Whimbrel Design

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A response to the rules outlined in

Volume 2 of the draft Central City Plan:


Height limits:

In each zone these are generally too low for the number of stories suggested, especially if the buildings are to make good use of natural light and ventilation.

Before fluorescent lighing became readily available, commercial buildings usually had ceiling heights of between 3 and 3.6 metres, sometimes more. Added to that is at least 300mm for the structural floor, likely more than that if the space is much more than 8 metres deep, and say at least another 300mm for space for services such as ducting and plumbing, either in the form of a raised floor above the structural floor, or a suspended ceiling below. This gives an absolute minimum floor to floor height of at least 3.6 metres for a modern energy efficient building, and closer to 4.4 metres for a better quality building, more flexible in its use, more efficient and more pleasant to live and work in. Adding another 4.5 metres for the ground floor ceiling height with a further 0.6m for floor and ceiling and at least a metre for the parapet (or handrail) at the top for the roof garden, this makes a three storey building at least 13.3 metres tall at the absolute minimum. A two storey building would need to be at least 9.7 metres tall, a four storey building would need to be at least 16.9 metres tall and a five storey building would need to be at least 20.5 metres tall. This leaves very little room for design flexibility, building quality, or for that matter stronger than usual structure or more efficient and potentially bulkier building services.

In a better quality and more flexible building the ground floor should be higher, to give more flexibility in the fitout and allow for bigger windows above the verandah to let in more light. A 5.6 metre ceiling would be just enough to allow a mezzanine floor in part of the ground floor, in say a bookshop or a restaurant, and again with a stronger floor and more space for more efficient but bulkier services, the ground floor to floor height would reach maybe six metres, and often more. This was not unusual in many older and heritage commercial buildings, both here and overseas. Allowing for a green roof and a 1.2 metre high parapet to make the roof garden feel more sheltered, a better quality commercial building would need to be at least 12.1 metres tall at two stories, 16.5 metres at 3 stories, 21.1 metres high at 4 stories, and 25.5 metres high at 5 stories. None of this would include a sloping roof.

The height limits will also need to allow for towers and turrets, such as wind scoops and thermal stacks to drive natural ventilation systems, as well as water towers, communications enclosures and the like. A tower can also add visual interest and perhaps even house a small apartment. Buildings with decorative (and functional) turrets were some of our best loved landmarks before the earthquakes. The roofs described in the plan will need dormers to be useful space, and these were shown in the illustrations in volume 1. Such dormers will need to be quite large structures to be useful, perhaps 4m or more wide, though wider dormers would be fewer in number. The massing or relative proportions of towers could be related to that of existing or destroyed buildings where these features  were especially effective.

Window size:

30 % of a building facade is too big as a minimum window size, and allows too little design flexibility. Good visual connection to the street below can achieved with considerably smaller windows, and smaller windows are often desirable, either facing North to avoid overheating in summer, or South to avoid excessive heat loss. Commercial buildings built before the 1940s were designed to rely on daylight for their primary illumination and open windows for ventilation. The old post office in Cathedral square has a window/wall ratio of about 15% above the ground floor (less if the parapet is included), and the former United Service Hotel (a Victorian building with particularly large and plentiful windows), had a window/wall ratio of about 27%. The first floor of the regent theatre building also had a window/wall ratio of about 27%, and the spaces behind that wall were flooded with light and had excellent views out. The Press building had a window/wall ratio of about 29%, but if the windows there were any bigger there would have been no room left for structure, shading or architecture. All three of these buildings maintained a good visual connection with the street, and when first built all were entirely dependant on natural light.

The visual connection with the street gained by the windows is also affected by the detailing of the windows, with a relatively small window carefully detailed having a rather greater effect than a very large plain window with no opening portion. Structure (especially in earthquake resistant buildings) takes up space and is most effective at the building perimeter. Other divisions, mullions, structural louvres, light shelves and similar necessary and potentially beautiful things all take up space on the front of a building.

At ground floor level we must be careful not to make things difficult for structural engineers. Structure takes up space, especially where lateral loads (such as those due to earthquakes) must be considered. We must allow enough solid in ground floor walls to accommodate any structure required.

