Tessellar Blog

Monday, March 20, 2017

Overcoming the Problem of Car Parks for High-Density High-Rise

THE PROBLEM OF CAR PARKS FOR HIGH RISE
Malaysia is reputed to have one of the highest levels of car ownership in the world. The planning requirement for apartments is two units of car parks for each unit, plus another 10% for visitors. This is a very high requirement compared to most other countries and has the effect of making our high-rise housing expensive.

MEETING HIGH CAR-PARKING REQUIREMENTS WITH THE CHECKERBOARD PLAN

As we design taller buildings to achieve higher densities, just adding on parks on the ground is not the way to do it. The additional area required to cater for the additional car parks increase the development land required: since density is units/land area, increasing the numerator is pointless if at the same time, we increase the denominator.

To achieve higher densities, multi-level car parks are necessary. They can be placed in an adjacent block or below the tower. Constructing an adjacent block is cheaper but at the cost of being requiring an additional area, hence resulting in a lower density. But whichever of the two, the effect on the distribution of built-up area is that a large built-up area is now dedicated for cars: the net sellable area becomes a smaller proportion of the total built-up area. Car parks takes up a lot of space. Each car needs an 8’ x 16’ space that works out to 128sf. The driveway takes up 20’. All in all, with ramps and having to consider building columns and staircases, the gross built-up area required for one car park is about 260sf: in fact, actual car parks make up less than half of the total area of a multilevel car park block. Two car parks for each apartment plus another 10% for visitors takes up 572sf of car park built-up area. This is more than half the size of a typical affordable apartment.

Net sellable floor area expressed as a percentage of total built-up area for high-rise, including the multi-level car park plummets is often less than 55%. The fact is, the car parking requirement for high-rise high-density housing has become a very heavy burden on the cost of construction.
Again, PR1MA is aware of this problem and have produced their own guidelines which try to address this problem. In their table, A1, the car park provision for rural areas is set at 2.2, suburban and urban areas at 1.65 and 1.1 in cities. Although this standard may face resistance from local authorities and householders used to the convenience of having two cars, in the longer term, promoting a less car-dependant life style makes sense.

Already, the average size of households in Malaysia has peaked , bringing down the average number of cars per household. With the expansion of public transport in Kuala Lumpur and the Klang Valley, plus the explosive growth in share-riding services like Uber and Grab, owning a car is not essential for young working people, as it once was. I believe that PR1MA can do a good job in convincing local authorities home-buyers to buy into the concept of the compact city that promotes high residential density, mixed use and is oriented towards pedestrians rather than cars.

The efficiency of car parks can be operationally improved by doing away with parking spaces that are strictly allotted. As currently practiced, car parking spaces are allotted as accessory parcels to each owner. However, this ends up with a lot of car parks being empty for long periods. A pooled system, as found in commercial buildings, can cut this slack, providing more car parking opportunities with fewer actual slots.

In fact, PR1MA’s guidelines presumes only two basic options – a stand-alone multi-level car park or a podium car park that sits below the building block.





Figure 15 Multi-level Podium Car Park

The latter is of course more efficient than the former. But the podium is still a poor choice. The podium takes up space larger than footprint of the tower or slab block above it. This increases the land area that is needed.  The car park podium also must be set back from the boundary by about 50’ from the front and 25’ from the side. Having to do so results in having fewer cars than car parks on the ground floor which are subject to much lower setback lines.

Is there a better solution?

DEEP PLANS: PROVIDING CAR PARKS MORE EFFICIENTLY

The checkerboard-plan was conceived to be car park design-friendly with columns spaced in an 8m grid. A car park circulation system also fits neatly into the 5-layered grid with two roads inside the building footprint feeding car parks on both sides.



Figure 16 Columns in 8.1m grid

There is a road that circles the outside of the building: it too feeds car parks on both sides. The ground floor plan is shown below.

Figure 17 Ground Floor Car Park Plan

On just one floor the design is already very efficiently with up to a density 136 units per acre and this one floor is good enough to support a residential density of 60 units per acre when the car park requirement is 2.2 car parks per apartment, 90 units per acre when the car park requirement is 1.65 car parks per apartment unit, and 120 units per acre when the car park requirement is 2.2 car parking spaces per apartment.

But can we provide for even higher densities? Is there an alternative to the conventional multi-level podium car park?

Our answer is to replicate the ground floor car parking layout in a basement floor. In fact, basement car parks are generally not considered at all for residential development because they are thought to be costly to build, needing temporary shoring and permanent waterproofed retaining walls, and costly to maintain, with a mechanical system to draw in fresh air and expel fumes as well as a smoke-spill system in case of fire.

