Flashing Block-Frame Windows In Stucco Walls

FLASHING BLOCK-FRAME WINDOWS
IN STUCCO WALLS
CHRIS NELSON
TECHNICAL ROOF SERVICES INC, A DNG GROUP COMPANY
2339 Stanwell Circle, Suite A, Concord, CA 94520
Phone: 925-356-7770 • Fax: 925-356-7776 • E-mail: cnelson@dng-group.com
AND
RICHARD E. NORRIS, RRC, PE
NORRIS CONSULTING SERVICES
43255 Mission Boulevard, Suite 203, Fremont, CA 94539
Phone: 510-440-0141 • Fax 510-440-0142 • E-mail: norris@members.asce.org
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ABSTRACT
Storefront windows are used in combination with stucco cladding on low-rise and midrise
commercial, institutional, and multifamily buildings. Storefront windows are characterized
by a lack of attachment flanges, which play an integral role in most published window-
flashing designs. This paper presents the results of pressure-differential testing of
selected flashing designs for storefront windows. Flashing systems tested represent the recommendations
of industry associations and manufacturers, common construction methods,
attempted improvements on existing designs, and a novel design. Testing results show
that improved flashing methods are required for newly installed storefront/stucco flashing
to resist leakage. Improved flashing designs are also expected to provide better long-term
performance.
SPEAKER AND COAUTHOR
CHRIS NELSON — TECHNICAL ROOF SERVICES INC., A DNG GROUP COMPANY
Chris Nelson is a senior consultant with the DNG Group, a roofing and waterproofing
consulting firm located in the San Francisco Bay area. Nelson joined the company in 1988,
after being a general contractor specializing in work needed to facilitate reroofing (sheet
metal, carpentry, stucco, window and door flashing, drywall, painting, etc.). Since joining
the company, he has worked as a roof installation observer, a roofing and waterproofing
consultant, and a leak investigator. For the most part, his work is now centered on leak
investigations throughout the building envelope. He has crafted details and specifications
and has served as project manager for numerous projects, ranging from roofing, waterproofing,
wall flashing, and cladding to window and door replacement. He is an RCI member
and a long-time member and board member of Western Construction Consultants
Association (Westcon), a San Francisco Bay area group of consultants.
RICHARD E. NORRIS, RRC, PE — NORRIS CONSULTING SERVICES
Richard E. Norris, RRC, PE, is the principal of Norris Consulting Services, a San
Francisco Bay area firm that identifies and documents defects, aids owners or builders and
their attorneys in reaching equitable settlements, and provides expert witness assistance
during legal proceedings. Dr. Norris specializes in roof covering, wall waterproofing, elevated
decks, and window- and door-flashing systems. He also designs and manages construction
projects for the replacement of roofs and the repair of roofs, walls, and decks.
Additionally, he is an expert in the biological deterioration of wood in service (decay, mold,
termites, etc.). He is a long-time member of RCI and has been a member of Westcon, where
he currently serves as a member of the board of directors.
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Figure 1 This manufacturer of storefront windows shows
installation in a mass wall. No detail is provided for
installation in a drainage-plane wall. Storefront windows
lack nail-on fins for attachment. Note that nail-on fins would
not be useful for attachment to a mass wall.
Figure 2 Test hut plan view.
FLASHING BLOCK-FRAME WINDOWS
IN STUCCO WALLS
INTENT
In their professional practice, the
authors have found that common practices
for the installation of storefront windows in
stucco walls have led to incidences of leakage
and associated damage. While the professional
experience of the consultants
involved in this testing is centered in the
western United States, there is recognition
that current practices for flashing storefront
windows present a widespread problem.1
The purpose of this research was to
review whether industry standards and
manufacturers’ literature provided adequate
guidance for the design of effective
flashing systems for use with storefront
windows in stucco walls.
INTRODUCTION
Storefront windows have aluminum
frames that lack attachment flanges (“nailon
fins”). (See Figure 1.) The general category
of nonflanged windows, which includes
conventional wood windows, is also referred
to as “block frame,” “box frame,” “nonflanged,”
and “finless.” Stucco wall cladding
consists of Portland cement plaster, metal
lath, and a water-resistive barrier (WRB).
This is considered a drainage plane
cladding, where the WRB serves as the
drainage plane behind the outer cladding of
stucco.
Flashings are critical components of
drainage plane systems; they form waterresistant
junctures between penetrations
such as windows and the WRB. Flashings
may also deter water from penetrating from
the surface of the plaster cladding to the
WRB. Flashings direct water from the WRB
back to the exterior at the bottoms of walls
or over the tops of penetrations, such as
windows. Increasingly, widely used pan
flashings direct water that penetrates the
window frame or perimeter seal back to the
cladding surface or down the WRB.
Flashing systems may be composed of sheet
metal, sealant, and flexible flashing.
LITERATURE REVIEW
While books showing window installation
were available early in the last century,
efforts to write consensus standards began
in 1992.2 Detailed
guidance on the
installation of windows
with attachment
flanges (nailon
fins) has been
available for at
least 14 years.3,4,5
However, a review
of literature reveals
that there is
very limited guidance
available for
flashing aluminum
storefront windows
that lack attachment
flanges.
TESTING
PROGRAM
Two woodframed
test “huts”
were constructed
in Richmond, CA,
during the summer of 2008. Refer to
Figures 2, 3, and 4 for views of the test huts.
