Architecture of Sidney

Lightweight construction and urban conservation in Sydney

The design for a two stories extension of a Heritage Building in Sydney Central Business District

In the city of Sydney, the central quarter called Central Business District (CBD) has been recently subject of experimentation for numerous types of architecture.

This area contains several historical edifices such as the Queen Victoria Building, designed by the Architect George McRae in the late 19th Century or the Sydney General Post Office designed and built in 1866 by the Colonial Architect James Barnet.

The settlement of the Central Business District began in the early days of its foundation when the British colony discovered Sydney Cove, a safe enclosure from the Pacific Ocean. This was a strategic place highly protected and therefore beneficial for the settlement of convicts in Australia.

From the early foundation until the present, Sydney CBD has witnessed a successful implementation of planning policies by the Local Government of City of Sydney Council, the authority that regulates the development for this area.

Sydney CBD, physical model in scale 1:500 made by City of Sydney Council. Source: Author.
Sydney CBD, physical model in scale 1:500 made by City of Sydney Council. Source: Author.

The Context

In fact, a series of Development Control Plans (DCP) have been launched and renewed every 5 years. These plans were assessing in detail any type of transformation within the CBD and their implementation process became more intensive as the land became more precious with the time, resulting in a lack of open spaces and a rise in the number of stories of the new developments.

Numerous planning instruments have been produced by City of Sydney Council along with the idea to encourage intervention in the CBD and, at the same time, to regulate height, density of the buildings together with the street setbacks which from the boundary of the single lots with the streets.

The main conservation policy adopted by City of Sydney Council includes the City of Sydney Development Control Plan (DCP) and the City of Sydney Heritage Development Control Plan (HDCP). The first policy is a comprehensive and detailed set of rules regarding new development. The latter is a document that put forward key principles for the conservation of historical buildings.

Although the two policies are different in relation to the type of buildings for which they applied, both of them have a common objective: they aim to minimize the impact of the new development against the historical artifacts in Sydney CBD, defined by the conservation policy as “Heritage items”.

In this context the HDCP refers to a series of Heritage conservation areas that includes buildings of Heritage significance in relation to their capability of representing historical architectural values commonly in terms of features, materials and typology.

In general, this policy assimilates the idea of creating homogeneous rules of intervention against Heritage items. However specifically, it establishes a prescribed use of architectural elements ‘In style’ with the design of each building period.

For this, architectural elements belonging to the exterior of the building such as balustrades, doors, separation fences, pediments and cladding, became important together with their colors composing a schedule of elements, typical of the Australian Federation architectural style.

‘Posh’ Hotel. Front view from Broadway. Source: Author.
‘Posh’ Hotel. Front view from Broadway. Source: Author.

Furthermore, an overall analysis of the Heritage policy suggests that the assimilation between the previous and the modern architectural style has played a more important role than previously believed. A critical review of the policy expressed in the DCP and in the HDCP, had enlighten the idea that this is based on criteria of distinction rather than homologation between the present and the past development: The policy accepts the modern and contemporary design as an example of a dissimilarity against pre-existence, investigating at the same time a comprehensive methodology of conservation.

This approach not only is supported and encouraged by the Heritage department of City of Sydney Council during the required meetings in regards to any development proposal, but also achieves public consensus from private Heritage consultants, lobby groups and residents of Sydney CBD.

According to these people, the ‘homologated’ approach is simply too restrictive and limitative in the way that makes the new development difficult to comply with a series of other regulation imposed by other building codes such the Building Code of Australia (BCA), a comprehensive text of detailed construction rules on fire resistance, acoustics, access for disables and construction in hearthquake prone zones.

It is mandatory that before every construction begin, every building passes the certification of compliance issued by a certifying authority (public or private) against the BCA.

Where assimilation of the new development with the old building is not possible for reasons such as scale, orientation, floor area or introduction of a new technology, The Heritage policy is willing to accept the modern totally in contrast with the preexisting building by endorsing the idea of a innovative design rather than a simplistic re-visitation of old construction methods.

Following this path, the policy goes even further by being open to an experimentation of new building technologies including green facades, low energy consumption architectural solutions and lightweight construction.

Among the examples of developments in Sydney CBD which have been conceived in the context of the Heritage policy described above, is the Pritzker Prize-winning “One Central Park” commercial and residential building designed by the architect Jean Nouvel. This building includes elements of lightweight construction combined with green facades, a novelty that marks the contrast with the Heritage surrounding environment.

View of Broadway with“One Central Park” in the background. Source: Author.
View of Broadway with“One Central Park” in the background. Source: Author.

The Design

In this context, Sydney based design firm Cityface Group was commissioned to undertake the design at construction stage of a two stories extension of the ‘Posh Hotel’ located on the commercial street called Broadway in Sydney CBD where the also mentioned “One Central Park” building is located. The existing Hotel was a tree stories red brick building constructed at the beginning of 1900.

The street of Broadway, once called George Street, connects the Central Station with the Sydney suburb of Parramatta, 20 km west of Sydney CBD. This street represents a collection of Heritage complexes, all built in the early years of the city settlement. Examples are the University of Sydney, the commercial building of Gross Brothers and the neo-Gothic Church of Saint Benedict.

