Why is roof leaking?

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Posted by: from Montreal
3/5/2015 at 3:39:18 PM


The roof of my house has small leaking because of ice dam buildup in winter and early spring. There is no leaking during heavy rain in summer. A roofing company came twice to put membrance under shingles, but fails to stop leaking.

I think the reasons that the membrane doesn't work:

A. not properly installed. Some shingles not removed before put membrane on roof deck;

B. Quality of Membrane not good, water filter through the nail. Due to the structure of roof, prevent the formation of ice-dam is not able to be done completely.

I put up heating cables. They did reduce the leaking significantly but not completely. I wonder whether two or more layers of ice-water membrane can be installed under shingles or a torch-down roof can stop ice-dam leaking.

Any suggestions are welcomed.

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Date/Time3/5/2015 at 4:06:31 PM

An ice and water shield membraine is used in case you have occasional ice build up, it does not prevent the cause of the ice in the first place. Which is what you should be addressing.

The ice builds up because of heat escaping from the house into the attic and not enough ventilation to remove it from the attic.

The whole attic needs to be the same temperature as outside.

First you need good insulation to keep the heat in the house and out of the attic.

Second you need proper ventilation in the attic from the eaves all the way to the peak of the roof to remove any heat and moisture.

Until you fix the cause of the problem your membraine it's going to fail.

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Date/Time3/5/2015 at 4:58:58 PM


As James mentioned, this would be my first suggestion (the insulation and venting). Many think that a warm attic will melt the snow and do wonderous things, just the opposite. The actual leaks may be the result of many factors some of which you have described. The leak may even be higher up on your roof. Water tends to follow it's easiest course which may begin anywhere and simply follow a seam in the sheathing or a truss down to where the water accumulates and then drips. So, it may be as you think, the ice guard, but it may also be something entirely different.

I'd suggest you inspect the attic to see if you can determine the actual source and go from there. I would also suggest that you NOT do a bandaid solution as you probably won't be happy in the long run.

What I do when I re cover a roof it to use something like Tyvek -Roofing or another synthetic membrane. The old way of using 15# building paper (tar paper) still works but the newer products appear to be better protection and the clain is that the material actually seals around the nails as the new shingles are applied. If you get to that stage (of stripping of the old) be sure to check and replace and broken or mouldy sheathing.

Sorry for you issues, but I wouldn't be too quick to accuse the last installer.

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David in Montreal
Date/Time3/9/2015 at 10:26:24 AM


Thanks for your advice. The leaking happens at the ends of long deep valleys, about 6-9 feet from the bottom. Improvement of insulation and ventilation already be done, but not able to solve the problem. The membrane installed under shingle was ice-water membrane, told by the roofer, supposed to prevent leaking from nails, but failed. I noticed that when the membrane was installed, the old shingles were not completely removed. That might be the reason.

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Date/Time3/15/2015 at 8:13:20 PM

As per the 1st post it is the most accurate response, hope your issue gets resolve and does not cause you more grief.

Why is roof leaking?

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