Download The Chief Secretary`s Building (CSB), a significant heritage

There is pleasure in the pain of
refurbishing heritage buildings
Vijay Badhwar B. Tech. M.I.E. Aust. C.P. Eng.
Mikhail Kogan B.Sc. Eng. (Civil), M.Eng. (Structure)
SUMMARY: The key to successfully refurbishing heritage-listed buildings is in the planning. Faced
with an extreme challenge to provide 21st century functionality in the nearly 150-year-old Chief
Secretary’s Building, spaces within the existing fabric were identified. These spaces accommodated
new services and strengthening elements - for example - a void above the corridor ceilings not only
provided an avenue for fresh air supply but also accommodated structural tie members to stabilize
walls against earthquake loads. Even when structural intervention was necessary to strengthen an ailing
arch, it was applied with sensitivity making the intervening elements visible and also reversible. The
choice of a piped VRV refrigeration system for air-conditioning the building and maintained the
background of highly ornate ceilings intact. The Engineering team exhibited best practice in the
planning, selection and installation of engineering systems and components. This ensured that all work
had minimum effect on the fabric of the heritage building while still providing an appropriate internal
environment for the functions of Courts, the Industrial Relations Commission and the Governor of
NSW. The project sets a benchmark in Australian engineering for the adaptive reuse of a significant
19th century heritage building.
Figure 1. Chief Secretary’s Building elevation
Figure 2. Typical plan
1. INTRODUCTION:
The Chief Secretary’s Building (CSB), a
significant heritage sandstone public building
designed by Colonial Architect James Barnet, was
built in 1880.
The building was initially
constructed as “a new and worthy building for the
office of Chief Secretary of the Colony as well as
providing offices for the Public Works
Department”. It has landmark national
significance and is a major state asset.
The key requirements of the redevelopment
project completed in 2005 were to provide
modern day services and comply with current
standards while preserving the building’s
landmark heritage features. The Engineering
Services group within the NSW Government
Architect’s Office applied an innovative and at
times unique approach to meet this challenge.
for the Chief Secretary and also accommodated
the Public Works Department. As the Chief
Secretary’s role was of considerable political and
administrative influence, the building was marked
as being of state and national significance.
It was customary then that important office
bearers occupied one floor above the entrance
level. The sloping site allowed Barnet multiple
main entrances – at level two (Macquarie Street)
for the Chief Secretary, a public entrance from
Bridge Street and the lowest from Phillip Street
for the Public Works. The executive offices on
level three were similarly arranged along the
street frontage while their subordinate staff
worked across the corridor towards the rear
courtyard. The building’s facades, finishes,
furnishings and artworks are of exceptional
architectural significance which lend due
importance the building deserved in the 19th
century.
While the CSB construction experienced building
2. HISTORICAL SIGNIFICANCE
The CSB, as implied by its name, was an office
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supports the timber-framed walls and pitched roof
from street sides.
The street facade is a mansard type roof. There is
a sandstone spandrel parapet on top of the facade
wall.
The roof towards the north is pitched and clad
with copper sheeting, while on the south, the roof
is flat with waterproofing membrane. The timber
roof structure comprises of king post trusses,
underpurlins and rafters. The central part of the
Barnet Wing has six storeys and a two-level dome
above with steel frames with bow trusses
supporting timber framing and boards. The dome
and attic on level five were later additions.
There were external toilets towards the rear
3. BUILDING STRUCTURE:
The Chief Secretary’s Building is sited in the courtyard which were connected to the main
north-eastern part of Sydney CBD along Bridge building with links that were subsequently
Street between Macquarie and Phillip Streets. The demolished.
The corridors consist of double brick arches with
site slopes down in east-west direction.
The building consists of two main blocks/wings:
a space in between. The upper arch supporting the
•
Barnet Wing (which includes original Barnet floor is very flat.
The original building was gas lighted and
building and Vernon Mansard addition) and
•
Vernon Wing (which includes original Vernon naturally ventilated.
extensions and levels above Phillip’s Lane).
The Barnet Wing is connected to the Vernon 4. REDEVELOPMENT STRATEGIES
Wing at each level above Phillip Lane. Over time Following the adage in relation to works on
there have been some alteration and refurbishment heritage structures ‘to do only as much as needed
and to do as little as possible’, dictated the
to the building (lift, engineering services etc).
