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Optimized Design of Combined Disciplines: Steep-Sloped Roofing and Exterior-Wall Cladding

May 15, 2008

The University of Chicago, chartered
July 1, 1890, is located in
the heart of the historic Hyde
Park neighborhood on the
South Side. The inventory of
buildings on the campus
includes an eclectic mix of Gothic forms
with ages varying from 70- to 100-plus
years to new facilities constructed within
the past four to six years and the ever-present
groundbreaking to accommodate continued
A common thread in the university’s
past and present is the master plan developed
by Henry Ives Cobb, the architect
hired by John D. Rockefeller to fulfill his
vision for the design of the campus. Central
to the vision (beyond academia), was the
requirement that the campus core be represented
by its connection to the surrounding
community, a design standard that the continued
expansion of facilities must acknowledge.
The Gothic theme of the first 40 years
of construction is characterized as an
immediate reference to the past but, perhaps
more importantly, as evidenced by the
grandeur and scale of the buildings, a commitment
to the future.
As grand and pleasing to the eye as the
inclusions of the master plan were, notably
absent was any discussion specific to the
standard of care and maintenance. This is
not entirely surprising, as the older, established
buildings on the campus were built
to last, of solid wall construction with multiple
brick wythe back-up walls, clad with
flat ashlar and carved limestone. Craftsmen
and building stewards of the era fully
expected to achieve robust returns in terms
of life cycle. Steep-slope roofs were covered
with clay tile and copper accessory flashings
and gutters. This type of construction
could easily deliver years of service in the
absence of regular maintenance, a truism
that up until the past 20 – 30 years held
The performance history of those buildings
in the inventory that are now ap –
proach ing 70 – 100 years in age would do
Cobb proud as they remain largely intact,
vibrant, and functional components of the
master plan. However, according to Barry
O’Quinn, senior manager of building envelope,
sheet metal, and masonry, “We find
ourselves faced with a large inventory of
historically significant buildings, all coming
of age at the same time in terms of muchneeded
and well-deserved large-scale maintenance,
most notably on the building envelope,
roofs, and exterior walls.” The current
condition indices of these buildings, when
comparing and contrasting service life to
capital expense and maintenance costs,
would establish a very gradual curve over
the first 50 – 60 years of service. Beyond the
50 – 60 year point in their respective life
cycles, the component assemblies are nearing
the end of their service lives and are
subject to replacement (reroofing) and
maintenance (tuckpointing, selective re –
mov al and replacement of stone cladding).
The majority of the steep-slope, tile roof
assemblies on the vintage buildings in the
inventory are representative of original construction,
combined with cut and carved
limestone façades (barrier walls) establishing
the building envelope. At and above the
roofline, the clay tiles transition to carved
copings at parapets and limestone-clad
sheer walls of higher, interior, partial elevations.
It is at these interfaces, where the
work scope becomes interdisciplinary, that
the discriminating eye turns toward the
overall condition of cladding features adjacent
to and above the roofline. These combined
elements of roofing and cut limestone
cladding result in complex geometries of
converging slopes and changes-in-plane,
with demanding needs specific to flashing.
The true success of the building envelope in
this instance is measured by the combined
performance characteristics and presentday
condition indices of the individual components
for the roof and exterior walls.
The current standard of care for the vintage
buildings continues to evolve, as evidenced
by expenditures in the tens of millions
of dollars over the past five years to
address deferred maintenance as identified
in response to the initial round of 2001 City
of Chicago Façade Ordinance inspections.
According to O’Quinn, “Compliance with the
ordinance on the older buildings has resulted
in the commitment of a significant
amount of money over the past five to six
years. Lessons learned through the development
of repair strategies specific to each
building and its particular nuances have
been helpful in establishing priorities and
the standard of care for the remaining
buildings on the campus that, by virtue of
height, may not necessarily fall under the
provisions of the code.”
