How to design buildings on Hilly or Sloping Terrain?

Building in hilly terrain can be a challenging task for architects and engineers. Due to the steep slopes, the construction of buildings in such topography requires special attention and careful planning. It is important to consider factors such as site context, site contours, and climate to ensure that the structure is safe and secure.

Here are various ways of designing buildings in hilly terrain, including the use of retaining walls, different forms & foundations, terracing, and other building techniques!

Orientation of the building

A diagram compares two building placements on a hilly terrain: across the contour with excessive cut and fill, and along the contour with less environmental impact.

Credits - Aishwarya Bomble

Placement of the building

Buildings tucked into the hillside without harming it.
The location of the building minimizes grading.
Preserve natural drainage courses and existing trees.
Less distance from the main road to minimize footprint.

Illustration showing topographical map features with contour lines, a cross-shaped object showing a building, circles showing trees on site, and arrows showing wind movement. A shaded triangle extends from the cross-shaped object toward a curved path in hilly terrain, showing the viewing area from the building.

Credits - Aishwarya Bomble

Types of forms

To ensure the safety of the structure, it is important to choose the right kind of form for the building. There are various types of forms that can be used for building on sloping terrain, depending upon the site conditions & building requirements.

An infographic illustrating six housing foundation types ideal for hilly terrain and steep slopes: Freestanding, Cut & Fill, Raised on Platform, Earth Berm, Hybrid, and Cantilever. Credits - Aishwarya Bomble

Cutting & Filling of Site

Cut and fill is a process that involves cutting into the ground to create a level surface for construction, as well as filling in areas with soil or other materials to bring the desired height of the building up. This process is often used in construction projects where there are large differences in ground levels, such as when constructing roads or houses on hillsides. Cut and fill is an important step in creating a safe and structurally sound building, and it requires careful planning and execution.

Diagram showing before and after images of slope terracing on hilly terrain. "Before" depicts an uneven slope, while "After" illustrates terracing with cut and fill, balancing masses.

Credits - Aishwarya Bomble

Diagram comparing building designs on hilly terrain. Incorrect design has heavy mass, high walls, and excessive filling. Correct design features staggered floors, equal cut and fill, a roof line following the terrain, and retaining walls to support the structure on steep slopes.

Credits - Aishwarya Bomble

Types of Sloping Sites

It is important to understand the different types of slopes and how they impact the construction process. Depending on the type of slope, different approaches may be required when building on them. Retaining walls may need to be built in order to stabilize the soil, and foundations may also need to be adjusted in order to accommodate for any changes in elevation.

Diagram illustrating house construction on different slopes: gentle (less than 10%, economical), moderate (10-20%, expensive), and steep (above 20%, very expensive) on hilly terrain, with cut and fill strategies and foundations like piers, piles, retaining walls, and terracing techniques.

Credits - Aishwarya Bomble

Retaining walls

Retaining walls are structures that are used to hold the slope of a hill or mountain in place. They are built in different forms in both uphill and downhill scenarios, depending on the grade of the hill.

Diagram illustrating four methods to manage hilly terrain: top-left features an L-shaped inward retaining wall for a flat upper level; top-right highlights an outward wall establishing a lower area; bottom diagrams depict terracing with slopes graded downhill and uphill along wall faces.

Credits - Aishwarya Bomble

Foundation & Drainage

Strong foundation & efficient drainage is necessary in case of sloping sites to tackle sedimentation and surface water runoff. It varies according to the grade of the slope and the form of the building.

Diagram illustrating types of building foundations on different slopes: gentle slopes use a slab/pad foundation, moderate slopes employ raised footings, and steep slopes feature piers.

Credits - Aishwarya Bomble

Here are a few important points to remember according to the building codes:

Any face of the hill (except hard stable rock outcrops) shall not be used as a building wall.
Minimum clearance of 1m, preferably 1.5m should be given between the retaining wall face & building wall for proper ventilation, lighting & minimum dampness.
The height of hill cutting for stepped-story buildings for any step shall not be more than 4m.
The kitchen, lavatory, water closets, etc, shall be located & oriented as far as possible from the hill face so as to avoid dampness due to seepage of water.
The upper stories should be as light as possible.

Conclusion

In conclusion, designing and constructing buildings on hilly terrain requires a deep understanding of the site’s topography, climate, and structural requirements. Architects must carefully plan the placement, form, and orientation of the building to minimize environmental impact and ensure safety. Techniques like cut and fill, retaining walls, and strategic foundation planning are essential in creating stable structures on slopes. By preserving natural elements such as drainage and vegetation, and adhering to building codes, construction on hilly terrain can be both sustainable and secure. Proper planning ensures that these projects enhance the landscape without compromising safety or functionality.

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FAQs

Q.1 How is slope used in architecture?

A. Slope is utilized in architecture to create visually interesting and functional designs. It can influence the orientation of buildings for optimal sunlight and ventilation, provide natural drainage, and integrate the structure into the landscape harmoniously.

Q.2 What type of foundation should be used on a sloping site?

On a sloping site, stepped or tiered foundations, pier and beam foundations, or retaining wall foundations are commonly used. These foundations help distribute the load evenly and provide stability to the structure.

Q.3 What is the best foundation for a sloped lot?

The best foundation for a sloped lot depends on the degree of the slope and soil conditions. Stepped foundations and pier and beam foundations are often preferred for their ability to accommodate uneven ground and provide robust support.

Q.4 What is the best slope for building?

A slope between 1:5 and 1:10 (vertical to horizontal) is generally considered ideal for building. This range provides a balance between natural drainage and structural stability.

Q.5 Can you build a wall on a slope?

Yes, you can build a wall on a slope. Retaining walls are commonly used to stabilize the soil and support the construction on sloping terrain. Proper design and engineering are crucial to ensure the wall's stability and longevity.