Terraced developments

Terraced houses are multi-story, multi-unit apartments which are directly connected by large roof terraces.

(In Hungary, this refers to buildings that are built as a staggered development on hill sides, although similar developments can occur on flat sites.)

Due to the sloping terrain, terraced houses are stepped back as the hill rises. A proportion of each home is below ground and below the home above. The roof of each apartment serves as a terrace to the place above.

There is a direct correlation between the terracing of apartments, depth of roof terraces and terrain.

(fig. 5.47) Theoretically, the leading edge of each roof terrace is parallel to the ground line. If the ground slopes gently, then so does the terracing of apartments, allowing for larger roof terraces. If the ground slopes steeply, then so does the terracing of apartments, resulting in small roof terraces.

In reality, this does not occur, as sites rarely have an even slope. Land must be adapted for access by pedestrians and vehicles, resulting in the need to modify terrain. (fig. 5.48)

Figure 5.43. Geometric relationship between terrace sizes and sloping terrain

Figure 5.44. Terraced housing in relationship to terrain (fictive schematic)

Apartments are usually accessed by exterior staircases. A straight flight of steps and required landings result in a slope of 47%. (fig. 5.49a) Steeper sites will require more complex arrangements of steps and landings. (fig.5.49b, 5.49c and 5.49d) Steps can provide access to apartments from both sides and are often covered by glazed roofs.

Figure 5.45. Design of external access stairs to terraced housing

Some form of visual protection should be provided to roof terraces for privacy reasons. To do so, parapet walls are often developed with integral planters, or they are dedicated to planting strips or green roofs. (fig. 5.50)

Figure 5.46. Visual shielding between roof terraces

Depending upon the site’s gradient, apartments can be placed perpendicularly or parallel to the site.

(fig. 5.51) The first case is better suited to narrow, steep sites. On not so steep sites, longer flights of steps will be required. If a slope is steep, then shorter flights of steps will be required. In both cases, the plan type is rectangular. Individual apartments are usually accessed from the side opposite the garden.

Figure 5.47. Common schematics for terraced housing

When apartments are placed on wider sites, then the development can run parallel to the slope. In this case, atrium-like homes are often planned, affording greater privacy to the roof terraces. (The smaller roof is often a green roof.)

As these homes are not planned directly above each other, some areas of design need greater attention.

So-called wet areas cannot be placed one above the other, so take care when situating windows and ventilation ducts. (Do not place them near the roof terrace of adjoining homes.) Therefore, direct ventilation of secondary spaces should be placed towards side elevations. The same applies to chimneys. This can be solved if the whole building is heated by a shared boiler placed on the upper floor. Sewage can be drained via external drains connected horizontally, at each level, to individual apartments.

As the back wall of each apartment is in fact a retaining wall, it might be wise to introduce a "buffer zone". Avoid using this area for habitable spaces. Try to ensure that living areas are placed in locations that do not require intense damp-proof insulation. (Damaged waterproofing to retaining walls is generally not repairable.) Developments on sloping sites present problems regarding groundwater extraction.

Another problem posed by these developments is that created by slab construction, acting in part as floor slab and part as roof terrace. The latter will need to be detailed differently to provide additional thermal insulation and waterproofing. A common aesthetic mistake occurs when access to the roof terrace requires a step up from the interior spaces.

Another problem with terraced housing occurs when attempts are made to install lifts. It is possible in developments of two or three levels to establish a central core that includes a lift. (There are examples of homes that are accessed by funicular railway, but this is not available as a product and results in the need for a high-cost custom item). When developments have four or more levels, the required amount of steps can detract from the market value, even when balanced against the positive aspect of having roof terraces. Barrier-free access can really only occur at street level.

Terraced developments are best suited to sites where a large build ratio is allowed for (also where the allowed build height is equivalent to that of a two-story home). The footprint of this building is also

considerably larger than that of a normal multi-story building. (Terraced house can be labeled as low-rise, high-density developments.) As these buildings occupy most of the site, attention to regulations regarding green areas should be accounted for by including the design of green roofs.

When terraced houses are developed on flat sites, interior arrangements will vary in relationship to roof terraces. These buildings have been described as "artificial hill houses" where each level is gradually smaller than the level below. These pose design problems, since each floor is different in plan. Roof terraces and structural walls remain the same in size, but apartments decrease in size. Take care that the upper level apartments and core sizes do not become absurdly small. (fig. 5.12)

Within reason, it is possible, where structural design allows, to terrace the back of the building. (fig.

