Ice Dam Prevention and Removal Q&A
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Your article on ice dams
(NH's complete ice dam article) was very informative. We just built our home this summer and we have
tons of ice in our gutters and icicles hanging way low. We have our
attic insulated well and we placed those Styrofoam vents in every
other truss. Our furnace is in our attic since we do not have a
basement. Our contractor put a ridge vent the whole length of the
We have run out of ideas… any suggestions?
My intuition tells me that the furnace in the attic is at least
partially responsible for your ice damming problems. Though I don't
touch on the topic specifically in the website article on ice damming,
the fact is that ANY source of heat in the attic can encourage ice
damming. This includes clothes dryer vents and bathroom ventilation
fans that exhaust into the attic space.
Most people need to be concerned about (1) attic ventilation
and (2) insulation on the attic floor. In your special case, as I see
it, you may also need to protect the roof deck directly from the heat
generated by your furnace.
One possible solution would be to insulate the attic ceiling
between the rafters. This would slow down heat transfer to the roof
and thus slow down (but not eliminate) the melt-off in the main area
of your roof that refreezes along the edges of the roof... a.k.a. ice
dam. But don't just staple up fiberglass insulation… you must use
attic rafter vents under the insulation to allow a flow of air from
the eaves to the ridge vent. These are shaped plastic foam spacers
that keep the insulation away from the roof deck. You can see one such
product at the Owens Corning website at:
From your description, I think that you have this or a similar product
where your attic floor insulation meets the roof deck. This air flow
keeps the roof decking from becoming damp, which can lead to rot.
Touch bases with your local building inspector to make sure that
method of insulation is acceptable in your area, as each climate poses
different problems. In my opinion, the best choice by far would be
professionally installed expanding foam insulation. It has the
greatest R-value per inch and also protects the roof deck from
interior moisture. However, for the do-it-yourselfer fiberglass rolls
or batts are the logical choice.
Thanks for the tips on ice dams. I have question concerning using the panty
hose and calcium chloride ice melt. Can calcium chloride and magnesium chloride
mix be used with out staining roof and aluminum siding?
I am not aware on anyone who has "tested" your situation so I can only
suggest caution in your experimentation. Calcium chloride or magnesium chloride
should not stain a normal asphalt shingle roof, though there may be a white
residue which will, over time, rinse off with normal rain or you can hose it
down in the spring. As far as aluminum siding goes, rock salt is much more
corrosive to metals than calcium chloride, but then again calcium chloride is
"somewhat" corrosive. Alternatively, there are non-salt ice melts available that
are even less corrosive and just, as if not more, effective… though also more
expensive. You may have to hunt for them, though.
There is perhaps one of the most informative articles I have read on the
various types of ice melting products available today at the following link. I
was written by a chemical engineer working with the US Postal Service. Now there
are people who know ice!
I recently read your article on ice dams at your website and found it quite
interesting. One thing not mentioned as a solution is to remove the gutter where
the ice builds up. A friend of mine mentioned this as a possible solution saying
that the only reason we have gutters on houses is so that rain water does not
just run down the roof and drop off in a wall of water. If that is the case,
does this make any sense? It seems to me that the gutters are the problem. No
gutters, no ice dam. Your thoughts?
TD from Schaumburg, IL
Though ice dams can and do form in gutters, the fact is that buildings
without gutters also develop ice dams so removing them may or may not be helpful
in a particular situation. I have seen ten foot icicles hanging off gutterless
So his suggestion may or may not work. You must also consider what will
happen to the roof runoff the rest of the year. Many homes may develop moisture
problems in their basements if rainwater is allowed to drop off the roof next to
the foundation... especially large roofs! In these situations, the ice melt bag
or installing a heating cable just might be more sensible solutions.
I have been a homeowner for less that a month, yet already had to deal with
some severe ice damming due to record snowfall here in the Midwest. I am new to
the problem so I thought about it for a day or so and then came up with this
solution. Take the garden hose with the spray gun on the end of it, hook it up
to the hot water spigot, and go at it. I started by melting away a channel in
the ice dam for accumulated water to escape. Then I worked from back of the dam
towards the eve, melting away the bottom layer. After some time I was able to
push the ice dam off the edge of the roof piece by piece. The advantage of this
method is that damage to the shingles is minimized. These ice dams were 6 to 8
inches thick. It took a while, and quite a bit of water, but seemed to work
better than the hammer-and-chisel method.
