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also a big factor in the building designs at that time. Hong Kong's government owned all the land and leased some out for private development through auctions for various terms, such as 50, 75, 99 and 999 years. Developers needed to pay tens of thousands of HK$ for leasing each square meter (11 sq ft) of land. Meanwhile, some innovative building designs emerged. The use of scissor staircases, in which two fire escape staircases intertwined, shrank the width of the fire escape void, allowing buildings to be narrower. These factors incentivized developers to build slender residential towers on small lots with one unit per floor. Developers only needed to acquire a lot with a frontage area of two small retail shops (two
448:
273:
214:
27:
382:, a 195-metre (640 ft) skyscraper that has the width of its base at 11.5 metres (38 ft). It slenderness ratio of 16.5:1 was the fourth most slender tower in the world at the time of completion. Collins House incorporated many of advancements in technology including the first of such towers to use
286:
In the early 21st century, the pencil tower concept for residential towers also expanded outside of Hong Kong and returned to New York City. Developers utilized the transferable development rights and innovative structural engineering to elevate the buildings as high as possible for spectacular views
75:
started developing pencil towers in the 1970s. Residential buildings of twenty or more stories with one unit per floor were built over small lots. It has become one of the most common types of buildings in the city, making Hong Kong the world's highest concentration of pencil towers. Hong Kong's most
360:
that are twisted over a long length, and small areas that can be used for fire fighting operations and medical staging. Another area of concern is their open-air mechanical floors, especially those of New York City pencil towers. If the doors are left open, wind could enter the staircase fueling the
236:
for 43,000 residents who suffered from a massive fire in 1953. Those public housing units were 280 square feet (26 m) to 450 square feet (42 m) which set a new expectation for the sizes of residential units in private developments. The cost of land leasing for residential developments was
339:
can be used. This is a passive device with a large mass mounted on shock absorbers to slow the movements of the building. Typically they are made of solid mass, but recently liquid damping systems have been used. A liquid damping system or sloshing damper is a tank of water with screens to control
377:
entered the global pencil tower scene with the construction of the
Phoenix Apartments building that rose up on a 6.7-metre (22 ft) wide lot in 2013. The plan originally called for a 40-story building. After oppositions from concerned neighbors, the design was revised down to 28 stories at a
287:
while requiring the smallest footprints possible. The term "pencil towers" has been used to describe a new type of tall and slender buildings in New York City as well. Early examples of the new trend were Sky House
Condominium, a 588-foot (179 m) building on a 45-foot (14 m) lot, and
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helped maximizing its floor space. In 2018, a design of a 330-metre (1,080 ft) tower sitting on to of a triangular plot in
Melbourne was submitted for planning approval. If built, The Magic would become world's slenderest by a ratio of 26.6:1 based on the shorter side of its widths in a
324:, a 15:1 ratio building that has many open-air mechanical floors. Another approach is to stiffen the structure to resist the loads. This can be done by using outrigger walls to connect the building core to the perimeter columns on two sides to distribute the loads. The structure of
241:
buildings) in order to build a tower of 20 stories or more. This was when the term "pencil towers" was used to describe these micro-developments. Currently, a 430-square-foot (40 m) unit on a pencil tower has an average price of HK$ 4.3 million. (US$ 0.55 million)
355:
Very tall and very narrow pencil towers present new challenges to fire fighting. With narrower buildings, the scissor staircases are narrower and they may need to have five or more turns to rise for each floor. This presents impacts to the performance of the
309:(100,000 psi, 690 MPa) became more available. Higher-strength materials can reduce thickness of concrete walls, reducing the amount of required interior structures. This is a critical factor that enables super-slender building designs.
304:
Building materials have improved in recent decades. The strengths of concrete have been changed from 10,000 to 12,000 psi to 18,000–20,000 psi (69–83 to 120–140 MPa). Reinforcing steel with higher strengths of 100
451:
432 Park Avenue (left, farmost), 111 West 57th Street (center left, under construction), One57 (middle, blue), 220 Central Park South (right foreground, gray) and
Central Park Tower (right background, blue)
253:
residential district, making Hong Kong the "world capital" of pencil-thin towers. In the 21st century Hong Kong pencil tower developments started to get much larger in scale than previous decades. In 2001,
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to replace a 12-story office building. It follows the form of pencil towers of New York. However, with its 11:1 ratio, the slenderest in
Toronto, it falls short of matching those New York towers.
