Perhaps the biggest challenge when we decide to build a house for ourselves is finding a suitable plot. Two of the most important characteristics are price and location. But what happens when we find a plot in a great location at a good price but it is sloping?
What are our options when we decide to build on a sloping plot?
When we decide to build on a sloping plot there are two basic options we can opt for:
- we can adjust the plot for the construction of an ordinary house:
- by leveling the plot by pouring earth on the lower side with the construction of a retaining wall,
- by leveling the plot by excavating and removing the excess soil from the higher side with the construction of a retaining wall or
- by making a series of terraced planes with the construction of several smaller retaining walls,
- or, we can design a house plan that is adapted to the sloping plane of the plot itself:
- by building a daylight basement with windows on the lower side of the plot,
- by building a garage or parking space above the living space,
- by building a house on a series of supporting stilts or columns or
- by building a split level house.
Which of these options, listed above, will we choose depends primarily on two things:
- On which side the plot is inclined in relation to the access road?
- the plot is above the road,
- the plot is below the road,
- the plot descends along the road,
- How much money are you willing to invest?
How to orient a house on sloping land?
The house on the sloping ground should be oriented so that the shorter side of the foundation (assuming that the base of the floor plan is rectangular) is in the direction of the slope. This actually means the following:
The slope of the land is expressed as a percentage and, let’s say, a 15 percent slope means that, for every 100 feet of horizontal distance, elevation changes 15 feet. If your floor plan has overall dimensions of 28 by 60 feet, and If you orient the house so that the 60-foot side is in the direction of the slope, the lower corners will be 9 feet lower than the upper corners. If you orient the house so the 28-foot side is along the slope, the lower corners will be about 4 feet below the upper corners. As you can see, the second solution involves less digging.
How safe is it to build on a sloping plot?
Construction on sloping land can be completely safe, but only if all precautions are taken, and, in order to do so, we must know what are the potential risks and challenges of building on such land.
1. Landslide
Landslide is a term for a rocky or loose rock mass separated from a surface that slides down a slope under the influence of gravity. Conditions for the formation and development of landslides are, among others: the slope of the terrain, the level, and regime of groundwater, higher rainfall, sudden melting of snow, cutting the slope during construction work, soaking the land with wastewater, deforestation…
As you can see, sloping land is often in danger of landslides. Although landslides are recorded in the documentation of construction authorities, so you can contact them before buying a plot and get information about the possibility of landslides at that particular location, keep in mind that both your construction actions and your intervention on the ground can cause this occurrence, so care should be taken.
In any case, for complete safety, it is advisable to pay an expert who will investigate whether there is moisture in the depth of the soil and how much danger it poses, if any.
2. Soil type
It is always important to determine the type of soil before making any decision to build on a plot, but on sloping land, it is even more important. There are so-called granular soils, such as gravel, sand, or silt, which contain little or no clay and they drain well and can withstand heavy loads. On the other hand, soils with a high clay content do neither. Not good, anyway.
Certain clays can damage foundations by swelling or spreading when wet or frozen and may require costly engineering repairs or additional filling of granular soil.
3. Steepness
Soil composition is directly related to terrain slope; this is called the angle of repose. For example, very solid clay can be laid at an angle of 35° or 40°, sandy clay at 15 ° and crushed rock at up to 45 °. This means that for each type of soil there is a maximum slope to which construction is possible.
Less than 10% incline is considered slight and is the easiest to build on, while 11-20% is considered moderate. Anything above 20% is deemed steep.
The general rule of thumb is that any slope with an incline less than 7 feet of fall is easier to build on, whilst a slope more than 7 feet increases the skill required from a design perspective and cost of the build.
4. Drainage
Water drainage, for both surface and subsurface water, is absolutely crucial to building on a slope. Rainfall-runoff has to be redirected away from your home’s foundation, as well as from retaining walls, without endangering any neighboring properties with water flows and without flooding public roads.
The biggest problem that may arise here is that local authorities do not allow your drainage system to be connected to a public rain sewer. This is one of the most important things you need to check before buying a plot on a slope because otherwise, the cost of construction can be sky-high.
Is sewerage a challenge when building a house on a sloping plot?
When it comes to sewage treatment, it also can be tricky, depending on where your home is relative to the sewage line. If the line is uphill, you may need to install a pump, and if it’s downhill, you may have to install tumble bays to slow the flow to a reasonable rate.
Does building a house on a sloping plot take longer?
Whether we decide to adapt the terrain or apply specific construction techniques, the time required for the works is extended by approximately 6 to 10 weeks. The rest of the construction process is flowing at the usual pace.
How do the specifics of building a house on a sloping plot affect the price?
From all the above, it is clear that the cost of building a house on a sloping plot simply must be higher than building a house on a flat plot, regardless of which of the possible solutions you choose.
As a general rule, we can say that the steeper the site is, the more expensive the project will be. Typically, building on a sloping site will add an additional cost of approximately $20,000 – $50,000 compared to a flat block. These are only approximate values because the exact figure can be determined only for a specific plot.
To get a rough idea and understand the additional expenses of building your new custom home on a slope plot, we will list a few of the common things (with estimated values) that might add to the cost:
- Geotech engineer, testing, special surveys, etc. $15,000
- Additional foundation costs $15,000
- Catchment system $30,000
- Special inspections performed by the City and billed to client $10,000
- Landscaping, retaining walls, etc. $30,000
- extra budget (worst case scenario) $100,000
It is unlikely that you will have all of the above costs, so the overall price increase is actually slightly less.
You need to remember that although even slightly sloping terrains cause an increase in the cost of construction, what interests you is the overall ratio of invested and obtained, and two more things contribute to this.
Firstly, the price of a sloping plot is always lower than the flat one of the same area and at the same location. Secondly, the resale price of the constructed real estate can be significantly higher if all the advantages and possibilities offered by construction on a slope are used. Only when all this is summed up it can be clear to us whether it pays off to build on sloping land.
Why should one build a house on a sloping plot?
So far we have only talked about the challenges, problems and additional costs of building on sloping land, but now is the time to list the good sides, opportunities and potentials that certainly exist and which actually attract people to build on such plots.
1. The views
You can enjoy stunning vistas of green valleys and wooded forests or urban panorama below, clear sky views above, and uninterrupted lines of sight for miles in some cases.
2. The landscaping
Although the cost of landscaping is higher, on the other hand, it offers many possibilities that can make your garden magical and unique. Just imagine:
- a set of stairs leading up to flatter ground
- waterfall feature
- a meandering pathway
- a lush rock garden
- an infinity pool
3. The space
Lots with steep slopes allow for the extra space of a walkout basement that serves as another floor of the house.
4. Natural lighting
Houses situated on the side of a hill are often perfectly situated to maximize lots of natural light, a prized feature that carries the bonus of tons of health benefits, such as better mood, better sleep, and higher productivity.
5. The seclusion
You can enjoy stunning vistas of green valleys and wooded forests or urban panorama below, clear sky views above, and uninterrupted lines of sight for miles in some cases.
6. Creative design
The greater the challenge, the greater the creativity. A home on a slope presents a chance to create stunning exterior designs that are set over multiple levels.
7. Energetic efficiency
Properties positioned on sloping sites generally offer more opportunities for energy efficiency than those on flat land. This is because they tend to be naturally isolated because part of the building is underground and also not overshadowed by surrounding buildings so there is a greater possibility of using passive solar energy.
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