The majority of the current capital projects
are focused on stewardship of the
building envelope for the vintage buildings
on campus, for these represent the past,
present, and future identity of the campus.
Provisions for maintenance and repair were
notably missing from Cobb’s master plan.
Arguably, there would be no need for a
structured maintenance and repair program,
as the projected life cycle for the
steep-sloped tile roofs and walls of cut limestone
would predictably exceed the tenure
of anyone involved in facilities management.
OC T O B E R 2008 I N T E R FA C E • 7
Project Profile –- Phased Steep-Slope
Roof/Exterior Wall Rehabilitation
Burton Judson Courts, completed in
1931, was built to house a burgeoning student
population. Construction of the steelreinforced,
concrete, and wood-framed
housing unit began in the late 1920s, providing
work for skilled Depression-era
craftsmen on what was, at the time, one of
the largest private construction projects in
all of Chicago (Photo 1 [Jean F. Block, The
Uses of Gothic Planning and Building on the
Campus of the University of Chicago, 1892-
1932]). The building, clad with cut and
carved limestone with roof slopes of clay tile
exceeding 16:12, consumes an area equivalent
to a quarter of a city block (Photo 2).
By The Numbers
The magnitude of the combined steep
roof/exterior wall rehabilitation, with a total
cost in excess of $10 million, justified an
initial bid package centered on a projected
five-year, phased construction period.
Summer 2008 represented the start of
Phase III as identified in the original solicitation
of bids (Photo 3). The abbreviated
annual construction window of June
through September
has presented a challenge
during Phases I
and II (Photo 4). The
university is currently
giving consideration to adding a sixth-year
phase to provide reasonable assurance that
the construction will be completed within
the time constraints established by the
annual scheduling parameters. With yearround
occupancy by resident heads and the
increased student traffic for spring departures
and fall arrivals, the schedule, beyond
the work itself, may be considered a determining
factor in establishing the overall
success of the project (Table 1).
Existing Conditions
During the summer of 2004, facilities
personnel reported that the individual clay
roof tiles were failing to the extent that
pieces were falling to grade at random locations
without apparent cause. In response to
the reports of
falling tiles, a
roof survey was
performed to
determine why
the tiles were
Areas by Phase (Sq Ft) –
Steep-Sloped Clay Tile,
Flat-Lock Seam,
Modified Bitumen, and Exterior
Roofs Walls
Phase I 11,114 17,210
Phase II 11,367 10,415
Phase III 20,504 21,806
Phase IV 13,208 14,502
Phase V 11,008 15,088
Totals 67,201 79,021
Photo 1 – Original construction of Burton Judson Courts,
circa 1931.
Photo 2 – Aerial photo of
the Burton Judson facility.
Photo 4 – Phase I, south exposure.
Photo 3 – Overall view of pending Phases III and IV.
8 • IN T E R FA C E OC T O B E R 2008
Table 1
exhibiting distress. Through a visual examination,
it became apparent that the tiles
were exhibiting severe cracking in sections,
across the full dimension or thickness of the
tiles (Photo 5). There was no apparent pattern
to the cracking or evidence to suggest
that it was induced by any impact.
Tiles were removed, and an initial rateof-
absorption test was performed. Inter est –
ingly, the results, when compared and contrasted
to tile from other buildings in excess
of 100 years of age, indicated the absorption
rate for the failing tiles was, by volume, 30 to
40 times greater than that of the older materials
that were not exhibiting distress or
cracking. The findings supported the theory
that the performance issues related to the
tile were the result of water retention and
subsequent freeze/thaw cycles. Under –
stand ing that the continued free-fall of fragmented
clay tile to pedestrian areas below
presented an unacceptable risk, the owner
opted to install nets to catch the projectiles
over the short term until funding for design
and construction could be secured (Photo 6).
