Tall buildings make no sense for Bristol

Why tower blocks make no sense for Bristol:

[1] Towers are expensive - land-efficient, but not floorspace efficient.

Towers inherently cost more to build (£/sf), take longer to construct, and are less space efficient.

Yet they obviously do get built, because they can maximise returns on investment, but only in circumstances where land costs are very high - and returns too. So the developer needs to be sure that he can sell to those in good jobs.

Tall buildings therefore will not increase housing supply for lower-income groups. Social providers shun them because their ongoing maintenance costs are so high (which is why so many council-owned tall buildings fell into disrepair and were demolished). And selling apartments in tall buildings can be difficult outside London, because mortgages on apartments above the 10th floor are hard to source. Students are another target market, because less cash-constrained due to student loans and willing to temporarily tolerate space-constrained housing conditions. But the student boom may well be temporary.

All these reasons explain why planning permissions for tall buildings in medium-income medium-cost locations lonce granted are often not followed up.

Exploring costs further

Towers can cost around 40% more than mid/low-rise buildings. A major issue is that connecting all of the stuff above ground to the ground requires taking space away from all the floors below.

Every additional floor requires a tiny slice of every single floor below. The result is that 15%-25% of a high-rise’s floor-space is typically wasted, much space in the middle of high rises being consumed by lift shafts and other utility areas. To illustrate the point the architect Tom Steidl shaded these diagrams of towers in Vancouver (88.8% efficient) and Los Angeles (80.9% efficient), with net square feet in orange:

In a tall structure, the lateral and vertical loads require additional restraints (outriggers, external bracing, enhanced cores, etc). Slenderness ratios drive up costs on towers, and there are additional requirements to deal with wind loadings, mitigation of solar gain, etc. More lifts are needed for taller buildings, taking up more space per floor. Services are more expensive in high buildings: the need to boost water supplies, the pressurization of heating and cooling solutions, also reducing efficiency due to additional intermediate plant floors. To mitigate fire risks, sprinklers rather than dry risers are needed above 60 metres. In residential buildings, balconies become less desirable at height and more expensive solutions such as recessed balconies and winter gardens tend to be adopted. Finally, typically, in desirable locations, the restricted sites have a profound effect on logistics, bringing working restrictions, reducing labour productivity and increasing the burdensomeness of health and safety measures.

Ground-related housing types can minimize this efficiency loss by eliminating interior hallways and vertical circulation. A typical three apartment low-rise building achieves almost 90% net-to-gross efficiency, and every additional flat makes the design even more efficient. Six flats can be accommodated in the same circulation area, yielding almost 95% efficiency.

All these costs add up. Between the 10th and the 50th floor there is typically a 43% uplift in construction costs, explains Paul Cohen, partner at the consultancy EC Harris. Their shape and height "make tall towers intrinsically less efficient, and therefore more expensive, than lower rise schemes."

Source: Aecom

Source: Aecom

Consultants are quick to add that these costs need not prevent tall buildings from being profitable. But the right conditions need to be met - high land costs, and clients with money. In London these are usually foreign clients - a Transparency International analysis of 14 London developments showed that 80% of known buyers came from abroad, with many properties appearing to be empty, judging by the electricity usage.

Funding costs

High levels of pre-sales are a pre-requisite for building tall towers. Where developers are relying on bank lending or other sources of senior debt to fund the development, the conditions can be onerous. "Some 30% of the units in the tower will need to be pre-sold as a minimum, although in some instances funders will demand that the value of the development funding advanced be matched pound for pound by the value of units sold off-plan," writes Gráine Gilmore of EC Harris. "It is worth noting that UK banks have been largely inactive in development funding for towers in recent years..."

Maintenance costs

High rises are generally significantly more expensive than low- or mid- rises to maintain.

For a high rise to remain functional, it requires cyclical maintenance and replacement of its major components over time. By the time it reaches 40 to 50 years of age it will have gone through several partial or complete retrofits, likely in stages.

The first major component that will need maintenance and replacement is the roof, which will usually last up to about 10 years, after which it will require maintenance, and replacement by the time it reaches 15 to 18 years.

The heating plant may last up to 20 years followed by required maintenance for another five years, after which it will have to be replaced altogether. The lifts may last up to 20 years, with more frequent maintenance for the following 10 years, and likely replacement after that.

Standard size windows may last about 50 years, requiring occasional maintenance such as replacement of screens and sealant.

All-glass buildings are problematic. Glass is a great selling feature — but building experts have long known that it less energy-efficient than the stone and concrete buildings of 40 or 50 years ago. Indeed, as energy costs climb, glass towers may become the “pariah” buildings of the future.