The building is a five-storey structure, ‘U’ shape strategies for adaptive reuse. There was an
configuration in plan, with load bearing walls in underutilized building which could be
sandstone and brickwork. The floors are mostly redeveloped for government accommodation
timber framed with some use of steel beams. within the heritage constraints. It was determined
Hardwood timber joists, 275mm deep x 75mm that Industrial Relations Commission and courts
wide at 450mm centres, span either from wall to would be appropriate users of the building.
wall or onto iron beams. In the central area in the Economic appraisals were undertaken to provide
north, the joists run east to west onto iron beams. only basic facilities such as air-conditioning,
Where there are balconies underneath, the joists electricity, communication, security and fire
span north–south sitting on the walls. In the east safety with Early Warning Interaction System
and west corners of the building the joists span (EWIS) and smoke detection.
Strategies were developed early to earmark areas
east-west.
The floor joists support 65mm thickness of for vertical travel of services while horizontal
concrete pugging on boards sitting on timber spaces had been identified in the corridor ceiling.
battens secured to the sides of the joists. The For structural strengthening works it was
appropriate
to
keep
them
floor construction is a 30mm thick tongue and considered
inconspicuous – inside ceiling spaces – without
groove boarding.
The timber lath and plaster ceiling is attached to being obtrusive. In a different application of
separate ceiling joists 145mm deep x 48mm wide visual rectification (at Phillip Lane arch), it was
at 450mm centres and supported from the floor decided to make the rectification works
structure in parts.
conspicuous and reversible.
The iron beams are I sections strengthened with
12mm thick plates riveted to the flanges.
5. ENGINEERING CHALLENGE
The Level five floor was built during The significant engineering challenge was to
reconstruction of offices and the dome. The floor comply with present day standards, fit out the
consists of softwood timber joists and steel building with leading technologies and an internal
beams. There is no pugging and timber lath and environment suitable for its functions without
plaster ceiling attached directly to the underside impacting on heritage features and finishes.
of the floor joists. The floor structure partly
delays and cost overruns, the Public Works
Department pressed for more space. Barnet’s
successor as the Government Architect, Walter
Liberty Vernon, undertook design for more space
and thus came extensions to the CSB along Phillip
Street. Vernon’s embellishments to the original
building in the form of mansard roof and a
grandiose dome added to the building’s
importance.
The CSB underwent major alterations and
additions after the Public Works Department
moved out from the premises in 1968. Spaces
were created for divorce courts and new lifts.
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•
Figure 3. Grand spaces of exceptional heritage
significance
The decorative timber finishes, ornate embossing
on walls and numerous features throughout
provided significant challenges and meant that
every detail had to be individually investigated
and thoroughly planned to minimise impact on
heritage fabric. The upgrade required sealing to
prevent noise and dust encroachment, the
inclusion of full air-conditioning and significant
upgrades in electrical, communications, security,
hydraulics and fire-engineering to modern
standards.
6. DESIGN
Surveys by specialists in the areas of structural,
mechanical, electrical and hydraulics engineering
identified limitations with the existing structure
and upgrade requirements. The main issues were
identified as follows:
6.1 Structural Engineering
Although massive in appearance, the CSB
footprint in the form of ‘U’ exposes the structure
to eccentric forces resulting from lateral loads
such as from earthquake forces. The vulnerability
of walls is further exacerbated as the floors do not
provide the required restraint at intermediate
levels, virtually making them free-standing for
their entire height. Similar concerns subject to
earthquake loads apply to elements such as
parapets, balustrades, pediments, architectural
ornamentations etc.
The complicated plan geometry and an irregular
vertical configuration of the building as a whole
significantly affect its performance during an
earthquake. Computer modeling of CSB was not
undertaken as from earlier experiences it was
known not to give satisfactory results for masonry
structures.
Significant Weaknesses in Main Structure
•
Load-bearing un-reinforced masonry walls
extending to the full height of the building –
approximately 27m (five storeys) and six
storeys in central part. According to AS3826
this type of building should be limited to three
storeys with all floors connected to walls.
The gross floor area at each level exceeds
300m2 recommended by AS3826.
•
Roof timber frames do not have bracing at roof
and ceiling planes and so can not act as
diaphragms.
•
Roof timber frames do not have any
connection to the masonry walls.
•
Floor timbers do not connect to the masonry
wall and do not have enough stiffness to act as
horizontal diaphragms.
•
Masonry parapet walls and chimneys have an
h/t ratio (height to thickness) greater than 3:1.
•
Masonry pediments at roof level and over
entrance are prone to instability.
•
Settlement of an arch over Phillip Lane due to
its inherent flat profile and large point loads
from above.
•
Connection to Vernon Wing above Phillip
Lane has resulted in twisting and cracking in
both wings and is detrimental to the structure.