In an effort to add value, the roof survey
included a cursory inspection of the building’s
exterior walls, in part due to the readily
discernable wall distress conditions in
exterior-wall features (parapets) adjacent to
and extending above rooflines. The roof side
of the parapet and stone copings had been
subjected to liberal applications of masticbased
repairs over the 75-year life cycle of
the installation (Photo 7). Removed from the
above-roofline features, it was noted that
much of the stone cladding in close proximity
to window heads was exhibiting out-ofplane
movement and localized distress in
the form of cracked, spalled stone.
The aforementioned wall distress conditions
were serious enough to warrant further
review through selective removals in
areas of interest to develop an improved
understanding of the as-built conditions,
most notably at the gabled roof features
present at regular intervals across the primary
N/S- and E/W-orientated wings of the
facility. As suspected, concealed steel
imbeds (loose steel lintels at the window
heads) had been subjected to moisture,
resulting in corrosion (Photos 8 and 9). The
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Photo 5 – Typical condition of the tile in the field of the roof.
Photo 6 – Netting installed as emergency response to falling tile.
OC T O B E R 2008 I N T E R FA C E • 9
volumetric expansion of the steel had shifted
the surrounding stone from its original
setting. The above-described rust jacking
(expansion of steel in sections due to corrosion)
of the loose-set steel lintels established
conditions warranting a complete
rebuild of the backup materials with new
steel and concrete-reinforced CMU wall sections.
At several locations,
it was noted that
the overall length of the
loose steel lintels fell
short of the full span
established by the window
opening, with the
ends not bearing of the
jamb stones as would be
prescribed by current
engineering conventions
(Photo 10). The presence
of corrosion and the
ques tionable integrity of
the condition established
by the incorrectly sized
lintels provided justification
for the complete
rebuild of the stone-clad
Further study showed cyclical exposure
to moisture as the catalyst for the accelerated
corrosion of the concealed steel imbeds
(loose lintels) at this location. As originally
constructed, a through-wall flashing was
installed as a supplement to the stone coping,
re plete
with an ex –
tended downward
or vertical
break on
the roof side
to provide coverage
for the
a c c e s s o r y
flashings for
the tile roof assembly. As previously stated,
liberal applications of mastic were present
through this change in plane from the roof
to the stone copings. Removal of the stone
coping at the transition of the sloped-rake
roof edge to the short, horizontally oriented
coping at the base of the gables was very
instructive. At this location, it was determined
that the through-wall flashing was
not continuous through the complex geometry
of differing planes as established by the
stone coping assemblies (Photo 11). The
ultimate demise of wall cladding at this
location can be attributed to this “disconnect”
of the drainage plane as witnessed in
the through-wall flashings below the stone
The required selective removals of wall
cladding materials to facilitate the removal
and replacement of the damaged loose steel
lintels typically stopped at the window
heads (Photo 12). All stone copings and
masonry backup materials were removed,
exposing the timber framing of the roof deck
(Photo 13). This accommodated the necessary
modifications to the wood roof deck
(cutting back flush with the timber frame)
and the installation of “J” hooks that would
be integrated with the new steel-reinforced
CMU back-up wall as it was built up (Photo
Subsequent to the complete reconstruction
of the gables, new through-wall flashing
was provided over the top of the underlying
stone cladding and fully grouted CMU
Photo 7 – Repeated applications of cold-process repairs at
rakes with adjacent stone coping.
Photo 8 – Inspection opening at area of
localized distress at gables.
Photo 9 – Typical
corrosion of loose steel
lintels at window head of
gable features.
10 • I N T E R FA C E OC T O B E R 2008
backup wall. Final roof system accessory
flashings were integrated with the new
through-wall flashing below the stone copings
(Photo 15). With all masonry and new
through-wall flashing components in place,
the work area was turned over to the roofing
contractor, and tile installation began
(Photo 16).
In an effort to expedite the remaining
portions of the project, each phase was
reviewed during the winter months for the
express intent of establishing unit quantities
of stone and loose steel lintel replacement.
