What is an Ice Dam?
That is when the snow begins to melt on the warm roof and
as the water runs down toward the edge, it freezes. The ice
build-up starts forming on the shingles about where the exterior
wall and the soffit/overhang meet. The ice forms here because
it is the coldest part of the roof. Ice Dams that form on
Toronto area homes are typically four to ten inches thick.
In some regions like eastern Ontario & Quebec, ice dams
can easily form up to two feet thick.
Once the Dam has formed, there is no place for the water to
drain. If enough water collects, it will back-up behind the
Dam under the shingles and leak into the wall cavity and interior
of the home.
Where Do Ice Dams Form?
Ice Dams generally occur on older homes that have inadequate
attic insulation and insufficient attic ventilation. [However,
newer homes can have the same problem - if these items were
"short-cut" during construction.] They also occur more often
on Low-Slope Roofs, Cathedral Ceilings and Flat Roof Cavities.
[Again however, steep roofs on "1/2" storey houses with
small side attics and dormers can experience severe Ice Dams.]
Just as irritating and expensive to repair, Ice Dams form
around skylights and exhaust fan vents. In these situations
the cause is slightly different, but the end result is similar.
The ponding water tends to back-up around the flashing and
find its way into the home. It should be remembered that layered
roof systems like asphalt or wood shingles were never intended
to keep out ponding water, but rely on gravity to drain the
water downhill and off at the eaves. Even shingles called
"self-sealing" because of the sealing strip on the back, will
not keep water out of a home - the sealing strip is only intended
to stick them to each other, to prevent wind blow-off.
What Causes Ice Dams?
Ice Dams are simply caused by warm air leaking through the
attic insulation and reaching the underneath of the roof sheathing
- plywood or board. If the insulation is inadequate or the
ventilation insufficient, you have set the stage for Ice Damming.
[It is almost always a combination of these two factors -
insulation and ventilation.]
But, Isn't My Roof Leaking?
Yes and No. It is a forced leak, due to the problems mentioned
above. When water is forced to find an escape, it will migrate
to the point of least resistance. Under normal conditions
and even with heavy rain, the roof will usually drain as it
was intended. The worst that happens in that case is an overflowing
gutter system that cannot keep up with the volume of water.
Gutter and downspout systems that are not properly maintained,
will eventually get plugged and cause water to back-up. The
most deluxe roof specification will keep exterior moisture
out of the house, but will not prevent condensed moisture
from being destructive to framing and siding [including brick],
if insulation and ventilation are weak.
Is It Possible To Get Temporary Relief From The Symptoms?
The only real relief once an Ice Dam has formed, is to clear
the snow above the Dam - so that it is not there to melt -
and to break-up some of the ice so that water can be channelled
off the roof when melting conditions exist. It is advisable
to turn the heat down and any humidifier off, inside the house.
This will reduce the humidity of interior warm air, as it
escapes through the insulation. If you have leaks in the ceiling
area, poke a small drain hole through the drywall or plaster.
This will reduce the interior damage by providing a positive
drain point, rather than the water spreading across the ceiling
to other relief points. For the Snow & Ice removal, rely
on professional roofing contractors who are trained and conditioned
to be on roofs. It becomes very dangerous for someone inexperienced
to be up there. [It is even dangerous for the professionals,
but they have the proper equipment and safety gear to handle
it.] An untrained person can also cause more damage than necessary
to the roof. However, be prepared to pay for this Service
- from $300.00 and up [+GST] - depending on size, pitch and
complications. Remember that you still must correct the source
of the problem.
How Can Future Ice Damming Be Prevented?
Three things have to be considered:
1) Air-Sealing of all electrical, plumbing and heating
penetrations from heated space into the attic space.
2) Ensure that the Insulation covers the top-plate
of walls around the exterior perimeter of the structure Also,
be sure to have a "true" R40 Insulation value in attic spaces.
[On an older house without a vapour barrier, but with fibreglass
insulation in the attic, the "true" R-value is only 60% of
the rated value. This is due to the fact that fibreglass is
really, only an air-filter that slows down the transfer of
heated air. Other insulation materials such as cellulose fibre
or icynene foam - trap air - the way it should function.]
3) Attic Ventilation - Soffit & Roof - must meet
or exceed the minimum standards of the Building Code. There
are various types of ventilation systems, some more efficient
than
others, but also more expensive [than the basic styles]. On
a double-brick house with no existing soffit ventilation,
one could almost be assured of Ice Dams in extreme weather
conditions [like January 1999].
Any one or a combination of these methods may be necessary in order to keep the deck cool so melting does not occur. The roof deck [underneath], must remain colder than the exterior which may not be possible during extremely cold periods or when there is a heavy accumulation of snow on the roof. Considering that the Toronto area had both conditions (from Jan. 1-15/99] simultaneously, it is no wonder that hundreds have experienced problems like never before.
What About The Roof Integrity?
According to the Building Code, all roofs must have Eave Protection.
