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Ice Dams in Existing Buildings
Remediation Process
Many people who come to us for help with ice dam concerns have already
tried various approaches to solving their building envelope problems. In
most cases, the owners have asked local contractors what would fix their ice
dam problems. The proposals usually focus on the areas in the buildings
where the problems manifest themselves, usually the cathedral ceiling areas,
lower roof areas, and overhangs. Common methods proposed will include new
roofing, membrane installation, increased ventilation, adding insulation,
and flashing repairs. These proposals may be made after looking at the
buildings, but usually do not include diagnostic methods aimed at
understanding the causes of the ice formations. Many of these proposals are
expensive and most include no guarantees that the problems will be
permanently eliminated. The owner(s) may select one of these proposals, or
sometimes, faced with selecting from such a broad range of approaches, may
hire an independent architect or engineer to advise them on making an
informed decision. Even after repairs are made, they may not prevent leaks;
and, even if they do, there still may be damage from ice formations that
require chopping and cause hazards due to ice falling from above entries,
lower roofs, and walkways.
In an effort to avoid this all-too-common scenario, the following
objective process has been developed. It focuses on achieving a scientific
understanding of the causes of the ice formation before any recommendations
for repairs are undertaken. Understanding the problems and attacking them in
a systematic phased process can guarantee that the real causes of the
problem conditions will be targeted, and that only the necessary repairs
will be undertaken.
To help the Owner(s) with the decision-making, the following process can
be used:
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Preparation for multi-family complexes: Select
accessible, typical problem unit(s) to serve as test unit(s) for
determining the feasibility and economic value of selected corrective
measures. Form a decision-making team comprised of the architect, the
diagnostician, the builder, and a designated member of the Owner’s
organization. In single-unit buildings projects, the process will be the
same, but the selection of test units will not be necessary.
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Phase I diagnostics and repairs: (See
“Theoretical Considerations” in the Thermal VII paper for details about
why the phase approach is required.)
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Collect all available data about the
problem. This includes frost, snow-melt, and ice formation pattern
photos or a map or description of the locations where the problems
occur. Information about when, under what type of weather conditions,
and where the problems occur is very important to understanding the
problem.
-
Review any available drawings and/or
construction photos and make any non-destructive physical inspections of
the building conditions.
-
Perform non-destructive diagnostic
procedures (natural and pressurized infrared thermography) on the test
units to identify and locate the most significant causes of ice
dams. The two major targets of this testing are air leakage (holes) and
conductive heat loss (missing or inadequate insulation) areas that could
warm the outer roof surface enough to melt the snow cover in
below-freezing weather conditions. Ventilation may also be an important
issue once major heat losses are determined to be under control.
-
Based on the project data collected and the
results of the non-destructive testing, develop any small-scale access
openings (destructive) in critical or typical areas for the inspection
of specific construction details associated with air-leakage, conductive
heat losses, and ventilation issues that are resulting in warming of the
outer roof surfaces.
-
Report on the findings, providing a list of
the likely causes of the problems, and propose corrective measures,
including estimated costs for these repairs.
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The team then meets to review the evidence,
prioritize the problem areas, and generate a phased plan of attack. The
evidence should be presented in a manner that clearly provides adequate
information to assess the direct relationship between the problematic
ice formations and the identified thermal envelope problems.
-
Contract with a builder to make the Phase I
repairs (designated as the highest priority) on the test unit(s).
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Phase II diagnostics and repairs
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After the Phase I repairs, operate the test
building(s) without preventive measures including snow shoveling or
raking and the use of electric eave heaters.
-
Monitor the performance of the repairs by
taking photos of the new frost, snow-melt, and ice formation patterns
and map or describe the locations where and to what degree the problems
still occur.
-
Perform a second series of non-destructive
diagnostic test procedures to locate the remaining causes of the ice
dams.
-
Report on the findings, providing a list of
the likely causes of the problems, and propose corrective measures,
including estimated costs for these repairs.
-
The team then meets to review the evidence,
prioritize the remaining problem areas, and generate the next plan of
attack for the areas that require additional repairs.
-
Contract with a builder to make the Phase II
repairs on the test unit(s).
-
Monitor the performance of the repairs by
taking photos of the new frost, snow-melt, and ice formation patterns and
map or describe the locations where and to what degree the problems still
occur, if any.
-
Report the results to the Team.
-
Identify the components of the process that
will be required to successfully repair the balance of the units.
-
Plan the long-term work for the rest of the
units.
-
This process may also include an assessment of
the resulting change in building performance.
-
Collect all data outlined above during the
winter season if the work will extend into the warmer months.
-
Determine and prioritize which units (and
where the problems are) will require repairs.
-
Perform non-destructive testing during the
winter season if the work will extend into the warmer months.
Theoretical Considerations
Excerpt from the Thermal VII paper
The process outlined above requires two phases of testing and remediation
work. In the first series of testing procedures (Phase I), only major
conductive and air-leakage loss areas could be identified because the larger
losses overwhelmed or “concealed” smaller ones. In the case of air leakage,
large openings reduced the pressure differential across the barrier, and the
smaller, more restricted openings had little or no flow. In conductive loss
areas, large un-insulated sections of wall or roof concealed or reduced the
apparent importance of relatively poor R-value areas. The initial (Phase I)
testing gave an overall sense of the problem and determined that the primary
causes of the ice formation were not failures in the insulation or
ventilation systems in the cathedral roofs. It identified the areas
requiring improvements and aided in prioritizing them. This procedure also
provided a benchmark for comparative quality assurance procedures for the
project.
After the Phase I improvements had been completed, the infrared and melt
patterns in Phase II testing provided much more concise information about
smaller, concentrated, heat-loss sites. The pressure differential across
the remaining small openings increased, allowing them to be easily
detected. The second round of testing also gave the contractor making the
improvements feedback about the initial round of work. Usually, this was
done prior to closing access areas and replacing finishes. By incorporating
a review step and fine-tuning into the planning, there was less pressure to
address potentially low-payback repairs in the first phase, resulting in
cost savings on several occasions. This also allowed everyone involved to
assess the impact of the initial work, and to develop and try alternative
techniques to overcome problems encountered in the first Phase. Creating a
cooperative effort where everyone worked together to accomplish practical
goals resulted in a much lower probability of failure. For all of these
reasons, it was clearly important that at least two series of tests be
performed.
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