This is the #1 Cause of Ice Dams According to Roofers

If you deal with ice dam issues on your roof each winter, it’s not because anything is wrong with your gutters or even the roof itself. In fact, the roof is most likely perectly fine. An  ice dam is actually the result of poor ventilation and insulation in your attic that's causing the snow on your roof to melt too quickly. We sought out several roofing experts to find out what homeowners can do to diagnose and prevent their ice dam dilemmas. 

What Causes Ice Dams?

Here’s what’s happening. Warm air in the living area escapes into the attic due to poor insulation and gaps in the attic floor. This warm air, coupled with poor ventilation in the attic, increases the temperature in the attic, melting the snow on the roof from the bottom layer up. As the snow melts, water runs down the roof. When that water hits the eaves which hover above cold air, it refreezes. That ice layer builds up, creating a dam that traps water behind it, leading to “leaks” in your roof. 

“The majority of the time this is an insulation or air sealing issue and not a roofing issue,” says Mike Feazel, CEO of Roof Maxx. “If your attic allows warm indoor air to rise and gather at the underside of the roof deck, you’ll get hot spots that prematurely melt snow.”

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How Can You Prevent Ice Dams?

To solve you ice dam issues, you‘ll need to determine if you’re dealing with poor attic ventilation, inadequate insulation or a combination of both. 

Poor Roof Ventilation 

Attics are supposed to breathe, according to Aaron Christy, CEO of Indy Roof and Restoration. Christy says home are designed so that air flows through the soffits in the overhang of the roof up through a vent in the ridge of the roof. “Roofs require a significant amount of air flow,” Christy says. “When the calculation is off, the attic will be a different temperature than the outside because it can't vent correctly.” Without good airflow, the attic gets warmer than the outside air, heating up the roof deck and causing the snow melt that leads to ice dams.

Here’s how to solve this issue:

• Check the soffits: go into the attic and check the soffits, the panels covering the underside of a roof’s overhang. Make sure they aren’t blocked by insulation or other material, so they can allow fresh air to flow into the attic.
  
• Check the ridge vent: examine the ridge vent, which runs along the ridgeline of the roof, to make sure there is an opening to allow air to flow out. You may need to get on the roof at some point to make sure it isn’t clogged from the outside.
  

Check your Insulation and gaps

Your attic floor should be well insulated to prevent heat from the living space from seeping into the attic and warming it up. “A lot of times thermal bypasses are the unseen culprits,” Feazel says. According to Feazel, openings around the pipes and wires and running through the floor, gaps around the attic hatch, recessed lighting cans, and bathroom fans can all allow warm air to seep into your attic. “Even very minor gaps in these areas can lead to big temperature swings that feed ice dam formation,” he says. 

• Check the insulation thickness: Inspect the insulation on the attic floor. It should be thick enough that you shouldn’t be able to see the floor joists. If you can see the joists, then you need to add insulation. If you live in a cold northern climate, install R-49 to R-60 insulation on the attic floor. Thinner R-38 insulation should suffice for southern climates.
  

• Recessed lighting: If you have recessed lighting that extends into the attic floor, there might be gaps around the cans that are allowing air to pass through. Examine the cans while standing in the attic. If you can see light from the room below through gaps around the cans, you have a significant leak. Feazel recommends using caulk or expanding foam to seal the gaps.
  
• Plumbing stacks and wire chases: Builders cut holes in the attic floor to run plumbing and wires up through the attic. These holes are often several inches larger in diameter than the pipes or wires running through them. Check for gaps and fill them with expanding spray foam or caulk.  

Pro Tip: When hunting for thermal bypasses, keep an eye out for patches of insulation that are gray or black. Insulation acts as a sort of air filter, blocking air that’s rising from the living space below. If there are any gaps under the insulation, changes in air pressure will pull that air up through that gap into the attic along with dust that’s in the air, creating gray or black areas in the insulation. If you see dirty insulation, pull it back to reveal the thermal bypass. 

• Attic Hatch: Check the weather stripping around the attic hatch. Turn a light on in the attic and close the hatch. If you can see light around the rim of the hatch, there’s a gap that’s allowing warm air to pass up into the attic. Replace the hatch’s weather stripping to seal this gap.