1054:
69:
that is very tall and thin. There is no universal definition of how slender these buildings are to be categorized, but some definitions of 10:1 or 12:1 ratios and higher have been used.
983:
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in the middle of a building to allow wind to flow through. This can reduce the wind loads and the resulting movements by 10%-15%. An example of this technique can be seen in
439:
approved a plan to construct a 9.5-metre (31 ft) wide and 116.5-metre (382 ft) tall building. This would be the first super-slender tower in the United
Kingdom.
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the movements of the water, specifically tuned such that when building is moved in one direction, the liquid force goes in the opposite direction to offset the movements.
130:
228:
In the 1970s Hong Kong was in a similar position of high land values and lax zoning laws, and started building pencil towers. Multiple factors contributed: in 1964 the
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316:, which can cause discomfort for occupants. Various engineering techniques are used to address this issue. One approach to manage the wind loads is to use an open
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is an example of the slim buildings of that era. Finished 1911, it is 700 feet (210 m) tall with floor dimensions of 75 by 85 feet (23 by 26 m).
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482:, a 18:1 ratio building that uses the first 200 feet (61 m) of its 950-foot (290 m) height for mechanical equipment to stiffen the building;
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but 25% of the property was exempt. This caused building designs of the era to have a wide base and thinner tower covering a quarter of the lot area.
490:, a 1,550-foot (470 m) tower that sets aside 350 feet (110 m) as mechanical space to build taller than would have otherwise been allowed.
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1138:
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Due to the shortage of land and the small lot sizes, the high-rise "pencil tower" is becoming the most common building type in urban Hong Kong.
467:, a 711-foot (217 m) tower that incorporates seven volumetric pods to extend the tower's floor plate, was completed soon after Sky House.
752:
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made the street the most expensive address in the global real estate market, with 41 transactions above US$ 25 million from 2015 to 2019.
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Building footing is another area of concerns. As the slender buildings have smaller footprints, the foundations need to go down deeper.
258:, a 65-story upscale residential building was completed. It was followed in 2003 by the world record 20:1 ratio, 72-story building, the
863:
161:
1220:
508:
1168:
925:
902:
888:
Carlow, Jason F. "Tiny
Footprints: Variations on the Hong Kong Pencil Tower". In Ameri, Amir; Dagg, Rebecca O'Neal (eds.).
198:
New York's subsequent 1961 Zoning
Resolution set tip height limits for the first time and replaced the shape limits with
958:
1008:
291:, a 50-story building with a 12:1 ratio. These were followed by more than a dozen pencil towers built in the 2010s.
92:
727:
564:
460:
203:
478:, a 15:1 ratio 1,396-foot (426 m) building that has five open-air mechanical floors throughout its height;
984:"111 West 57th Street's Super-Slender Concrete Formwork Officially Tops Out Atop Billionaires' Row, in Midtown"
386:
of 3D structural elements to help navigate narrow project site. A combination of air rights purchase and large
168:
156:). The new designs were encouraged by an increase in the price of land and enabled by the use of elevators and
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height of 88.5 metres (290 ft), still with a high slenderness ratio of 13.5:1. That was soon followed by
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on the east and west facades to stiffen the structure while leaving the north and south views unobstructed.
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triangular footprint. If it would have a rectangular base, a similar size building would be at 18:1 ratio.
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In 2020, Dutch developers proposed to build an 87-story mixed-use pencil tower at 1200 Bay Street in
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cited Sky House (2008), a 55-story building made possible by a purchase of air rights from the
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Pencil towers became one of the most typical building types in Hong Kong, beside tong lau and
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A main challenge of super-slender buildings is the management of lateral movements due to
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8:
783:"Super-tall, super-skinny, super-expensive: the 'pencil towers' of New York's super-rich"
249:
apartments. Overall, buildings with a slenderness ratio of up to 18:1 have dominated the
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Maxluck Court (left) and Fook Kee Court (brown) are examples of typical pencil towers in
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at 24:1. These developments highlighted the potentials of tall luxury pencil towers.
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are examples of slender towers of the time which were allowed to be built close to
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area, was the world's slenderest tower (20:1 ratio) at the time of completion.
