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Introduction
The steep, wooded and inaccessible site
chosen for building this small house for Margot and Ken
Suber overlooks the Huon valley in Tasmania's south east.
Difficult ground conditions of exposed rock and a 1:2 ground
slope generated a "thin plan form, one room wide and thirty
metres long" (Jones 1988), that provides a single level
platform for living. As the only approach to the proposed
site for building was from above, the roof became a key
element in the design of the house. As expressed by Jones,
the idea for the building was to make "one, big, hovering
roof in the landscape with no flashings or roof plumbing
other than a gutter", initially conceived as "a huge
longitudinal trough resting on structural water tanks". Such
reference to the Australian vernacular for building "sheds"
- flimsy structures, clad in iron, underpins the
architectural language of this house. It also reflects the
influence on Jones of the work of Australian architects,
Richard Leplastrier (Palm House) and Glenn Murcutt (Ball
House). The roof acts to screen the interior from the public
approach to the house whilst presenting the most readable
facade of the building. Being remote from town services, the
roof also plays an important role in collecting water for
the occupants' amenity and to fight fire. The house
therefore makes a platform for living under a sheltering
roof plane. This was given architectural expression through
the use of timber, particularly the laminated curved roof
beams used to achieve the low slung sine wave of the ceiling
which opens the view from the interior "up and out into the
landscape beyond" (Jones 1988).
Description
Originally conceived as a studio for
Margot, the brief for the building was controlled by a
limited budget. To address economy and provide a unique
building, architect James Jones designed a highly refined
post and beam structure determined by a regular grid based
on standard sheet sizes. The building comprises one
repetitive structural section with perimeter infill stud
work. Such a strategy allowed for a planning flexibility
whilst providing a clear series of datums that produce a
proportional language to the building envelope.
Standardised, low cost cladding materials, door and window
joinery systems then dress and punctuate the frame. The
house has a simple parti of orienting the living spaces and
decks to the north and valley outlook. The building provides
its own water supply, with water tanks, fire hose reel and
generator located beneath the floor. The roof has a
catchment area of 200m 2 covering 130m 2 of internal space
and 70m 2 of deck. Given the steep slope, the provision of
covered and accessible external space was critical in the
design. Access to the platform is provided under the roof
overhang to the east, the aspect protected from Tasmania's
notorious "roaring forties" - a weather pattern resulting in
boisterous, cool westerly or north-westerly weather that
affects the whole of Tasmania.
Structural Description
The primary grid of the post and beam
system deployed in the building works on a module of 2400mm.
Dimensionally therefore, walls and openings are multiples of
300mm, 450mm, 600mm, 900mm and 1200mm. In section, a datum
of 600mm (sill) and 2400mm (head height) is established with
highlight glazing, continuous to the perimeter walls,
expressing the roof profile. This dimensional rigour, based
on standard sheet sizes, therefore allows for a certain
planning flexibility in determining 'wall' and 'opening'
within the frame. The platform floor of the house is
supported on and braced between steel columns and beams that
rest on isolated concrete piers. Oregon Pine joists sit over
the 200UB sub floor beams. The primary frame that comprises
the extruded structural section is constructed of laminated
Tasmanian Oak columns and roof beams. Long span Tasmanian
Oak purlins sit over the curved roof beams. At the platform
level, therefore, the material changes to timber with infill
braced stud work and "drop in window and door panels" (Jones
1988).
The platform cantilevers to accommodate
decks and utility spaces below. Tasmanian Oak and Myrtle
tongue and groove flooring is used inside and marine grade
Celery Top Pine decking is used externally. The Tasmanian
Oak roof beams are double curved, each curve 25m in radius,
forming a low slung wave. The beams are made from short
sections of 29mm glue laminated, finger jointed members. The
members are 2 laminates wide to enable easy housing and
minimal chisel work on site. The laminated columns are made
of 4 laminates in the same 29mm glue laminated finger
jointed method, whereby the laminates of the column members
continue past the beam. Plywood sheets, designed to sit on
top of the beam edges, fit between the dressed roof purlins
to form the ceiling and brace the roof through diaphragm
action. Rather than using cover strips, the plywood joints
are expressed as a 5 mm shadow line. The open joint to some
degree also allows for dimensional tolerance within the
ceiling geometry. Externally the building is clad
horizontally in corrugated sheet with ridge caps deployed as
vertical corner flashings. Internal walls are standard stud
wall construction sheeted in plasterboard to 2400mm high.
Glass infill below the roof beams are again used to
accentuate the hovering roof plane.
A Strategy for Design with
Timber
Bracing Light
Structures
Bracing in light weight structures can be achieved by
locating shear panels or skins at various locations. A shear
panel is a solid panel that is constrained top, bottom and
at the sides thereby "filling in" the frame. This may occur
as a vertical panel between the post and beam or
horizontally between rafters and purlins. The panel acts to
resist lateral movement in the building by restricting the
relative movement between the parallel members. Not all bays
of a framed structure require bracing. For example, a long
shear panel in the plane of the ceiling that extends the
length of a structure can act to brace the entire building
when connected to end wall shear panels.
Architectural Expression of Timber as
Exposed Structural Element
The lines of the expressed
structural beams and columns deployed in the Suber House,
express a harmony and direction in the building that work to
establish an architectural vocabulary. When left unpainted,
the choice of timber species also acts to determine a
colour, a warmth and therefore a palette in the
building.
The Use of Timber in Standardised
Elements
The use of post and beam provides a means of eliminating
determinants on the positions of walls in a building and
therefore the way that living spaces are created. To
establish a grid like structure permits open planning, free
of visual obstruction. Repetitive spacing, inherent in the
nature of the grid, therefore promotes a standardisation of
elements in the post and beam structure. As discussed in the
Suber House, such a language of architectural elements also
promotes a proportional language in the building. To use
repetitive elements, such as doors and windows, achieves
economy and also a flexibility, in terms of retrofit.
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