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what to do AFTER an ice dam

george_hairston's picture

recent ice storm in central NC caused lots of ice dams and resulting interior ceiling and wall damage.

I would appreciate any input about exterior preventative measures.

(post #169826, reply #1 of 20)


I'm not sure how familiar you are with roofing, but here is one thing I use here in the northeast. The same type of product is made by variuos roofing material manufacturers. It is a tar based product with an adhesive back. It looks like roll roofing, and comes in rolls of 1 and 2 square. It is applied directly on top of the plywood on your eves(I also use it in valleys where the pitch is slight) . The only drawback in your situation is the fact that you would have to tear off the first three feet of shingles. You can shingle over top of it, and the material seals around the nails as they go through it.

Both GAF Corp. and Certainteed Corp. make a decent product that you can find at any roofing supply house. In this area, Home Depot has started to carry the GAF "weatherguard". They are both good products, and my customers have not had any complaints.

Good luck!

(post #169826, reply #4 of 20)


I have not used the Grace product yet. I agree with Geoff about the "grit" surface. I have seen guys step on it, then lose their footing when they walk on the tar paper above it(luckily no one got hurt).

Thanks for the info, I'll give Grace a shot on my next roof job.


(post #169826, reply #19 of 20)

The previously mentioned product is in fact your best protection. Also as mentioned though, it does not prevent ice dams, but acts as a shield. Ice dams occur when snow melts from the roof over warm living spaces, hits the portion of the roof over unheated eaves and refreezes. As successive water melts and refreezes, it creates the aformentioned ice dam, letting water that hits it eventually back up under the shingles and run down through the roof deck in to wall cavities and in to living spaces. There are products that help melt the ice (electric tape in the gutter, etc.), but you are probably in an area where another occurrance would be rare. Unless you want to go to the time and effort to install the ice/water shield, you may be able to get by with out it.


(post #169826, reply #6 of 20)

Ditto on the product to use, however, up here in Canada where ice dams are very common the practice is to have ice and water sheild start at the edge of the roof and continue AT LEAST 2 ft up beyond the outside wall of the house. Or to be sure this is clear, if your house has a 2 ft overhang a 3ft wide piece is not enough. In that case I would go 6 ft in our climate. SteveM

(post #169826, reply #8 of 20)

Bituthene-type products at the eaves and up past the wall line at least 36" is the best measure to keep water behind an ice dam from entering the house. Trouble is you have to pull off the roofing to apply the bituthene. Another route is to build a cold roof
b with adequate ventilation
directly over the problem roof.

Another issue altogether is the danger posed to people, pets, automobiles, hot tubs, and so on by icicle formation at the roof edge. Heat tapes have been used for decades, but pose their own problems, having been identified as the culprit in many house fires due to their constant-wattage heat delivery. However, there exist professionally-designed and installed heat cable systems that have proven highly effective. Bylin Engineered Systems makes the
i Roof Ice Melt
System (RIM). It uses self-regulating heat cables (they get hotter as the air temperature drops and vice-versa) placed in a sandwich of 17-inch wide copper or aluminum panels which spread the heat evenly over the entire panel. The panels can be installed directly over the existing roofing. Bylin can customize to each house to match roof color. The panels can be made for roof edges, gutters, and valleys. Bylin's phone number is 916-933-5666. Another similar product is Technitrace out of Salt lake City.

(post #169826, reply #9 of 20)

Here in NE PA, we've had two horrendous winters in the last five years. I'm glad I was here, because I've learned a hell of a lot about ice dams. When we got hammered with 2-3 feet of snow a couple of years ago, there was some money to be made shoveling snow off roofs. I had a chance to look at lots of roof systems in ideal ice dam formation conditions ( read- lots of snow, with low temps. for 2-4 weeks ). There is a lot of literature out there that explains how ice dams form, so I won't go into that. Any of the ice dam products that adhere to the deck are a nice, somewhat helpful, band-aid, but they sure don't eliminate them!

Out of the 100 or so roofs I looked at, only two of them had no ice dam problems. Reason: sufficient ventilation at the ridge and soffit, sufficient insulation over the heated area of the living space ( double layer R-19 ).

"sufficient "ventilation is defined by dividing total square feet of the homes footprint by 150. This will give you a "free air" number expressed in square feet. Half of this belongs at, or near the ridge, half belongs at or near the soffit.

Insulation MUST NOT interfer with air flow.