While initial quantities were published
in the bid set documents, it has been
noted that over the term of the project,
additional distressed stones (beyond those
catalogued in the initial inventory) will be
presented in increased numbers, primarily
at window heads and mullions. Steel, stone,
and roof tile are ordered in advance of the
phase start-up to minimize the possibility of
delays attributed to lead time. The masonry
res to ration service provider fulfills the role
of general contractor,
all responsibility
for establishing
work platforms
(scaffolding) as
necessary for
both trades.
As a result
of the project
approach on the
Burton Judson
facility, the university
has saved approximately $400,000 –
$500,000 in scaffolding costs over that
which would have been required if the project
had been solicited separately, by discipline.
In addition, added value is derived
from having the two trades work concurrently
on building features removed from
one another by trade yet related by function
in the combined assembly of the building
envelope. The repair of the walls and aboveroofline
features established
a sound
substrate for the
termination of ac –
cessory roof flashings
and continuity
of through- wall
flashing conditions
that previously
proved to be the
apparent cause of
significant wall
distress conditions.
Beyond the
readily discernable
cost savings specific
to scaffolding,
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Photo 10 – Loose steel lintels did not provide adequate span across
the full dimension of the window opening. The area between the
lines indicates approximate revised bearing limits of new steel
window head lintel.
Photo 11 – Lack of continuity in through-wall flashing
resulting in corrosion of loose steel lintel below.
Photo 12 – Cataloguing of stone cladding ahead of required selective
removals for the gable, backup wall rebuild.
OC T O B E R 2008 I N T E R FA C E • 1 1
the optimized building envelope management protocols bring
added value through:
• Minimized facilities disruption with targeted, manageable
work scopes.
• Matching site-specific building features and trades to a
well-defined annual construction period at which time
all building envelope distress conditions were given
equal consideration.
• Early in the planning stages, proactively addressing at
the face of the work condition indices of building features
that are categorized as supplemental to one another in
the component assembly.
• The new roof and accessory flashings are integrated with
restored, adjacent, and above-roofline wall sections,
establishing baseline total systems performance that will
result in a projected life cycle rivaling that of the original
Closing Thoughts
Beyond the obvious challenges relative to access are the
ever-present needs specific to the balance of the building envelope.
In summary, steep-slope roof assemblies present a set of
challenges unique from the perspective of design routinely not
given consideration in the low-slope arena. Steep roofing components
of building envelopes are dynamic in form and function
as defined by their simple but demanding needs related to the
critical placement and integrity of accessory flashings. The continuum of a functional
drainage plane through complex geometries of dissimilar materials must be acknowledged
in the design process.
If the present roof system, with an industry-accepted standard service life in the range
of 60 to 80 years, is in a condition warranting replacement, then it is reasonable to assume
that everything around it should be given equal consideration during the design phase of
the project. By some measure, all above-roofline features on vintage buildings should be
considered extensions of the roof assembly.
In the absence of due diligence centered on
the understanding that a roof represents
only a portion of the building envelope,
economies in volume may be overlooked,
and the integrity of a significant investment
in the roof component of the assembly will
predictably be compromised.
Donald Kilpatrick has been with INSPEC, Inc., since 1985.
Don has performed numerous building envelope investigations
on a variety of new and vintage structures. Information
derived from the investigations has been used successfully in
the development of design and repair strategies. Kilpatrick
received the Horowitz Award for outstanding contribution to
Interface journal in 2004.
Donald Kilpatrick
Photo 13 – General limits of demolition at gables with temporary
roof covering established.
Photo 14 – Gable end rebuild with new bond beam
and “J” hooks that will interface with fully grouted,
steel-reinforced CMU backup wall.
12 • I N T E R FA C E OC T O B E R 2008
Photo 15 – Completely
reinstalled stone coping
with integrated throughwall
and accessory
counterflashing assembly
ready for the installation
of clay tile.
Photo 16 – Installation of
clay tile subsequent to the
completion of adjacent
cladding repairs.