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  • Writer's pictureCameron Home Inspections

All About Ice Dams

Updated: Feb 20, 2023

If your home is located in a climate with cold winters and snow, you likely have heard of, or maybe even experienced, an ice dam. This combination of snow, heat, melting and re-freezing can cause a blockage near the edge of the roof as depicted below. Ice dams often lead to moisture intrusion into the roof structure and attic, and depending on the severity of the leak, can cause water damage to insulation and even the ceilings or walls within your home.

How do ice dams form?

When warm air leaks out of the conditioned building envelope into an unconditioned attic, that heat melts some of the snow that has accumulated on the roof. The resulting water then flows down and re-freezes at the colder edge of the roof, creating a damming effect. As more snow melts above, water continues to pool at the dam and can seep through the roofing material underneath.

Energy Star diagram of a building envelope

Warm air generally escapes into the attic due to insufficient insulation. Other common heat transfer paths are the various openings in the ceiling such as light fixtures, plumbing vents, ducting, and attic hatches. The examples below were identified with a thermal camera and illustrate a few of these problem areas that are relatively easy to fix!

Where do ice dams form?

Roof valley areas are particularly susceptible to ice damming as they direct the most water to the dam below. In the following example, this large dam formed at the base of a valley. It caused significant moisture intrusion which led to mold growth in the attic and water damage in the ceiling and wall below.

When ice dams form at the edge of the roof like in the following example, their weight can damage gutters. The moisture intrusion problem can be seen as the fascia, rafter tails, and lower areas of roof decking are all wet from this dam.

Insulation depth

Both ice dam examples above indicate that each attic lacked sufficient insulation and more than likely, the roof system was missing an appropriate ice and water membrane. Depending on your climate zone, a minimum depth of insulation should be achieved. This R-value correlates to the insulation's ability to resist heat transfer. The following image also depicts insufficient insulation.

Insufficient attic insulation that can lead to heat loss

Here in Montana (Climate Zone 6), the minimum required R-value in an attic is 49. This equates to an insulation depth of approximately 16", but different types of insulation have unique R-values which may require more or less material.

Energy Star diagram of Climate Zones and insulation requirements

Blower door test, thermal imaging, and air sealing

Another part of the heat transfer solution is to seal any gaps or openings around various ceiling penetrations with caulking, spray foam, or rigid foam board depending on the area. To quickly locate these leaking spots, a contractor can perform a blower door test in which a specialized fan and gauge are used to create a pressure differential between the inside and outside of the home. A thermal camera is often used to quickly pinpoint these areas which can then be sealed. The example below shows the cold air being sucked into the home through an unsealed light fixture - this is also where warm air escapes into the attic and can contribute to an ice dam.

The Family Handyman sealing holes in an attic with caulking and spray foam

Fixing air leaks and ensuring adequate attic insulation will have an appreciable impact on minimizing ice dams, and can also really help lower utility costs as the conditioned areas in your home don't lose as much heat as they did before. Interested in a blower door test, thermal scan, and actionable plan to help mitigate your attic's heat loss in Western Montana? Send me a message and I'll put you in touch with the local pros!

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-Jonathan 406-306-1331 ASHI #265859

ICA #18243

ITC #273199 *The views and opinions expressed in this blog are those of the author and do not necessarily reflect the official policy or position of any other agency, organization, employer or company.

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