Hut walls were constructed of 2 x 4 framing
with 15/32-in plywood exterior sheathing.
Framing and sheathing layouts were the
same for each wall. Each hut had one wall
closed with a sliding glass door used for
access. The remaining walls (a total of six)
were framed to receive a 6-ft x 6-ft “storefront”
window.
Test walls are divided into two sides
–
each, labeled Area A and Area B (Figures 3
and 4). Two walls are flashed the same on
both sides (Areas 1A and 1B and Areas 2A
and 2B). Three walls have major or minor
variations in flashings on each side (Areas
3A and 3B, Areas 4A and 4B, and Areas 5A
and 5B). The sixth wall has different WRB
combinations on each side (Areas 6A and
6B).
All of the windows were Arcadia AR 400.
These windows are rated to withstand 8 psf
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Figure 3 Typical test hut wall. Area A was the left
side, and Area B was the right side. Control joints
were installed at both sides areas) of windows on four
walls and on one side of the windows on two walls.
Area 1B and Area 2B did not have control joints.)
Figure 4 The dividers allowed spray testing to be
conducted on one area of three windows at a time.
(384 pa) differential air pressure in laboratory
water testing (AAMA 501.1). All window
installations were in the plane of the wall.
(Recessed windows present special challenges
that were not explored in this testing.)
Stucco was a conventional sand-andcement
mix.
Each area had two layers of WRB. Areas
1, 2, 4, and 5 had two layers of grade D 60-
minute building paper. Area 3 had a polymeric,
water-resistive barrier overlaid with
rate results.
Each mock-up wall
panel was water-tested
using a calibrated
spray rack. Each area
was water-tested with
the same series of
tests:
• One hour – static,
water only,
no differential
air pressure.
–
(
(
–
a grade D 60-minute building paper. Area 6
had a layer of polymeric WRB (different
from that used in Area 3) overlaid on one
side with a second layer of polymeric WRB
(Area 6A) and on the other side, overlaid
with grade D 60-minute building paper
(Area 6B).
WATER TESTING
Water testing of the wall assemblies was
performed using Test Method ASTM E1105,
Standard Test Method for Field Determination
of Water Penetration of Installed
Exterior Windows, Skylights, Doors, and
Curtain Walls, by Uniform or Cyclic Static
Air Pressure Difference (2008). However,
test periods were extended to explore
whether leakage would occur or increase
after the typical 15-minute (17 minutes for
cyclic testing) test period. In addition, a
period of testing without differential air
pressure was employed to explore what
effect zero differential air pressure had on
results, as it is impractical at times to
employ differential air pressure during field
testing. Drain-down periods were employed
between test series in an attempt to sepa-
• On e – q u a r t e r
hour – no water, drain down.
• One-half hour – 3 psf (143.64 pa)
differential air pressure, cyclic pressure:
✓ Five cycles of five minutes of differential
air pressure, with one
minute without differential air
pressure; continuous water
spray.
• One-quarter hour – drain down, no
water, no pressure.
• One-half hour – 6.24 psf (298.77 pa)
differential air pressure.
✓ Five cycles of five minutes of differential
air pressure, with one
minute without differential air
pressure; continuous water
spray.
Wood and peel-and-stick membrane
“mask” dividers (Figures 3 and 4) were
installed to segregate flashings on one side
of a wall from flashings on the other side of
the wall. Masks allowed observation of the
bottom of stucco panels. Gutters placed
below stucco panels collected water drained
from the bottom of the WRB.
Flashings were joined in the middle
where flashing configurations differed
between Areas A and B of a wall (metal
flashings were generally soldered together),
and sealant or spray foam generally was
used to keep water from migrating from one
side to the other.
Where sheet metal pan flashings were
used (Areas 2, 3, 4, and 5), their vertical
turn-ups (at the inside face of the window
sill) were formed at least 1 5/8 in high,
exceeding ASTM E2112, Appendix 3 recommendations
for the test pressures
employed.6
CRACKS IN STUCCO
Areas were constructed to induce a horizontal
crack in the stucco 2 ft above the
windows. This crack was varied in width
during testing. Each area was tested with
the stucco crack at approximately 0.010 in,
and again, one to two weeks later, with the
stucco crack at approximately 0.030 in. The
crack was configured with a self-adhering
membrane behind it to prevent water from
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Figure 5 Areas 1A and 1B, with folded corners of
casing bead. No sealant or flexible flashing was
employed. WRB and stucco are not shown.
Figure 6 Test Areas 2A and 2B, flashing collar.
migrating directly into
the hut.
Selected removal of
stucco at Area 3 revealed
the building paper was
adhered to the stucco
just below the crack.
Thus, it is likely that
there was limited
drainage down the WRB
below the crack.
TEST ASSEMBLIES
AND TEST RESULTS
GENERAL COMMENTS
One of the window
flashing systems tested,
Test Area 1, represents a
method of flashing that –
is reportedly used locally
in the San Francisco Bay
area (and in other parts
of California) as a common
practice and observed to have leaked
in several leak investigations performed by
the authors. Another of the flashing systems,
Area 2, was designed and successfully
field-tested in several repair projects by
one of the authors. Areas 1 and 2 were
intended to serve as benchmarks for ineffective
and effective flashing, respectively.
Neither system is described in industry literature.
TEST AREAS 1A AND 1B, COMMON
LOCAL FLASHING PRACTICE
✓ Leakage occurred quickly, beginning
at 0 psf. At the end of testing, at
6.24 psf, water had spread 7 ft
across the floor.
