Roofing/Waterproofing Details and The Architect’s Standards of Care

May 15, 2005

Across the nation, most states
or jurisdictions have adopted
the new International
Building Code and/or
International Residential
Code (the ‘I-Codes’) to replace
the three older building codes (ICBO
Uniform Building Code, BOCA National
Building Code and SBCCI Standard
Building Code) that had divided the country
into distinct areas of model building code
influence.
During the lengthy processes that led to
the melding of these three “model” codes
into the unified I-Codes, the negotiators
added new language that helps clarify an
issue that has been argued for decades in
various forums for building defects mediation
and litigation: The project designer’s
standard of care for ensuring that the contractor
has all details and guidance
required for weatherproof construction of
the exterior walls and roof covering.
In the past, it was not uncommon for a
project architect or specifier to pass a major
portion of the design responsibility over to
the building contractor by simply calling
out “flashing” on a typical wall section or
roof plan within the project documents. We
have seen construction drawings in which
the designer’s entire guidance for proper
flashing and weatherproofing of the exterior
wall and roof covering systems consisted
solely of the brief specification, “Comply
with applicable code requirements” inserted
into the General Notes. In these cases, the
project’s design professional quite simply is
stating that while it is his/her general
“design intent” that the building envelope
shall not leak, it is up to the contractor to
figure out how to carry out this broad mandate.
Note that while the Request for
Information (RFI) and submittal processes,
where applicable, can induce further clarification
as to the design, the architect may
not be contractually bound to respond once
the construction drawing phase is complete.
Further, after the project has been bid
and the work has commenced, there are
generally time and/or cost constraints that
significantly limit the potential processes of
design clarification when all the contractor
has been provided is the “intent.”
If, at a later period, these building walls
or roof do experience leakage or mold proliferation
due to waterproofing or flashing
defects, it has been our experience that this
“design intent” defense by the project architect
can be successful in the litigation
process. The builder’s continuation of the
construction, even when the design guidance
has been minimal, can be considered
to represent an acceptance of the additional
design responsibility and a commitment
by the builder to carry out the work in conformance
with the controlling building code.
• “The contractor is charged with
knowing, understanding, and complying
with code provisions and is
liable when there is a violation.”1
However, the referenced new I-Codes2
now make it completely clear that the final
responsibility for a detailed and effective
design for the building envelope remains
with the project’s designated design professional
and/or the qualified roofing and
waterproofing design professionals assisting
the project. Prior to issuance of the
building permit, the construction documents
must include comprehensive waterproofing
details:
• “… including flashing, intersections
with dissimilar materials, corners,
end details, control joints, intersections
at roof, eaves, or parapets,
means of drainage, water-resistive
membrane, and details around
openings.”3
Further:
• “The exterior wall envelope shall be
designed [bold emphasis added] and constructed in such a manner
as to prevent the accumulation of
water within the wall assembly by
providing a water-resistive barrier
behind the exterior veneer…”4
• “Roof coverings shall be designed
[bold emphasis added], installed,
and maintained in accordance with
this code and the approved manufacturer’s
instructions such that the
roof covering shall serve to protect
the building or structure.”5
Note in the code language quoted above
the addition (new to the I-Codes) of the
short phrase “be designed,” which advises
the project’s design professional that
his/her standard of care typically will
include project-specific detailing (typically
during the pre-construction process) of the
wall and roof covering systems and their
associated flashings. No longer should it be
argued that these critical tasks can simply
be passed on to the contractor and his/her
subcontractors.
“Be designed” is an example of a “performance”
requirement within the I-Codes;
the project architect is being advised that
his/her envelope design must be welldetailed
and well-specified and must provide
long-term weatherproof performance. If
the design fails to perform properly, the
38 • I N T E R FA C E OC T O B E R 2005
“NO LONGER SHOULD IT
BE ARGUED THAT THESE
CRITICAL TASKS CAN SIMPLY
BE PASSED ON TO THE
CONTRACTOR AND HIS/HER
SUBCONTRACTORS.”
responsibility for this failure rests primarily
with the project’s design professional, while
it is the contractor and subcontractors who
remain responsible for proper installation of
the well-conceived waterproofing design in
accordance with industry standards.
