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FLASHING PROBLEMS |
Flashing is one of the most critical details of
construction and is often improperly installed.
It is the component that keeps water from entering joints between
dissimilar building materials or other locations subject to water penetration.
Flashing comes in many different shapes and sizes and is made of a number of
different materials. Aluminum,
galvanized metal, plastic, rubberized asphalt, butyl rubber and other specialty components are supposed to be
installed in a manner that will prevent water from
entering the structure.
A large percentage of Austin's construction problems are water issues that can usually be traced back to the omission of or incorrect installation of roof and wall flashing. Most roof leaks and almost all wall leaks are directly related to flashing problems. Unfortunately the building codes have very little to say about flashing. The 2000 International One & Two Family Dwelling Code (residential) is a 566 page document that has only a few paragraphs dedicated to flashing. I have included those paragraphs at the end of this newsletter. Below are pictures that will help you to understand how flashing works and where it belongs.
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| There should be a metal Z-bar type flashing installed above
the piece of trim that spans horizontally over the window. Flashing
in this location would help to prevent the water that will run off the
roof directly above the window from entering behind the trim and
creating a leak. The roof to sidewall flashing also terminates
behind the siding and is guaranteed to leak into the wall anyway;
contributing to wood rot, probably interior staining and possibly other
issues such as mold growth. Other issues evident in this picture
include the fact that the siding is too close to the roof shingles and
caulking is missing at gaps between the siding and trim.
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Once water enters behind the siding at the window and is
channeled down the wall, it is likely to find another line of defense that
has not been properly installed. The moisture barrier at the base of
these windows should be turned up the sides of the windows. As it
sits, any water channeled into this area will simply leak into through the
joint at the window jamb.
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| This is a picture of what happens when you don't flash a
stucco wall system properly. Rot and mold are inevitable when
water is allowed to penetrate the building envelope. This is not a
scare tactic. This is reality! This was found in a
multi-million dollar lake home in the heart of Austin. It was estimated that the 5,000
square foot home needed approximately $100,000 of repairs.
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The sheathing at the exterior of this home has
not been set in shingle fashion. Any water draining down the center
section between the two upper windows will be directed into the wall when
it hits the piece of horizontal sheathing that is installed directly below the upper
windows.
Of course this is not even to mention the fact that sheathing is not a good substitute for flashing in the first place. However, in this instance, the building code allows the flanges on the windows to act as a substitution for flashing. This is why it is not uncommon to find leaking windows in a 5-7 year old home.
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| This home was inspected in the framing stage and was
supposed to have stucco installed in the near future. It is my
opinion that the builder should have considered installing the exterior
sheathing prior to installing the windows. It is inevitable that the
stucco to window junctions are going to leak at this home. When you
start out wrong, you are guaranteed to end up with problems later.
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This brick mason is about to
install brick over a lintel that has not been flashed into the wall
properly. You can guarantee that at least a portion of the water
that is absorbed into brick and mortar will leak past the lintel.
Weep holes above lintels are not effective if the water never makes it to
the weep hole in the first place. Unfortunately, many homes
around the Austin area are built with this same carelessness.
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| This weep hole is not installed at an appropriate
location
in the brick veneer wall. This leads me to be fairly certain that there
is no flashing in the wall assembly behind the brick. If the
flashing is present, chances are good that it is not properly
installed. The weep hole will allow air to enter the brick veneer
system and dry out the wall, but it is not set in a location
that will allow water that has entered the system to drain out of the
wall. Weep holes should be installed at the first course of masonry
above the foundation and at the base of the wall system in all other
applicable locations, such as above doors and windows.
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This is a fine example of what happens when
flashing is not installed below a door that is subject to splash back or
wind driven rain. The city of Austin does not require pan flashings at exterior doors.
Regardless of minimal standards, proper
threshold flashing is always a good idea. While it is very uncommon to
find this piece of flashing installed, water penetrations,
wood rot and damage at exterior doors is not uncommon at all.
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| This is the most common method of shingle
installation in Central Texas. The underlayment has been installed
beneath the metal drip edge. The manufacturer requires this on the
rake edge of the roof. The underlayment should be installed
on top of the drip edge at the downhill side of the roof.
The starter course has not been installed in accordance with manufacturer installation recommendations either. The lower tabs of the shingles should be removed from the starter course. This allows the sealant on the shingle to provide a tight seal right at the edge of the roof and helps to prevent leaks from occurring.
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To start with, the masonry sidewall at this
brand new home is not
supported properly. (another newsletter entirely) The
flashing issue here is complicated. For starters, the roofing
contractor has installed turn-back flashing behind the brick wall which is
a no-no. Now he is going back and installing step and counter
flashing after the fact. There is
still no through-wall flashing or weep system to handle water that is
absorbed through the brick wall though. Inevitably, water will be
absorbed into the wall space and will not have a way to escape the
structure without creating unwanted problems. This issue goes right to the heart of the entire flashing problem. That is that no one is directly responsible for flashing as a "system". While the roofer is responsible for the step and counter flashing that keeps water from entering the roof / wall junction, he should not be responsible for the brick flashing that handles water after it is absorbed into the brick veneer wall. It seems to me that that is the mason's responsibility. The builder obviously does not know enough to tell his subcontractors what to do and the subcontractors claim to have done it to industry standards or builder specifications. In many examples, the building code is either not enforced or does not specifically address the issue at hand. The fact is that the industry standard is outdated and today's complicated structures require more forethought and planning than we are finding in the field.
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2000 International One & Two Family Dwelling Code
Flashing
shall be located beneath the first course of masonry above finished ground
level above the foundation wall or slab and at other points of support,
including structural floors, shelf angles and lintels when masonry veneers
are designed in accordance with Section R703.7. See Section R703.8 for
additional requirements. R703.7.6
Weep holes. Weep holes
shall be provided in the outside wythe of masonry walls at a maximum
spacing of 33 inches (838 mm) on center. Weep holes shall not be less than
3 /16 inch (4.8 mm) in diameter. Weep holes shall be located immediately
above the flashing. R703.8
Flashing. Approved
corrosion-resistive flashing shall be provided in the exterior wall
envelope in such a manner as to prevent entry of water into the wall
cavity or penetration of water to the building structural framing
components. The flashing shall extend to the surface of the exterior wall
finish and shall be installed to prevent water from reentering the
exterior wall envelope. Approved corrosion-resistant flashings shall be
installed at all of the following locations:
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| I have only scratched the surface on the issue of
residential construction flashing. The idea is make you aware of just how
important it is. I believe that it is far and away the most overlooked
component of construction today. As our systems get more and more
complicated, it seems that pride in construction has become less
common. It is up to me to try and help you and the builders
understand the importance of quality construction. It is up to you
to be aware of these issues so that you can monitor or correct them in
your own homes and hopefully avoid more serious issues in the
future.
To learn more about proper flashing, visit the following links listed below. Through Wall Flashing of Brick Veneer
(Journal of Light Construction) Stucco Construction Guidelines Stucco Flashing (Journal of Light
Construction) Making EIFS Watertight (Journal of Light
Construction) Flexible Flashing (Journal of Light
Construction) Trouble Shooting Roof Leaks (Journal of
Light Construction) Sealing and Flashing Metal Roofs (Journal of
Light Construction) The Masonry Society Home Page The Northwest Wall & Ceiling Bureau Home Page Exterior Design Institute Hardie Plank Siding Installation Guide Certainteed Composition Shingle Installation Guide
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