin kit that is delivered flat-packed and ready to put together by owners or occupants.

“And you don’t even need an IKEA Allen key,” says its inventor Adriano Pupilli, who’s been trialling one at his own home on the south coast of NSW to provide an extra guest bedroom and home studio beside his small two-bedroom cottage. “It’s designed for easy DIY assembly with no real specific tools needed.

“There’s no nails or glue either; it’s just wedges that lock into each other in a Japanese-style of joinery, and you then just tap them in with a wooden mallet. You can then add extras or take them away, according to how much, or the kind of space you need.”

The kit models start at $9800 for a studio, $15,400 for a sleepout, $22,800 for a guest pavilion and $27,600 for a full bach, or basic holiday home.

The invention has been welcomed by housing affordability expert Adrian Pisarski, executive officer of National Shelter. “I think it’s helpful for a range of people to extend family living, or allowing teenagers to have some separate space,” he says.

“It could be a useful addition for many people, and it will also help to increase the density of middle-range suburbs which have good infrastructure, rather than pushing people into an endless suburban sprawl without it.”

Michael Lennon, director of Housing Choices Australia, is also enthusiastic, saying it’s great to see local innovation following global companies producing prefabricated housing. “We also know that the costs associated with moving are a major influence on housing prices and affordability, so the flexibility this gives householders is a great way to get better utilisation of existing housing,” he says.

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“People looking for that flexibility also provide planning authorities with the opportunity to consider the approvals required, and the necessary zonings.”

That’s because enormous confusion exists around whether such structures need planning permission. As long as they’re smaller than 20 square metres in area, under three metres in height, and are called a shed, then they probably won’t, says Mr Pupilli, director of the Manly-based Adriano Pupilli Architects.

If they’re termed a home studio or granny flat, on the other hand, yet are under 60 square metres, then they’ll probably be a complying development and can be fast-tracked through the planning system, advises Michelle Riepsamen, NSW and education executive officer of the Planning Institute Australia.

“Then the requirements aren’t as stringent as a development application, and such buildings are being used more and more in Sydney and can be a great solution to the need for extra space,” she says.

But the legislation is by no means clear on this point. “That’s the $64-million-dollar question,” says Max Fragar, principal consultant with Fragar Planning and Development. “There’s no easy answer on whether something is an exempt or complying development.

“I’ve been doing this for 52 years and I can’t answer the question because the legislators haven’t made it easy. It can depend on a range of factors, from size, distance to boundary, setback, what it’s going to be used for, whether it’s in a bushfire area.”

As for the buildings themselves, all standard IMBY kits include clear acrylic windows, plywood internal lining, Colorbond roofing and external cladding, bulk insulation to walls and roof, plywood flooring panels and doors, fold-down table and internal partitions as per the plans. Electrics and plumbing are extra, as are shipping, skylights, pop-out windows and decks.

“We strongly believe that the use of digital fabrication techniques such as those used in the IMBY Kit can bring architectural design within reach of the wider population,” says Mr Pupilli.

“And when the occupant’s needs change, simple screw pile foundations and interlocking parts mean that the kit can be re-configured, relocated or flat packed and placed in storage. I personally love this notion of being able to easily assemble, with no special skills, a small structure that’s cost-effective, has a small footprint and can be changed along with a family’s needs.”