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Ice Dam Prevention Tip: Check Your Exhaust Fans

Your home probably has an exhaust fan in every single bathroom, possibly in your kitchen and other rooms as well.  If you are interested in preventing ice dams, check to see where those exhaust fans are venting.

Often you’ll find those fans venting straight into the attic.  Maybe the person who built your home cut a corner, or maybe the previous homeowner was an overly ambitious DIY type who didn’t really know what he was doing.

Either way, you’ve got a problem.  The exhaust fans are now forming easy-access points for hot air to rise (or be forced) into your attic.  When these exhaust fans are turned ON, they blow hot air straight into your attic – which is exactly what ice dams need to form on your warmed-up roof.  When these exhaust fans are turned OFF, warm air simply rises through these voids naturally.

As we’ve discussed in previous articles, hot attics help ice dams form by bringing the surface temperature of the roof above freezing.  If you didn’t have a freezing-cold overhang at the end of that road, you’d never have a problem.  But you do have a cold overhang, and as a result, ice dams tend to form.

Flip on your bathroom fan (or whatever exhaust fans you’ve got), and then head up into your attic with a flashlight to see if you can spot where it’s venting.

If you find an exhaust fan venting directly into your attic you need to call a contractor to extend the ventilation shaft up through your roof.  Make sure they install a ventilation hood and shield it from leaks with flashing, and not just with caulking. 

Of course, ideally you’d seal up every attic bypass, increase attic ventilation, and revamp your insulation while you’re at it.  But if this is the only improvement you make this year you may still see a significant decrease in your ice dam risk.

Note: correcting this problem of improperly installed exhaust vents will not make your home “ice-dam-proof.”  It will however decrease your likelihood of getting ice dams. To an extent, ice dam formation is a game of chance we play with Mother Nature every winter.  If you combine proper exhaust-venting with regularly raking your roof, you’ll improve your chances of coming into spring smelling like a rose.







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