This assembly reflects a method of construction
encountered by the authors on a
number of Northern California projects. The
main elements of this approach are the use
of sheet-metal casing beads (Figure 5),
which are commonly used in stucco installation
as screeds (to create a straight termination
for the stucco panel and as an aid in
providing a uniform stucco thickness).
Flashing was the same at both sides (1A
and 1B) of the window. Control joints were
installed in stucco on side A. Control joints
intersected the window flashing corners.
Flashing consisted of a casing bead
(“stucco stop,” “J bead,” “J mold”) stucco
accessory placed around the window frame
with building paper lapped over it at the
head, jamb, and sill (nonshingle fashion at
sill). Casing beads commonly available in
Northern California have a wall flange
roughly 1 3/8-in wide with numerous prepunched
nail-fastener holes.
Thus, building paper is lapped onto a
relatively narrow flange with holes in it.
(ASTM E2112 recommends a 9-in lap
between building paper and flashing.)
Casing beads were lapped at their midpoints.
Casing bead wall
flanges were cut and folded
at corners, leaving
open corners (Figure 5).
Casing beads were
caulked to window frame
perimeters. Casing beads
were spaced far enough
from the windows to permit
installation of a
backer rod behind the
sealant.
WATER TEST RESULTS
Testing at 0 psf:
Water began running
down the back of the
jamb-casing bead shortly
after testing began.
Subsequently, water was
observed entering from
holes in casing bead
flanges and migrating in
from the WRB sides of
casing beads. At the end
of an hour, water had
spread a few feet onto the
floor.
Testing at 3 psf: Leakage increased
down the jamb-casing bead. By the end of
this test period, water had migrated 3 ft
(Area 1B) to 5 ft (Area 1A) out onto the floor.
Water also dripped from the casing bead
above the window head shortly after application
of differential air pressure. A water
pool 30 in long formed on top of the window
frame during this test period.
Testing at 6.24 psf: All leaks
increased. At the end this test cycle, water
had spread 5 ft (Area 1B) to 7 ft (Area 1A)
out across the floor.
TEST AREAS 2A AND 2B, CUSTOM
FLASHING COLLAR
✓ A small amount of water appeared
on top of the metal head flashing at
6.24 psf.
Flashing was the same at both sides
(Areas 2A and 2B) of the window. Area 2A
had control joints in the stucco, and Area
2B did not.
This design was developed by one of the
authors. It had been successfully installed
and tested to 6 psf differential air pressure
in three leak renovation projects prior to
this testing. It is a one-piece sheet-metal
collar (Figures 6 8)
that provides:
• An unbroken substrate for window
perimeter sealant,
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Figure 8 Area 2 Windowsill with pan flashing integrated into the sheet-metal
collar. The metal collar counterflashes the top of the stucco and has a nail-on fin
for integration into the WRB and flexible flashing.
Figure 7 Area 2 Window head with weep screed formed into the sheet-metal
collar along with a nail-on fin. Note the sheet-metal collar forms a substrate for
window perimeter sealant to adhere to. Several minutes into testing at 6.24 psf,
water was observed on top of metal flashing at head aligned with jamb.
“ ”
– –
Integration with the water-resistive barrier
(Figures 78)
follows ASTM E2112 flashing
Method B at jamb and head and both
Methods A and B at jambs (membrane
flashing both under and over the jamb
flange of the flashing collar). Nail-on flanges
of the flashing collar were embedded in
sealant. Building paper (WRB) was integrated
shingle fashion, with the flexible flashing
over at head and under at sill, and was integrated
between flexible flashings at jambs.
Weep tubes were soldered into the pan
flashing and exited out of the face of the
downturned “key” edge of the flashing.
TEST RESULTS
Testing at 0 psf and 3 psf: No leakage
observed.
Testing at 6.24 psf: Water was found
on top of the head-to-jamb joint of the window,
midway and just minutes into testing.
This was traced to a window joint and subsequently
was caulked (wet sealed) and did
not reappear.
Water was found on top of the head
flashing (Figure 7) on Area 2A midway into
testing Area 2B. The amount of water
appeared to be small – less than a thimble
full. It appeared water entered though a solder
joint in the flashing. How water reached
this side of the wall is unexplained.
AREA 3A. POLYMERIC WRB
MANUFACTURER’S DETAILS
✓ Leakage began at 3.0 psf and
became very rapid.
VaproShield is a manufacturer of polymeric
weather-resistive barriers and accessory
products. Area 3A is based on the
authors’ understanding of 12 detail drawings
for “nonflanged window flashing,”
which are designated VaproShield-0007 and
dated 6/20/07. Details focus on the integration
of VaproShield’s WRB and flashing
products. Products shown in the company’s
literature for the flashing of storefront windows
include “3-D Preformed Corners,”
“VaproTape,” and “VaproFlashing.” The
assembly follows VaproShield recommendations
to the extent possible, with some variances
as described below (Figures 1011).
VaproShield Expanding-Foam Tape,
shown on VaproShield’s drawings was
reportedly not available, and thus, none
was used. Low-rise expanding-foam spray
between window frame and flashing was
added during testing to reduce leakage and
as an attempt to simulate expanding-foam
tape.
No sealant was shown in VaproShield’s
drawings between the window perimeter
and flashing, and thus, none was used.