Australian Standards
The underlying design principle of AS1170.4,
“Earthquake Loads”, is based on an estimated
90% probability of the ground motions not being
exceeded in a 50 year period.
“Buildings that are designed to contain a large
number of people” are classed as Type II and
“buildings that are essential to post-earthquake
recovery” are classed as Type III in accordance
with Australian Standard AS1170.4 Earthquake
Loads.
The Chief Secretary’s Building is classed as Type
III for its Heritage Significance and capacity to
contain a large number of people. The main
structure of building does not comply with
requirements for either Type II or III structures.
Another Australian Standard AS3826 applies to
‘Strengthening existing buildings for earthquake’.
The CSB building structure also does not comply
with its ‘Deemed-to-satisfy requirement’ specified
in clause 2.3.
It was considered that without major interference
to the fabric of the structure, compliance to
AS1170.4 as a new building or even application
of AS3826 with a reduction of earthquake loads to
33% could not be achieved.
Accepting a lower standard of earthquake
protection to minimise disturbance to the
exceptional heritage significant items in the
building and strengthening of only the critical
items was considered.
These critical items were:
•
Tie whole building at roof level by
connecting roof structure to masonry walls
and providing bracing/diaphragm.
•
Connect large wall elements to floor beams
to avoid collapse.
•
Carry out strengthening of the chimneys,
parapets, pediments and slender wall panels.
•
Take
any
opportunity
in
future
alteration/repair work (such as new lift,
stairs, services etc.) to improve the capability
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of building structure to withstand the threshold
load as a minimum.
Figure 4. Phillip Lane arch strengthening; inset:
finite element analysis
•
Carry out rectification of the arch over Phillip
Lane. Following finite element analysis of the
arch, individual stones were identified for the
level of stress each one carried. Several
options were prepared which included: a)
relieving the arch of loads from above, b)
prestressing the arch, c) repair by carbon fibres
to enhance arch’s tensile capacity, d) providing
an external support to the arch by steel rods.
Option d) was adopted in consultation with the
Heritage Architect and the Heritage Council as
it contrasted as rectification and was also
reversible.
The earthquake strengthening works were limited
to avoid a major collapse as it is not mandatory to
apply the current Australian Standard on existing
structures as AS3826 is not listed in the Building
Code of Australia. Nevertheless, due care was
applied to design the earthquake strengthening for
the building, applying it more rigorously to
elements that are prone to catastrophic collapse
(such as chimneys, balustrades etc) and tieing
elements elsewhere.
Majority of earthquake strengthening works were
inconspicuous – turning floors into diaphragms by
providing plywood sheets; connecting the east and
west parts of the structure through steel
connections in the corridor ceiling arch and
introducing cross bracing.
The balustrades, however, needed more work as
cracks at several locations were noticed, being in
an exposed part of a building and liable to become
wet and subject to extremes of temperature.
Besides injecting epoxy to repair the cracks, the
balustrades were tied to steel struts to safeguard
against collapse. The struts, in turn, were
connected to the wall framing of the mansard
structure. The struts were not easily noticeable as
these were placed behind the balustrades. The
procedure was also in line with the conservation
strategy as the whole process is reversible.
6.2 Services
The original building services were open fireplace
heating, gas lighting, natural ventilation and
basic water and drainage systems. The major
areas of the building had timber flooring and
ornate plaster ceilings fixed to a common set of
floor joists providing minimum or no ceiling
void spaces. Concrete corridor floors were not
reinforced but relied on brick arch support,
making any addition of modern services
extremely difficult.
An extensive upgrade was required to ensure
compliance with current standards and meet
modern functional needs. New services were
installed throughout the building including,
electrical, communications, data, fire safety,
security, mechanical, hydraulics, lifts, an
elevated link to 50 Phillip Street and a glazed
courtyard canopy.
During investigation of existing services, records
were found that showed a single piped system,
approximately 125 years old, that conveyed both
sewer and stormwater from the building to
discharge into a Sydney Water Sewer main in
Phillip Street. When the existing system was
examined via a CCTV survey, the pipe was
found to be unsuitable for re-use for either sewer
or stormwater. The only solution was to install
new dedicated sewer and stormwater systems.
The original single pipe system reticulated from
the building via the adjoining laneway
connecting Phillip and Macquarie Streets.
Heritage paving stones were known to be located
below the road surface of the laneway and no
disturbance of the laneway was allowed.
Additionally, the courtyard within the CSB was
also of heritage importance and only minimal
disturbance was permitted.
