Page 32 —
COLORADO REAL ESTATE JOURNAL
— May 18-May 31, 2016
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Construction, Design & Engineering
U
rban infill develop-
ment in Colorado is
hot right now. How
hot? It has its own blog: www.
denverinfill.com/blog.
So,
developers who tackle these
projects clearly have their finger
firmly on the pulse of the mar-
ket, along with ample amounts
of courage, vision and drive.
But are these developers aware
of the hidden challenges that can
create substantial cost overruns?
In this two-part series, experts
will share how to avoid some of
these obstacles and explain how
proper planning with the right
team can save you time, money
and headaches. In first part, we
look at the challenges of below-
grade construction and what to
look for when your property is
surrounded by existing struc-
tures.
When Parking Goes Down,
Challenges Go Up
It’s no secret that land is a lim-
ited resource in popular urban
locations. That’s why infill proj-
ects often involve below-grade
construction for parking or leas-
able floor area. However, there
has been an increasing trend
toward construction of above-
grade parking structures to
avoid the significant costs of
excavation, shoring and, more
recently, groundwater treatment.
“Conventional soldier beams
and lagging are still fairly com-
mon,” said Tom Soell, principal
at JVA Consulting Engineers.
“But, in some instances, neigh-
boring properties and munici-
palities either won’t accommo-
date temporary easements to
allow for tiebacks that cross the
property line, or they’ll have
special requirements within the
right of way.”
When alternative secant
pier systems or other methods
of shoring must be used that
dimensionally protrude into
your property, then proper plan-
ning can accommodate the addi-
tional thickness of the shoring
into the final basement layout.
It’s also important to note that
certain shoring systems (secant
piers, for instance) provide bet-
ter protection from groundwa-
ter infiltration during construc-
tion. So if high groundwater is
an issue, then the selection of
a more robust shoring solution
can offer significant savings.
“With Studio Architecture’s
guidance, we figured out how
to add significant value to our
recent infill project,” said Jeff
Wingert, president and chief
operating officer of W.W. Reyn-
olds Cos. “They helped us
achieve nearly 20 percent more
leasable floor area in the build-
ing by creating a below-grade
courtyard. And adjacent to (the
courtyard) is more below-grade
office space that gets ample
daylight but doesn’t exceed the
allowable floor area on the site.
This was a huge bonus for us.”
So, balancing below-grade
construction costs against the
added value of the leasable area
needs to be weighed early in the
conceptual design and entitle-
ment phase. If you have the right
team on board, it can uncover
these unique
oppo r t un i -
ties. If not,
you
could
be burying
p o t e n t i a l
profit.
What’s Next
Door?
Surround-
ing structures
raise a num-
ber of con-
cerns during
urban infill
construction. When building
adjacent to an existing structure,
meticulous planning must go
into the selection and coordina-
tion of the new building’s foun-
dation and below-grade shor-
ing system. If not, the resulting
challenges rapidly increase costs
and can significantly delay con-
struction.
“It’s extremely valuable for the
owner and contractor to invest
in specialty services that moni-
tor movement at the interface of
adjacent properties,” said Soell.
According to Aldo Sebben,
design director and principal
at Studio Architecture, historic
buildings, and some contem-
porary existing structures, also
may violate fire ratings associat-
ed with the existing walls along
property lines.
“On a recent project in Boul-
der, the building on our site was
built adjacent to an existing his-
toric structure and development
plans required demolition of the
contemporary building to make
room for our new project,” said
Sebben. “Since the neighboring
building was over 100 years
old, the temporary condition we
uncovered on the other property
made the neighbor’s exterior
walls completely inadequate.
That’s why it’s important to
evaluate everything surround-
ing the property. If you don’t it
could be a disaster.”
How To Go With the
Groundwater Flow
If groundwater is going to
impact the excavation for pro-
posed below-grade structures,
then it is important to evaluate
whether you will treat ground-
water permanently or build a
watertight foundation. An early
and detailed assessment of
groundwater conditions, includ-
ing groundwater monitoring to
identify seasonal groundwater
fluctuations, will help guide the
design of shoring and founda-
tion systems.
“Within the last 10 years,
Colorado has adopted new
EPA standards on the dis-
charge of groundwater into
the storm sewer system,” said
Soell. “When projects encounter
groundwater during construc-
tion, and testing identifies the
presence of excessive amounts
of naturally occurring metals,
the groundwater must be treat-
ed prior to discharge into the
public sewer system. There’s just
no getting around this incredibly
costly issue.”
According to Sebben, perma-
nent groundwater treatment is
necessary if a traditional perim-
eter drain and/or underslab
drainage system is used prior to
discharging the water.
“Often, a small environmental
plant must be built into the proj-
ect at significant cost depending
on the depth of the structure,
the flow rate of the groundwa-
ter present and the extent of
treatment required,” said Seb-
ben. “Not only that, but with the
addition of a permanent water
treatment system, the owner has
to absorb the system’s annual
operating costs for the life of
the building. On a recent proj-
ect, evaluation of both options
with the GC revealed that by
raising the building slightly and
building a watertight ‘bathtub’
we could eliminate the need for
permanent groundwater treat-
ment.”
According to Sebben, this
“bathtub” approach was used
on our firm’s 17Walnut project
with Element Properties and
it eliminated the permanent
groundwater treatment system.
However, the basement walls
and foundation had to be sized
to resist higher hydrostatic loads
and counteract buoyancy forces
on the building.
“This more robust solution
can also be accomplished with a
structural slab isolated from the
soil and supported on drilled
piers socketed into the bedrock,”
added Sebben.
“There are obviously signifi-
cant construction costs associat-
ed with the ‘bathtub’ approach,”
Jeff Dawson
Founder and
managing partner,
Studio Architecture,
Boulder