Building separation:

While it is clearly desirable to have a continuous street frontage along a city block, it is still necessary to separate the individual buildings so they do not pound against one another during earthquakes. In many cases in our city the seismic separation provided was insufficient and buildings were badly damaged as a consequence. Recent studies being carried out by structural engineers are showing that we have previously underestimated the amount that buildings move in earthquakes, and seismic protection systems such as base isolation (which is generally regarded as the best overall approach, if not a cheap one) tend to need more room to move. A large base isolated building may need to be up to 250mm away from the boundary, and it may end up being better to put a narrow footpath between the buildings, which would also be useful for maintenance and perhaps even ventilation.

Awnings, canopies and arcades:

While there may be benefits to having all awnings at a uniform height on any one block, this does seem unnecessarily restrictive. A high canopy may feel more open and generous, but it also offers less shelter from sun and driven rain. A lower awning allows more room for windows above the awnings, making ground floor spaces more pleasant and energy efficient. So long as there are no excessive gaps in the roof and the transitions are detailed gracefully, a range of different canopy heights along a block can do little harm, but allow the design of each building to be optimised, both aesthetically and for its intended use. 2.6 metres seems to be a reasonable minimum height, though in some cases an argument could be made for less.

There does not appear to be any allowance for buildings having a ground floor arcade instead of a verandah. As long as there is an effective transition from an awning to the space under an arcade, or if the developers of an entire block frontage choose to design a ground floor arcade instead of an awning the experience for pedestrians should be no less pleasant than under an awning. It may potentially be more beautiful. Because an arcade will generally result in more footpath space, it could be desirable to allow a developer to encroach over the footpath on the upper floors, provided that the public space provided at ground level was wider than the standard footpath and free movement of pedestrians was not compromised.

Horizontal and vertical lines to building frontages:

It is not clear what is meant by ‘visible horizontal separation of floors’ or how rigidly this would be enforced. Will clear distinction between ‘window’ and ‘not window’ be sufficient? Many buildings, both heritage and modern have windows grouped in vertical bands with the floor levels only implied by the spandrel panels above and below each window. In these cases it is perfectly easy to count the number of stories the building has, but there are no continuous horizontal demarcations, and in most buildings the exact floor level relative to the window sills is almost never obvious, even in our best loved heritage buildings.
It is not clear how rigorously the concept of ‘floor to ceiling solid vertical elements at not more then 6 metre centres or less’ is to be interpreted. If for example the ground floor facade consists of a row of 5.5 metre diameter arches resting on short columns, then there is clearly a continuous vertical support, even though there is no continuous vertical line. Another example might be a column that forks or branches out to support the wall above, but while visibly providing support does not offer a solid vertical. Would either of these be acceptable? By the same token would a slender vertical window mullion running floor to ceiling be acceptable? Many heritage commercial buildings had a row of small steel columns set behind the shop windows holding up the facade above, with only thin window mullions providing a clear vertical line, yet the frontage was pleasant and offered a clear connection with the street. The exact intent of this rule is not clear.

Balconies to apartments:

The minimum private outdoor living space requirements for apartments are excessive, and no other city in the world where people commonly live in apartments has such requirements. The 10 square metres of private outdoor space accessible directly off a living area is a space the size of a bedroom. At the minimum depth of 1.5 metres, such a balcony would be 6.6 metres wide and take up the entire width of a small apartment. On a site with buildings on either side this would make an apartment rather dark, and prevent it from having windows directly overlooking the street. The front of such a building would have the appearance of a series of dark caverns, much like a parking building. If the balconies were squarer in proportion then any room behind the balcony would be too dark to use. This balcony requirement could only really work if the building stepped back at each floor, but this would effectively prevent the building of apartments at a level below the minimum building height for any given area, and even then the lower floors would end up being deeper and so less well lit. It would also result in balconies and roof terraces where each terrace is directly overlooked by that of the apartment above.

Requiring such vast balconies will also make it uneconomic to design a building with space that could be readily converted from apartments to office or light industrial space or vice versa, thus reducing the flexibility of our buildings.

