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Sliding Ice and Snow Cause Roof and Property Damage

May 15, 2004

The power of ice and snow is seldom apparent as individual
snowflakes fall to the ground. But when snow accumulates
on a roof, the damage that can be caused by sliding ice and
snow is a major concern. Tim Ryan, president of the Arrowhead
Condominium Association and head of the property management
firm for the association, has first-hand experience in dealing with
sliding ice and snow.
Located in Big Sky, Montana, the
Arrowhead Condominium Association
consists of 24 units with metal standing
seam roofs on a 12/12 slope. The
homes are only 10 to 15 feet apart, and
each is a ski-in, ski-out unit on a hillside.
During harsh winters, snow, ice
dams, and icicles were sliding off the
units and damaging neighboring
homes. The front door of one unit collapsed
three different times from sliding
snow. The decks on the buildings had
to be closed for the winter, since many
rails and decks had been torn off by
snow and ice. On lower shed roofs, not
only was the metal roofing torn and bent, but the 3/4″ plywood
sheathing was crushed between the roof’s rafters.
On several occasions, Ryan had worked with the association’s
insurance company assessing the damage. The insurance company
said it would not renew the association’s policy due to the continuing
problems. “Their concern that the ice and snow could
potentially cause great personal injury was too great,” noted
Ryan. “We did not know how to eliminate these problems, so we
contacted a professional in providing solutions to stop the movement
of ice and snow.”
“The consultant [Terry E. Anderson of Anderson Assoc. Consulting
Inc.] recommended an engineered snow retention system,”
Ryan continued, “and a good ventilation system that, once
installed, would stop most of the ice dam and icicle problems. He
visited with the board and gave several options. After reviewing
the choices, the Arrowhead Condominium Association chose concrete
tiles. The association felt concrete tiles had the longest
proven performance record in Europe on cold roof designs, and
they also liked the look of the tile.”
After the specifications and details were written, the project
was bid by qualified roofing companies who were familiar with the
specified cold roof system. Trojan Roofing of Salt Lake City, Utah,
Arrowhead condominiums in Big Sky, Montana.
Arrowhead condos from a distance.
January 2004 Interface • 11
12 • Interface January 2004
was selected. The tile chosen was one
produced by Westile, Inc. of Littleton,
Since the engineered ground snow
loads increased after the units were built,
a local engineering firm was hired to
check the structural integrity of the
buildings for retaining snow and ice on
the roof. Securing the rafters properly to
the top plate and purlins was the only
minor change required.
Because it was late in the year and
winter was approaching, the Arrowhead Association chose to re-roof 14 of the 24 units
immediately. It was difficult for Trojan Roofing to work in the cold and snowy conditions,
but it gave all involved
a great opportunity to
see the difference
between the old and
new systems.
Many of the homeowners
were concerned
that the
buildings could not
retain snow on a
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Right: New concrete tile roof
with snow retention brackets.
Damage to metal roof and sheathing from
snow and ice falling from the roof above.
Snow and ice sliding off metal roof and curling
into window.
Above: New cold-roof system framework for
concrete tile roof.
January 2004 Interface • 13
12/12 slope.
However, with
proper engineering
of fences
and brackets,
the system
retains the snow
and ice on the
roof. The system
was designed
using a fully
engineered snow
retention system
with TRA Snow
Brackets and a
“Cold Roof
The cold roof
system stops ice dams and icicles by venting air outside
below the roof tile and above the sheathing from
the eave to the ridge. The equalized temperature
minimizes thawing and refreezing of the snow on the
roof by venting away heat from the living space. The
system is based on the Roof Tile Institute and
Western States Roofing Contractors’ Association’s
Cold Roof Manual and air ventilation charts from
Since adequate ventilation was critical to the
success of the roof system, calculating the air openings
needed from eave to ridge was essential. The
designed air intake system at the eave and the ridge
exhaust system at the raised-ridge vent were to work
in tandem to achieve the major difference between
the old and new systems. This was immediately
apparent when icicles were eliminated and snow was
retained on the roof.
Homeowners of the first completed re-roofed units were very
pleased with the results. The owners commented on how exceptional
the tile looked with all the copper flashings and the copper
TRA Snow Brackets. The real proof of the improvements between
the two roof systems became clear as the snow began to fall; the
difference in the two roof systems was obvious. The newly
designed cold roof system allows the snow to compact
naturally with ice in the bottom three inches. This ice
freezes around the triangular portion of the snow
bracket and permits run-off between the ice and the
tile when the outside temperature is above freezing.
“The new units have stopped all snow and ice movement
as well as icicles,” stated Ryan. “The old units
still have leaks, icicles, ice dams, damaged decks, and
snow and ice hazards. Our association and our homeowners
are very happy with the look and design of the
units. We are looking forward to having the last ten
units completed this spring and summer. Retaining the
snow on the roof has also reduced the high snow
removal cost.”
According to Ryan, “Credit needs to go to Anderson
Associates Consulting, Western States Roofing
Contractors Association, and the Roof Tile Institute for
the work on The Cold Roof Manual that made this system possible,
as well as the great work done by Trojan Roofing while working
in such bad winter snow and ice conditions. The units look
beautiful; they are safe and insurable,” concluded Ryan. ■
Rick Olson is director of technical
services for the Roof Tile Institute
(RTI). He has been in the tile industry
for over 25 years, first as owner of a
small tile company, then president of
Marley Rooftiles USA, and subsequently
president of RTI. Olson is a
member of ASTM (chairman of
C15.06), vice chairman of the Roofing
Industry Committee on Weather
Issuees (RICOWI), and a member of
the Western States Roofing
Contractors Association (WSRCA), National Roofing Contractors
Association (NRCA), and the Florida Roofing, Sheet Metal and
Air Conditioning Contractors Association (FRSA).
Below: Note the contrasts between the old and new
systems. The roofs to the left and the right still have the
old system – metal with no snow retention devices,
causing ice dams and hazardous conditions. The center
slope is a cold-roof system with concrete tiles and a
snow retention system at work. It is safe, attractive, and
Left: Note difference in snow retention. Middle building
with new tiling and snow guards is providing safe snow
and ice retention. Far building with old metal roof has
had its deck torn off from sliding snow and ice.