The ‘tree house’ design that could lead to more greenery in Australia’s drying suburbs

A new subdivision described as an “adult tree house” crossed with “Noah’s Ark” is hoped to become a blueprint for developing property without razing the land of all its trees. 

New planning laws to prevent tree loss on private land coming into effect in Western Australia mean innovative designs like this will need to be considered.

Nestled in the backstreets of Hamilton Hill in Perth’s southern suburbs, the 800-square metre block has been split into four titles containing a two storey apartment, a granny flat, stand-alone office and main house.

And most importantly to its developer, 40 trees including a 25-metre tall Jacaranda tree, get to stay. 

“People feel the only way they can capitalise on a zoning change is to knock everything down and then just put apartments there or units and townhouses,” developer Chris Ferreira said.

A tree house covered in greenery
The tree house project has been described by some as having a “Noah’s Ark” look about it.(ABC News: Tyne Logan)

“But the urban forest is so precious and it’s such an important part of what makes our community liveable.

“It gets sacrificed because that’s the only way we can do infill.”

New planning laws limit tree clearing

As Perth’s population swells, infill and green-fill developments have been crucial, but concerns have been raised over the rampant clearing required.

A row of houses on a suburban street
Dayton in Perth’s northern suburbs is densely packed with houses and very few large trees. (ABC News: Phil Hemingway)

Data has shown Perth’s tree canopy is the lowest of all capital Australian cities.

In a bid to buck the trend, the state government has introduced new planning laws for residential areas. 

Planning minister Rita Saffioti admitted existing laws had been inadequate for tree retention.

Rita Saffioti mid-sentence while speaking to a journalist.
Rita Saffioti says the government is trying to reverse the trend that had seen trees disappear from the suburbs. (ABC News: Keane Bourke)

“We need to have more infill and more density,” she said.

“But in many developments of the past, you can see the entire block is either roof cover or paving. This is aimed at removing that.”

A satellite image of Nollamara in 2000 / A satellite image of Nollamara in 2022.

The new medium density codes include “minimum tree requirements” for each block which vary based on the number of houses on a block and the block size.

Dwelling

Tree requirement

Single house 

1 small tree

Grouped dwellings

1 small tree or

2 small trees where primary garden area is reduced

Multiple 

Dwellings 

1 medium tree and 2 small trees on sites less than 700sqm

2 medium trees or 1 large tree and 1 small tree on sites of 700 to 1000sqm

2 medium trees or 1 large tree and 1 small tree in addition to 1 medium tree per 400sqm in excess of 1000sqm – or part thereof – for sites greater than 1000sqm

In addition, 15 per cent of a site must be allocated to “soft landscaping”, such as grass.

As an incentive, that area is reduced to 10 per cent if a significant existing tree is kept.

A giant tree pictured in front of a house
St Leonards Avenue in West Leederville has plenty of canopy. (ABC News: Glyn Jones)

“We need more canopy to ensure there’s more shade, cooler suburbs and also places for animals and birds,” Ms Saffioti said. 

Trees play role in cooling environment

Up until now, there have been very few planning laws like it in Western Australia, apart from those imposed by individual local governments.

Environmental geographer Bryan Boruff, from the University of Western Australia, said trees played a significant role in cooling the environment — an aspect particularly important in a warming, drying climate.

A blad man wearing a shirt leans against a limestone wall smiling.
Bryan Boruff says trees are particularly important in a warming, drying climate.(Supplied)

“It really can make a dramatic impact, particularly when we start increasing the human-made materials in our neighbourhoods,” Dr Boruff said.

“The more human-made materials that we have, the greater the chance of those absorbing and remitting that heat and that increases the overall temperatures of our neighbourhoods overall. 

“That’s the storied urban heat island effect.”

A silhouette of a man as he looks at a tree house through trees
Chris Ferreira admiring his tree house-like creation. (ABC News: Tyne Logan)

Research from Macquarie University from 2020 found tree canopy could make up to six degrees difference on days of extreme heat.

Some ‘trade-offs’ when keeping trees

Mr Ferreira said the Hamilton Hill subdivision – dubbed ‘The Forever Project’ — was a “passion” designed to test whether you could strike the balance of new housing with tree retention, while still remaining profitable.

“These are as profitable as any other style of development because these will sell at a premium,” he said.

But the design hasn’t been without some trade-offs.

A man leaning over a desk with a sketch in front of him
The Forever Project architect Matt Wallwork says the car park needed to be moved to accommodate trees.(ABC News: Tyne Logan)

Architect Matt Wallwork said moving the carpark was crucial to retaining the trees on the property.

“They’re actually out the front of the property and you walk down to your residence,” he said.

Town planner Melinda Marshall said the cost per square metre was also likely to higher, but not the cost of the overall development.

Two hands touch a piece of paper laid on a desk
The project was designed to test whether a balance could be struck between new housing tree retention and profitability.(ABC News: Tyne Logan)

“In order to fit the same amount of dwellings on the property, but also keep the trees and more open space, you either have to go up to two storeys, which will cost more in construction or build smaller,” she said.

“So rather than a three or four bedroom house, you’re building a two bedroom house.”

A woman standing in a garden
Town planner Melinda Marshall says the cost per square metre is likely to higher, but not the overall  cost of the development.(ABC News: Tyne Logan)

But she said that was suited to market needs.

“The majority of households now are one or two people, yet we still keep on building three and four bedroom homes,” she said.

“We’re not building the homes that we need, developers are building the homes that are making the most profit.”

New codes widely supported

The codes have been widely supported, including by local governments, the WA Master Builders Association and the Urban Development Institute of Australia.

City of Stirling Mayor Mark Irwin said he hoped the new planning laws would address what felt like a losing battle between public planting and private clearing.

A man standing next to a tree
City of Stirling Mayor Mark Irwin says council planted 130 hectares of trees on city-owned land over seven years, but it wasn’t enough to make up for the number of trees lost to development over that time.(ABC News: Jon Sambell)

“We’ve planted 130 hectares of trees on city owned land over the last seven years,” he said.

“Across that same period of time we’ve seen 135 hectares of land cleared on private land, through development.

“So it’s a net loss.”

A treeless street with parked cars under a blazing sun in suburban Perth.
There are concerns about the declining tree canopy in suburban Perth, especially in newer suburbs. (ABC News: Phil Hemingway)

But, like many others, he said the new laws were not a silver bullet.

Mr Irwin said local government, developers and the community all needed to reflect on their own role.

“People know that trees bring shade, they provide amenity, they increase value of streets,” he said.

“But when you try to plant trees in front of people’s houses, and it’s going to affect where they park their car or drop leaves into people’s gutters, it creates issues and complaints for us.

A leafy street pictured down the middle
Trees can make a difference of up to six degrees Celsius on days of extreme heat. (ABC News: Glynn Jones)

“I think we’ve seen a ramping up of efforts.

“But we’re a long way off people accepting they’re going to have to retain trees on private property.”

The WALGA has asked the state government for $20 million in the next budget to expand the Urban Forest Grant Program, which would focus on tree planting in areas of low canopy cover and increased exposure to heat.

An aerial image of Perth suburbs
Perth has the lowest tree canopy of all Australian capital cities. (ABC News: Kenith Png)

The WA Tree Canopy Advocates group also wants the state government to set a target for tree canopy in Perth, similar to that in the City of Sydney.

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