Major challenges of building on sloping land
There are a number of contributing factors that affect the complexity of building on a slope:
The gradient – A gradient incline rating of less than 10% is considered slight and is the easiest to build on, while 11-20% is considered moderate and anything above 20% is considered steep. Beyond about a 15% gradient, costs begin to increase significantly as the risks become greater and the construction becomes more difficult.
Upslope or downslope orientation – An upslope plot – where the front of the house rises up to the back – is more challenging than a downslope plot. These types of plots usually require some amount of cutting or even blasting, plus transporting and disposing of rocks and soil.
Drainage and sewage – Proper attention to drainage for both surface and subsurface water, is absolutely crucial. It’s important that rainfall is redirected away from the foundations of the property without flooding any public areas or neighbours. The sewage system must be set up properly, and if the line is uphill, may require a pump, and if downhill, may require tumble bays to slow the flow to a reasonable rate.
Access to the house – Properties situated in unusual locations can be challenging to create access to both while building and once the house is occupied. Switchback and curved driveways are useful and attractive, but small properties may have no choice but to install a steep driveway that can be hazardous in inclement weather.
Soil type – The type of soil can be easily overlooked as an issue but this too can pose a problem. While granular soils (gravel, sand, or silt with little or no clay) drain well and can bear high loads, soils with high clay, do neither very well. Certain clays can damage foundations by swelling or expanding when wet or frozen and may require expensive engineering fixes or additional fill of granular soil.
Building approaches on a sloped site
It’s not uncommon to see two or more building strategies used to ensure maximum advantage of the site is taken, rather than only levelling off the grade to build the house. When it comes to building on a sloped site, four methods are most commonly used and a good design concept could include one or more of these strategies:
- Sitting the house on the ground is the most traditional and straightforward approach and is also one of the easiest and most economical construction methods as it minimizes excavation and foundation costs, provided there is not a lot of site grading required to level off the earth.
- Embedding the house into the ground helps to integrate it better with the land and is more responsive to the terrain. It can sit lower to the ground in a reverse floor plan where the main public spaces are on the upper level (where the front entrance may be) and the private bedroom spaces are on the lower level that is buried in the hillside. This low-slung appearance minimizes the massing of the home as seen from the road or from elevations and offers the best view in the main living spaces because they are higher up in the house. However, with this approach comes with increased excavation and foundation costs.
- Floating the house above the ground raises the house on supports, whether on stilts, columns, or solid walls. The benefit of this approach is minimized site disturbance and a smaller footprint. This can be especially important when trying to navigate large tree root structures, bedrock, or steep slopes. It is also possible to see under the house clear through to the other side of the site depending on the floor plan, which is another way of connecting with the site visually.
- Sticking out over the slope or cantilevering the home, allows part of the home to be anchored to the site and the other half to extent out over the terrain. This creates dramatic overlooks and surrounding views for an immersive experience. However, it does come at a cost with the structural implications but this approach can also minimize site disturbance and help avoid significant foundation expenses.
Make use of experts
Building on a sloping site has its pros and cons and a thorough site analysis from experts is vital in order to get an accurate view of the cost of the project and how the home might be designed so that it will work with the land. Employ experts with experience to ensure the best possible outcome and make use of the best quality products to build a house that will last for decades. For expert advice, contact the Sephaku call centre on 0861 32 42 52 or speak to your technical representative for more information.