VaproShield’s literature shows the windowsill
bedded in sealant at the inside corner
of the pan flashing. As shims under the
window prevent the window frame from
seating on the pan flashing and thus bedding
into sealant, no sealant was used at
– –
• Stucco “key” returns (at jamb and
sill) into the stucco surface,
• A head flashing that directs water
from the WRB to weep out,
• A “nail-on” flange for conventional
integration with flexible flashing and
WRB (ASTM E2112 Method A or B),
• A pan flashing, and
• An integral weep for the pan flashing.
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Figure 9 Area 3A Window jamb-tohead
flashing transition. Head
flashing extends beyond the end of the
window and turns up at the end. The
casing bead butts up to the bottom of
the head flashing, leaving a small gap.
The head flashing laps over the window
without forming a conventional
gap for backer rod and sealant.
Figure 10 Area 3A Manufacturer s
detail did not show sealant between
window and sill-pan flashing. Water
was drawn over the pan flashing,
starting at 3 psf. Leakage was so rapid
that sealant was applied between top
of the pan flashing and window frame.
This controlled leakage over the pan.
Figure 11 Area 3A Manufacturer s
detail did not show sealant between
window and head flashing. Water was
drawn over the head of the window
starting at 3 psf differential air
pressure. Leakage was so rapid that
spray foam was applied between
window and wood framing. This
greatly slowed leakage.
– –
– – ’
this location. Sealant at the top of the pan flashing
was added during testing to control leakage and to
attempt to simulate the bedding seal.
A casing bead was installed at the jamb in order
to terminate the stucco. (The published design did
not include details for cladding termination.) No casing
beads were embedded in the sealant.
Note that the head flashing extends past the
jamb (Figure 9) roughly 1½ in, or about the width of
a typical casing-bead wall flange. This arrangement
is consistent with details from the Northwest Wall
and Ceiling Bureau (Areas 4A and 4B).
Per discussions with Vaproshield, a layer of
building paper was added over the VaproShield WRB
to act as a break (“intervening layer”) between stucco
and VaproShield.
TEST RESULTS:
Testing at 0 psf: No leakage observed.
Testing at 3 psf: Water was drawn up
and over the pan flashing in less than one
minute into testing (Figure 10) and was
drawn over the head of the window (Figure
11). To control rapid leakage, testing was
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Figure 12 Area 3B Window-jamb metal flashing. Two-inch-wide,
nonperforated flange of the casing bead was embedded in butyl tape over
the building paper.
Figure 13 Area 3B Head-to-jamb transition flashing.
Weep screed above head flashing. End turn-up of head
flashing. Jamb flashing lapped under soldered
extension attached to the bottom of the head flashing.
Figure 14 Area 3B Head-to-jamb transition.
Opening found in sealant allowed initial leakage.
After removal of stucco residue from head
flashing and reapplying sealant, no leakage was
observed in subsequent testing.
– –
halted, and sealant was applied between the top of
the pan flashing and the windowsill. Spray foam
was also applied between the wood framing and
the window frame at the head and jamb.
Testing at 6.24 psf: Water ran down the head
of the window, aligned with the jamb, shortly after
testing began. Soon after, moisture was detected
below the corner of the pan flashing.
AREA 3B, MODIFIED POLYMERIC WRB
MANUFACTURER’S DETAILS
✓ After repair of an opening in the perimeter
sealant, no leakage was observed.
Test Area 3B is based on a combination of
Vaproshield’s information, typical stucco termination
needs, typical storefront-window manufacturers’
requirements, and the authors’ experience. It
varies from Area 3A as described below.
Perimeter sealant joints were added between
the window and flashings at the head and jamb. A
sloped-head flashing was added as opposed to a “flat” nondraininghead
flashing. A weep screed was used above the head flashing
(Figure 13) as opposed to a casing bead in Area 3A.
The jamb- and sill-casing beads had 2-in-wide nonperforated
flanges as opposed to a 1-3/8-in-wide perforated flange in Area 3A.
The wall flanges of the jamb-casing bead were embedded in
Vaprotape (butyl tape) over building paper (Figure 12), under the
assumption that this might control water migrating between the
WRB and casing bead. A short section of casing bead was soldered
to the end of the head flashing to allow the jamb-casing bead to lap
into it (Figure 13), avoiding the butt joints between head flashings
and jamb-casing beads found at Areas 3A, 4A, and 4B. The end of
the sill-pan flashing had a return flange as opposed to no return
flange at Area 3A. A “wing” diverter was soldered to the end of the
pan flashing in line with the jamb-casing bead, and the jambcasing
bead was lapped over the diverter shingle-fashion.
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Figure 17 Area 4B Head-to-jamb transition prior to application
of stucco. Sealant application changes plane between head and
jamb, requiring careful tooling at the transition. Note control
joints intersecting the head corner are similar at all areas where
control joints are installed. See also Figure 9.
Figure 16 Area 4A bottom) Windowsill flashing. No sealant was
installed between pan flashing and windowsill at inside or outside).
Figure 15 Area 4A top) Window jamb
flashing. No sealant under casing bead and
no flexible flashing, similar to Area 1. Water
leaked in and down the jamb beginning at 0
psf.
– ( –
– ( –
Weep holes with wind baffles were inserted into
sill sealant. The pan flashing was spaced further
inward, and backer rod and sealant were installed
between the windowsill and turn-up of the pan
flashing.
TEST RESULTS:
Testing at 0 psf: No leakage observed.
