The balance of hard cover and soft cover on your site shapes stormwater, heat and the long-term liveability of your home.

In this episode, I share how to think about the sustainability of your landscape design in terms of hard and soft cover, what your council may already require, and the options worth considering when hard surfaces are required functionally.

Listen to the episode now.

Hello! This is Episode 434. This is Way #34 of the 44 Ways to Create Your Sustainable Home series, and we’re continuing through Section Seven: A Sustainable Site: Landscape Design.

Way #34 is: Soft Cover vs Hard Cover.

As we build with greater density in our suburbs and urban locations, we increase the amount of hard cover, or hard surfaces. Concrete, paving, and other hard cover surfaces prevent water during rain periods and general overland flow from being able to enter locally back into ground water, restoring the water table. 

Instead, water runs over these surfaces, and into stormwater systems, potentially overloading them (especially during heavy rain periods) and taking potential pollutants as well as soil and silt with it from these surfaces.

These hard surfaces also absorb heat, and contribute to higher temperatures in higher density areas through something known as the urban heat island effect.

When you’re considering the landscape design of your project, you’ll be working with a combination of planting, soft cover and hard cover, or hardscape.

Hard cover is any impervious surface on your site: concrete slabs, concrete or bitumen driveways, paved or tiled terraces, and of course the building footprint itself. These surfaces do not allow water to pass through them into the ground. When it rains, water that lands on hard cover will run off the surface, picking up speed, temperature, and whatever is sitting on top of the surface as it travels.

Soft cover is everything that isn’t hard cover. This includes lawn, garden beds, planted areas, trees, mulched zones, and the open soil between them. These surfaces absorb water, and allow water to slow down, filter through, and return to the ground, and into the water table.

When it comes to your site, you actually have a responsibility to manage the stormwater that it generates.

This means any rain that falls on your site, and any water that then flows over the ground, should be contained and dealt with on your site, so it doesn’t negatively impact your neighbours.

The stormwater system in most Australian suburbs was designed for a specific rainfall intensity and runoff volume. And as climate change has increased the severity of rain events, stormwater systems have struggled to keep up and it can be common, especially in certain suburbs or areas of suburbs, for stormwater systems to back up during storm events, and for flooding to occur.

There’s also the water quality issue. Hard surfaces don’t just redirect water, they collect what’s sitting on them: oil from driveways, heavy metals from tyre wear on roads, fertilisers and pesticides from garden chemicals, sediment, and other pollutants. All of this gets washed into the stormwater system and eventually into waterways. Unlike the sewage system, stormwater typically flows untreated to its end destination.

Hard surfaces can absorb solar radiation during the day and re-radiate it as heat at night, especially when they’re dark in colour.

This is urban heat island effect: urban areas are measurably hotter than surrounding rural areas, largely due to the proportion of hard cover and the lack of vegetation.

Soft cover, or planted areas, can reduce the radiant heat load in areas like this. 

Also, the additional shade provided by planting, the improvement of water management and water retention where it’s needed, and the impact on lower air temperatures and moisture levels, contributes to improve the way these areas feel.

Many local councils in Australia have controls on the proportion of hard cover allowed on a residential site. These might appear in a Development Control Plan as a maximum site coverage, an impervious surface limit, a deep soil zone requirement, a minimum landscape area, or some combination of these.

Lawn is the most obvious soft cover, but it’s not the only one and not always the best one. Garden beds with deep soil and good organic mulch perform well as soft cover. The mulch slows evaporation, keeps the soil below it cooler, suppresses weeds, and allows rain to penetrate rather than run off.

Trees are worth thinking about separately from ground-level planting, because their contribution to the site extends beyond the area of ground they occupy. A tree’s canopy intercepts rainfall before it reaches the ground, releasing it more slowly. The canopy also shades the ground beneath it, dramatically reducing surface temperature. And tree roots create channels through which water can move into the soil. A single mature tree is doing a lot of sustainability work on a site.

Permeable paving allows water to pass through the surface and into the ground below, rather than running off. 

Options include concrete or asphalt specifically manufactured with a porous structure, pavers laid with open-jointed gravel or planting between them, gravel and decomposed granite, as well as reinforced grass areas that have a structural substrate under them that holds the soil and turf together.

There’s also other large planes of hard surfaces that are shedding water and could be considered differently. 

This is where roof gardens, and planter beds for balconies or terraces can come into play in a design. 

They’re less mainstream in standard residential construction, however I’m definitely seeing people consider them, especially in denser areas where the overall footprint of their home and block is compact.

In this Episode, I cover:

• What hard cover and soft cover actually are, and why the balance between them matters more than most homeowners realise
• Why you have a responsibility to manage stormwater on your own site
• The water quality issue: what hard surfaces collect and transport into waterways untreated
• The urban heat island effect and how hard cover around your own home fights the passive cooling you’ve designed in
• How councils are using heat mapping and tree planting to manage temperatures at a city scale
• The council controls you can expect: site coverage, impervious surface limits, deep soil zones, minimum landscape area, and tree protection
• Why lawn isn’t always the best soft cover, and when drought-tolerant or no-mow alternatives make sense
• Why a single mature tree does a lot of sustainability work, and where to put trees early in the design
• Permeable paving options, including porous concrete / asphalt, open-jointed pavers, gravel and reinforced grass
• Roof gardens, planter beds and the approaches available to you
• How to treat the surround of your home with pathways that enable visibility and protection,

Plus a whole lot more.

LISTEN TO THE EPISODE NOW.

RESOURCES:

44 Ways #32, on designing your outdoor room >>> Design Your Outdoor Room

Season 4 Episode 6, on what a landscape architect does, with Luke Jones >>> Landscape Architect

Season 4 Episode 10, on what a landscape designer does, with Sticks and Stones >>> Landscape Designer

Episode 264 with Emilio Fuscaldo, Nest Architects >>> Green Roofs

Western Sydney University news article on urban heat in Western Sydney and the research projects working to cool the region >>> Western Sydney’s overheating urban regions

Sydney business offering sustainable small space gardening products, including waterpot ollas and grow bags >>> Up On The Rooftop

Up On The Rooftop on Instagram >>> @up_on_the_rooftop

Joost Bakker’s roof garden setup >>> Instagram reel

A free guide to simplifying sustainability across research, planning, design, materials, and building, from Amelia Lee’s 30+ years in residential design and construction >>> 44 Ways to Create a Sustainable Home

Access the support and guidance you need to be confident and empowered when renovating and building your family home inside my signature online program >>> HOME Method