The challenge was to separate the existing single
combined system and to find a suitable
reticulation route to Phillip Street that would not
impact the critical heritage restraints and the
options were severely limited. The only location
available to create an external services corridor
was below the existing footpath that ran between
the building’s Southern external wall and the
courtyard retaining wall. Because of the limited
space allowed owing to structural footing
restraints, extensive services coordination was
required as electrical and hydraulic services had
to share the common trench.
Geotechnical surveys involved bore holes being
taken from areas below the buildings floor
structure and the courtyard to determine the
suitability of boring at certain depths without
structurally impacting upon the buildings
stability. Extensive co-ordination with other
service providers such as Telstra were carried
out to ensure the proposed bores would clear all
the services below the street and footpath, while
ensuring connections could be achieved at the
required levels at either end of the thrust bores.
Finally two thrust bore holes extending below
Phillip St and the eastern side of the building to
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the new service corridor near the courtyard were
decided on. The bores provided a 330mm and 440
mm diameter conduit to install the new
stormwater, water and sewer to service the site.
Localised boring was also carried out below the
buildings floor structure where service pipes were
required to pass below heritage slate and marble
tiled floors.
Existing services pipes in a variety of materials
and configurations including plastic (PVC) were
fixed to the external walls and within the building
detracting from the buildings appearance.
Hot water was supplied where required via
discretely located compact slimline instantaneous
electric heaters, as natural gas was not an option
for an energy source owing to the impact of gas
flues penetrating the buildings external walls.
•
Environmentally
sustainable
design
principles were adopted throughout the
project and a range of low-energy solutions
of lighting sources and air-conditioning
systems were implemented including a state
of the art air-cooled reverse cycle heat
recovery Variable Refrigerant Flow (VRF)
system employing environmental friendly
R410A refrigerant. This system was different
from the conventional four-pipe system
which are on average 250mm diameter.
Instead the VRF system utilised 25 mm
diameter pipes with 20 mm insulation. This
system is also energy efficient as it cools and
heats simultaneously, extracting heat from
one part to supply where it is needed.
Figure 5. Corridor ceiling arch – used as a fresh
air duct and to accommodate structural members
for earthquake strengthening
• Use of confined ceiling void space above
corridors as a major services thoroughfare.
• Development of a fire-engineered solution
within the timber flooring to meet BCA fire
requirements, maintaining fire isolation
between floors and smoke zoning between
rooms. The existing east and west stairs had
to converted to fire stairs and pressurised.
The supply of fresh air on every floor was
achieved through the corridor arch duct that was
connected on each end to the vertical risers. In
case of a fire, the corridor arch duct would go into
reverse mode to suck air out from the fire-affected
floor.
•
Searching investigation of the building’s
construction was undertaken to minimise
impact on heritage finishes to find:
¾
cable access pathways for wiring
electrical and security services i.e. reuse
of both disused gas flues built into walls
from wall mounted gas lights and pipes
and old conduits associated with earlier
building refurbishments;
¾
access routes in the limited void spaces
to install new hydraulic services,
particularly gravity pipes;
¾
positioning the plant room on the roof
area where it would be inconspicuous
behind a 1.6 metres high parapet
•
Use of large diameter core boring under
significant on-ground floor finishes to
provide access for a wide range of
engineering services.
7. CONCLUSIONS
The Chief Secretary’s Building is a major NSW
Government asset both in its heritage status and as
accommodation for the provision of public
The adaptive reuse of the Chief
services.
Secretary’s Building has ensured that it remains a
landmark public building of national heritage
significance. The building is now home to the
Industrial Relations Commission’s Courts and the
NSW Governor’s Office. Both are appropriate
and distinguished uses for a building of this
significance.
In recognition of a work of
conservation excellence the NSW Government
Architect’s Office has recently been awarded the
National Trust’s foremost Heritage Award,
Conservation Built Heritage for a project over $1
million.
8. ACKNOWLEDGMENTS
Design team at NSW Government Architect’s
Office: Terry King, Project Architect; Christine
Scantlebury, Hydraulic Engineer; Ian Gordon,
Electrical Engineer, San Mai, Mechanical
Engineer.
9. REFERENCES
Chief
Secretary’s
Building
Conservation
Management Plan 2002
Heritage Design Services
Department of Public Works & Services
Jackson Teece Chestterman Willis Consultants
Pty Ltd, Conservation Architect
Wendy Thorp, Historian and Archaeologist
October 1994
Chief Secretary’s Building, Conservation Plan for
the Minister of Planning
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