20:
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1195:"Suggested Block Plan for 1200 Bay Supertall Among Details in Planning Docs"
26:
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617:
192:
100:
1169:"Super-skinny triangular tower proposed as Melbourne's tallest skyscraper"
87:
In the 2010s, pencil towers became a new phenomenon of building design in
1247:"Part 2: The Loopholes That Help to Send NYC Skyscrapers into the Clouds"
464:
288:
276:
266:
157:
153:
838:"New York Tops Ultra-Prime Residential Sales List As 'Pencil Thin' Wins"
810:
753:"What happens if you inject Hong Kong's density into Zurich's history?"
470:
There were several more buildings completed after 2014. These include:
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699:"Try a Little Slenderness: Explorations on the Hong Kong Pencil Tower"
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149:
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119:
107:. The first of this new crop of super-slim towers was the 1,005 foot
104:
77:
72:
1146:
Proceeding of CTBUH 2016 Shenzhen - Guangzhou - Hong Kong
Conference
238:
400:
80:
Tower, which has a slenderness ratio of 20:1, and its neighbor,
415:
area is home of many pencil towers, such as
Tregunter 3 of the
1221:"Go-ahead for UK's first habitable 'super-slender' skyscraper"
891:
106th ACSA Annual Meeting Proceedings, The Ethical Imperative
471:
160:
construction which allowed buildings to be built taller. The
108:
463:, as an early example of New York's super-slender towers.
1113:"Phoenix Apartments brings the skinny tower to Melbourne"
486:, the world's slenderest tower at a ratio of 24:1; and
701:. Faculty of Architecture, The University of Hong Kong
19:
For the skyscraper in France known as The Pencil, see
897:. Association of Collegiate Schools of Architecture.
1139:"A Case Study on Designing Superslim in Melbourne"
674:"The Vertical City, Part I: How Hong Kong Grew Up"
1269:
864:"Why Melbourne will see more skinny skyscrapers"
722:
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532:
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474:, the first supertall pencil tower in New York;
152:in the late 19th and early 20th century (before
509:"Keeping Skyscrapers from Blowing in the Wind"
776:
774:
713:
519:
344:is one of the early adopters of such system.
1035:. NUS Department of Architecture. p. 29
612:. Vol. 89, no. 7. pp. 44–53.
1059:Council on Tall Buildings and Urban Habitat
1244:
1001:
948:"New Tower Designs: Freespace in the City"
780:
771:
206:which gave birth to the concept of buying
91:. The newer pencil towers on Manhattan's "
1192:
1032:2019/2020 M.Arch Studio Sequence Handbook
811:"Tall Building Numbers Again on the Rise"
565:"What's Happening to New York's Skyline?"
162:Metropolitan Life Insurance Company Tower
111:tower. Two pencil towers on a section of
33:(middle), a pencil tower in New York City
667:
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271:
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122:has become the center of pencil towers.
118:Outside of Hong Kong and New York City,
25:
1218:
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808:
638:
636:
634:
506:
1270:
1245:Herzenberg, Michael (7 January 2020).
926:"Hong Kong: Property Tenure/Ownership"
861:
835:
781:Wainwright, Oliver (5 February 2019).
747:
745:
672:Dewolf, Christopher (6 October 2016).
671:
562:
171:'s shadow influenced the passage of a
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836:Howley, Kathleen (29 December 2019).
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563:Clines, Francis X. (1 January 2015).
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507:Higgins, Michelle (7 August 2015).
423:tower, located in the neighbouring
84:, a 65-story residential building.
13:
1219:Gerrard, Neil (14 February 2020).
1193:Mirabelli, Julian (10 June 2020).
887:
728:"Future City:20-21 Slender Towers"
14:
1294:
1083:
1055:"One Madison Park, New York City"
959:Hong Kong Institute of Architects
645:"Melbourne's next 'pencil tower'"
643:Cheng, Linda (16 February 2016).
584:
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862:Cheung, Alison (17 April 2019).
442:
335:To manage building movements, a
76:notable towers are the 72-story
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1111:Rollo, Joe (29 November 2013).
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809:Safarik, Daniel; Wood, Antony.
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461:Little Church Around the Corner
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204:transferable development rights
1009:"Future City:20-21 Mid-Levels"
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1:
1061:. August 2011. Archived from
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1167:Block, India (18 May 2018).
406:
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7:
542:"New York's Super-Slenders"
364:
230:Hong Kong Housing Authority
10:
1299:
610:Civil Engineering Magazine
125:
18:
16:Slender type of skyscraper
1137:Whittle, Kristen (2016).