Like the older model building codes, the
Chapters and Sections of the I-Codes are
written in a combination of “prescriptive”
and “performance” language. It is interesting
to note that a comparison of the flashing
requirements of Chapter 14 (Exterior
Walls) and Chapter 15 (Roof Assemblies and
Rooftop Structures) of the International
Building Code reveals a higher proportion of
general performance language in Chapter
14 while Chapter 15 presents a greater
degree of prescriptive instructions about
proper flashing materials, dimensions, and
securement. These differences can be
attributed to the decades of service by past
and present roofing manufacturers, industry
organizations, and associated roofing
professionals dedicated to identifying the
minimum requirements for assured longterm,
weather-resistive performance of the
various roof covering systems. In comparison,
the overall body of knowledge for proper
exterior wall cladding and below-grade
waterproofing is less developed, less validated,
and more inconsistent and scattered. To
address this lack, the authors of Chapter 14
have fallen back on broad performance language:
• “Flashing shall be installed in such
a manner so as to prevent moisture
from entering the wall or to redirect
it to the exterior.”6
A good example of the difference
between “performance” and “prescriptive”
language in the I-Codes is a brief comparison
of how the International Building Code
(IBC) and International Residential Code
(IRC) address joint overlaps of loose-laid
sheet goods (e.g., asphalt-saturated building
paper or polyolefin housewraps) used as
the weather resistive barrier at exterior
walls. The IRC (Section R703.2) simply prescribes
minimum 6″ vertical overlaps and
minimum 2″ horizontal overlaps. The IBC
(Section 1404.2) requires the overlaps to be
appropriately configured to provide “continuous
water-resistive” performance. In other
words, the IBC expects the project designer
(or its qualified representatives) to evaluate
local climate conditions, the building’s
exposure, and the expected weather-resistive
performance of the cladding and flashing
designs in order to determine appropriate
overlap dimensions of the loose-laid
sheet weather-resistive barrier installed at
the exterior walls.
Similar design responsibilities are associated
with the roof covering system:
• “The designer will typically include
in his or her roof specification compatibility
of materials, deck type,
weather conditions, roof slope,
structural loads, roof drainage, roof
penetrations, energy, and future
reroofing.”7
It is important to recognize that in most
cases, the design responsibility mandated
by the I-Codes cannot be fulfilled simply by
providing to the contractor a manufacturer’s
packet of generic details and guide
specifications. The I-Codes task the design
professional with project-specific design
responsibilities that are greater in scope
than the downloadable product information
promoted by sales representatives across
the nation. Unless these sales and technical
The International Residential Code provides prescriptive instructions for proper
installation of the weather-resistive barrier, while the International Building Code
simply specifies an installation that provides proper weather-resistive performance.
“A MINIMUM OF ONE LAYER OF NO. 15 ASPHALT FELT…SHALL BE
ATTACHED TO THE SHEATHING,WITH FLASHING…IN SUCH A MANNER AS
TO PROVIDE A CONTINUOUS WATER-RESISTIVE BARRIER BEHIND THE
EXTERIOR WALL ENVELOPE.” — 2003 IBC
“ASPHALT-SATURATED FELT FREE FROM HOLES AND BREAKS…SHALL BE
APPLIED HORIZONTALLY,WITH THE UPPER LAYER LAPPED OVER THE
LOWER LAYER NOT LESS THAN 2 INCHES…” — 2003 IRC
OC T O B E R 2005 I N T E R FA C E • 3 9
personnel and their employers formally
accept project-specific responsibility for the
successful long-term performance of the
roofing, cladding, or waterproofing design
that they are marketing, then this burden
continues to rest with the project’s design
professional.
