Building on the side of a hill has always been an attractive prospect for builders, architects and homeowners alike. Why? Aside from the spectacular views, hillside builds represent the ultimate challenge. For builders and architects, building on a slope brings a unique opportunity to excel at their craft and be creative in a way that standard flat site builds don’t allow for. And for homeowners, the chance to tailor the build in ways that better express their individual personalities.
Understandably building on a slope is not quite as straightforward as building on a standard flat site. The build process is far more complicated, and each site faces its own unique challenges. But, being aware of how hard it is to build on a slope will ensure the rewards are worth the extra effort!
In New Zealand, several construction methods are commonly used when building a house on a sloped section. These are discussed below.
Building on a slope also provides a unique setting for the most innovative design. Housing is tailored to the landscape, and every home is different – there are no cookie-cutter designs on the hill! This is why hillside suburbs are often some of the most sought after places to build or buy a house. Check out some more of the benefits of building on a slope below.
There are two types of hillside builds – an upslope where the house rises up away from the road, and a downslope where the house follows the slope downward away from the road. Both of these offer slightly different challenges, however, overall, it comes down to the gradient of the slope. Less than 10% incline is considered the easiest to build on. Anywhere between 10-20% is considered a moderate slope, with anything over 20% considered steep. As the gradient increases, so do the associated costs. Some of the additional challenges associated with hillside builds are:
The cost of the complex foundation systems will always add to the price of hillside houses. This is because they typically require more materials like concrete and reinforcing and timber, more research, more excavation, more labour, and more time.
Proper attention to drainage for both surface and subsurface water is one of the most important factors to consider when building on a slope. Runoff from rainfall needs to be collected to avoid runoff to neighbouring properties. In many locations this will require use of a stormwater storage tank so that older council infrastructure isn’t overwhelmed by rainwater collected by the increasing number of houses being built around the Port Hills. Retaining walls also need adequate drainage to prevent water from pooling and undermining their structural integrity. On the other hand, sewage may need to be pumped upward or have its flow restricted downward depending on the building location in relation to the sewerage connections.
Getting building materials, trucks and contractors on site is also an essential aspect of hillside builds. Even flat sections can become muddy and difficult to access after the slightest bit of rain; sloped sections are much more difficult to access even in drier weather. Additional site works may be required just to provide the necessary access for cranes, concrete trucks, infill trucks, subcontractors etc. which may then need to be reversed or corrected once the build is complete.
The type of soil you are building on can affect any build situation in New Zealand, but it is even more important for a sloped property. Christchurch’s Port Hills have been analysed very closely since the earthquakes, and there are many factors that will influence how easy a site is to build on. It is important to find out where rock is located, as rock excavation is time-consuming and expensive. The ideal situation is where most excavation is through loess and other easily-excavated materials, with foundations able to extend down to solid bearing on rock. Of course some of the most spectacular sites are in areas with shallow or exposed rock, so if you’re considering a site like this then you should allow a bit more in your budget for rock excavation.
While the challenge of landscaping your sloped section might seem like fun at first, it is going to cost you more and take longer than a simple flat section. You will need to pay specific attention to the types of plants you choose and will likely have to build up areas or flatten off areas to form suitable useable outdoor spaces. It is particularly important to consider the design of the house in relation to the landscaping – on an exposed site the house can be positioned to create sheltered outdoor living areas where you can escape the wind.
Yes, it is more expensive to build on a slope. But how much extra will it cost? When it comes to building on a hill, figuring out the ‘how’ is the most important part of pricing the build. Once you know how you are going to build it – then you can more accurately estimate the cost of the build. Quantity surveyors are experienced in pricing all types of house construction, and will be able to make allowances for factors such as site access, steepness of slope, foundation type etc. when preparing a cost estimate at an early stage of the project.
If it costs more and takes longer, you might be wondering why bother to build on a slope? The views from the hillside suburbs of Christchurch such as Cashmere, Clifton, Huntsbury, Mount Pleasant, Redcliffs and Sumner speak for themselves! No matter where you live, building on a hill almost always means the guarantee of spectacular views throughout the home. Here are some tips on pulling it all together and proceeding with a confident and successful hillside build.
Building on a hill means innovative design and a home that is unique. Working with the slope can turn it into a distinct advantage for both everyday living and resale value. Thinking of building on a sloped section and need some advice from an experienced architect? Call Chaplin Crooks Architects today for a free consultation to discuss your project.