sun, light and wind in central wellington

8/7/2019 SUN, LIGHT AND WIND IN CENTRAL WELLINGTON

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SUN, LIGHT AND WIND IN CENTRAL WELLINGTON

Michael Donn, Werner Osterhaus and Andrew Bluck

Centre for Building Performance Research

School of Architecture, Victoria U niversity of Wellington

PO Box 600, Wellington, New Zealand .

Paper submitted to the 1999 ACSA/CIB Technology Conference

Technology in Transition: From the 20th to the 21st Century

Under the theme:Architectural design and the building industry

Montreal, Canada

June 25-30, 1999

Phone: + 64 4 802 6200

Fax: + 64 4 802 6204

email addresses: [email protected], , [email protected]


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Topic category:Architectural design and the building industry

ABSTRACT

This paper examines the application of wind tunnel te sting and solar access assessment in the Central

Business District of Wellington, New Zealand. A wind tunnel test report must be submitted for all

new buildings over four storeys in the Centra l Business District before planning permission is granted.

Solar access is much less thoroughly considered. Practical barrier s that impede the full achievement of

the po tential promised by these techniques are identified. The bar riers are pr incipally ones related to

economic efficiency and the speed of the approval process. Developers like to have straightforward

processes. The system has to look fair and this often leads to a demand for a simple compliance

procedure. Performance requirements are seen as expensive with respect to consultants=time.

Whichever is the cheapest building design idea in te rms of design effort and construction costs, is

seen to be the most desirable. There is apparently a strong desire amongst developers to bring a

formula-based approach ba ck into urban design practice. The paper concludes with a proposal for a

revision to the Wellington City Council wind tunnel test procedure . It is neither a pure performance,

nor a pure prescription procedure . Rather, it is a hybrid. A detailed prescription is proposed for the

dete rmination o f which buildings must be tested. Those buildings that are tested must comply with

the existing performance specifications.


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Topic category:Architectural design and the building industry

Most educators specialising in architectural technology believe that their science can contribute

positively to the qua lity of the bu ilt environment. This paper examines the application in the Centr al

Business District of Wellington, New Zealand, of two architectural science techniques for the

assessment o f the per formance of a building. It ident ifies the practical barriers that impede the full

achievement of the potential promised by these techniques.

Wellington city is the cap ital of New Ze aland. The city itself has a population of around 125,000. The

Central Business District serves a greater Wellington area o f population close to 500,000. It perches

on the edge of a harbour surrounded by three 500m high hills. At least partly because of the small

area of flat land available for development the CBD has the a ir and style of a much larger city. The

financial and shopping districts have buildings that are mostly 15-20 storeys tall. The traditional

harbour edge of the CBD is being slowly reclaimed by the city for recrea tional and other uses now

that its port functions are being reorganised and modernised.

High ambient wind speeds are experienced on a regular basis in Wellington. At least one CBD

building had been causing wind problems at ground level for pedestrians since the 1920's. Traffic

police were stationed on these windy corners in the 1920's and 30's to assist people across the street.

And well into the 1960's ropes were placed a t pa rticularly windy corners to prevent people from being

thrown inadvertently in front of passing traffic.

A Wind Ordinance [1] was introduced in Wellington as an apparent response to the public debate

abou t the predicted impact on the wind of a thirty-storey building on a prominent corner in the main

downtown shopping p recinct. This debate was fostered by a wind tunnel test that was made public. It

changed the mind-set of the local populace and hence the City Council. That early Wind Ordinance

required developers merely to submit a AWind Report@if they were constructing a building of over 4

storeys in the CBD . A revision brought into force in 1985 [2] required wind tunn el testing for all new


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construction and a lso specified performance criteria. Buildings which failed to meet t hese criteria

would not gain a permit for construction. For the Standard and Full Wind Tunnel Tests the

Performance requirements were:

Existing Wind Speeds Wind speeds resulting from

development proposal

Requirements on developer

If exceeding 10m/second within a

proposed open space or

landscaping area for which a

development bonus is sought.