University of Waterloo Professor John Straub was quoted by CBC Toronto as saying that “With these buildings — both skin and the mechanical systems are going to have to be redone in a 25-year time frame. The concrete structure will be there for a long time but in 20, 25 years time, we are going to see a lot of scaffolding on the outside of the buildings to replace the glazing, sealants and the glass itself”.

High rises do not provide housing for the less wealthy

These high costs have an obvious effect - only the wealthy can afford them. Therefore high rises are no solution for the housing crisis.

"Ken Livingstone's support for tower blocks has not increased the supply of family-sized affordable housing in London," Duncan Bowie, senior lecturer in social planning at the University of Westminster told the Guardian in 2008.

"There is a direct correlation between height of building, high density and the low proportion of social rented family homes." Yet this is the type of housing London, with its chronic and increasing overcrowding, most badly needs. However the bulk of what's being built is laughably unaffordable and mostly small - one and two-bedroom apartments.

The same will undoubtedly be true in Bristol.

Fire risks

Fire hazards present several challenges in high rises that are not found in traditional buildings, including:

    • greater difficulties for firefighters to access a smoldering high-rise building,

    • longer egress times and distances,

    • complex evacuation strategies,

    • smoke movement and fire control.

Typical dangers in fires involve flame, smoke, heat, toxic gases, flashover, and backdraft explosions. The multiple floors of a high-rise building mean more firefighters are needed to travel the great vertical distances on stairs to evacuate the building. Therefore, it takes a much longer time for fighters to rescue tenants of high-rises than that of low-rises.

As Simon Jenkins says in the Guardian (15 June 2017): "How many times should we say it? Don’t build residential towers. Don’t make or let people live in them, least of all families. They are antisocial, high-maintenance, disempowering, unnecessary, mostly ugly, and they can never be truly safe. No tower is fireproof. No fire engine can reach up 20 storeys, period."

High rises age poorly

Bristol is full of examples where single-family homes have been adapted to house two or three or four families, with dormers added here and garage suites there, and basement inserted. But try as we may, we can't think of an example where a high-rise had been adapted to a different circumstance. It seems a high-rise is forever.

The fact is that most glass towers will not be able to be renovated. Studies have shown that "the mid-century modern glass tower, a staple of American urban environments, often cannot be adapted to out-perform a new, more efficient building," says architect Lance Hosey. These buildings are very expensive to upgrade and to make efficient.

It usually costs more to upgrade than to demolish and replace. For example the modernist 52-floor 270 Park Avenue building, totally renovated in 2011, is now to be torn down.

Are High Rises Even Green?

Contrary to public opinion, which thinks high-rises must be sustainable because they allow for so much density, Patrick Condon of the University of British Columbia says that high-rise buildings are not green at all. He says, "high-rise buildings are subject to the effects of too much sun and too much wind on their all-glass skins. And all-glass skins are, despite many improvements to the technology, inherently inefficient. Glass is simply not very good at keeping excessive heat out, or desirable heat in. Our high-rises, according to BC Hydro (the province of British Columbia's main electric utility) data, use almost twice as much energy per square metre as mid-rise structures."

[2] High rises: depression, loneliness, and anti-social behaviour

In Britain, local governments have been knocking down tower blocks by the dozens since the late-1980s. A recent example was the spectacular controlled explosion of one of Glasgow’s Red Road flats. The horrors of high rise living have even got into a remake of JG Ballard's classic 1975 novel 'High Rise'.

Psychological effects:

It is hard to escape the conclusion that although high rises are fine for many people, in general high-rise residents are more depressed than people of the same income and status would be in mid-rise or low-rise buildings; they know their neighbours less, are less socially trusting, are lonelier, and are more likely to commit suicide. High rises are specially bad for children, who make less friends.

The most thorough survey of the literature on happiness in high rises is a 2007 review by Robert Gifford. Here are Gifford's findings (compressed). Many of the studies are rather old, but the issue remains live: Bath and Exeter Universities are now conducting a study into the curious phenomenon of high rise induced motion sickness, itself a suspected cause of depression.

Depression. Mothers who lived in flats reported more depressive symptoms than those who lived in houses, in an English study (Richman, 1974). Rates of mental illness rose with floor level (Goodman, 1974). When residents moved out of high-rise dwellings, they reported fewer symptoms of depression (Littlewood & Tinker, 1981).

Low- and mid- rises encourage pro-social behaviour. Students who lived in low rises said they were more willing to offer help and to seek help than those who lived in high rises (Nadler, Bar-Tal & Drukman, 1982). Students in the high-rise dormitories reported knowing fewer others of whom they felt they could ask a favour.

Other studies have examined positive social behaviour in a more concrete manner, by measuring actions, as opposed to asking opinions. For example, stamped, addressed letters without a return address were placed on hallway floors in college dormitories that were 22-25 storeys, 4-7 storeys, or 2-4 storeys (Bickman et al., 1973). The number of letters mailed was the measure of pro-social behaviour. Letters were mailed in inverse proportion to building height in both studies, a significant difference in favour of low-rise buildings.

