“Adapting Buildings and Cities for Climate Change” by Sue Roaf (2nd Edition, Architectural Press, 2009).
Below are passages from Chapter 12, “The End of the Age of Tall Buildings,” that are especially relevant to Vancouver.
Table 12.1 Results of a study of the embodied energy of buildings showing that the taller they are the more energy is embedded in them per metre square during construction. The case study buildings in Melbourne, Australia, show embodied energy results in GJ/m 2 gross floor area by element group
|Height in storeys||3||7||15||42||52|
Taken from Treloar, G.J., Fay, R., Ilozor, B. and Love, P.E.D. (2001) An analysis of the embodied energy of office buildings by height. Facilities , 19(5/6), 204 – 14.
In addition, the higher the building, the more it costs to run because of the increased need to raise people (lifts), goods and services and also, importantly, because the more exposed the building is to the elements the more it costs to heat and cool. The higher the building, the higher the wind speeds around the building, the more difficult to keep the wind out, and the more the wind pressure on the envelope sucks heat from the structure, particularly as with many twentieth century tower blocks the envelope leaks. The higher the building, if standing alone, the more exposed to the sun it is and the more it can overheat. And hence the higher the building the more it costs to keep the internal environment comfortable. Lifts are very energy expensive and costly to run, maintain and replace. Lifts alone can account for at least 5 – 15% of the building running costs and the higher the building, the more it costs.
The higher the building, the greater the annual maintenance costs to keep it clean, repaired and safe. The failure of a single building element can be catastrophic. For example, the silicone mastic used to weatherproof glazing panels was given in its early forms only a 15-year performance guarantee. If mastic fails, it can result in the need to remove and/or repair every single glazing panel in the surface of a building, which in a high-rise building would prove to be a crippling expense. Day to-day maintenance of buildings can be similarly expensive and where building envelopes are problematic to access, they can have enormous annual cleaning costs. One famous tall building in the City of London has allegedly proved impossible to sell because of its astronomical maintenance and running costs, and even relatively lower rise buildings such as the Greater London Authority headquarters can run up annual window-cleaning bills in the region of £ 100 000. Many tower blocks have fallen into a very poor state of repair because their owners cannot afford their upkeep. The historical reality has proved that it is often cheaper to blow up tower blocks than repair them…
Particularly vulnerable to a more extreme climate will be leaky envelopes, typical of concrete panel tower blocks; and glass and steel structures that suffer from very high levels of solar gain are very difficult to shade high up and have traditionally had extreme cold bridging problems through the structure. Tower blocks also typically have to have air conditioning, as they are of sealed envelope construction, a decision that can quadruple energy costs at a stroke, and in turn gives them a disproportionately high carbon emitter status, at a time when carbon taxes for homeowners are being spoken of. So on top of high running costs homeowners would have also to consider that they may have to pay far higher carbon taxes associated with high-rise buildings in the future.
SOLAR, WIND AND LIGHT ACCESS RIGHTS
There are real issues of solar rights with high-rise buildings that have to be addressed and agreed. The higher a building is the greater the shadow it casts on the buildings around it. The shadow cast by a two-storey building is larger than the shadow of a one-storey building of identical floor plan by 2%. A building of 16 storeys casts a shadow 43% larger than a one-storey building, at noon on the winter solstice. 24 A high-rise building will cast a shadow over a huge area of a city, affecting the light and warmth and ability of the shadowed building to generate solar energy. Naturally, if the building is close to the high rise it will be shadowed for most of the year and if it is distant it will be shadowed perhaps for only a period in the day; however, this could be when the solar energy is most needed. Solar rights legislation is being passed in cities around the world and an excellent example is that of the Solar Law of Boulder, Colorado, where legislation has been enforced to ensure that buildings do not steal the sunlight from adjacent properties. There is also a case to be made for wind rights to ensure that new buildings do not cut off the air flow around buildings that may be needed to power ventilation systems or generate electricity.
Two conditions conspire to make daylighting difficult in high-density buildings. One is how wide they are, from one external wall to another. Once the width of a building increases beyond about 12 m it is difficult to daylight it. Not withstanding the depth of a building, the amount of daylight reaching an interior is dependent on how much clear sky is visible from any particular window. The more sky can be seen from a window, the greater the amount of daylight that can enter a
room. In a dense urban setting, it becomes clear that windows close to the ground will not provide significant daylight to interiors in high-rise districts.
Perhaps the worst climatic impacts that are associated with high-rise buildings result from the wind. The increasing height of a building results in two major factors:
● The speed of the wind increases the higher it is off the ground, resulting in higher air pressure experienced on the surface of the building.
● The higher the pressure at the top of the building the greater the difference in pressure between the top and the bottom of the building, increasing the speed of the wind between the apex and the base of the building.
The increasing high-level air pressure causes accelerated air speeds on the surface of the building, significantly increasing air penetration into the building, and out on the leeward side of the building through openings and cracks. This can substantially increase the heating or the cooling load of an exposed high building over the loads of a low- to medium-rise building, often requiring expensive systems of climate control to even maintain a comfortable indoor climate the higher up the building one goes, but perhaps the potentially most severe impacts of wind discomfort occur in the outdoor spaces around high-rise buildings. Many of us will experience such discomfort daily. In the city of London, for example, it is difficult not to notice the significantly increased wind speeds on an ordinary summer’s day in say, Threadneedle Street, adjacent to a high-rise tower. Wind becomes an annoyance at about 5 m/s, by causing clothes to flap and disturbance to the hair. At 10 m/s it becomes definitely disagreeable and dust and litter are picked up and by 20 m/s it is likely to be dangerous. In studies the Building Research Establishment (BRE) found that wind speeds of 5 m/s were exceeded less than 5% of the time in areas of low-rise developments but were exceeded over 20% of the time in areas with high-rise buildings. With the increasingly deep low-pressure systems currently being associated with climate change and their associated increases in wind speeds, the ground-level turbulence and wind speeds in city streets may become increasingly less tolerable for the ordinary citizen in areas adjacent to tower blocks.
Higher wind speeds at street level are also associated with higher windchill factors, making the outdoors even more uncomfortable. Where today problems of outdoor air comfort may result from wind flow down and up from high-rise buildings, they may in future climates become the cause of increasingly dangerous street conditions as wind speeds increase. There are several laboratories in the UK where the wind impacts of new city developments can be tested on models in wind tunnels or through simulation, as for instance at the Universities of Cardiff, Sheffield, Cambridge, UMIST and at the BRE and the National Physical Laboratory. Such wind testing is required by local authorities and by independent bodies, but for current climates only, and not future wind environments.
End of excerpt.