Reduce to 10m/second where

public have access within open

space/landscaping area or

relinquish the development

bonus.

Up to 15m/second If exceeding 15m/second 1) Reduce to 15m/second

2) Although other directionalwind speeds may be increased

towards 15m/second, the overall

impact is to be no worse than

existing.

15-18m/second If exceeding 15m/second Reduce to 15m/second

Above 18m/second If more than 18m/second Reduce to max. 18m/second.

The Ordinance re-write in 1985 concentr ated on two flaws with the previous format: a) it required

developers to state in the wind report how they would alter the building in response to the wind

tunnel test r esults; and b) it tried to encourage architects to consider wind issues early in the design

process. A two-stage testing process was set up, the first stage of which was simple and exploratory to

encourage consideration of aerodynamics ear ly in the design process. The incentive to use this simple

do-it -yourself test was that successful completion avoided the necessity for the deta iled second stage

which was more complex, more expensive, and normally had to be done once the design was complete ,

necessitating expensive a lterat ions if the design was shown not to perform.

The simple wind tunnel test procedure was intended to make it easy for wind environmenta l design to

be an integral part of the ea rly design phase of all CBD bu ildings in Wellington. It was predicated on

the philosophy that decisions made ear ly in the building design process are crucial to the success or

otherwise of a building=s environmental performance [3]. ARemedial@measures tacked onto a

fundamentally flawed basic design would be far less successful than getting the design r ight to star t


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with. The 1985 Wellington City Council Wind Ordinance specified three Wind Tunnel Tests: a Pre-

Design Test, a Standard Testand a Full Wind Report. Where t he re sults of the simple Pre-Design Wind

Reportmet the Council=s performance criteria, the Council=s requirements in respect of wind design will

be deemed satisfied [2].

Ot her cities around the world haveAwind ordinances@. San Francisco, Boston, Edmonton , Calgary all

have varying levels of complexity of wind ordinance. For many cities consider ing introduction o f such

an ordinance Criteria are not specified in the legislation, which results in negotiation between developer

and city authorities on a case-by-case basis [3]. The situat ion varies from Wellington in two key areas:

the definition ofAll high rise developments in the centra l area. In Wellington in 1985 the O rdinance

applied to all buildings no matter what their height. The argument was that placing a large park in

the middle of a set of 20 storey buildings could cause more problems of exposing the pedestrian to

high winds than a t en storey building would.

Criteria for acceptable performance are often given in terms of mean wind speed, and a lso depend on

the use of the area and the season of occurrence. In places like Calgary they have more severe winter

criteria to counter the wind chill effect. At the time of introduction of the Wind Ordinance in

Wellington the approach of specifying acceptable performance rather than building size and shape

was an innovative notion.

Six year s after the O rdinance was revised a survey [4] sought to ascertain designers=attitudes towards

the wind. Wind reports on 51 buildings designed by 23 architectural firms had by this time been

presented to Council as part of the planning approval process. Sixteen architects from fourteen firms

involved in the design of t hese buildings agreed to be interviewed for the survey.

There are three very strong trends in the data above:

Gen eral recognition of the need for consideration of the wind environment when

designing buildings in Wellington. I don=t think that any clients or developers or

architects dispute that the Ordinance has improved the environm ent for Wellington.Has

made it better in terms of it would have been worse if it [the Ordinance] hadn=t been


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there.

The genera l level of unde rstanding of aerodynamics of buildings is disapp ointing. A

number o f the a rchitects showed an unde rstanding of the importance oftower podium

curved facade, verandahs, canopies ... and increasing wind speeds with height. However,

on many other occasions they spoke ofwind baffles or aerofoils; and said things like:

Buildings create wind, nothing can be done about it; Tower-podium concept for wind is

really bad.

The ar chitects thought that t aking part in wind tunnel tests helped them to design

better - Provides increased awareness of problems and a feel for why they happen.

