This
design for a 720,000 square foot office building for downtown Los Angeles was
one of three finalists in the Fall 2001 design-build competition sponsored by
the California Department of Transportation. The design team, led by Koll Construction
of Los Angeles, submitted a cost-and performance guaranteed building design. Included
was a full technical submittal that addressed in detail the measures of sustainability
required by CalTrans. The building performance was predicted to beat the 2001
California Title 24 by 31.7% and to ensure a LEED silver rating. We worked
with the design team first to identify and establish massing and sustainable strategies
related to daylighting. This was followed by collaborations with the architect
on glazing and massing details, the curtain wall manufacturer on glazing and curtain
wall details, materials performance testing, and with the full design team (including
engineers, code specialists and cost estimators) on issues of performance, cost
and LEED certification. The program requires large blocks of space of at
least 48 feet deep. Past designs of this type have resulted in double-loaded corridor
schemes that yield floor plates of about 110 foot depths. We worked with the architect
to develop a strategy of thin sections wherever possible, a massing approach consistent
with their interest in expressing the plasticity of Los Angeles freeways. The
design organizes the floor planes into 50 foot sections, most with an exterior
wall on one side and a large light court on the other. In areas where the floor
plan is deeper, the 120 foot section includes a core and two 50 foot sections
lighted on one side. The floor to floor height is 12'-0", with the clear ceiling
height held to 10'-0" for code reasons. In order to maximize daylight penetration,
we worked with the structural and mechanical engineers to upturn the spandrel
beam, keeping the ceiling flush with the head of the clerestory glazing. Additional
building elements which are integral to the daylighting performance are high quality
glazing, light redirecting glass, reflecting louvers, exterior overhangs, interior
light shelves and manually operated diffusing shades. Throughout, white ceiling
surfaces near the window wall and photosensor-based light controls optimize visual
comfort and energy savings from daylight. The typical window wall is divided into
the upper clerestory glazing assembly, which controls sun penetration, and the
lower vision glass. It allows the occupants to adjust the shades on the vision
glass, giving them control while not denying those deeper inside the availability
of daylight. The building facades, including glazing, proportions and aesthetics,
were largely determined by the daylighting strategies and curtain wall details
we developed with the architect and the fabricators. On the north and south facades,
special light redirection glass was specified to allow deep light penetration.
Light redirection glazing is a spin-off from the automotive world that uses total
internal reflection to redirect daylight toward the ceiling. It is similar in
performance to prismatic glass, which was used historically, but without the weight
and cost penalty. We tested full scale samples of Serraglaze,a film employing
total internal reflection, manufactured in Great Britain. (http://www.serraglaze.redbus.co.uk).
The product effectively increases the usable daylight deeper than any currently
used technology within standard office building budgets. On the south, the glazing
does not redirect all solar radiation, so a shading system is also necessary.
A 4'-0" interior lightshelf controls sun penetration on the south faŤade for 98%
of the annual working hours. The vision glass is protected by a 12" exterior overhang
to control both glare and solar radiation. In addition, there is an interior roller
shade. On the east and west facades, we worked with the curtain wall fabricator
to design a cost-effective, custom fixed louver system. This was optically designed
to shade direct sun from all solar angles while admitting usable indirect daylight
with a double reflection system. The fins are extruded aluminum, coated with a
reflective finish to increase effectiveness. The optics are designed to diffuse
the reflected light on the ceiling, coupling daylight with the electrical lighting
system controls. This system provides daylighting in the thinner sections of the
building providing illumination from both sides. |
