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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.
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!
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 roofs!
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.
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 holidays!
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 a problem.
(NOTE: If you would like to know more specifically about calcium chloride and its many uses besides melting ice, visit this site: http://www.calciumchloride.com
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 overlooked!
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!