If you're doing this over a walkway, beware of ice formation on objects
below. Also, have someone in the house checking to make sure the water is not
leaking in. Thanks for the useful site!
P from Cedar Rapids, IA
Thanks for sharing your ice dam remedy. I hope it helps our readers as much
as I think it will! Of course, it will also get a chuckle from our friends "down
South" and "out West" who think snow is a decoration we put out for the
I've been reading your page on ice dams and am not sure whether my problem
is ice dams or not. My eaves seem to flow fine during the summer even in heavy
rain, but during the winter the ice build up is consistent and in the same spot
all the time. The section of the roofing we are talking about is on the east
side of the building on a reasonably graded roof. I went up on a ladder the
other day,( not the smartest thing to do) but did not pay special attention to
the roof. The eaves were iced all the way to the down pipe.
Any suggestions you have would be appreciated. I am not the handiest guy in
the world, but I'm willing to learn.
Yes... definitely an ice dam! I would suggest trying the ice melt bag first
since your area of trouble is small. If it doesn't do the trick, you might find
that installing a heating cable just in the troublesome area might be the magic
bullet for your situation!
If you read the suggestion above concerning using hot water to melt a channel
in the dam, do that first… then lay the ice melt bag in the channel to keep it
open so water can flow through!
Be really careful with the ladder… they are dangerous enough to use when the
weather is warm and dry! Make sure you have someone nearby just in case there is
(NOTE: If you would like to know more specifically about calcium chloride and
its many uses besides melting ice, visit this site:
I read your article on ice dams, and while there are a number
of preventions of ice dams agreed to by most, there are also
You seem to be in a distinct minority with the view that
gutters do not play a role in ice damming. The majority say:
"It's the gutters, stupid!" and some recommend the use
of deflectors instead. We live in a newly constructed condo and
have had leaks twice from ice dams. An "ice and water
shield" has been installed but I'm still nervous. We want
both prevention of the dams as well as the barrier shield.
Honestly, you should be more nervous that a modern condominium
in "snow country" would be built without an ice and
water shield on the roof!! Makes you wonder what else the builder
Assuming the shield has been installed correctly, your leak
worries from ice dams should be over, so sleep well. Believe me...
if there were a way to absolutely prevent ice dams, the ice and
water shield would be unnecessary!
Regarding my "minority" position on the role of
gutters, let me expound. If you take a moment to consider how ice
dams form, it is obvious that gutters are the "victims"
of ice dams, not the cause. Ice dams are caused by water which
melts off the central part of a roof due to warmth in the attic
but refreezes along the cooler edge of the roof causing a wall of
ice, or dam, to grow. A pool of unfrozen water can form behind
this dam and, if large enough, will leak under the shingles and
into the house.
It is a fact that attics with maximum ventilation AND a
temperature approaching the outside temperature will have minimal
damming. This is because there is minimal melting and runoff when
the outside temperature is below freezing. The critical factor is
the "speed" at which the snow melts when outside
temperatures are below freezing. The greater the difference
between the attic and the outside temperature, the greater the
potential for dam-caused leakage due to the quickly melting snow.
Gutters are involved in ice dams only as far as they are in the
path of ice that forms on the roof. A gutter may cause an ice dam
to become larger, but the reality is that roofs without gutters
also form ice dams! Therefore you cannot blame the gutters... at
most they are innocent bystanders.
Another thought, but an important one. Gutters have a
purpose... to direct water away from the house's foundation.
Without them, year-round moisture problems or even basement
flooding can occur. So the choice of whether or not to have
gutters is a moot one for many homeowners with basements.
Roof water deflectors, or "diverters", are useful in
redirecting the flow of water on a roof, but they cannot take the
place of a good gutter/leader system in controlling rainwater. I
have known some condominiums that do not use gutters, but the
reason is not to control ice dams but to lower the maintenance
cost associated with regular gutter cleaning and maintenance.
Join the minority... it's not very crowded here and there's
always room for one more thoughtful person!
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