However they do not favour being the people who do pre-design wind tunnel tests

because with it, the Ordinance is too complex and because they feel they lack ...

expertise in the office and because it was likely to be not econom ical or time efficient ...

The analysis demonstrated that architects acknowledge the importance of getting the design right

ear ly, but want to do less work to get the design right. Can=t stop progress;Architect will build model

and observe testing as part of fee but not pay for testing or analysis; If costs were lower, situation could

change.

In recent years the Ordinance has been simplified. It was argued successfully during a major review of

the whole City Plan that a) so few architects had used the pre-design options; and b) the quality

assurance specifications in the Ordinance for the self-certification of wind tunnel tests done by

architects were so complex that the pro visions were counter-productive.

A further simplification in the new District Plan [5] saw the re -introduction of the 4 storey minimum

building height before wind tunnel testing was required. This latter action was based largely on

economic grounds. It was argued that it was unreasonable to impose the high cost of a wind tunne l

test on the developer of a small building. The positive value to the city of the wind tu nnel te sting of a


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new one storey supermarket bu ilding was not enough to out weigh the negative feedback from several

developers abou t the wind tunnel testing of their one storey low cost building.

Overall, the survey analysis shows Architectural Technology as a very positive contributor to the

quality of life in Wellington City. Wind tunnel simulation o f reality contributes grea tly to the nature

and developmen t of this improved qua lity of life. In the time that the Ordinance has been in place a

complete shift has occurred in the thinking of Wellingtonians. Every Wellingtonian who walks

through the City on a regular basis has encountered the >Lido effect=. The Lido was the first caf to

put its tables out on the street. Now many others do the same. The Lido caf benefits from the

shelter provided by the aerodynamically sound new Civic Centre buildings. During the debates in 1984

about th e Wind O rdinance the suggestion that good design could make sheltered outdoor caf s a

possibility was laughed at. Now we this quality of life is expected by all.

On the basis of this success, it has been suggested t hat the City could set up performance criteria for

all desirable environmental qua lities and not set he ight or other physical limits at all. It would make

the conflicts that sometimes arise in wind analysis less complex. In studies of the aerodynamics of

buildings it is sometimes found that making a building taller while retaining the same volume will

improve the wind at ground level. This taller bu ilding is in direct conflict with the height limits and

other physical restrictions set out in the Ordinance.

It is possible to imagine a performance requ irement for the sun in urban areas. In fact, following the

leads of places like San Francisco and Calgary one might even create an index of outdoor comfort

that accounted for the combinations of wind sun and temperature. Several CAD packages exist that

permit the designer to assess solar shading in the street while modelling their building in 3D. The

requirements of buildings for daylight can be easily quan tified. It should be re latively easy to establish

the amount of sun that is wanted at street level in parks and boulevards and the amount of indirect

light that must shine on windows for their interiors to be well lit. The pot ential exists for a rchitects to

be able to contribute more widely to the improvement of the health of the city.

Reviews of past and current daylight and sunlight requirements [6,7,8,9] show that rights to solar


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access for buildings were recognised in Roman Law as early as the first century A.D.. And daylight

requirements in urban planning have existed for at least 800 years, since the British enacted the

>Ancient Lights=Law in 1189.

This type of>right to light=is still the basis for the current British standard for daylighting. Current

British practice sets simpler standards for daylight protection. New buildings should not reduce

daylight to existing buildings by more than 20 percent. Daylight on the boundary of undeveloped

sites must be retained with a sky access of 17 percent, 2 metres above the ground.

The Amer icans take a different approach to daylight access. Their approach was pioneered by

William Atkinson in 1912. He proposed tha t beyond a permitted vertical height (equal to the street

width) buildings should step back from the street facade un til the building floor ar ea is less than 25

percent of the site. From t here th e building could continue up to any height.

Boston and many other cities in the USA required similar building standards until the 1960=s. At that

point they were abandoned in favour of Floor Area R atios. The new approach, however, showed no

considerat ion for sunlight or da ylight.


