Roofing roof leak from ice dam, Ice dams, I&W shield

Roofing roof leak from ice dam, Ice dams, I&W shield

Roofing /roof leak from ice dam


Expert: Dan Merrill — 2/7/2009


QUESTION: Hi Dan, thanks for taking my question.

My house is about 25 yrs ago. My great room has cathedral ceilings with no attic space above it. The room opens up to our outside deck/porch. In summer of ’07, we screened in the porch so that the two rooftops now connect. The main roof above the cathedral is cape-sloped, while the porch roof has a lower pitch (and I should note that the porch roof has a gable configuration with roofline perpendicular to the main roofline, i.e, new valleys were created). Last winter, we saw ice dams over the unheated porch area, but no other apparent problem. This winter however, the ice dams are associated with some leaking in the porch, and also to the adjacent mudroom ceiling (which lies lower than the porch ceiling). I had the porch installer come out, and he helped remove snow off the porch roof and said de-icing cable will help. I had a roofing contractor come out and he said that putting vents in my soffits to ventilate the cathedral ceiling/roof (and putting the cables on) will help. I’m not sold on either suggestion at this time. I’ve researched the cables and they seem to be a treatment of the symptom but not really the underlying problem. As for the soffit vents, they generally seem to be a good idea, but this house is 25+ years old and never had such vents or apparent problems. So I’m not convinced it will solve the problem.

By the way, I did replace the main roof this past summer. A ridge vent was added (where it did not exist before).

Any advice would greatly be appreciated. Thanks again.

ANSWER: Sorry about the really slow response, we have a bit of the flu here.

This is an article I wrote recently for a periodical. It looks appropriate to your question.


What is Ice damming?

Ice damming is when snow & ice melts on your roof, flows down and refreezes at the eaves, valleys or gutters. This ice can build up to the point of pushing melt (water) back up under your roofing material, it can do interior damage to walls and ceilings as well as doing structural damage in extreme cases. It can “appear” to be a roof-leak, but is not usually caused by your roofing material.

What causes Ice damming?

The most common cause of ice damming is when the heat from your home rises through your ceiling to the roof and melts snow and ice on your roof. This melt runs down your roof until it contacts the colder Eave area and refreezes. The Eave area is the area hanging out beyond the outside walls of your home. This ice can build up a lot of mass and in extreme cases do structural damage to your roof structure. The escaping heat is due to insufficient insulation, vapor barriers and air flow barriers in your home.

This problem can be corrected with the proper application of insulation barriers, insulation, vapor barriers and sometimes radiant barriers.

The second most common cause of ice damming is when your roofing material is a dark color and has significant mass to hold heat (like black or brown asphalt shingles). The suns energy is drawn to the roofing material and warms it to a temperature above ambient. The melt runs down the roof and refreezes when it contacts the colder gutter material. The ice builds up until it starts backing up the roof at the eaves. This type of ice damming can also do significant structural damage if not corrected.

All kinds of ice damming can be at least partially improved by installing proper soffit and ridge venting. This helps keep the roof surface more consistent in temperature and helps exhaust excessive moisture and heat rising from the living areas.

The best solution by far is to contact a contractor who is qualified to give advice on roofing, ventilation, insulation and the home as a complete “system”. Try to find a contractor who has a certificate from Green Builder College. This College has the best overall curriculum we have seen as pertaining to the home as a complete “system”. Every little change you make will affect other areas, and there is no “one” cause of ice damming, you could have several contributing factors.


These are the basic causes of ice damming. Most often a home with problems will end up have 2 or more causes. Your’s sounds like escaping heat is going to be at least part of the problem. The heat cables are not a «fix» as you mentioned, they are just a temporary patch.

When you had a new roof installed last year, did they do a tear-off? If so, code does require Ice & Water Shield to run up the roof to protect from ice damming. If you imagine a vertical line, 24 inches from the inside of the outside wall, project this line up to the roof surface, from this point down to the gutters should all be protected by Ice & Water Shield.

This is a moot point if they did not do a tear-off of the old roof.

QUESTION: Dan, thanks for your initial response. I had another roofing contractor come out as you suggested. He took a look up on my porch roof and thought the ice damming at the gutter was causing water to back up behind the fascia board and into the soffit, possibly even UNDER the ice and water shield. Does this make sense to you? By the way, I called the town inspector and the code here is 3 feet up. thanks

Roofing roof leak from ice dam, Ice dams, I&W shield


Sorry about the terribly slow response, I have been down with the flu for awhile.

The melt from ice dams can back up the roof quite a way. We had one home that had «leaks» up a mail valley. It turned out that a significant ice dam had pushed the melt up the valley about 7 foot! The I&W shield was 2 full rows and covered the lower 6 foot of the eave.

The point is that a roof that can be subject to ice damming must be thought out well as a complete system from the start. When doing additions or changes in roof lines, there are commonly areas that are subject to ice damming that were never originally intended to be.

We always use 2 rows of I&W shield on eaves, it will end up being 6 foot or 8 foot nominal width.

In areas that are expected to be problematic, we install very wide valleys, custom Crickets and Saddles. All these are made from the widest sheet of metal we can fit into the area. Then all the metal edges and seams are carefully sealed and taped.

It seems obvious to me that the roofer who installed your roof did not understand ice damming and how to protect your home from it.

The roofing in the problem area should be torn off up to the Ridge, the deck inspected for damage, then new roofing materials installed properly to handle the Ice Dams.

In areas that are expected to be problematic, we also tape the edges and seams of the I&W shield (I&W shield to I&W shield) with some kind of Butyl tape. The asphalt in the I&W shield doesn’t always seal well when cold. The Butyl products seal in any temperature and don’t break down much with age.

A building official misunderstanding the IRC code is quite common. But like I said, you measure in from the inside of the outside wall 24 inches, project this theoretical line up to the roof deck, this line must be sealed down to the drip edge.

On a typical Ranch with 12″ eaves and a 4L12 slope usually ends up being 4 foot.

In our area 8L12 and 10L12 are most common slopes. Eaves are most often 24 inches. You add these up and you end up with an an area requiring I&W shield protection of around 71-72 inches. This is the International Residential Code adopted by most areas.

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