There are a couple of factors to be considered: how
wide should it be and what product should it be? The Building
Code states that the Eave Protection should be at least wide
enough to give protection [from water back-up], to a point
one foot beyond the interior side of an exterior wall. Therefore,
a three foot width of membrane is really only sufficient for
a structure with up to a 12" overhang/soffit, on a pitch up
to 6/12. Any overhang wider and any pitch steeper, requires
wider Eave Protection. The Building Code also approves four
materials and methods for the Eave Protection, but only two
of these are commonly used. The products are known as #28
- Base Sheet which is a fibreglass reinforced, tarpaper, or
Waterproofing Shingle Underlayment [WSU] which is an adhesive-backed,
bituminous rubber membrane [that self-seals at nail penetrations].
Both of these products come in a three-foot [approx.] wide
roll and therefore, can be installed in 3'-6'-9' widths on
a roof [as may be necessary]. At the perimeter of skylights,
chimneys and other roof penetrations, this WSU should be mandatory
on any roof.
Consideration should be given to a complete underlay, besides the Eave Protection, if the Pitch is between 4 & 8/12. Most people wonder why this would be necessary? This winter has been one very good reason, again because shingles on there own shed water, but do not seal water out. Besides a winter like this, hard, wind-driven rain can easily be pushed under shingles, causing water to get through to the interior of the house. Another reason to consider this underlay, is when used with fibreglass base-mat shingles, a Class-A, fire-rated roof system is achieved. On the other hand, organic shingles [or a paper base-mat], provide only Class-C fire-rating; with or without the underlay. The common material used for Underlay [on the balance of the wood roof deck] is #15 Roofing Felt or newer, deluxe products, such as Shingle-Mate [by GAF].
Why Has This Never Happened Before?
or Why Did This Happen After I Had A New Roof Installed?
It has been happening before and it did happen before the
new roof. The difference this time was that we had constant
subzero temperatures for two weeks and we had more snowfall
during the same two weeks than we [in Toronto], have [recently]
been used to in a whole winter. It has absolutely nothing
to do with a new roof this year - as long as Building Code
standards were met or exceeded. Actually, January of 1998
was just as harsh on structures, if not more so because of
the little amount of snow in Toronto - quite a bit of rain
- but also many "freeze - thaw cycles". What is a "Freeze
- Thaw Cycle"? It is when the temperature climbs above the
freezing point during the day, but drops below again at night.
Whenever, that happens in the house that has been described
throughout this article, there is moisture present. The difference
is that it is working away where it is not seen or detected.
However, it is still causing damage to wood framing members
and wetting the insulation.
During January 1999, the factor that compounded all of this was that the standard types of roof vents were totally covered by snow for many days. Hence, the title of this article - Could you survive two weeks without air? We expected our houses to, but they need to breathe as well. Even houses with the proper amount of both soffit and roof venting struggled The intake air was initially getting in, but the exhaust air [through the top] could not get out The depth of snow - up to five feet [where drifted] on some roofs - acted as an outside insulation When the warm interior air is transferred to the underneath of a cold wood deck, there can be up to 3/4" of frost/ice. As more warm air escapes from inside and when the outside temperatures begin to rise, there will be a layer of slush between the snow and the roofing shingles. This water will also back-up and help to melt the frost/ice underneath the wood What really happens, is that there is now a complete weather cycle taking place within the attic space - yes rain in the attic - High School Physics.
Okay, I Got Through This With Only Traces Of Moisture
- I Should Be Okay For Another 70 Years Shouldn't I?
If you got by with a minimal evidence of moisture, you are
not necessarily okay for the future. Studies have shown
that once "water migration pathways" are established, the
roof is more susceptible to further damage. These pathways
often do not close during warmer conditions and the roof is
less resistant to rain and snow. Water will easily travel
on the established path.
Is It Possible To Correct The Problem Without Replacing
The Entire Roof?
It is possible to repair the problem areas where Ice Dams
have caused leakage without replacing the entire roof. [If
however, the problem is around the entire perimeter, rather
than one area, you probably need to do the whole roof.]
A section prone to this problem can be replaced on its own.
You should ask for the "Arctic Specification". Shingles and
colours can usually be matched, quite closely. The Arctic
Specification will assure that weak sides or areas are protected
against water migrating back into the structure from outside.
Only the upgrading of insulation and ventilation will take
care of condensed moisture - weather cycling.
What About Skylights, Cathedral Ceilings & Flat
Roof, Ceiling Cavities?
These are specialized situations that must be thoroughly inspected
and dealt with on an individual basis. Again roofing specifications,
insulation and ventilation are key to solving the problem.
You need to deal with someone who has training in the "Building
as a System" - discipline. Most roofers do not understand
the symptoms well enough to offer a complete solution. LET
IT RAIN INC. - Building Science Experts have qualified Consultants,
who can assist you.
How Do I Get The Right Solutions To The Problems I
Have?
Ask for a Roof & Attic Consultant to come and conduct
a detailed inspection, followed by written report that lists
the problem[s], purpose, observations and then details a specified
remedy to eliminate future occurrences. LET IT RAIN INC. offers
this service at a fee beginning at $ 150.00 and up, depending
on the number of roofs, attics and other complexities. Don't
wait for another occurrence that causes damage to your home
and property. Call today and "request an appointment".