The design brief that Cityface Group followed included the construction of two more stories with 13 rooms accessed by the existing lift shaft leading to the main entry on Broadway, this to be extended for two extra floors. In this design, Cityface Group selected for the new extension a so-called “lightweight” structure, commonly used in Australia as an innovative applied technology of construction.

The lightweight construction technology is used often on the highest floors of residential buildings and mainly consists on framed walls usually of the thickness of 900 mm. The frame is usually made of timber or galvanized steel.

The skin of this structure it is normally made of plasterboard in the interior and cladding (timber, metal or stone lining) on the exterior. This is behind a waterproofing membrane. Where the use of a framed structure is not possible, the designer may choose instead light concrete blocks or light structural panels.

For the ‘Posh Hotel’, has been designed a framing structure made of metal and two masonry lightweight walls made of “Hebel” Blocks, a light composite concrete material.

‘Posh’ Hotel. Set out of lightweight construction walls and floor. Source: Author.
‘Posh’ Hotel. Set out of lightweight construction walls and floor. Source: Author.

The framing structure is placed along the facade of the building towards Broadway and consists on a mounted setting with plasterboard on the interior side and zinc cladding on the exterior. The frame also incorporates metal columns where necessary functioning as a support for the roof. The lightweight walls are commonly shared with the Western and Eastern adjoining properties, and they serve as a support for the structure of the roof.

Eventually, this choice is increasing the variety of the materials has been already used in the surrounding context of Broadway: examples in this regard are buildings such as the “One Central Park” with green plants on its facades and the new houses the UTS Faculty of Engineering and Information Technology (FEIT) designed by the architects Denton Corker Marshall. The latter is a 5-Star green star rating building made of angled, semi-transparent ‘screens’ of aluminum sheets perforated with binary code witch represents a landmark for Broadway and for the Sydney CBD.

The Building Code of Australia indicates metal frame as the preferable material for lightweight construction this is primarily for non-combustible properties of the metal. In fact the frame it is required to achieve a minimum level of fire resistance required by the BCA. A range of fire resistance levels it also required by the floor between the new two levels made instead of a dressed timber fire resistance coated with an intumescent paint, which offered a passive fire protection technology. The designers of Cityface Group coordinated this solution also with the consulting structural and fire Engineers during the construction stage.

‘Posh’Hotel. Finishing of lightweight construction walls with external Zinc cladding. Source: Author.
‘Posh’Hotel. Finishing of lightweight construction walls with external Zinc cladding. Source: Author.

The choice of this lightweight construction method applied to the top two stories of the ‘Posh Hotel’ derived essentially from a structural necessity, functionally associated to the need of not overloading the existing bricks of the lower floors.

However, choosing zinc as the material for the skin of the extension was a way to maintain the upper walls as light as possible and detached from the original existing masonry building.

‘Posh’ Hotel. Detail of lightweight construction walls and floor. Source: Author.
‘Posh’ Hotel. Detail of lightweight construction walls and floor. Source: Author.

In fact, not only the two story extension of the ‘Posh Hotel’ contrast the 1920’s bricks also for the dark color characteristics of the zinc of the facade on Broadway, but also the facade itself is carefully measured to set back about 6 m from the street boundary of the building block.

This layout also function as a sort of background for the masonry building enhancing the difference between the bulky and the light, the contemporary design and the preexistence.

Once achieved the right structural properties, the lightweight construction used in the ‘Posh Hotel’ turn out to be correlated to lightness as a proper characteristic of the design intent. In this way, the structural properties of this technological composition became secondary with a respect for a grater concern for other parameters such as appropriateness of material, suitability of the surface appearance and satisfaction of the visual relationship with the surrounding environment.

From the point of view of the streetscape of each building with their variety of materials saturates Broadway as a whole: the new modern architecture relates and communicate visually with the preexistence living the perception of the red bricks buildings marked by the heights of the existing parapets as ‘another city’ worth of recovery and enhancing.

An analysis review of the Heritage policy of City of Sydney Council reveals that set backs from the original boundary of the buildings are key ideas also endorsed by the Council and listed in one of the main objective of the DCP: Setting back the new development in relation to the existing building alignments is one way to achieve this outcome.

Final notes

In conclusion, it is clear that the new two stories extension of the ‘Posh Hotel’ by embracing the lightweight as the main technological assembly method has shown interest by the designer in investigating the relationship between the Heritage and the contemporary architectural style in a new way. This is by combining the aim of a policy with a technical task commonly conceived as a second stage of design.

In this context, lightweight construction rather than being simply a manner of introducing an innovative methodology appears also to be an important contribution to the conservation for Sydney Heritage architecture.

As mentioned, the role of lightweight construction within the built environment is changing, establishing new significances for different contextual city environments. Perhaps this change is to be read as a signal that shows the Australian approach for specific building technologies as a significant step towards the European tradition, where the specificity of the building site and its Heritage surrounding environment stands out as a primary element.


Reference

Posh Hotel

Designers: Cityface Group Pty Ltd

Structural Engineers: NITMA Civil & Structural Consulting Engineers

Fire Engineers: Holmesfire