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In 1984, Boston adapted of process for measuring daylight access in a street developed by Swedish

architect Pleijel. This method uses a fish eye camera lens and transparen t overlays to calculate

daylight access. The goal of the Boston scheme is to ensure that new buildings do not create any new

shading on existing structures. It involved measuring the curren t daylight for t he cent ral city.

New York and San Francisco also under took daylight zoning studies around the same t ime. New

York initially adopted a complicated system based on the Waldram d iagram. Daylight, along with

other environmental factors, was considered to determine a building=s impact, with differen t zones of

daylight access being given different value ratings. A building was required to reach certain daylight

ratings, and a cer tain to tal ra ting to receive building consent. This system proved overly complicated

and was changed to a simple building envelope r equirement, which is easy to apply, but of far less

sophistication in its treatment of daylight access. San Francisco developed a system related to

sunlight, rather than daylight, based on Ralph Knowles=work. This system provides set sunlight

penet ration into city blocks, with different blocks requiring differen t penetra tion times, depending on

zoning classifications.

Te Aro is an area stre tching South from the harbour, past Te Papa Tongarewa, - the Museum of New

Zealand - across the major shopping and enterta inment boulevard Cour tenay Place and on up t he


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slope of Mount Cook to the Wellington Polytechnic campus. It is largely filled with low-rise industrial

or warehouse buildings. Increasingly, many of the old warehouses and the spaces between them are

being transformed into apar tmen t buildings. At present the Wellington City Council (WCC) has no

regulations at all regarding daylight, and very few relating to sunlight. Court enay Place is well suited

to the application of daylight or sunlight performance criteria. The surrounding area has building

height restr ictions of between 10.2 metres and 43.8 metre s, and is defined in the Wellington D istrict

Plan [5] as the Te Aro basin end of the >Low Cent ral City=. Overall, changes in the Te Aro Basin are

contributing to improved life quality for We llington by providing intermediate scale resident ial and

commercial developments between the residential areas of Mount Victoria and Oriental Bay to the

East and th e high-rise Central Business District to the West of the Te Aro Basin. The immediate

Cour tenay Place precinct is classified as a character a rea , and it is limited to less intense development .

This area has great potential for relatively low scale development, an ideal base for daylight and

sunlight planning.


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Daylighting in this area of

Wellington has been proven to be

a viable option in te rms of energy

savings. A study in 1978 by Chan


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[10] concluded th at, even on the Sout h side of a building, energy cost savings for lighting and extra

cooling costs outweigh the increased cost for heat lost th rough the glazing for standard single glazed

windows.

Chan concluded that if British daylight standard were to be adopted, it would make many of the

potential developments in the area impossible. To fit in amongst a set of existing 2-storey buildings

with a minimum height of 10.2 metres, a new structure would have to be 17.5 metres away, on sites

tha t can be as nar row as 7.5 metres wide. A single storey building would have to be 4.1 metres away.

A building at the 43.8 metre height limit would need to be 50 metres away.

The old New York me thod would create semi-acceptable building envelopes, and could work well

down Tory Stree t, which runs nor th-south and is fairly narrow. The problem with this method is that

it only applies to the str eet edge of a building. The area of Wellington under considera tion is made

up of a very few blocks, with some sites having dimensions of 7.5 metres by 34 metres. To ensure any

sort of daylighting levels for the se sites, new stree ts or daylight corr idors would need to be provided.

The complex Boston method is possibly the optimum method to apply in the interests of quality

daylight assessment. As the Waldram diagram attempted for New York can a lso be computerised, it

would allow quick and easy assessment of a new building. Both these methods are based on the

amount of sky blocked by the building, and would require the WCC to set limiting values for sky

access. These values would balance the character and overall building volume of the area without

discouraging potential development.

Assured access to sunlight can only benefit the character of Courtenay Place which is part of

Wellington=s >Golden (shopping) Mile=and an area specifically defined as low density. It is also likely

to contribute to the areas=economic profitability.


