Building On Steep Sites
It is now common practice around the coast of Australia, and particularly in the Northern Beaches for new houses to be built on steep sites that a few decades ago would have been considered to be structurally and economically unviable.
In fact it was not uncommon for banks to refuse mortgages on these sites due to the Geotechnical risks.
Four major changes have occurred since those earlier days, so that these properties are now highly sought after.
The first major change is improved awareness of Geotechnical, Civil and Structural Engineering issues and construction techniques. Pittwater Council’s recently upgraded Landslip Hazard Policy was originally instigated by Warringah Council in response to numerous houses sliding down the slope in the early seventies, particularly in the Pittwater area. Since the introduction of that policy , a Geotech report has been mandatory on any site considered to be at risk. The Geotech Engineer is obliged to thoroughly analyse all risks associated with the site, including hazards further up the slope such as unstable boulders and slopes, failing retaining walls etc, and recommend the footing design for the house, and remedial action for the external hazards. Once the project has been completed, the site is often much more stable than it was in it’s natural state. The Geotech Engineer also plays a strategic role during construction, inspecting the site during excavation, and fine tuning his recommendations as required. More sophisticated and flexible excavation machinery has been developed by the construction industry in response to increased demand.
The second major change is increased land values. Steep sites that may have been worth $10 to $15,000 in the early seventies can now be worth millions, well and truly justifying the extra building costs. Most of these steep sites have spectacular views, and those views themselves have been increasingly valued by our society.
The third major change has been scarcity of land. The Northern Beaches has been recognised as one of the best places on the planet to live, and the amount of land available is geographically limited. Changing demographics and work practices mean that more people do not have to commute to the city, so the distance from the CBD is much less of an inhibiting factor. Predictably, the flat or moderately sloping sites were used up first, so with time, the only available vacant sites are the previously unwanted steep ones.
The fourth major change has been a revolution in Australian residential architecture. In the last 10 to 20 years, and particularly on the coast, there has been a general trend away from the brick and tile mentality, and cold climate architecture that resulted from our colonisation history. We are now designing, building and living in houses that suit our semi tropical climate, our informal outdoor lifestyle, and our iconic building materials, such as corrugated iron and weatherboards. This trend towards lightweight construction suits steep sites perfectly as the houses can be designed to be supported on strategically placed posts on concrete piers, rather than on the continuous and expensive footings needed for masonry, resulting in major cost savings.
It is essential when designing houses for these sites to incorporate large balconies, as there is generally no usable level garden area.
The resulting houses can be wonderful places to live, with excellent views, balconies amongst the tree tops, and little or no garden to maintain. The steep topography usually means 3, 4 or even 5 floor levels, so virtually all the rooms can take advantage of the views.