Testing at 3.0 psf: Water leaked at the head of
the window midway through testing. An opening
was found in the sealant at the end of the head
flashing where stucco residue was not completely
cleaned off of the metal flashing (Figure 14; also, see
Figure 17). After the metal was cleaned and the end
was recaulked, no leakage was observed.
Testing at 6.24 psf: No leakage observed.
AREA 4A, INDUSTRY TRADE GROUP
DETAILS (
✓ Leakage began at 0 psf and became very
rapid once differential pressure was applied.
Area 4A follows the Northwest Wall and Ceiling Bureau’s
1997 details as published and as confirmed in a telephone
call and e-mails. The jamb-casing bead butts to the bottom
of the head flashing (similar to Figure 9). The end turn-up of
the pan flashing does not have a wall-return flange. Casing
beads are used around the perimeter and are not embedded
in sealant (Figure 15). There is no sealant between the pan
flashing and window, inside or out (Figure 16). The jamb-tosill
joint of the casing bead has an open corner (similar to
Figure 5). The head flashing and pan flashing have drip lips
that project out from the plane of the stucco (Figures 16 and
similar to Figure 17).
TEST RESULTS:
Testing at 0 psf: Water ran down jamb-casing bead
(Figure 15) and reached the framing below.
Testing at 3.0 psf: Leakage was observed early in the
test at the top of the jamb-casing bead where it butts into the
bottom of the head flashing.
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Figure 19 Area 4B Sill flashing. Sealant was added
between the window and pan flashing at the exterior. Twoinch-
long weep holes were included in the sealant. Wind
baffles were installed in the weep holes.
Figure 18 Area 4B Window-jamb flashing. Nonadhering,
flexible flashing installed that wrapped into
opening. Casing bead was not embedded in sealant.
One minute into testing, water was
drawn up and over the top of the pan flashing
and splattered onto the floor and framing.
Testing at 6.24 psf: Testing had to be
halted, as leakage out of the top of the pan
flashing had wet an area of the floor 6 ft x 8
Testing at 3.0
psf: Water entered
at the top of the casing
bead (where it
butts up to the head
flashing) early in the
test. Water ran
– –
ft, mostly aligned with the end of the pan
flashing. To slow leakage, spray foam was
injected between the end of the pan and
window frame. This decreased leakage.
Leakage down the jamb-casing bead
increased and flowed steadily down the casing
bead from several locations. Water
leaked onto the window head. The path of
entry was unclear, but may be related to
leakage at the head-to-jamb butt joint in
flashing.
AREA 4B, INDUSTRY TRADE GROUP
MODIFIED DETAILS
✓ Leakage began at 0 psf and became
very rapid once differential pressure
was applied.
Area 4B is a modification of Area 4A as
follows:
Sealant was installed between the pan
flashing and windowsill (Figure 19). Two-inlong
weep holes (per ASTM E2112) with
reticulated foam wind baffles were installed
in the sill sealant. The pan flashing end
turn-up was tapered so that the entire edge
of the metal did not extend out to the plane
of the perimeter sealant. The head flashing
was sloped.
At the recommendation of NWCB, it
included a flexible flashing (not a selfadhering
membrane) that wrapped into the
jamb.
TEST RESULTS
Testing at 0 psf: Water ran down the
jamb-casing bead.
down the jamb cavi- –
ty, dripped off of the
shims, and wet the
framing and floor
below. Water also
collected over the
head of the window early into this test.
Testing at 6.24 psf: Leakage increased
over and down the jamb-casing bead. A 2-ftlong
pool of water formed on top of the window.
The path of entry was unclear but may
be related to leakage at the head-to-jamb
joint of the flashing.
As an experiment following the full testing
program, the foam wind baffles were
removed (Figure 19) from the weep holes in
the sealant. (Note, ASTM E2112 does not
require wind baffles in sealant weep holes.)
Testing resumed at 6.24 psf, and water
quickly began “spitting” out of the pan
flashing, rapidly wetting the floor and framing.
AREA 5A, COLLAR, PAN, AND HEAD
FLASHING
✓ Area 5A is an attempt to improve on
Area 1 flashing. It has a perimetercasing
bead embedded in sealant,
self-adhered membrane flashing,
pan flashing, and head-weep flashing.
Leakage began at 0 psf at the
lap joint in the jamb-casing bead.
Test Area 5A was an assembly of commercially
available stucco accessories and
self-adhering flashing with the addition of a
custom-formed sheet-metal pan flashing. A
–
casing bead was used around the perimeter
of the window. Corner joint flanges of the
casing bead were infilled with sheet metal
and then soldered closed (Figure 20).
Backer rod and sealant were used between
the window and the casing bead. The jambcasing
bead had a lap joint midway up
(Figure 22). The lap joint was not sealed to
avoid potential compatibility issues with the
perimeter sealant or sealant beneath the
casing bead.
Self-adhered membrane was integrated
with the casing bead (Figure 21), per ASTM
E2112, method B for flashing nail-on fin
windows (at 9-in wide, flashing membrane
was installed first at sills and jambs, then
the casing bead was embedded in sealant,
and finally, flashing membrane was
installed over the head flange of the casing
bead). A soffit-drip flashing was lapped over
the head-casing bead (Figure 21). Building
paper was integrated shingle fashion with
the flashing membrane (under at the sill
and over at the jamb and head).