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Assuring sunlight for Courtenay Place itself is not a difficult task. At present, between the hour s of

10 am and 4 pm, between mid-September and mid-March only the new apartments at the Eastern end

of the street cast significant shadows. This same period could be chosen for sunlight access for

Courtenay Place in an ordinance.

If this period were chosen, and the extent of acceptable shadow were set at th e edge of the footpath

on the South side of the street, then the maximum height of buildings to the Nor th would be set by

an angle of approximately 26.5 degrees measured normal to the South side of the street. This

equa tes to a street wall of approximately 7.8 metres in height to the Nor th for the most narrow centre

port ion of the street . If the stree t wall was set at 10.2 metres, the longest shadows during the defined

per iod would fall just short of the building footings on the south side of the stree t. Areas of the

footpat h would be shaded to a degree for small periods after 3 pm in the afternoon unt il November

30 and from February 28.

However, even such mild suggestions as a Knowles style solar envelope over each CBD block of the

city raises problems that the Council has backed away from. The most obvious problem is that

buildings on the north side of an east west street must be lower than those on the south side

(Wellington is in the Southern Hemisphere). The Council does not want to deal with aggrieved

property owners whose proper ty values are largely determined by the potential size of a development

on the ir site. They would feel that it was unjust that t he peo ple on the opposite side of the road h ad

higher value properties as a result

of a Council decision.

An important aspect to be

discussed alongside solar access is

the para llel need for selective solar

shading due to New Zealand=s

harsh UV radiation conditions.


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Schools, for example, of necessity provide solar shading for outdoor play and break areas to p rotect

children from the harmful effects of the sun. For outdoor seating areas at cafs and re staurants,

patrons desire shading even on days with pleasant air temperatures as the intense solar radiation

raises people=s body temperatu res unpleasantly. However, providing flexible and simple shading

devices which can easily be removed is often made impossible due to Wellington=s windy environment.

European type r etractable canvas awnings or free-standing umbrellas are clearly unsuitable.

Ensuring sunlight access for the roofs of buildings is an issue tha t may be re levant in the future, as

active solar design technologies improve. Developments in photovoltaic cell cost and efficiency in

Sweden and at Massey University may mean that PV cells may become economically viable. This is an

issue for the future which can be planned for now, but requires further investigation.

For both the wind environment and solar access assessment in Wellington the expected intractable

problem with performance specification is the t raining required by Council officers who are to check

the performance calculation. Checking a reported wind speed in a wind tunnel test against the

published criteria is relatively easy. But total performance specification and compliance checking

require that the Council staff be knowledgeable in all the relevant environmental performance

simulation techniques. Without this knowledge they have little hope of negotiating trade-offs

between different performance requirements.

The following table illustrates a possible solution to the problem increasingly found with

administering the Wind requirements in the Te Aro precinct in the Wellington CBD. As noted

ear lier, solar access is not current ly a significant part of the WCC building performance requ irements.

Over the past couple of years, few wind tunnel tests have been per formed for new buildings or for

altera tions to existing buildings in the Te Aro area. Sometimes a building under four storeys has one

storey added . Sometimes a further four storeys are added. In most cases, the Council does not

requ ire a wind tunnel test because the scale of the work is similar to or smaller t han that involved in


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constructing a building under four storeys from the ground up. To ask the developers to wind tunne l

test is to place a great er re lative financial burden on th em than they would encoun ter when plann ing

a new building. However, the system is clearly flawed when a four-storey building is effectively

doubled in height in an area where its neighbours are two to three storeys in height. Equally it is

flawed if a developer has to perform a wind tunnel test when placing an extra penthouse on a ten-

storey building which is otherwise aerodynamically sound.

With the high turnover in the City=s plan checking department it has not been possible for people

checking the wind reports to gain sufficient experience to make informed judgments about the

importance or not of a wind tunnel test. The apparent freedom of the performance approach requires

one person with considerable experience and tr aining to oversee t he planning process. This cannot

easily be done . It also has the potential to place considerable responsibility on tha t one person not t o

abuse his/her position of power. It also has the fur ther potent ial to make the planning appr oval

process appear extreme ly complex to the outsider. Developers like to have straightforward planning

approval processes. The system, therefore, has to look fair and this often requires that it have a

simple procedure to be followed.

