Page 28
— Multifamily Properties Quarterly — July 2015
Design
I
t has long been argued that
one structural framing material
has advantages over another.
Steel is dimensionally stable,
noncombustible and more pre-
dictable than concrete or wood. But,
wood is less expensive than concrete
or steel.Wood is
wasteful due to
cut-offs, which can
reach 20 percent for
site-built framing.
However, wood is
more economical
and easier to work
with. Concrete is
expensive and not
as sustainable as
highly recycled con-
tent steel. But, con-
crete can be used
on taller buildings,
and so on.
The truth is that all of these materi-
als have their place.Wood has been
king of the single-family home and
multiunit buildings from one to five
stories. Light-gauge steel fits the five
and six story niche, but doesn’t offer
significant cost advantages over con-
crete and is limited to seven stories.
Concrete (with light-gauge framing
as infill) rules above six stories, but
because of cost its real advantage is
in taller buildings.
This has pretty much been the story
since the late 1800s. However, now
there is a technology and manufac-
turing company that is changing this
paradigm.
Our Denver-based company is gain-
ing significant traction nationwide
with our integration platform for the
architecture, engineering and con-
struction industry. The technology
features a proprietary Revit-based
design integration software applica-
tion, coupled with a computer-aided
design to computer-aided manufac-
tured light-gauge framing system,
which is capable of being built as
high as 12 stories, and offers several
distinct advantages over the typical
design and construction practices.
Advances in engineering technology,
design and planning software, auto-
mated fabrication and lean instal-
lation offer more efficient design
and planning, construction schedule
compression and significant cost sav-
ings over other structural framing
approaches.
It starts with a three-dimensional
software-based design. Typically, 3-D
models of a building’s structure are
not developed and used on multi-unit
or multifamily projects because they
are expensive and often not accurate
as it relates to what is eventually
built.
The key to driving down the cost
of modelling is through automation,
which is achieved through the stan-
dardization of components.When a
standardized, structural system can
be mapped and engineered, it auto-
matically creates a precise 3-D struc-
tural model of a building. A tool that
can create an exact replica of what
will be built is powerful, especially
when demonstrating a construction
project in model-centric design and
virtual construction to stakehold-
ers. The match between model and
building is possible because of the
dimensional precision of the light-
gauge and cold-rolled steel framing
system, and the manufacturing pro-
cess, which produces components at
tolerances of one-thirty-second of an
inch through computerized numeri-
cal control machines and robotic
welding.
Model-centric design is the direc-
tion the industry is moving. Building
information modeling allows archi-
tects, engineers, contractors, vendors
and suppliers to collaborate and
design and build the building virtu-
ally, providing an opportunity for all
participants to be better integrated.
Complications that invariably come
up in the field and add significant risk
and cost to a project can be eliminat-
ed before reaching the uncontrolled
environment of a jobsite.
Bring a lean manufacturing
approach to the chaotic environment
of the jobsite. Supplying and install-
ing the entire structure above trans-
fer slab eliminates phasing of subs
during framing and the potential for
scope creep and missed scope.
Having all components labeled
and set for a specific location in the
building makes installation quick and
predictable. This saves time in layout,
measuring, cutting and sizing materi-
als, which is typical in wood or con-
crete framing.
This framing system is dimension-
ally stable – it will not shrink or twist
and needs no time for compression
or curing, which is another significant
advantage over lumber or concrete.
Mechanical, plumbing and electrical
contractors can start rough-in work
immediately because the process
moves quickly from floor to floor. This
leads to significant schedule com-
pression and shorter overall construc-
tion schedule durations. General con-
ditions and contingencies are reduced
and all stakeholders can measure risk
more effectively, leading to buy-out
savings, which helps projects cash
flow sooner (a pro forma booster).
The process of architecture, engi-
neering and construction are frag-
mented and difficult to integrate. The
lack of integration leads to risk and
inefficiency. But through software,
manufacturing and system-build
installation, there is a platform that
can change the old design and build
ways.
s
A
rchitects need to design
multifamily housing build-
ings to accommodate many
interacting components
including functionality,
structural integrity and fire separa-
tion. However, one factor that is typ-
ically on the mind of the occupants
in the units is sound attenuation. In
other words, it is important to know
if and how much they hear the
neighbor next door. In multifamily
housing, sound attenuation, gov-
erned by the International Building
Code, can be a major leasing factor.
An architect can design methods
and details to attenuate sound if
they have a strong understanding
of how sound behaves. In physics,
sound is a vibration that typically
propagates as an audible mechani-
cal wave of pressure and displace-
ment through air, solid material or
liquid. Sound is measured in pres-
sure level units
called decibels. The
larger the vibra-
tion of the source,
the louder a sound
is heard by the
human ear. Stan-
dard noise levels
of some common
sources consist of a
“quiet home” at 25
to 35 dBA, “human
voice at three feet”
at 55 to 60 dBA and
the “average TV or
radio” at 80 to 100 dBA.
There are also two types of sound
– airborne and impact. Airborne
sound is vibration, like music or
conversation. Impact sounds are
generated by foot traffic on the floor
above or the pounding of a hammer
on the wall.
The sound rating classifications
established by U.S. Department of
Housing and Urban Development
and the National Bureau of Stan-
dards are recognized by the building
construction industry and found
in building codes. There are two
rating systems that compare the
acoustic quality of various building
assemblies. In each classification,
the higher the number, the better
the sound isolation performance of
the assembly. Sound Transmission
Class rates a wall assembly’s resis-
tance to airborne sound transfer at
the speech frequencies (125 to 4000
Hertz). Impact Insulation Class rates
a floor/ceiling assembly’s resistance
to structure borne or impact noise
transfer.
The IBC contains requirements for
sound isolation between dwelling
units in apartments and condomini-
ums. It requires partitions and floor/
ceiling assemblies to have an STC
rating of 50 (lab tested). It requires
that floor/ceiling assemblies have
an IIC rating of 50 (lab tested). This
is recognized as a minimum indus-
try standard.
Architects consider the quality of
the dwelling unit when determining
STC level for design. The minimum
code requirement is not necessar-
ily best design practice. Multifamily
housing can be grouped into three
distinct occupancy types:
1. Minimum (standard apartment):
Code required STC/IIC 50, recom-
mended STC/IIC 55
2. Medium (good apartments and
normal condominiums):
recommend-
ed STC/IIC 65
3. High (luxury condominiums):
rec-
ommended STC/IIC 75
In general, the more mass a wall
has, the better it is at attenuating
John Vanker
Founder and CEO,
Prescient, Denver
Keith Moore
Architect, Rocky
Mountain Group,
Englewood
The light-gauge framing system is capable of being built as high as 12 stories tall.