Yet, a single basement level 7’ or more away from the boundary does not need temporary shoring or an expensive water-proofed retaining wall. An 8’ rubble retaining wall at the boundary plus a low 1’ concrete one on the car park building line will suffice, creating an air-well that provides natural ventilation, daylighting, a green planting strip and setback distance to meet current planning requirements.




Figure 18 Perimeter Retaining Wall and Air-well
It is also easy to design an access to a single basement floor, doing away with having too many ramps as shown in the plan below.




Figure 19 Basement Car Park Plan


As shown in the basement car park plan above, just two car park levels can already support a building above it that contains 133 units per acre when the standard is 2.2 car parks per acre, 170 units per acre when the standard is 1.65 car parks per acre, and 275 units per acre when the standard is 1.1 car parks per acre.

The options available are displayed in the drawings below.





A design strategy that achieves high-density with shorter buildings and which either eliminates the car-park podium or else substitutes it with a low-cost single basement floor will surely reduce construction cost and time. Combining it with a lower car parking standard and as well as a loosening of the cap on density will further multiply the savings.

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Wednesday, March 15, 2017

Tall Buildings Cost More than Shorter Ones; How to Maximize Site Coverage

Even if authorities allow higher densities, high-rise would still be expensive. Taller buildings cost more to build compared to lower ones. As we go higher, there are thresholds above which costs become disproportionately more onerous.

Structures cost more the higher we go, as the columns on the lower floors need to be stronger and as lateral forces become more critical.

Below five storeys, lifts are not considered to be necessary, but at five storeys or above, we must provide them. As we go higher, more lifts are required, not only increasing the cost of installing and maintaining them, but also taking up more space, and thus reducing net sellable area. Lifts above 20, 30 and 50 stories also get disproportionately expensive as they need to move faster and must carry longer and heavier cable ropes.

With respect to fire-safety, above seven stories (top most floor 18.3m above fire appliance access level), fire-fighting lifts and “dry-risers” to pipe up water and hose-reels are required. Above 10 storeys (30.5m fire appliance access level), a wet riser, associated storage tanks and hose reels are required.

As for construction, taller buildings take longer to build because there are more floor cycles to work through, because materials must be transported higher. Blocks lower than 10 stories do not even need a tower crane. In short, shorter buildings are cheaper. But can we design them to a high density?

DEEP PLANS: MAXIMIZING SITE COVERAGE

Current high-rise typologies are narrow buildings: the slab block with a single-loading corridor can be described as a single-layer of apartments; the slab block with a double loading corridor is a double-layer arrangement; the tower block, a circular layer of apartments.

In housing, we want almost every room to have natural light and ventilation. There cannot be deep plans like that found for offices, where mechanical and electrical systems bring in artificial ventilation and lighting to the central portion of the building which are far away or cut off from the windows and the building’s edge.

The typical Malaysian apartment will have at least the living room and master bedroom having windows on the external walls of the building and less important rooms facing an air well. The depth of the unit measured from the external wall is about 8 metres. With a 2m corridor in the middle, the total width of this double-loading corridor block layout, with two layers of apartments, is not much more than 16m.

The width of the single loading corridor with only a single layer of apartments, is about half of this. The tower block, with a circular layer of apartments, can be wider; each side is typically 24m.
In contrast to these existing typologies, the Honeycomb checkerboard-plan has a depth of over 40 metres. This deep plan results in a residential floor plan that covers more of the land available on as site compared to that achieved by skinny conventional floor plans. Using the available land more efficiently allows more units to be built on every floor and so can provide higher densities without having to go taller; it should become easier to achieve high plot ratios like deep plan offices.


Figure 14Apartment Typologies and Minimum Land Required

For a comparison, we take the different floor plans, apply 60’ front setback and 25’side and rear setbacks to form the minimum site boundaries for each example. We measure the area and divide it by the number of apartment units on a typical floor to show how big an area is needed to accommodate one apartment unit. The checkerboard-plan is the most efficient as it takes up the least amount of land compared with the other examples.

Table 1 Comparison of Site Coverage: Per floor Density


No of Units /Floor
Site Area (sf)
Site Area /Unit
Units on Floor/Acre
Woodlands Drive, Singapore
6
35,731
553.4
7.3
Single Loading Corridor
Blues Point Tower , Sydney
4
22,555
524.1
7.7
Tower Block
Membina Court, Singapore
10
50,903
473.1
8.6
Cluster Block
Binapuri Tower, Selangor
8
37,554
436.3
9.3
Double Loading Corridor
Honeycomb
10.67
43,264
376.8
10.7
Checkerboard -Plan