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Introduction
Bud Brannigan's own house, set on a
narrow, lushly vegetated block in the suburban Brisbane
suburb of St. Lucia, is a contemporary interpretation of the
traditional Queensland elevated lightweight timber house, a
building type ideally suited to the sub-tropical climate.
Fighting against the tide of ground dwelling masonry clad
structures that owe more to the building traditions of the
southern regions of Australia, this design takes advantage
of the economy, environmental performance and the natural
warmth and beauty of modest timber products, and uses them
in a simple and ingenious way. It is a light and breezy
building, with a generous interplay of outdoor and indoor
spaces that relates to its site, climate, and function in a
relaxed and unpretentious, yet intelligent way. Fittingly,
the house won the 1994 Robin Boyd National Architecture
Award for housing.
Description
The site, measuring 42 metres by 9
metres, generated the form of the house and dictated that it
follow a narrow north west axis up the block. The two-story
building is elevated off the ground on steel posts allowing
the sloping landform to run undisturbed beneath the house,
providing a carport at the front and reaching grade at the
rear. Timber is extensively used throughout the building for
internal flooring and external decks, and plywood for lining
of ceilings, and for the cladding of exterior walls. The
downstairs living spaces are connected to a series of decks
and wrap around a large court cut into the heart of the
building between the living room and the kitchen. This is
then connected to a narrow verandah running along the north
east side to the rear of the building, where it reaches
grade. The inside spaces are connected to the decks and
court via large openings in the wall. The second storey of
bedrooms and studio is to the southeast end with the roof
gradually sloping and stepping down to the living room on
the ground floor. The roof continues over the courtyard
adding to the ambiguity of its nature as a room or outside
space. Louvres and external timber blinds ventilate and
shade the building although the dense vegetation of the
landscape, which comes right up to the edge of the building,
has a role in the climate control of the building. The thin
form of the house allows for cross ventilation from cooling
breezes. On the south west, and south east side the exterior
walls are angled in to provide a roof overhang yet allow the
walls to go right up to the minimum setback.
Structural Description
The building is supported on braced
steel posts and bearers set to a grid 3600mm wide and six
bays of 3600mm long. In places the steel bearers cantilever
beyond the grid to allow rooms and decks to follow the
irregular shape of the block at the minimum setback allowed.
Fibre cement sheet was used to line the internal walls. All
flooring in the house is hardwood. The exterior of the
building is clad in exterior grade plywood, except around
the internal court yard, which is clad like the interior
walls with fibre cement sheets, and the south east wall,
which is clad with corrugated steel. The plywood cladding in
the Brannigan residence is a 12mm thick type A bonded,
structural ply. It was pressure treated with preservative
chemicals to protect it against fungal and insect attack,
and painted on site with a clear finish.
The joints between plywood panels must
have a two or three millimetre gap to allow for expansion,
but the edges of each sheet cannot be exposed to the
weather. In the Brannigan residence they are covered with
pine cover strips. The horizontal joins have a "Z" flashing
from the inside of the top sheet to the outside of the lower
sheet. The timber members of the structure are arranged at
centres of 600mm, 900mm, and 1200mm. These modules relate to
the size of the cladding and lining used. For instance the
wall studs are at 600 centres. As the sheets of plywood
cladding and fibre cement lining are 1200 mm wide the
spacing of the studs provide attachment points for the edge
of each sheet. Door openings and windows are also at
multiples of 600, 900 and 1200 to fit within the module of
the structural grid. The roof overhangs, while controlling
the sun, also help in protecting the exterior of the
building from weathering. The floor joists of the second
story are cantilevered out on the north east side to provide
a sunshade that also helps in weather protection.
A Strategy for Design with
Timber
Plywood as a Cladding Material
Plywood is an attractive and
economical material for use in cladding and lining. With all
the natural colour and variation of timber, it is
particularly suited to combination with timber framing. When
the plywood is attached to a timber frame it creates one
structural unit, much stronger than a normal timber frame.
The strength of this means that stud spacing can be wider
than normal. In the Brannigan residence, stud spacing was
600mm. It also means that noggings between the studs are not
necessary, their role taken over by the plywood. As the wall
acts as one structural unit, rafters or trusses do not have
to fall directly above studs. The strength of the plywood
lining and cladding, acting in composite with the timber
frame, creates a very strong and rigid structure, resisting
roof uplift, an important consideration in cyclonic and high
wind areas. The plywood braces the building, eliminating the
need for separate bracing elements. When each sheet is
secured, 3 square metres of the building is covered at a
time, offering saving in labour costs. Unlike a lot of other
cladding materials plywood can be worked and fixed with
normal wood working tools and is easily bent to clad curved
surfaces. To achieve the desired results, the detailing and
selection of the correct plywood for each application is
important.
Environmental Benefits of
Plywood
Plywood offers many environmental benefits to the designer.
It is manufactured from plantation-grown timber, a
sustainable resource. Compared to other materials, low
amounts of energy are used in its manufacture. Its high
strength to weight ratio means plywood structures are very
economical in the amount of material, and thus resource,
used. Plywood can also play an important role in passive
solar design. With a low thermal mass, plywood cools
rapidly, dissipating the heat of the day, and lessening the
dependence on energy consuming air conditioners.
Designing to the 300 module
The sizes of most materials used
in the Australian building industry are multiples of a 300mm
module. This dimension is the metric equivalent of the
imperial foot, and the size of most building materials are
multiples of this module. By designing a building to a
structural grid based on the standard sizes of building
materials, an architect can ensure that all the elements
used within a design relate to each other. This approach
helps minimise material wastage and reduces labour costs
caused by the need to trim, cut and manipulate building
materials.
An intelligent designer, however, does
not let this result in a sterile, repetitive building. Bud
Brannigan, while working to a structural grid, is not a
slave to it. His own house, in parts, breaks the repetition
by extending beyond the grid or having courts scooped inside
it.
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