A better solution would be to put that outdoor space into the communal outdoor living space allowance as part of a roof and/or courtyard garden, which could then be considerably larger or developed to a higher standard, and give each apartment a required balcony of say 1 or 2 square metres minimum, more akin to that found in most European and American cities. In many cases balconies will get little or no use outside of summer, and will merely become an unsightly roosting place for pigeons. Many apartment dwellers would prefer most of their windows looked directly out onto the street rather than onto a grimy balcony, especially if less balcony space meant more daylight and solar gain through less shaded windows.

Green Building:

The focus put on green building is commendable, but the points system appears to put too much weight on gadgets which are easily retrofitted later, or are at risk of being ‘value engineered’ out by project managers late in the project. More emphasis should be placed on important green building principles that must be incorporated into the overall structure and design of the building in order to be effective, and cannot easily be retrofitted later. Three of these are as follows:

Daylighting:

To make effective use of natural light, a building must have high enough ceilings and relatively narrow floor plates. A good principle to bear in mind is that in the USA before cheap electric lighting was readily available, a space was only considered to have enough light to be lettable if it was no more than about 8.5 metres from a window. These buildings had high ceilings, between 3 and 3.6 metres, with relatively tall windows to cast light deep into the space. With lower ceilings the rooms would need to be shallower, but with higher ceilings deeper spaces would be effective. Window mullions and light shelves can help distribute light more effectively, especially if they are carefully designed. This is fundamental to the very shape of a building.

Natural ventilation:

Natural ventilation can also save considerable amounts of energy, especially air conditioning costs. Building can use things like solar stacks and/or wind scoops to drive ventilation systems, and air temperature can be managed with careful use of thermal mass and even simply the considered placement of openable windows. All of these things tend to be expensive, but will generally pay for themselves in the long term. They all need to be considered from the outset in the design of a building, as they tend to be difficult or even impossible to economically retrofit later.

Stairs:

In a building less than 10 stories high there is no excuse for not having at least one staircase as readily available to all users as the lifts. Certainly for the first three or four stories of any building a good many occupants will choose to use the stairs if at all possible. If at all possible the main stair should also have sufficient natural light, and should be a pleasant space to be in. Ideally the lifts should occupy the same firecell as the main stairway, so as to better present the stairs as an alternative to the lift and make the stairs easier to find.

Recession Planes in Central City Living Zone:

While recession places are understandable in single-storey areas with large quarter acre sections, they are generally unhelpful in higher density areas. The recession plane on the boundaries forces houses to conform to a truncated pyramid outline, and fitting in windows and a convenient floor plan leaves little scope to make such buildings attractive. Because these houses cannot have large upper floors, they tend to cover most of the site and most of the outdoor space is a narrow strip right around the building. Most multi-storey developments subject to recession planes are usually very ugly. Generally the most attractive and pleasant  high density housing built today is in larger developments where recession planes do not apply, and a developer can build a row of terrace houses or a well proportioned apartment building without arbitrary restrictions on it overall shape. In high density areas requirements for steps in the side walls of buildings also seems to be an arbitrary and often unhelpful requirement, as we have all seen beautiful buildings where this is not adhered to, and ugly ones where it is. Most of us in the design professions have encountered situations where we could have designed a more efficient and more attractive building if it weren’t for these requirements.

Where relatively high density is required (such as all of the Central City Living Zone) a better approach would be to set a front and back setback line and perhaps a maximum site coverage, but then only restrict the volume of building that could be built, which depending on the location and width of the site could be a zero lot line on narrow sites or in high density areas, or up to a couple of metres on larger sites in lower density areas. This simple volume restriction would allow considerably more design freedom while still controlling density, as a designer could concentrate that mass in a simple geometric form, if their client preferred in a much more sculpted building, or even an intricate assembly of turrets and gables. This approach would effectively sacrifice light at the sides of a building, but we readily accept this in terraced housing, ownership flats and apartments already. This approach would give us the freedom of individual houses designed to the individual requirements and tastes of their owners, with the benefits of higher density. The streetscape could be far more attractive with designers able to compose the houses to be beautiful and not merely rule-compliant.
James Carr - October 2011