Just think of the cleaning.

"Big is good!" announces the ad for a 505m² home in Bunnythorpe, Manawatu. That's five bedrooms and five bathrooms to scrub and vacuum.

"All the hard work is done," promises a brand new, 475m² home in Canterbury's West Melton. With five double bedrooms, three lounges and separate dining space, more likely the work has only just begun.

And what about the 455m² of "space galore" in Wellington's Churton Park with the latest must-have – an eight-seat cinema, complete with recliner chairs.

Big is good has been a cultural mantra for Kiwis when building houses, with the average new standalone house swelling from 153m² in 1991 to 209m² today. That puts us among the most space-hungry builders in the world, behind Australia and the United States. And all while families and households are shrinking.

But with a housing affordability crisis and growing concerns about sustainability, critics are questioning the ever-ballooning Kiwi home. And there are signs the tide may be turning.

"Why do you want to talk to us?" asks architect Tomek Piatek. "Our house isn't that small."

He's right – at 89m², their 1900s bungalow in the Wellington suburb of Newtown is similar to the 98m² three-bedroom state houses that dotted the country from the 1930s to the 1980s. But by today's standards the home he shares with his wife and twin 6-year-olds is positively teeny.

The couple have modernised, knocking out a wall between the kitchen and lounge to open the living area, adding a folding ladder to the ceiling space to create long-term storage and building wall-to-wall, floor-to-ceiling closets in each of the three bedrooms, faced with recycled floorboards so they resemble a false wall.

It's not just the space, it's how you use it. Tomek and Nada Piatek live with their 6-year-old twins Rio and Mila in an 89m² bungalow. PHOTO: ROBERT KITCHIN/STUFF

Twins Rio and Mila each occupy one side of their bedroom, with shared Snakes-and-Ladders playing space in between.

The Piateks have been here since the twins were babies, and mostly love it. Having grown up in a family of four squeezed into a 54m² apartment in Poland, Tomek is used to small living.

Nothing has a single purpose – the dining table is for eating, entertaining, puzzles and the kids' homework. The third bedroom is a study but when visitors stay, mattresses emerge from the gigantic closet.

He's repulsed by redundant space – the dedicated home theatre used for 2-3 hours a week.

"Having a guest room that's unused for 95 per cent of the year – that's incredibly wasteful. There are people sleeping in the street."

Nada grew up in a big family home. They'd heat one room and scurry down the hall to turn on heaters 10 minutes before bed. Here, the space is small enough to leave doors open to economically heat all the rooms.

But there are challenges. The guest room abuts the lounge so there's nowhere for Nada's noise-sensitive mother to escape talking, television and noisy kids. And the bathroom goes off the kitchen, so embarrassing noises are heard by all.

It also changes the way you think about spaces, says Nada, who works for Sustainability Trust. While she reads in her bedroom, her mother finds that strange – because in her world bedrooms are not "doing things rooms".

Mila likes sharing her bedroom with her brother. Except when she doesn't. When the pair hit their teens, the Piateks expect they'll need their own rooms. But for now, it doesn't cramp their style.

"We're quite loud, vivacious people," Tomek says. "We don't just scurry away doing our things. We sing and dance in here and we do all kinds of crazy things."

In 2016, plans were consented for 12 new houses with a floor area larger than 800m² – that's almost ⅔ of an Olympic pool. Seven were in Auckland, two in Christchurch, and one each in the Far North, Bay of Plenty and Hastings. The area may include pool houses or boatsheds. Wellington's largest house consent for 2016 stretched to 460m².

Pinpointing just when and why the big house love affair began is tricky. House sizes have grown steadily since records began in 1974, with a brief flattening off in the 1980s.

It certainly wasn't to accommodate bigger families. Fertility peaked in 1961, at 4.3 children per family. Since 1980, it's hovered around two children per family.

Household size has also fallen, from five people at the start of the 20th century, to 2.7 today. And with more split families and retirees living longer, that's expected to fall still further. At the same time, housing affordability has plummeted.

So it sounds like a no-brainer to build smaller, cheaper houses, right?

It's not quite that simple, says Alan Wood, A1 Homes Kapiti, Horowhenua and Manawatu franchisee.

They're at the more affordable end of the custom-build market, so probably build smaller-than-average homes, with one option measuring just 50m².

"For us, our average-sized house would be 170, 180 square metres, whereas 10 years ago it might have been 100 to 120."

Why? Wood laughs. Greed; rising land prices; subdivision rules; and the perverse incentives created by quoting building prices per square metre.

Let's start with rising land prices. If you're paying $250,000 just for the section, buyers and developers – and their banks – want to build a bigger, better home to ensure an attractive resale package, Wood says.

Making smaller houses more economic would require smaller, cheaper sections.

Subdivisions also often specify a minimum build size, which increases with the site's status. In Tauranga's The Lakes development, most sites have a 100m² or 120m² minimum size (excluding garages), but lakeside homes must be at least 140m².

In Porirua's Aotea subdivision, most lots have a 130m² minimum, but the premium Baxter's Knob covenant specifies nothing smaller than 150m². The subtext is obvious – a crappy little house will lower the tone of our neighbourhood.

That obviously affects house affordability. In Otaki, where you can buy a section for $170,000 with no house size stipulation, Wood can get a first-home buyer in for $450,000. But in Kapiti, where it's more like $280,000 for a section and a 170m² minimum, prices quickly blow out.