The pan flashing was installed before
the casing bead and directs collected water
down between the stucco and building
paper (WRB). Pieces of flashing membrane
were used as spacers between the casing
bead and the downturned lip of the pan
flashing to provide gaps for drainage. The
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Figure 20 Area 5A Window flashing. Casing-bead corners
infilled and soldered. Sheet-metal pan flashing installed.
WRB, flexible flashing, and stucco are not shown.
Figure 21 Area 5A Window flashing. Flexible flashing
added. Casing bead embedded in sealant as though it were a
nail-on fin. Head weep flashing added. WRB and stucco are
not shown.
Figure 22 Area 5A Window jamb flashing. Lap joint in jamb-casing bead was
not sealed to avoid potential sealant compatibility issues. Water leaked through
the unsealed lap joint.
– –
bottom “fin” of the casing bead was not
embedded in sealant to allow drainage from
the pan flashing. The ends of the pan flashing
had end turn-ups and wall return
flanges. Wall flanges of the pan flashing
were not embedded in sealant.
TEST RESULTS
Testing at 0 psf: Water appeared late
into testing at the lap joint in the casing
bead. Leakage also appeared on the floor
and wall about 6 and 12 inches to the side
of the window near the bottom of the wall.
Testing at 3.0 psf: Leakage at the
jamb-casing bead repeated rapidly, as did
leakage on the framing, sheathing, and
floor. The framing below the end of the pan
flashing also became wet.
Testing at 6.24 psf: Leakage repeated
quickly and spread further out onto the
floor.
AREA 5B, WIDE FLANGE COLLAR,
PAN, AND HEAD FLASHING
✓ Area 5B uses a wide flange-casing
bead and in other ways is identical
to Area 5A. Leakage began at 3 psf
at the lap joint in the jamb-casing
bead.
Area 5B is a modification of Area 5A.
Casing beads are 2 in wide and have solid
(nonperforated) flanges. The lap joint in the
jamb-casing bead was slightly different.
TEST RESULTS
Testing at 0 psf: No leakage observed.
Testing at 3.0 psf: Water began to
–
migrate through the lap joint in the jambcasing
bead early in testing.
Testing at 6.24 psf: Leakage sped up
nearly immediately at the lap joint in the
jamb-casing bead. Midway into testing,
water “spit” over the top of the casing bead
joint, wetting the framing. Most water ran
down the casing bead and into the pan
flashing. Late into the test, the floor below
the jamb became wet.
AREA 6A, CREPE-SURFACED
POLYMERIC WRB MANUFACTURER’S
DETAILS OVERLAID WITH
POLYMERIC INTERVENING LAYER
✓ Leakage first appeared late in testing
at 0 psf.
–
DuPont Tyvek (2007) is a pioneering
manufacturer of polymeric weather-resistive
barriers and accessory products.
StraightFlash VF is the principal product
recommended by DuPont for the flashing of
storefront windows. StraightFlash VF is a
novel, self-adhering flashing that has butyl
adhesive on half of one side and butyl adhesive
on the other half of the opposite side.
This product is intended to add a “fin” to
finless windows to facilitate integration with
the WRB (Figure 23).
Note that the details available at the
DuPont Tyvek Web site have been updated
since our testing was completed (2009).
Areas 6A and 6B are based on the
authors’ understanding of the eight pages of
– –
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Figure 23 Area 6A Drawings from Dupont illustrating
Straightflash VF flashing concept for a nonflanged
aluminum window.
Figure 24 Area 6B Window head flashing.
Figure 26 Area 6A Windowsill flashing.
Figure 25 Area 6B Window jamb flashing.
drawings found on the Web site (circa June
2008) showing the installation sequence for
“Nonflanged Aluminum Windows Using
StraightFlash VF” (as also discussed with
the local Tyvek representative).
The crepe-surfaced polymeric sheet was
in plane with the
stucco and window-
frame face
(Figure 24). Ends of
the metal head
flashing are turned
– –
“
”
– –
installed over the wall and wrapped into the
opening as shown in ASTM E2112 for
installation methods A1 or B1.
Self-adhering and conformable, flexible
flashing membrane was installed over the
frame sill (Figure 26) and turned-up jambs.
It did not turn up at the inside edge of the
window to form a full pan flashing. The
DuPont sealant was installed between the
inside of the windowsill and the flexible
flashing beneath it. This sealant was
applied about three inches up the jambs.
The Straight-flash VF was adhered to
the head and jambs of the window and then
adhered over the crepe-surfaced WRB at
jambs and under the WRB at the head.
Metal head flashing was embedded in
sealant over the head flange of the
Straightflash VF. A flap of WRB was taped
over the head flashing. The metal head
flashing was installed with a gap between it
and the window to allow sealant installation
down.
The manufacturer’s details did not show
how stucco terminates around the window.
Casing beads were spaced away from the
window sufficiently to allow installation of
backer rod and sealant (Figures 25 and 26).
The casing bead was installed with openfolded
corners at sill-to-jamb transitions
and was not embedded in sealant when
applied over the crepe-surfaced WRB. A
casing bead was butted up under the ends
of the metal head flashing (similar to Figure
9). A casing bead was installed above the
metal head flashing.
The crinkled
surface of
the crepe-surfaced
WRB is
intended by the
manufacturer
to promote
drainage be-
–
hind cladding. An intervening layer of standard,
flat-surfaced, nonwoven polymeric
WRB was installed over the creped WRB
and casing beads prior to lath installation.
Lap joints in the polymeric WRB intervening
layer were taped.