1117:The Sydney Morning Herald
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146:Early slender skyscrapers
757:South China Morning Post
604:Reid, Robert L. (2019).
148:were first developed in
1011:. The Skyscraper Museum
730:. The Skyscraper Museum
544:. The Skyscraper Museum
437:Birmingham City Council
868:Commercial Real Estate
618:10.1061/ciegag.0001404
480:220 Central Park South
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202:ones. It also allowed
173:1916 Zoning Resolution
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1086:"Different By Design"
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189:The Sherry-Netherland
133:
29:
1225:Construction Manager
484:111 West 57th Street
326:111 West 57th Street
264:111 West 57th Street
224:(right) in Hong Kong
1283:Skyscrapers by type
1065:on January 28, 2018
95:" (a thin strip of
51:super-slender tower
1092:(March April 2017)
815:Structure Magazine
606:"Skinny 'Scrapers"
570:The New York Times
513:The New York Times
488:Central Park Tower
453:
411:In Hong Kong, the
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210:from nearby lots.
169:Equitable Building
143:
59:high-rise building
35:
904:978-1-944214-14-2
759:. 26 January 2016
457:Skyscraper Museum
337:tuned mass damper
93:Billionaires' Row
67:slenderness ratio
65:with a very high
47:pencil-thin tower
43:skinny skyscraper
41:(also known as a
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181:became regulated
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1254:. Retrieved
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1228:. Retrieved
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1202:. Retrieved
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1176:. Retrieved
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1150:. Retrieved
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1120:. Retrieved
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1094:. Retrieved
1090:NFPA Journal
1089:
1079:
1067:. Retrieved
1063:the original
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1037:. Retrieved
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1025:
1013:. Retrieved
1003:
992:. Retrieved
990:. 2019-04-24
987:
978:
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963:. Retrieved
955:HKIA Journal
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930:. Retrieved
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908:. Retrieved
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871:. Retrieved
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845:. Retrieved
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792:. Retrieved
788:The Guardian
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761:. Retrieved
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732:. Retrieved
703:. Retrieved
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681:. Retrieved
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652:. Retrieved
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621:. Retrieved
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546:. Retrieved
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101:Central Park
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46:
42:
39:pencil tower
38:
36:
1148:: 1208–1215
817:(June 2014)
465:One Madison
388:cantilevers
330:shear walls
300:Engineering
289:One Madison
277:One Madison
220:(left) and
158:steel frame
154:zoning laws
113:57th Street
1272:Categories
1256:3 December
1230:4 December
1204:3 December
1178:3 December
1152:3 December
1122:3 December
1096:7 December
1039:7 December
1015:1 December
994:2021-02-14
965:7 December
961:: 86. 2019
932:5 December
910:5 December
873:1 December
847:1 December
821:3 December
794:1 December
763:7 December
734:1 December
705:1 December
683:5 December
654:3 December
623:3 December
576:7 December
548:1 December
494:References
413:Mid-Levels
358:fire hoses
314:wind loads
295:Challenges
267:topped out
256:The Summit
251:Mid-Levels
218:The Summit
208:air rights
185:The Pierre
136:Mid-Levels
105:supertalls
82:The Summit
63:skyscraper
435:In 2020,
421:Highcliff
407:Hong Kong
375:Melbourne
370:Australia
342:Highcliff
281:Manhattan
260:Highcliff
247:cruciform
222:Highcliff
167:When the
150:Manhattan
140:Hong Kong
120:Melbourne
78:Highcliff
73:Hong Kong
1069:April 6,
365:Examples
239:tong lau
401:Toronto
179:shapes
126:History
97:Midtown
57:) is a
1173:Dezeen
957:(75).
901:
842:Forbes
419:. The
395:Canada
361:fire.
1142:(PDF)
951:(PDF)
928:. JLL
895:(PDF)
472:One57
328:uses
109:One57
99:near
53:, or
1258:2020
1232:2020
1206:2020
1180:2020
1154:2020
1124:2020
1098:2020
1071:2020
1041:2020
1017:2020
967:2020
934:2020
912:2020
899:ISBN
875:2020
849:2020
823:2020
796:2020
765:2020
736:2020
707:2020
685:2020
656:2020
625:2020
578:2020
550:2020
455:The
187:and
1251:NY1
614:doi
307:ksi
61:or
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