One of the biggest motivations for building bigger, Wood says, is perceived value for money. Small houses cost more, per square metre, because the expensive bits – bathrooms, kitchen, site costs – are divided by a smaller number. But they still cost less overall.

Rene Genet, business development manager at David Reid Homes, says expectations have changed. Sizes have dipped since 2009, but 200+ m² homes remain very common. Even first-home buyers want four bedrooms, an ensuite, separate media room and double garage.

Building consent figures show the region building the biggest houses is also the region with the worst housing crisis – Auckland. Consents for new standalone houses averaged 235m² in 2016, compared with 175m² on the West Coast.

Wood agrees societal norms have shifted. No-one wants to get wet taking the groceries from the car to the house, they expect internal garaging.

"To protect your investment and get a return, you have to build something similar to what the neighbour's building. Otherwise it's the worst house in the best street."

If people want – and can afford – mansions, surely that's their right? Absolutely, agrees Helen Viggers. As long as they can afford to heat them to a healthy standard.

While most people seemed to think ballooning houses were a good thing, Viggers, an Otago University health researcher, wondered about the bleed of warmth in a bigger space. But even she was staggered by what she found.

In a paper in May, she revealed that increasing size had effectively eliminated 40 years of gains in energy efficiency through insulation and technology. In other words, an average 2017 house built to code uses the same amount of energy as an average 1970s house built to code.

If the extra space was doubly useful, that might be a reasonable tradeoff, Viggers says. But most modern houses have the same number of bedrooms as their 1970s counterparts, with maybe an extra ensuite bathroom. Large families still need large houses – but with more bedrooms, not the same number of super-sized bedrooms.

"What is the point, on a societal level, of building a massive house which we're not willing to heat or live in during winter? ... The families moving into these new houses – it might be fine for them, they are rich enough to be buying a new house. But the point is 10 or 20 years down the track, other people are going to move in. It's about thinking as a society – what kind of legacy are the houses we're building now going to be for the future?"

That's something Wellington architecture firm First Light Studio has been considering. "Bigger is not necessarily better, it's just bigger," says the blurb for the award-winning 100m², solar First Light Home which the firm designed as architectural students.

Architect Ben Jagersma has just come back from a year in Amsterdam, where he and his fiancee lived in a 40m² apartment. It's a lifestyle change, he says. You have to think about what you buy. Shop as you need, rather than in bulk. And treat city parks as your back yard.

And small design also needs to be thoughtful – considered spaces, clever storage, built-in joinery. But they're still hamstrung by bang for your buck – the average small-build cost is expensive at $3500-$4000 per square metre. "It's just a maths thing" – dividing the expensive essentials by a smaller number, Jagersma says.

Tucked among the gracious villas of upmarket Seatoun, Christeen McKenzie's 84m² First Light home stands out both for its striking design and small stature. But inside, it feels far from mean, which is why it won the 2017 Wellington Architecture Award for best small project.

The kitchen and lounge ceiling rises to a high gable, giving a sense of space, while the ceilings of the two bedrooms are lower for ease of heating. It's an easy arm stretch between dishwasher and cupboards, but there's still room for granddaughter Rachel to draw and play. McKenzie had five adults and three kids for lunch the other day; eleven for Christmas Day.

McKenzie is retired and has downsized from a family home with swimming pool in Napier. She looked in horror at big houses – all that cleaning. And a small house was a licence to offload those wedding presents she'd never used but felt obliged to keep.

Now, everything is either useful, or beloved. "It forces you to justify what you have."

First Light is also building a 160m² house for a family of six – soon to be seven – in the South Island. With his $600,000 budget, owner Joseph preferred to go "small and good", rather than "big and crap".

With three bedrooms, one with the ability to split into two as the kids get older, the constrained space will probably mean more fights. But it also promises "more moments and opportunities to create memories".

"When you have a family with kids, they're only here for a certain amount of time. Do you really want them to be stuck up in their rooms all day long or be in their own living room or their own private space all day?

"Or do you want to increase the chances of interaction and try to actually build bonds with them while they're there for that limited window, before they go off and live their life."

Michael O'Sullivan's 112m² home was ample when his four children were young. They added 30m² of personal sleeping spaces when the kids got older. PHOTO: JOHN SELKIRK/STUFF

The other day "some egg" told Michael O'Sullivan the minimum size for a child's bedroom should be 4m x 4m. He laughed. The Auckland architect designed his 112m2 home in 2008, with his four young kids sharing a room.

As the kids became teens they added "D Block" – an extra 30m², including three 2.4m wide sleeping spaces. For context, the still-in-force 1947 housing regulations stipulate a minimum bedroom width of 1.8m.

Like Tomek, O'Sullivan insists the place is not small. "It's highly appropriate. Anything bigger would be just grotesque, wasted."

And it hasn't hurt the kids. The eldest has now left home, and the three others bunk down in their old shared room as a school holiday treat. "We survived," he laughs. "I've still got both my arms and both my legs. I'm not in jail. We spend more time laughing than crying."

He's appalled at the "horrific" mansions popping up in exclusive spots such as Jack's Point, near Queenstown. They conflate size and beauty, he says.

"It's the same reason why people are indulging in really excessive desserts after dinner, there's no difference. Pure, unadulterated greed and indulgence."