Similarly, while the generic MasterSpec
and MasterFormat guide specifications
published respectively by the American
Institute of Architects (AIA) and the
Construction Specifications Institute (CSI)
are important resources for the design professional,
neither of these tools can provide
the code-required design review necessary
to ensure weather-resistive performance of
the building envelope. Even the comprehensive
standards and details published by the
nation’s most respected industry organizations
(e.g., the National Roofing Contractors
Association and the Asphalt Roofing Manufacturers
Association) cannot be blindly
substituted for the project-specific design
review prescribed by the I-Codes.
In all of these cases, the referenced
standards, details, and guide specifications
can be invaluable components of the project-
specific design review, but the I-Codes
make it clear that ultimately someone must
assume responsibility for design performance.
For large projects in most jurisdictions,
this person likely will be the “registered
design professional in responsible
charge.”
• “The registered design professional
in responsible charge shall be
responsible for reviewing and coordinating
submittal documents prepared
by others, including phased
and deferred submittal items, for
compatibility with the design of the
building.” 8
For some small projects, depending on
the requirements of the local jurisdictions,
the responsible design professional may not
even be a “registered” professional (i.e., a
licensed architect or engineer), but this lack
of formal credentials does not absolve him
or her from code-prescribed responsibility
for a successful envelope design.
While there are many architects who are
well qualified to fully evaluate, detail, and
specify even the most complex flashing,
cladding, and roof covering systems, for
most designers and specifiers these critical
tasks are best carried out by qualified roofing
and waterproofing specialists whose
professional services for each project will
include acceptance of the mantle of design
liability imposed by the I-Codes. Without
doubt, the nation’s most qualified and
knowledgeable body of roofing and waterproofing
experts are the registered roof consultants
(RRCs) who comprise the foundation
of the Roof Consultants Institute.
1 Legal Aspects of Code Administration,
International Code Council, Falls
Church, VA, 2002.
2 In addition to the 2003 International
Building Code and 2003 International
Residential Code, the I-Code
series includes the 2003 International
Fire Code, 2003 International
Plumbing Code, 2003 International
Mechanical Code, 2003 International
Fuel Gas Code, 2003 International
Energy Conservation Code,
2003 International Private Sewage
Code, 2003 ICC Performance Code
for Buildings and Facilities, 2003 International
Property Maintenance
Code, 2003 International Zoning
Code, 2003 International Existing
Building Code, and the 2003 International
Urban-Wildland Code. Most
jurisdictions, however, have adopted
only some (or just one) of these
many model codes.
3 2003 IBC, Section 106.1.3.
4 2003 IBC, Section 1403.2 and 2003
IRC, Section R703.1.
5 2003 IBC, Section 1503.1 and 2003
IRC, Section R903.1.
6 2003 IBC, Section 1405.3.
7 IBC Commentary, Vol. I, Section
1503.1.
8 2003 IBC, Section 106.3.4.1.
Colin Murphy founded Exterior Research & Design, LLC (originally
Trinity Engineering, Inc.) in Seattle, WA, in 1986 and
has since expanded the firm to include offices in Waterbury,
CT, and Portland, OR. Colin is a Registered Roof Consultant
and has been elected to the RCI Jury of Fellows. He also is a
LEED® Accredited Professional, a certified EIFS Third Party
Inspector, and an ICC-certified Building Inspector. Colin is
the principal author of The Roof Construction Guide for
General Contractors, published in 1998 by RCI.
Colin Murphy
Lonnie Haughton serves as a construction consultant for
Richard Avelar & Associates in Oakland, CA, and is one of
fewer than 400 individuals nationwide who has been certified
by the International Code Council as a Master Code
Professional. Lonnie is a LEED® Accredited Professional, a
certified EIFS Third Party Inspector, and an accredited
instructor for the InstallationMasters window/door installation
training and certification program developed by AAMA.
Lonnie Haughton
40 • I N T E R FA C E OC T O B E R 2005
“THE I-CODES TASK THE DESIGN PROFESSIONAL WITH PROJECTSPECIFIC
DESIGN RESPONSIBILITIES THAT ARE GREATER IN SCOPE
THAN THE DOWNLOADABLE PRODUCT INFORMATION PROMOTED
BY SALES REPRESENTATIVES ACROSS THE NATION.”