TEST RESULTS
Testing at 0 psf: At the end of this test,
water was found on the floor, beneath the
framing, about a foot off to the side of the
window.
Testing at 3.0 psf: Leakage below fram-
– –
–
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ing repeated and slowly grew larger.
Testing at 6.24 psf: Leakage below
framing repeated and slowly grew larger.
Midway into testing, water dripped off of
the membrane sill flashing onto the floor,
starting below the sill-to-jamb corner of the
window. Sealant was not completely adhered
to the self-adhered sill flashing or
window, allowing water to migrate between
these two components.
AREA 6B, CREPE-SURFACED
POLYMERIC WRB MANUFACTURER’S
DETAILS OVERLAID WITH BUILDING
PAPER
✓ Leakage began at 6.24 psf beneath
the sill sealant.
Test Area 6B is the same as test Area
6A, except that the “intervening layer” is 60-
minute Grade D building paper.
TEST RESULTS
Testing at 0 psf and 3.0 psf: No leakage
was observed.
Testing at 6.24 psf: Water was found
on the self-adhered membrane flashing
below the windowsill corner, midway into
testing. Sealant was not well adhered to the
window frame or to the self-adhered membrane
beneath. Sealant was easily removed
intact when pulled on. Sill sealant was completely
removed, and testing was repeated.
Water quickly began draining off of the sill
self-adhered membrane and onto the floor
below.
CONCLUSIONS
In general, Areas 2A, 2B, and 3B
worked. The others leaked. With some
improvements, Areas 5 and 6 would likely
work. In summary, the concepts that helped
designs to work and those issues that led to
observed leakage are summarized below.
WHAT WORKED
• Providing a continuous flashing
substrate for sealant applied around
the perimeter of the window is
important. Assemblies that had discontinuities
in the sealant substrate,
such as unsealed casingbead
joints, open corners in casing
beads, and unsealed butt joints
between casing beads and head
flashings, were not successful.
Areas 2A and 2B had a continuous
substrate. Area 3B had a shingled
lap between the jamb-casing bead
and the sill flashing (via a formed rib
in the pan flashing to notch and lap
the casing bead over,) as well as
“nested” lap between the jamb-casing
bead and head flashing (via a
soldered-on extension to the head
flashing). Areas 5A and 5B had soldered
corners for casing beads and
no leakage at the top of the head-tojamb
corners, while Areas 1A and
1B which had open corners, leaked.
Note: caution needs to be taken
when sealant is used to caulk joints
in perimeter flashings if the perimeter
sealant or window frame joint is
of a different type or brand; adhesion
testing would be prudent.7
• Forming a continuous seal between
the jamb flashing and the WRB or
forming an adequately wide lap
between the WRB and jamb flashing,
per ASTM E2112, should form a
successful flashing. For instance,
encapsulating the edge of the WRB
with self-adhering flashing proved
adequate for these 6-ft-tall windows
(Areas 2A and 2B), and bedding a 2-
in-wide casing bead in butyl tape
over the WRB (Area 3B) also proved
adequate. Both of these walls used
solid flanges (no prepunched nail
holes). Additional effort would likely
be needed to form a complete seal
when using casing beads with perforated
flanges (prepunched nail
holes).
• Head flashings that allow a uniform
sealant bead around the window
were successful, as witnessed by
results at Areas 2A, 2B, 3B, 5A, 5B,
6A, and 6B.
• It is unclear whether pan flashings
need to weep to the exterior or if they
can just weep down the WRB. Areas
5A and 5B and 6A and 6B directed
pan-flashing water down the WRB.
No dedicated weep path was provided
between the pan flashing and
casing bead in front of it at Areas 6A
and 6B, possibly contributing to the
volume of water in the pan there.
Pan flashings at Areas 2A, 2B, and
3B drained to the exterior. Areas 4A
and 4B also drained to the exterior,
and with a baffled weep in the
sealant testing, was successful at
4B.
• Wind baffles in sill-pan flashing
sealant weep holes seem prudent, as
witnessed by the test results at Area
4B, where leakage from the pan only
occurred after the wind baffle was
removed. Note that reticulated-foam
wind baffles are prone to erosion by
the sun.8
• Pan flashings with turn-ups at the
backside of the window were successful
(see results at Areas 2A, 2B,
3B, and 4B), while Areas 6A and 6B
failed, due to sole reliance on
sealant adhesion to form a vertical
leg for the pan flashing. If flashing
strategies are to rely solely on
sealant adhesion, then pretesting for
adhesion is all that more important
(ASTM C1193, 2005).
• As witnessed by greater leakage at
Area 1A (with control joints) than at
Area 1B (without designs), there is a
need to consider control joints as
allowing greater amounts of water to
reach the drainage plane behind
them. Flashings need to be appropriately
robust to manage this volume
of water.
WHAT LEAKED
• Lack of perimeter sealant between
windows and flashings allowed leakage,
particularly under differential
pressure, as witnessed by test
results at Areas 3A and 4A. Head
flashing alone is not sufficient without
a sealed connection to the window
frame, as witnessed by the test
results at Area 3A.
• Pan flashing vertical height alone
will not prevent leakage. Air currents
are sufficient to carry water up
pan flashings that lack exterior
and/or interior seals, as witnessed
by test results at Areas 3A, 4A, and
4B.
• Unsealed joints, butt joints, or
incompletely soldered joints in
perimeter flashings allow water to
bypass perimeter sealant and run to
the interior, as witnessed by test
results at Areas 1A, 1B, 4A, 4B, 5A,
and 5B.
