Architectural Record 2015-04

PHOTOGRAPHY: © JEREMY BITTERMANN
the passive House concept for ultra-lowenergy
buildings first developed in the United
States during the 1970s energy crisis, only to
be adopted and refined into a codified
certification system in Germany, after funding
in this country dried up. But, like a prodigal
son, Passive House has reemerged in the U.S.,
with use of the certification system steadily
gaining ground over the last decade. Currently,
there are more than 140 U.S. projects that
have met the rigorous German-born standards.
Satisfying the stringent criteria requires
airtight, super-insulated envelopes that are
shaped by ambitious performance goals.
Growing interest in Passive House certification,
applicable to new construction,
renovation, and a diversity of building types,
helped prompt the U.S. Department of Energy
(DOE) to form a partnership, in 2012, with the
Passive House Institute U.S. (PHIUS), the nonprofit
organization responsible for certifying
Passive House projects in this country. The
DOE also funded a study to reshape the existing
standards and adapt them to the varied
U.S. climate. The result of the study is the
PHIUS+ 2015 standards, just released in March.
The original standards made sense in the
relatively consistent maritime climate of
north-central Europe, says Katrin Klingenberg,
executive director of PHIUS. “But in the
context of the extreme climates of the U.S.,
designers were sometimes forced to choose
strategies that had unintended consequences,”
such as overheating from too much glazing,
she explains. The new standards also represent
PHIUS’s further divergence from the criteria
set by its parent organization, the Passivhaus
Institute (PHI) in Darmstadt, Germany. The
two broke contractual ties in 2011.
The original Passive House standards, devised
to minimize energy loads, were balanced
on just three pillars: a space-conditioning limit
of 4.75 Btu’s per square foot per year; a source
energy cap (usually the total electrical demand)
of 38,000 Btu’s per square foot per year;
and an airtight envelope criterion of no more
than 0.6 air changes per hour at 50 Pascals of
pressure. The revamped standards maintain
these three pillars, but expand them.
While it is too early to say what the impact
of the new North American requirements
will be, the German standards have made
their mark on a variety of projects in the U.S.,
including houses, apartment buildings, and
even a laboratory. One example is In Situ
Architecture’s Skidmore Passivhaus in Portland,
Oregon. Completed in 2013, the single-family
house, made up of two shed-roofed cedar-clad
volumes, met the original benchmarks by
creating a super-insulated shell. It consists of a
hefty frame of 2-by-8 wood studs that is filled
with cellulose insulation and wrapped with 3
inches of rigid insulation. And since the Pacific
Northwest receives a relatively small amount
SKIDMORE PASSIVHAUS
In Situ Architecture’s
house in Portland, Oregon,
is clad in cedar rainscreen
panels over a wellinsulated
wood frame.
Glazing on the northfacing,
street facade
(opposite) is limited, while
it is more generous on
the south-facing facade
(above), in order to
capture desirable solar
gain. Motorized external
shades can be deployed
to prevent overheating.