Ravine House
Fox Point, Wisconsin
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Structural Concrete Forms Cantilevers in Ravine
House
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| Photo courtesy of Kevin Miyazaki. |
The Ravine House in Fox Point, Wisconsin was conceived by the architectural
firm La Dallman. This unique 4,500 sq. ft. residence wrapped with
expansive windows faces a 50-foot deep wooded ravine to the south
and southeast. The structure is located on a mildly sloping site
at the top of the bluff and consists of two floors, a partial basement,
and an exterior deck on the south elevation. Floor and roof cantilevers
exist in several strategic corners of the house providing unrestricted
views towards the ravine. A structural system utilizing cast-in-place
post-tensioned reinforced concrete was selected to bring the architect’s
vision to life. Quoting La Dallman:
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| Photo courtesy of Kevin Miyazaki. |
“The house offers a rich set of intentional juxtapositions:
the second floor slab of post-tensioned concrete allows for the
progressively cantilevered massing, … box hovering above
a long-span living space, and a delicate, 42’ length of
wrapping window wall; the reserved front facade gives way to the
unexpected, extroverted, and expansive rear façade; the
sharpness of the form contrasts with the velvet texture of the
weathering steel; the striking composition of the mass blends
against the backdrop of the forest; the glass, prismatic volumes
sculpt shafts of natural light deep into the interior; the warm
copper stain softens the toughness of the concrete. Woven together,
these opposing qualities produce a project that celebrates and
roots itself in the site.”
Design collaboration started in January 2005 and the Ravine House
was completed in January 2008. Several key challenges were encountered
and overcome during the design process, which are described in more
detail below.
Second Floor Post-Tensioned Reinforced Concrete Slab
 The
architectural design concept called for a second floor that cantilevered
to the east beyond the first floor and was supported by a thin structural
system profile. In addition, load-bearing walls from the second
floor needed to be transferred out above an open living space below
while accommodating an irregular column layout. Close collaboration
between La Dallman and consulting structural firm Pierce Engineers,
Inc. (PE) resulted in the choice of a post-tensioned reinforced
concrete slab as the second floor framing system supported on reinforced
concrete columns and walls. The 2,000 sq. ft. cast-in-place slab
was designed to transfer out the roof framing loads above and provide
for a 10’-0” cantilever to the east and 6’-10”
cantilever to the south while maintaining a thin profile (10”
thick). This approach allowed for the extended length of “wrapping
window wall” at the first floor as well as provide support
for a hanging masonry chimney and CorTen weathering steel cladding
under the main cantilever. The prestressing tendon layout was adapted
considering the irregular column and wall spacing. Maximum long
term slab deflection, including creep effects, at the main cantilever
is anticipated to be approximately a half inch.
High Roof Cantilever
Windows that wrap around wall corners were located at opposite
corners of the second floor. The intent of the architect was to
support the high roof framing above these windows without any vertical
structural member in the corner. To accomplish this, HSS columns
were embedded within the wood stud walls and steel channels were
cantilevered 7’-0” and 10’-0” out over the
top of the windows. To maintain a thin roof framing profile, the
channels were hidden up in the roof joist framing.
First Floor Cantilever Reinforced Concrete Slab-on-Grade
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| Photo courtesy of La Dallman. |
The architect’s intent was to cantilever the first floor slab
on grade 4’-2” towards the east and south of the expansive
living space over the mildly sloping grade. To achieve this, the reinforced
concrete slab-on-grade was thickened to 8" and cantilevered out
over the top of the perimeter foundation wall. To maintain rotational
stability, the thickened slab was extended 7’-0” inside
the perimeter foundation wall.
Custom Dining Table Utilizing Concrete
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| Photo courtesy of La Dallman. |
Designing some of the house furnishings, La Dallman desired to create
a custom dining table consisting of a poured clear urethane top set
above a monolithic concrete base. To keep with the vocabulary of using
structural concrete to form the cantilevers of the house, reinforced
concrete was selected for the cantilever supports for the custom dining
table. The design of the base required a single post, eccentric in
two directions, to support a cantilever slab stiffened with a tapered
beam. Checking the table cantilever for deflection and the whole unit
for overturning in the short direction, the structural engineer helped
determine the dimensions for the mildly reinforced concrete base (14”
wide x 10” high footing, 9” x 21” eccentric post,
and a 3” cantilever slab with 5” to 8” deep integral
tapered beam). The 1½” thick poured urethane tabletop
was secured to the top of the concrete base with embedded angles and
concrete screws. Complete fabrication of the table was performed by
Rock Elements.
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| Architects: La
Dallman
Structural Engineer: PIERCE ENGINEERS,
INC.
General Contractor: Ruvin Brothers
Post-Tensioned Slab Contractor
KBS
Custom Dining Table Fabricator
Rock Elements
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