Everything about Mechanical Floor totally explained
A
mechanical floor,
mechanical penthouse, or
mechanical level is a
storey of a
high-rise building that's dedicated to
mechanical and
electronics equipment. "Mechanical" is the most commonly-used term, but words such as
utility,
technical,
service, and
plant are also used. They are present in all tall buildings including the
world's tallest skyscrapers with significant
structural,
mechanical and
aesthetics concerns.
While most buildings have
mechanical rooms, typically in the
basement, tall buildings require dedicated floors throughout the structure for this purpose, for a variety of reasons discussed below. Because they use up valuable floor area (just like elevator shafts), engineers try to minimize the number of mechanical floors while allowing for sufficient
redundancy in the services they provide. As a
rule of thumb, skyscrapers require a mechanical floor for every 10 tenant floors (10%) although this percentage can vary widely (see
examples below). In some buildings they're clustered in groups that divide the building into blocks, in others they're spread evenly through the structure, in others still they're mostly concentrated at the top.
Mechanical floors are generally counted in the building's
floor numbering (this is required by some
building codes) but are accessed only by service elevators. In some legislations they've been excluded from maximum floor area calculations, leading to significant increases in building sizes; this is the case in
New York City. Sometimes the building's designer has arranged a mechanical floor to be located on the
thirteenth floor, to avoid problems in renting the space due to
superstitions about that number.
Structural concerns
Skyscrapers have narrow building cores that require stabilization to prevent collapse. Typically this is accomplished by joining the core to the external supercolumns at regular intervals using
outrigger trusses. The triangular shape of the
struts precludes the laying of tenant floors, so these sections house mechanical floors instead, typically in groups of two. Additional stabilizer elements such as
tuned mass dampers also require mechanical floors to contain or service them.
This layout is usually reflected in the internal
elevator zoning. Since nearly all elevators require machine rooms above the last floor they service, mechanical floors are often used to divide shafts that are stacked on top of each other to save space. A transfer level or
skylobby is sometimes placed just below those floors.
Elevators that reach the top tenant floor also require overhead machine rooms; those are sometimes put into full-size mechanical floors but most often into a mechanical
penthouse, which can also contain communications gear and window-washing equipment. On most building designs this is a simple "box" on the
roof, on others it's concealed inside a decorative
spire. A consequence of this is that if the topmost mechanical floors are counted in the total, there can be no such thing as a true "top-floor office" in a skyscraper with this design.
Mechanical concerns
Besides structural support and elevator management, the primary purpose of mechanical floors is
heating, ventilation and air-conditioning, and other services. They contain
electrical generators,
chiller plants,
water pumps, and so on.
In particular, the problem of bringing and keeping water on the upper floors is an important constraint in the design of skyscrapers. Water is necessary for tenant use,
air conditioning, equipment
cooling, and basic
firefighting through
sprinklers (especially important since ground-based firefighting equipment usually can't reach higher than a dozen floors or so). It is inefficient, and seldom feasible, for
water pumps to send water directly to a height of several hundred meters, so intermediate pumps and water tanks are used. The pumps on each group of mechanical floors acts as a relay to the next one up, while the tanks hold water in reserve for normal and emergency use. Usually the pumps have enough power to bypass a level if the pumps there have failed, and send water two levels up.
Special care is taken towards fire safety on mechanical floors that contain generators, compressors and elevator machine rooms, since
oil is used as either a
fuel or
lubricant in those elements.
Mechanical floors also contain communication and control systems that service the building and sometimes outbound communications, such as through a large rooftop
antenna (which is also physically held in place inside the top-floor mechanical levels).
Modern computerized
HVAC control systems minimize the problem of equipment distribution among floors, by enabling central remote control.
Aesthetics concerns
Most mechanical floors require external
vents or
louvers for
ventilation and
heat rejection along most or all of their perimeter, precluding the use of glass
windows. The resulting visible "dark bands" can disrupt the overall
facade design especially if it's fully glass-clad. Different
architectural styles approach this challenge in different ways.
In the
Modern and
International styles of the
1960s and
1970s where
form follows function, the vents' presence isn't seen as undesirable. Rather it emphasizes the functional layout of the building by dividing it neatly into equal blocks, mirroring the layout of the elevators and offices inside. This could be clearly seen on the
World Trade Center twin towers and can be seen on the
Sears Tower. In the
IDS Tower in
Minneapolis, the lowest mechanical floor serves as a visual separation from the street- and
skyway-level Crystal Court shopping center and the office tower above; the upper mechanical floor (above the 50th and 51st floors, the uppermost occupied floors) serves as a "crown" to the building.
Conversely, designers of the recent
postmodern-style skyscrapers strive to mask the vents and other mechanical elements in clever and ingenious ways. This is accomplished through such means as complex wall angles (
Petronas Towers), intricate
latticework cladding (
Jin Mao Building), or non-glassed sections that appear to be
ornamental (
Taipei 101, roof of Jin Mao Building).
Examples
These are examples of above-ground mechanical floor layouts for some of the world's tallest buildings. In each case, mechanical penthouses and spires are counted as floors, leading to higher total floor counts than usual.
- Taipei 101: Floors 7-8, 17-18, 25-26, 34, 42, 50, 58, 66, 74, 82, 87, 90-91, and 102 in the penthouse (total 17/102, or 17%). The official count
of 11 corresponds to the number of groups in the office section. Floors 92-100 contain "communications equipment" and so are not typically counted as mechanical since they don't service the building itself.
World Trade Center Twin Towers: Floors 7-8, 41-42, 75-76, and 108-109 (total 8/110, 7%). The 110th Floor of 1 WTC (North Tower) housed television and radio transmission equipment. Some sources erroneously mention 12 floors, in groups of 3, due to the height of the vents (actually the ceilings there were higher) and because levels 44 and 78 were skylobbies which in many buildings sit directly on top of the mechanical floors. However the twin towers had one occupied office floor under each skylobby, accessible through escalators.
Sears Tower: Levels 30-31, 48-49, 64-65, 104-108, and 109-110 in the penthouse (total 13/110, 12%).
Petronas Towers: Floors 2-7, 38-40, 43, 84, 87-88 (total 13/88, 15%) (New York Times, Elevator World magazine)
Jin Mao Building: Floors 51-52, and 89-93 in the penthouse (total 7/93, 7.5%) (SkyscraperPage)Further Information
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