Using a different measure of pro-social behaviour, donations of milk cartons for an art project were sought. Again, the fewest donations per capita were received in the high rises. Interviews of residents performed also indicated that the high-rise building was perceived as having the least amount of resident cooperation.

Friendships. During ongoing research into social isolation among older people in Leeds, residents of high-rise buildings reported feeling lonely and isolated – some were afraid to even open their front doors.

Because high-rises tend to separate people from the street and each other, they greatly reduce the number of chance encounters that happen, which are crucial to the liveliness of a city and to creating social capital. And because people are cooped up in tall buildings, they are less likely to experience propinquity, according to Wikipedia "one of the main factors leading to interpersonal attraction. It refers to the physical or psychological proximity between people. Propinquity can mean physical proximity, a kinship between people, or a similarity in nature between things." Propinquity happens in public spaces – on the street, in parks, public transportation and city squares. High-rises diminish people's participation in public spaces and therefore diminish propinquity.

In one study three-quarters of low-rise residents reported they had made good friendships within their estate, but only half of the residents of a high rise could make the same claim (Stevenson, Martin & O’Neil, 1967). Saegert’s (1979) study of U.S. public housing estates found poorer social relations in high-, as compared to low-rise buildings.

In a study that investigated the sense of community in high-rise and garden apartments in public housing for the elderly, the residents of garden apartments had a significantly greater overall sense of community, and expressed a greater sense of membership (Za & Devlin, 1988).

None of this is surprising. In a high rise you share the lifts with many people. You rarely see neighbours that you know. The lift and lobbies are barely more personal than the street.

In Hong Kong, a high-rise, high-density city, interview results suggest that the overall sense of residential community is low, and that where respondents had a very strong sense of neighbourhood, their interactions were often work- or school-based, with colleagues or schoolmates living in the same area (Forrest, La Grange & Ngai-Ming, 2002).

Paradoxically residents of high rises meet more other residents. But they don't meet them enough to get to know them. So they have fewer friendships in the development, per capita, than residents of low rises.

Children: Numerous studies suggest that children have problems in high-rises; none suggest benefits for them. Two Israeli studies found that raising children in high-rises, especially on higher floors, is problematic (Broyer, 2002; Landau, 1999). Children under 8 were not allowed to go downstairs by themselves, but after they were allowed to go down, parents found it difficult to supervise their play.

A Japanese investigation (Oda, Taniguchi, Wen & Higurashi, 1989) concluded that the development of infants raised above the fifth floor in high-rise buildings is delayed, compared to those raised below the fifth floor. The development of numerous skills, such as dressing, helping and appropriate urination was slower. Children who live on higher floors also go outside to play less often (Nitta, 1980, in Oda et al., 1989).

Suicide: Suicide may be greater in high rises than in low rises; the issue is whether tall building leapers would have used some other method if they did not happen to have a high window available.

Source: Lily Bernheimer, The Shaping of Us. Robinson 2017

The leading psychologically-oriented urban planners agree - high rises are bad for our mood

Notable are the views of Jan Gehl, the world's leading student of building forms' impact on human happiness. In a career devoted to empirically researching the architectural environment as it affects human connectedness and sociability, Gehl has concluded that the maximum desirable urban residential height is around five or six storeys. Above six floors people lose touch with the street, and lose their sense of human connection.

Similarly Jane Jacobs argued in The Death and Life of Great American Cities that traditional low-rise neighbourhoods with front porches, facilitate “eyes on the street” natural surveillance, and promote a sense of security and community spirit.

Effects on surroundings

Inhumanely high towers often shatter the human scale by dwarfing nearby public spaces and buildings, particularly those of a historic character. When tall buildings are juxtapositioned next to low-rise buildings, they often deprive nearby streets of light, looming over their neighbours, and shadowing their gardens. Their ground floors often present little of interest to the world, diminishing the fun and sense of joy of being on the street. They fail, unlike ordinary streets, to give passers-by a warm welcome, but rather present a cold, impersonal face.

Architect Robert Freedman comments that in walk-up apartment neighborhoods in Manhattan residents or a passers-by feel a sense of warmth, almost a welcome, which is not found in Manhattan's towering skyscraper neighborhoods - a human feeling.

Award-winning Myatts Fields, London

He explains: “While walking, you have the sense that you ‘fit’." Freedman argues that vernacular brick, wood, and stone low-rise is more humane than the glittering, steel-and-glass of high rises.

Wapping Wharf, a successful Bristol mid-rise development, which follows Jan

Gehl's 5-floor advice. We should build more like this.

Part 3: Densification is great. But it doesn't require tower blocks.