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The Root Cause of Ice Dams

21 February 2019

An ice dam is a sheet of ice that manifests itself on a roof edge.  Instead of allowing the melting snow to filter off the roof, the sheet of ice backs up onto the roof, underneath the shingles, into the soffits, and eventually into the interior of the home causing water damage.  One misconception about ice dams is that they are caused by gutters.  In actuality, ice dams are the result of inconsistent roof temperatures.  Here are a few ways that can happen.

Inadequate Attic Insulation

The primary cause of hot spots on the roof is heat loss from the home.  Over time, it is possible for attic insulation to settle, compromising the insulation’s R-value.  In addition, insulation that has become wet from thawing attic frost does little to protect your home.insulation

Attic Air Sealing is Needed

It’s astonishing how many homeowners have never seen their attic’s interior.  Therefore, it should come as no surprise that air gaps in an attic can easily go undetected.  Popular spots include areas surrounding roof penetrations and can lights.  These spots allow warm air to escape and come in contact with the cold exterior air, causing the formation of an ice dam.

Subpar Attic Ventilation

Attic ventilation that allows for the open circulation of air underneath a roof can offset temperature discrepancies, making it an effective method for warding off ice dam formation.  The majority of attics are constructed to consider that heat rises throughout a home.  Clogged or missing soffit vents create the perfect environment for ice dams because the roof becomes warmed by the home’s interior air.  Attic ventilation also acts as an ice dam preventative because it can curtail roof air temperature variations that naturally occur due to sunlight hitting the dam

Your Chimney

Routine use of a wood stove or fireplace create a scenario where heat is relocated from the chimney to a home’s attic.  Poorly insulated or cracked ductwork in an attic creates a source of heat.  The heat flows outward and causes variable roof temperatures, leading to the creation of an ice dam.

Exhaust Fans

Many historic homes have bath or kitchen exhaust fans that blow warm, humid air into a home’s attic instead of outdoors.  This creates an environment for warm spots to form.  In addition, moist air can compromise the integrity of the attic’s insulation.  Exhaust fans should be run at length while cooking and during and after shower use.

How to Pinpoint Home Ice Dam Issues

Beware of any contractor that blindly proposes adding more insulation to stop the formation of ice dams a home.  Thermal imaging and blower door testing allow a contractor to understand where and why warm air is escaping.  With this information, they can put together a customized plan that addresses the root cause(s) of a home’s ice dam issues.

Here’s How Blower Door Testing Can Determine Where Your Home is Leaking Energy: 

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