Kim Talarsky

(post #169826, reply #10 of 20)

Just a note on heat tape. There are basically two types of heat tape ; self regulating and non self regulating. you can tell the difference by looking at the price. Self reg will cost you about $5-$8 per foot while non self reg will be in the $1-$2 range. I have self reg on my roof to prevent ice dams and I have bituthane as well. The falicy is that ALL heat tape causes fires and the people who sell other alternatives to the ice damn problem are very quick to forget the very great distinction. Self reg tape is UL listed and when it comes in contact with heat either by ambient temps or heat generated by itself when a section comes loose from its roof clip and folds over itself. Non self reg does not do this and when it folds over itself it continues to generate heat until it melts the outer jacket and the buss wires come in contact with each other and , presto, you got a dead short and a fire. Look at the end section of the wire and if it has 2 buss wires looking like a TV anteanna wire it is self reg cable. Self reg tape will draw about 10 watts on start up at 0 F and go dowm to about 5-6 watts per foot at 32F then down to about 1-2 watts at 50F therefore you dont need a thermostat with self reg. Non self reg is a constant wattage product that will generate 10 watts per foot all the time regardless of temp. We use self regulating tape all over the place here in New England. A statement like " electric heat tape causes fires' is a case of hearsay information being taken as gospel.

Heating cables (post #169826, reply #20 of 20)

I have a switch on my heating (tape) cables to use it only when it is melting and not when it is really cold. I had a controller that was supposed to do that but they keep messing up so the manual way is better.

(post #169826, reply #12 of 20)

Gene, heat tape is not supposed to do away with the ice dam but merely make holes in it so that water will drain off your roof. While it does appear that they are encrusted with ice they have air all around them ( if you turn them on anyway !) and allow that water that would build up under your shingles to drain off.

(post #169826, reply #13 of 20)

Don't be too quick to write off the weather as one of the causes of ice dams. I've seen this mentioned several times now. My home has absolutely no snow melt on the roof when it is very cold out. I can go for weeks or months on end without any water dripping to the overhangs. but when we get one of these extended January thaws, I start to get a lot of snow melt from the sun on the south and west side of the house. During the day this is no problem, but toward evening when it gets below freezing, that water is still trickling down through the snow layer and finds its way out to the roof edge where it freezes and starts to form dams.

We always install two rows ( 6') of ice and water barrier on any roof flatter than 6/12. The product Gene mentioned is by far the best material I have used. It is hard to find at many yards around here and seems to have been replaced by this cheap junk with the granules on it. Could someone tell me if this is still available?? Thanks

(post #169826, reply #14 of 20)

Ice Dams: While improper insulation and ventilation are frequently mentioned as causes of roof snow melting and forming ice dams, other items such a bathroom vent pipes exiting out the roof and sunshine also melt the snow and contribute liquid snow into the ice dam mix.

(post #169826, reply #17 of 20)

recent ice storm in central NC caused lots of ice dams and resulting interior ceiling and wall damage.

I would appreciate any input about exterior preventative measures.

(post #169826, reply #2 of 20)

George and Greg. The best known of these products is W.R. Grace's Ice and Water Shield, more commonly known as Bituthane. It is a polyethylene coated rubberized asphalt.

Contrary to the claims of self appointed TV gurus, it does not stop ice dams. But it does provide some protection from water backedup by the ice dam.The roll I use is 3 feet wide by 75 feet long, 225 sq. ft. Gene L.

(post #169826, reply #3 of 20)

George and Greg, Ditto on the Grace ice and water sheild, It's thew best product by far, the others have some "grit" to their surface, this is to make it safer to walk on when wet(early A.M. dew?, I think they've compromised on the performance of the product to add this "feature".As Gene stated, it doesn't prevent ice dams, just protects against damage from them,go with the Grace product.

(post #169826, reply #5 of 20)

The thread is old but the title fits.

By the way W.R. Grace sold this product to "Hycor"

I found that a few more holes combined with unusual amounts of accumulating snow has casued a pretty good ice dam on my house. Thi is no biggie cuz the new roof will be here in three months.

I decided that I had to do two things 1 - eliminate the source of water (snow) and 2 - stop heat leaks.

To remove the snow I bought a roof rake, a little unweildy but cheap insurance. I got on the roof and was amazed at the damage it does to the shingles. They are heaved and pushed up and buckled (5 layers including the shakes - may compound the heaving part) Not at all the usual smooth appearance.

