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Tuesday, December 10, 2013

Ice Dam Leaks are Caused by Bad Attic Ventilation

For no reason, for the first time, your roof leaked when it was covered with ice. You may think this is a normal occurrence just because of all the ice. But did you notice the leak occurred while it was still freezing? The roofing materials may be properly installed but lack of application of aerothermodynamics  to the entire roof system, which encompassing the living and breathing aspect of the roof and attic, has allowed your attic to heat up and melt the ice, which refreezes on the overhang, resulting in ice dams.

At a very technical training and certification program for roof mounted photovoltaic systems a fellow trainee stated that roofing was not rocket science. I begged to differ with him and then proceeded to go on an hour long, the short version, of Bernoulli as applied to the Venturi Effect. Not withstanding, the equations are not what is important to understand. Just accept the principle that air can be moved and if it is not, and it is near a heat source, it will become heated. Heat always goes where heat isn't and as no attic is perfect in containing climatized air, attic air become accelerated on a molecular level by the absorption of joules, BTU's or calories, depending on your field. These units then move into the roof and deck where the ice is melted. The resulting water then refreezes once past the warm wall and then enters your home, usually near the outside wall.

If a proper venturi had been established in your attic so that cold outside air could displace the warmed air, the freeze/thaw would not have happened. This vertical movement will not work if the exhaust vents are misplaced so as to short circuit this train of heat removal. In fact, lower exhaust vents actually become intake vents and will suck in snow and ice causing further damage.

The common misunderstanding amount the few educated roofing contractors is that the International Building Code, the governing body of law (code is law), requires the 300 Rule of Ventilation for roofs. The roof is required to add this so a roof is more than nailed on shingles. It is a comprehensive system.. Truth be told, if their is no vapor barrier between the sheetrock and the ceiling joists, the 150 Rule of Ventilation is the standard. I won't bore you with all the details as I've written extensively about this before.

The most important part is the roof leak caused by melting ice on a freezing day is just one symptom of an overall sick roof and home. Even the roofing manufacturers require the 300 Rule unless there is no straight bottom to top air/humidity exchange mechanism occurring. Then the 150 Rule kicks in.

If you actually believe that ice dam leak yesterday was bad, just wait until your roof and deck fails, which will cost you tens of thousands of dollars all at once. In the meantime increased utility usage, failed exterior paint, compressed insulation and childhood respiratory diseases and air condition system repairs and replacement will work their magic on your budget until the big one falls. Sure it might hail but your roof might fail in the next five years and that is when you get transferred or decide to move to a better school district. The home inspector will surprise you and the roof manufacturer will say that he told you so. 

You don't need to know all this. You just need to know that your leak is the result of a poorly designed balanced ventilation system. Or no design at all. Add a turbine, shut down your ventilation. Put on siding and don't remove the screened soffit vents, spray paint them shut, blow in insulation like a banshee on steroids with her eyes closed, or whatever poison you pick.

Your roof leak is only a symptom of much worse things to pass.

Jon Alan Wright
Jon Wright Roofing, Siding, and Windows
1915 Peters Rd., Suite 310
Irving, TX 75061
972.251.1818 Office
214.718.3748 Cell
972.554.8090 Fax
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