Home Repair

Do I have Ice Dams? What is an Ice Dam?

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Hey there Guru,

I have had my roof replaced about a year ago and it has started to leak. It didn't leak all summer even with all that rain we had. It has started this winter during a cold spell. The water has come in at the wall facing the street under the gutter. Now the ceiling and wall is stained too.

Should I call back or look for a new roofer?
How do I even find the leak?

Someone told me that I might have a nice dam. After a wondering for a few minutes, I realized he said I might have an Ice Dam. What is that?

Thanks for any help
Well it most likely isn't the roofers fault, but then again it could be. You would need to tell me the roof pitch and wether or not your roofer used a rubber bitithane bituminous membrane for the first 3 feet going up the roof and in any valleys.

Then I will give you a lesson on ICE DAMS. That is what most likely caused your problem.
The roofer only used 15 pound felt on the roof under the shingles.
There are no valleys.
And the roof pitch is about '6' I was told. (What does 6 mean?)

Thanks for the help!
Ahhh here is the problem... 15 lb felt is OK for the upper areas but the area just above the gutter needs special attention. The 6 pitch also called 6 in 12 is fine for shingle roofs. Generally, 4 pitch and higher is OK. The '6' means there is 6" of rise in the roof for each foot of run. So if you measured 12' from the bottom edge of the roof straight back (not up the roof but level with the ground) then the roof surface will be 6' straight up. And now for the ice dam question...

Roofs depend on gravity to keep water from penetrating your house. Here’s how it all works.

Shingles (asphalt or fiberglass), slate, tile, etc. are installed in the same way. They are individual pieces which overlap so as to shed water to the next lower one. Roofers begin installing these materials at the bottom of your roof (where the gutter or eves trough would be) and continue up the roof putting the next piece of roofing material on top of the one below. The steeper pitch your roof, the better this system works.

However, if water flows backwards up your roof and gets underneath and behind the individual roofing pieces, you will have leaks. An Ice dams could cause this to happen. An Ice Dam is caused when heat from the sun, or heat leaking from your house causes the snow on your roof to begin to melt. This melt water travels beneath the snow towards the gutter. The temperature of the overhang and gutter is below freezing. The water hits the cold overhang or metal gutter and instantly freezes.

Within a short period of time, the gutter is solid ice and the ice is beginning to grow up the roof on top of the overhang. Eventually, the water hits this ice dam and puddles. Before it can freeze, it flows underneath the pieces of roofing and leaks into your house.

You cannot easily stop ice dams from forming. However, you can do several things to minimize the possibility of leaking. If you are building a new house, consider building large roof overhangs and have your builder use trusses or roof rafters with high heel cuts. This allows insulation to be placed at full depth where the roof passes over exterior walls. Standard trusses or framing can reduce ceiling insulation in these areas to as little as three inches.

If you have an existing home, or even in new construction I recommend installing specialized roofing products designed specifically to combat water buildup from ice dams. These products are manufactured using modified asphalt and rubber bitithane bituminous membrane. They are applied (self adhesive peel and stick) directly to the wood sheathing just above your gutter line. Your regular roofing material is then applied directly over these products. This membrane is self sealing so when a roof nail penetrates during the roofing installation the membrane seals around every nail. The water from an ice dam will still back up under the roofing materials, but it can’t get through the membrane and into your home.

These specialized roof membranes form a barrier which resists water infiltration. If this rubber bitithane bituminous membrane is used at the edges of roofs, in valleys, for 18” around skylights, chimneys, etc., your roof should resist all but the worst ice dam.

Here are some common manufacturers of modified asphalt and rubber bitithane bituminous membrane

GAF Materials Corporation - “Weather Watch Ice & Water Barrier”
W. R. Grace & Co. - “Ice and Water Shield”
Johns Manville – “JM Ice and Water Guard” “RS 4740”
Bakor – “Eaveguard”


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