5.13)

5.11. Vehicular storage

Regulations currently state that multi-story, multi-unit buildings should provide an amount of onsite parking spaces equal to the number of apartments planned. However, if the building program demands that more spaces be provided (as affluent home owners may have two or three cars), then the design should account for this.

The easiest place to locate parking spaces is at ground level. This is only applicable where a low ratio of the site is to be developed, usually on smaller developments of "affordable housing" where land prices are relatively low. In these situations, it might also be possible to provide for a second parking space instead of the single parking place required by law.

Semi-enclosed carports are simple enough to build, since they are simple shelters on legs. The advantage is that they create little visual obstruction. Disadvantages include the fact that they occupy area that might be developed for other, more useful purposes. Often the architectural execution of these carports can be poor in quality, so they are best avoided when designing multi-story, multi-unit buildings.

Enclosed garages are more secure and can even be sold or rented out depending upon market requirements.

Sizes for single and double garages were included in Sections 3.22. and 3.23. This is better suited to low-level buildings at street level. If a larger building has its entire width occupied by garage doors, the entire elevation may appear rugged, desolate and even architecturally poor. Also, developing the entire ground floor as garages can detract from the property value and space allocated by build ratio. This does not make sense in terms of selling or renting, because the profit margin achievable by developing ground-floor apartments is still higher. Try to avoid ground-level development of car parking garages at all costs for aesthetic, financial and build ratio reasons.

Underground garages are usually built on more expensive plots, providing freedom for the better development of the area allowed in build ratio calculations. For this reason, seemingly expensive construction costs can be justified. When used in residential buildings, underground garage plans can take many forms that provide for low-volume use, usually parking in perpendicular rows as shown in figure 5.42.

Special attention must be paid to the design of access ramps. The head and foot of the ramp should have an arc radius of 20.00 m to allow for the transition between horizontal surfaces and the main body of the ramp, the length of which depends on the depth of garage from ground level (fig. 5.53) In some situations such as urban infill sites, a car lift will be used, since there might not be enough room to build a ramp. The cost of this can be offset by the cost of space saved by excluding a ramp. The disadvantages are that these lifts are slow and costly to maintain. If they fail, it may be impossible to enter or exit the garage, thus necessitating a back-up lift.

Figure 5.48. Dimensioning of garage access ramps

The preferred location for an underground garage is in the building’s basement. To achieve this, opposing rows of parking spaces and a central access road must be provided, requiring a width of around 16.00 meters. (fig. 5.55) Sections 5.7.4 and 5.8.4. describe economical depth arrangements.

From this, it can be seen that satisfactory structural solutions are limited.

Figure 5.49. Relationship between garages and residential buildings

Figure 5.52 shows where pillars can be placed in relation to parking spaces. Pillars are best located centrally with spacing of 5.00 or 7.20 meters. This location of pillars must be continued throughout the building at higher floor levels. Given the fact that most homes are based on a structural pillar center spacing of 3.60 or 4.20 meters, this should be reflected in the parking area. Therefore, to create structural harmony, car parking spaces are often oversized, leading to increased construction costs.

Figure 5.50. Dimensioning of garages

As most residential building developments are usually about 11.00-12.00 m deep, basement parking only provides enough room for a single row of parking spaces and the access road. This, in effect, increases the cost of parking spaces by 40% per unit, which is not economical.

To resolve this, additional parking must be provided below the garden area, protruding from the building’s contour. This will reduce the development’s green area, perhaps requiring expensive green roofs or resulting in different floor slab levels.

Another option is to place the underground garage next to the building. This will not interfere with the residential building’s structural composition. Allow the basement to be used for general storage and provide more distance to develop an access ramp to the garage. (fig. 5.55)

Access to and from an underground garage must be via a ventilated, smoke-free, fire resistant staircase through an "airlock". No other access (lifts included) should be available to this area.

Due to the nature of car exhaust fumes, mechanical ventilation must be provided. The mechanical service room for this purpose must be placed beside the garage, within the building’s volume, ensuring that all exhaust fumes are extracted vertically to above the building’s highest roof level. These extractor fans can have ducts with cross-sections of around 1.00 m². Design of such systems should be undertaken by mechanical engineers employed from at the initial stage of building design.