• Unsealed, prepunched holes in casing
beads allowed leakage, as witnessed
by test results at Areas 1A,
1B, and 4A. Sealant or self-adhering
membrane flashings are needed to
close these holes.
• Complex perimeter-sealant transitions
are prone to leakage. Where
head flashings extend into stucco
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past jambs, they are prone to contamination
(for bonding sealant) during
stucco application, as witnessed
by initial test results at Area 3B.
Where head flashings extend out
over window heads, sealant must
change plane from the jamb to the
head – a maneuver requiring some
skill and understanding by the
installer as well as the designer (see
Figure 17).
• Omission of a pan flashing likely
contributed to the volume of leakage
at Areas 1A and 1B. A pan flashing
may have collected some of the leakage
and directed it to the exterior.
• Lack of a return flange at the end of
the pan flashing leaves an opening
for water to migrate under the pan
flashing. Some of the leakage at Area
3A may have migrated through such
an opening.
• Lack of a clear path for pan-flashing
drainage is thought to have allowed
water to build up in Areas 6A and
6B and bear against sealant, contributing
to the volume of leakage. A
drainage space between casing bead
and pan-flashing membrane would
seem prudent, as would the inclusion
of a pan flashing that weeps to
the exterior.
• Lack of sealed and/or weatherlapped
integration between the casing
bead flange and WRB allowed
leakage at Areas 1A, 1B, 4A, and 4B.
• Flexible flashing wrapping into the
opening at Area 4B did not prevent
leakage. Water draining down the
jamb cavity encountered window
shims, ran over the shims, and
dripped to the interior.
RECOMMENDATIONS
When publishing designs for window
flashing and installation, all important elements
of the assembly should be included.
For example, drawings should not omit
perimeter sealant or pan-flashing weeps,
and drawings should not omit details for
terminating claddings such as stucco
around windows. Conditions at head/jamb
and jamb/sill corners that are vulnerable to
failure and at times left up to interpretation
of installers should be illustrated or
described.
Careful detailing is needed when
changes in plane between the head and
jamb-perimeter sealant are included.
Consider eliminating such changes.
Consideration should be given regarding
how successfully typical installation crews
may implement designs.
Published designs for window flashing
should be tested via mock-ups that include
cladding to verify that the systems are leakfree.
It would be helpful if test data for
designs were included in literature indicating
level of testing the assembly has withstood
or should be expected to endure (differential
air pressure, amount of water, test
type, and duration). Designs should indicate
if air seals, such as spray foam or
expanding tape, need to be in place for successful
water-resistance performance.
It would seem prudent to include cracks
in stucco (or other types of typical openings
in claddings) above the flashing mock-up to
review how well the assembly manages
water draining down WRB from above. Why
the crack mechanism included in these
mock-ups did not seem to function as
intended is unknown. Previous testing with
cracks in 2007 (as yet unpublished) was
successful at allowing water to drain down
WRB behind stucco.
The industry should develop consensus
standards for adapting ASTM E1105 methods
to verify the performance of cladding
such as stucco and flashing systems that
surround windows. The new standards
should include duration of water spray and
pressure differential.
Additional analysis of the findings of
this testing and additional testing of components
and assemblies is needed to develop
effective, readily constructible, and economical
flashing systems for the installation of
storefront windows in stucco walls.
ACKNOWLEDGEMENTS
Any shortcomings in this paper are the
responsibility of the authors alone and not
of the organizations and individuals who
generously supported our work.
The testing described in this paper was
supported by the volunteer efforts of 18
experienced construction consultants who
also have experience in investigating water
leakage in buildings. The testing was sponsored
and principally funded by Westcon,
the Western Construction Consultants
Association, which is based in the San
Francisco Bay area. Additional funding was
provided by the RCI Foundation. Donations
of time, materials, and yard space were provided
by Westcon member contractors and
some manufacturers.
FOOTNOTES
1. Francesco J. Spagna and Jason S.
Der Ananian, “Flashing and Integration
(or Lack Thereof) of Windows
with Weather-Resistive Barriers,”
Walls & Ceilings, November 9, 2006.
www.wc o n l i n e . c om/ A r t i c l e s
/Feature_Article/e61b4141a7dce01
0VgnVCM100000f932a8c0_, (accessed
June 2, 2009).
2. Barry G. Hardman, and James D.
Katsaros, “Fenestration Installation:
Somehow We Have Forgotten the
Past,” Interface, pp. 19 – 22, June
2007.
3. Robert Bateman, NailOn
Windows:
Installation and Flashing Procedures
for Windows & Sliding Glass Doors.
Mill Valley, CA, DTA, Inc., 1995.
4. Standard Practice For Installation of
Windows With Integral Mounting
Flanges in Wood Frame Construction.
California Association of Window
Manufacturers, 1995.
5. AAMA, 2002.
6. ASTM E2112, Standard Practice for
Installation of Exterior Windows,
Doors, and Skylights. West Conshohocken,
PA, ASTM International,
2007.
7. ASTM C1193-05a, Standard Guide
for Use of Joint Sealants, West Conshohocken,
PA, ASTM International,
2005.
8. Robert Bateman, “Sill-Pan Flashing
for Block-Frame Windows in Recessed
Concrete Openings: Case
Studies,” Journal of ASTM International,
Volume: 5, Issue 3, West
Conshohocken, PA, ASTM International,
2008.
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