Terrain management

It is common in the suburbs of large cities and towns to find sloping plots. Relationship between the building and the terrain is dependent on the plot’s geometric area (wider or narrower plot), as well as the size and height (numbers of floors) of the building affected.

It is common to see buildings that have been designed for flat sites where the plot has been partially leveled to accommodate this. This is only really acceptable when a building is relatively narrow (when comparing the site contours to the building’s depth) or the site has a gentle slope. Site terrain may be manageable when the difference between heights on the uphill side and the valley vary little. If a building is placed perpendicular to the slope, it may incur a significant discrepancy in level, even on a gentle slope.

Effort should be made to retain the original morphological characteristics of a site – first, to avoid significant increases in excavation and foundation costs; and second, to reduce disruption to the existing vegetation.

Improper location of a building on a sloping site can necessitate the creation of an unpleasant and unsightly false hill, which is costly in terms of soil movement and foundation. (fig. 3.27)

Figure 3.24. Matching building to terrain

If one excavates a hole in the side of a hill, this creates a ditch that acts as a water collection point. Large amounts of soil must be removed from the site, and windows facing the hillside will face an artificial slope. (fig. 3.27b) Generally accepted is the "natural balance" principle, where soil excavated on the higher side is deposited on the downhill side. It is not only necessary to reduce costs of earthworks, but it also results in minimal disruption to the original terrain. This is ideal for narrow buildings that are to be placed higher than the intersection the ground floor and original ground line. (fig. 3.27c) However, if the same principle is applied to a building placed lengthwise along the site, it will result in some of the excavation/false hill problems previously mentioned. (fig. 3.27d) In this situation, it would be better to design the home in such a way that floor levels vary in accordance with the terrain.

The following approaches offer solutions to this situation and provide homes with a richer spatial layout. Plans can offer unique responses to the site conditions, allowing the architects to explore their ingenuity and imaginations.

If the slope varies little from the upper to the lower end of the site (1.00 m perhaps), then it may be possible to terrace the floor – making some rooms higher than others, while the ceiling follows the same horizontal plane. Spacious daytime rooms (e.g., the living room) can be created. (fig. 3.28a) It is possible that two (or more) spatial groups within the home are placed on different vertical levels. This split-level shift (fig. 3.28b) can create imposing interior connections, although the obvious disadvantage will be the increased need for stairs within the home.

Figure 3.25. Matching building levels to the terrain

If the difference between the site varies greatly (2.00 m or more), then a three-dimensional solution will be required. Spaces on the lower side are used for daytime congregation, while spaces on the hillside become cellar space. (fig. 3.28c) With this arrangement, care must be taken when using the "natural balance" system, because the site’s infill and excavations run the risk of becoming too extensive.

Sloping sites often have a soil condition that follows the inclined plane, which is impermeable and results in water collection. Should a basement be built on the uphill side, care must be taken to build drainage solutions to protect against groundwater pressure.

A building’s connection to the site is usually made along the horizontal planes (apart from the rare exceptions when buildings are set upon legs, or when architectural intervention is required to remove paths around the home). Paths around the home might slope by a few degrees, and during winter, these may not be viable or functional. The building is suited to the site in fields and paths that follow the slope of the terrain. The outside terrain should not be higher than the internal living spaces. Therefore, any junction between the home and the terrain, possibly covering the whole plot, might require retaining walls and incorporated drainage systems. Water must be prevented from flowing towards the building.

Towards the hillside, a slight "fall" must be provided. To protect damage to neighbor’s land, the terrain must not vary near the boundary. No retaining walls are acceptable; the fence must be left in its original position. Rainwater should not be directed onto neighbor’s land. Groundwork around the building should be as indicate in figure 3.29.

Figure 3.26. Arranging terrain adjacent to building

Steep slopes can cause another problem, especially when approached by car. Cars generally cannot negotiate slopes steeper than 15-16%, so parking is often located at ground level on the valley side of the road. (fig. 3.30)

Figure 3.27. Motor car parking on sloping sites

Sloping sites usually offer great views. If the lower part of a site has the building line close to the street, this is the best place to build a garage with a retaining wall. (fig. 3.31) In this case, the distance from the street to the home's entrance may be longer than usual and not connected to the garage, which can be viewed as a drawback. These different contradictory values often lead to ad hoc decisions.