I was surprised at how much heat was apparently leaking around the water heater vent flashing. Melted a 20" diameter area around it. That's all sealed now. I got to thinking all technically (which I usually do) and I got thinking about how the roof was applying more heat than the latent heat and the conductivity of the snow could dissipate. Then I got thinking that a poorly insulated roof is better of with no snow, is a well insulated roof better off with a good blanket of snow to absorb the heat? Would a thin layer of snow melt because it didn't need much energy to overcome the latent heat? Could a well insulated roof ice dam with succesive layers of light snow? This snow is unusual because it is not being blown thus the accumulation on the roof is quite large.

It was amusing to watch the local TV's treat the ice damning as a symptom of the weather rather than a symptom of leaky construction. BTW - plenty of new and fairly new houses with the requisite ridge vent are damming up on the TV. A roofer interviewed didn't do much to change my impression of contractors in general either. Maybe each trade should establish a spokesperson for these situations. Then I had another idea - You can simply drive down the street and see the people that need weatherization work done! It couldn't get easier. Then I remembereed the Better Business Bureau tells you not to hire anyone who goes door to door.

Damming really is a double whammy - you paid for the heat to melt the snow to form the dam to ruin your roof and your walls that you have to pay to fix - that is if you are the typical consumer.


(post #169826, reply #7 of 20)

Just an anecdotal comment on heat tapes - two house fires - one over 2 million and burned to the ground - both blamed on heat tapes by the fire department.

(post #169826, reply #11 of 20)

Gentlemen.We've had some beautiful ice dam winters over the last half-dozen years. As Henri DeMarne said, one of those winters was the worst in 20 years he has seen in Vermont.

Imagine the look of disbelief on the faces of homeowners when they saw ice dams on their metal roofs.What was running through the minds of those who were sold a bill of goods about heat tapes? They found their heat tapes surrounded by ice: on top and below the tapes, over and under the tapes.And yes, those houses ventilated to the code 1/150 ratiosported ice dams, as did most of the houses with ridge/soffit vents.But how can this be? Gene L.

(post #169826, reply #15 of 20)

The "FHB posting insulation, envelope gurus" know why todays combo new/old building techniques may be causing ice dams more often these days than in the past and I believe they are at least half right...

The other half of the story might be as follows; Deep snow is always wet underneath in my neck of the woods, either on the ground or on a roof. Pools of water and the "plural" in the "membrane" being used is the problem. "Shingles" not good "membranes" as a group. Steep roofs of old hold less snow, Steep is better. Not so steep (the build it cheaper since the 50's styles?), then a continuous membrane is mucho better. So if you must use $7/bundle stuff then [CUTE LITTLE PUPPY] the underlay; [CUTE LITTLE PUPPY] it all or you'll b*tch forever. If heavy snow is rare(NC?), the best answer is the time tested "remove the snow" (no snow, no pool) with a shovel and or snow rake idea, used on all but the 12/12 pitch roofs with metal or slate (Self-snow removing hardly ever leak and rarely replaced (every 50 to 150 years or so)) roofs!

I would think a Gene Leger House would be one of the rare exceptions to the rule. Is it true Gene?

(post #169826, reply #16 of 20)

Jack. I've had no reports of icedams on the manmy houses I designed and built. The poeople who bnought the 1st Leger house 20 years ago claim they have never has ice dams on their house.So guys, let's get into the basement and seal those holes and openings in the basement ceiling. And do the same thing in the attic to the openings in the floor.GeneL.

(post #169826, reply #18 of 20)

Ah - Another Adirondacker - ( I live a bit North of Saranac Lake)

I went with 12/12 metal, though the neighbors laughed when the 30' sheets arrived for the N. side of our saltbox. Got them up in a day though, and have certainly never regretted it. Never any ice dams at all, surely the way to go. I don't want to be shovelling the roof after the big dumps, I want to be on cloudspinner at Whiteface!

But for those who have to "remove the snow", consider an idea my uncle from Chicago came up with. He has a simple ranch house (6/12 roof perhaps). He put a 3/16" steel cable along the ridge, well fastened at either end, and rather tight. On the cable was two steel rings, ~1-2"diameter. From each ring came another cable, one on each side of the house, that reached the ground. After a big dump he would wait till the bottom of the snowpack moistened(usually wet snow),then he simply walked under the eves, pulling the cable to the other end of the house, and the whole snowload would shed, then he would do the other side. Pretty clever I thought!