New Zea land has recent ly introduced a performance-based Building Code. It specifies minimum

acceptable levels of performance in the interests of health and safety of people in buildings. It does

not specify good practice. It is unfortunate ly still viewed by the building community as the definition

of good practice that the codes of old were . The performance option is seen as expensive with

respect to consultants= time and thus the >barely legal=acceptable solutions described in the

document s accompanying the Code are the norm. Whichever is the cheapest building design idea in

these documents, in terms of design effort and construction costs, is commonplace. There is

apparent ly a strong desire amongst developers to bring the same formula-based approach back into

urban design practice.

It seems that the re are improvements needed in the Wind Ordinance in Wellington: a) cheapness and


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simplicity on the par t of the d eveloper; and b) application of the wind tunnel test requirement only

to appropriate situations. To codify or otherwise establish a reliable procedure for a wind tunnel test,

or indeed any other building performance evaluation requires a checklist like that shown in the

following table. The d ifficulty with checklists of this type is that they risk immediate ly a return of the

Ordinance to the prescriptive state it occupied prior to introduction of the performance

requ irements. The po tent ial design freedom of the performance app roach is likely to be limited by

the checklist. As far as the authors can ascertain, this is a risk that must be taken. There is no

alternative.

A wind tunnel test shall be performed on any building that at the completion of its

construction or r econstruction or refurbishment is over four storeys in he ight, with the

following provisos:

IF t he addition to a building is less than one third the height of the

original building,

AND

IF the t otal building height is not greater than on e and a half times the

average height of the n eighbouring buildings (to a distance of one block

in each windward direction)

No wind tunnel te st

is needed.

IF th e addition to a building is greate r than one th ird the he ight of the

original building,

AND

IF the total building height is not more than 30% taller than the

average height of the n eighbouring buildings (to a distance of one block

in each windward direction)


is needed.

IF the building is adjacent to a public park or other public area where

people might reasonably expect to be able to sit in comfort for longperiods of time (greater than 30 minutes)

A wind and a solar

access study must beundertaken.

IF the building height after construction will be within 20% of the

median height of the buildings (including open sites in this calculation

as 0.0m high if they exist) within one block in all directions,

AND

IF the building is of tower-on-top-of-podium construction

AND

IF the building has a verandah over the full length and width of the


is needed.


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footpath on the public frontage of the building.

References

[1] Wellington City Council (WCC). Wellington District Schem e - Ordinance 3, Section B5, WCC,

Wellington, 19??.

[2} Wellington City Council (WCC). Wellington District Schem e - Ordinance 3, Section B5, WCC,

Wellington, 1985.

[3] Lawson, T. V. Wind Effects on Buildings - Vol.1, Design Applications, Applied Science

Publishers, London, 1980.

[4] Davies, Kathryn J. Wind tunnel modelling of the pedestrian wind environment: modelling the built

environment, MBSc Thesis, Victoria University Wellington, 1992.

[5] Wellington City Council (WCC). Wellington District Plan , WCC, Wellington, 24 Febr uary

1998.

[6] Butti, Ken and John PerlinA Golden T hread - 2500 years of solar architecture and technology

Van Nostrand R einhold, New York, NY, 1980.

[7] Littlefair, Pau l J. Site L ayout Planning for Daylight, BRE Information Paper, British Research

Establishment, G arston, Wa tford, 5/1992.

[8] Knowles, Ralph L. Energy and Form, MIT Press, Cambridge, MA, 1974.

[9] Knowles, Ralph L. Sun Rhythm Form, MIT Press, Cambridge, MA, 1981.

[10] Chan, Seong Aun. The Effect of Daylight and Sunlight Requirements on the Energy Balance of

New Zealand Window Systems, March Thesis, Victoria University of Wellington, 1978.


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