While some offer parking for up to 14 cars, these underground havens aren't just garages. They're wine cellars, gyms, theatres and car showrooms too.

For a "particular" group of buyers, basements are high on the checklist, real estate agent Michael Lyristakis of Berkely Residential said.

It can add substantial value to a home, Mr Lyristakis said, so it's often a case of "if they're going to build a basement, build it big".

"It's a no-brainer in our mind that you give your buyer as much space as they can possibly have."

Berkely Residential is selling a home in Griffith that could have one of the most extravagant basements in Canberra.

The sub-floor level was built as a "showpiece" for the owner and a place to house his extensive wine collection, Mr Lyristakis said.

Accessible via a lift, the basement in the Landsborough Street house includes a large wine cellar with room for more than 2000 wine bottles and a tasting table.

Next to that, there's a cinema room, gym and parking space for up to 10 cars. There's even a showroom space to display the owner's favourite car (a Ferrari features in the listing photos).

On the same street is a home with a similarly extravagant basement, with parking for 14 cars. It sold for $6 million in June.

Basements have become big business for Dean Papas, a local builder who started his career working on commercial buildings.

Over the last five years, Mr Papas has seen demand grow for homes "built to a commercial standard" in terms of their size and concrete structure.

With that comes a desire for basements, allowing clients to increase the size of their house without sacrificing land, he said.

"Rather than putting in a four-car garage which is going to take up their pool and backyard space, they put it underground," Mr Papas said.

But these aren't your run-of-the-mill new homes.

Construction of a basement level can cost anywhere between $250,000 and $450,000 depending on the size, Mr Papas said.

"We roughly work off about $1300 a square metre for a basement and that includes the slabs, the walls, the excavation," he said.

"When you're in the realm of $2 million-plus [house builds], that's usually your basement clients."

Registered architect Paul Tilse said there is "quite a push for more and more car storage" from clients who also don't want a house that looks "massive".

"We're certainly getting a lot more people asking for basements," he said.

"They can have all that area but then it doesn't look like they've overdeveloped on the block."

Aside from in ultra-modern homes, the basement movement is making its way into Canberra's heritage areas as a savvy workaround to plot ratio limits.

In the heritage housing precinct in Reid, where Mr Papas has two house builds under way, the maximum roof coverage area is 27.5 per cent.

The heritage register also stipulates no more than a double garage, with doors the width of a single car, can be visible from the street.

By putting it underground, the garage becomes invisible from the street, Mr Papas said.

"It ticks that box but also gives the amenity of having storage without losing the roof coverage area," he said.

Going underground is the "only opportunity to get more space" in a heritage precinct, Mr Tilse said.

For that reason, owners of heritage homes are also looking at ways to create liveable spaces in their basements.

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One of Mr Tilse's projects in the Griffith heritage precinct has a basement that won't be used for car parking at all. Instead there will a gym, study and a bedroom.

"By putting a light well down through the house, you can actually get lots of light and a garden down on a lower level," he said.

"It makes quite a lot of sense for heritage projects."

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