How to Fix Ice Dam Roof Leaks

Unfortunately, for many, ice dams and the related water  leakage problems are an unwelcome wintertime tradition here in New England. We’ll soon see fall colors turn to bare branches and ice dam season will be upon us again – so what better time to write about how to fix ice dam roof leaks!

You might think that after all these years and all these people getting their houses ruined on a semi-regular basis that we’d have figured out how to resolve ice dam leaks in a reliable way. The good news is that many of us do know how to fix ice dam roof leaks. But there’s still a lot of confusion out there.

So this post is meant to help un-confuse things. Here, in simple terms, is what you need to know about fixing ice dam roof leaks.

What is an ice dam?

An ice dam is ice that forms near the bottom of a sloped roof and blocks water from draining over the roof edge. Just like a dam in a river – it’s an obstacle that keeps water from going where it otherwise would want to go.

Ice dams are usually pretty easy to spot. Big mounds of ice at roof eaves are a dead giveaway. So are giant icicles1. So is water pouring into your living room a day or two after a big snow storm.

How do ice dams form?

Ice dams form as a result of snow on the roof melting and then re-freezing at the eave.

There are lots of great diagrams of the ice dam phenomenon scattered around the Internet. Here is one.

Basically the roof gets too hot and the snow melts. This is mostly the result of heat from inside the house that moves through the roof and melts the snow, which then flows as water downhill to the eave. When the eave is outside of the exterior wall, it is cold (no heat from below) and the water freezes again.

Photo by Amber Kipp on Unsplash

Why do ice dams cause roof leaks?

A roof that works great during torrential rain may leak like a sieve during ice dam conditions. Why?

Most steep sloped roofs are built like rain coats – not submarines.

A major component of steep sloped roofing that often (inexplicably) goes unnoticed is… the steep slope. The slope is crucial to the roof’s performance.

If the slope is removed, or if it’s exposed to conditions that are just like if the slope was removed, then a crucial element of the roof’s defense against the weather has been compromised.

Low sloped roofs (like on top of your favorite big box store) are often exposed to “ponding water” – i.e. standing water that stays on the roof for a long time. No one likes this but it happens a lot and low sloped roofing materials are (usually) able to deal with it pretty well.

But if a steep sloped roof is exposed to ponding water (like when a big chunk of ice blocks the drainage path) then we need to take some additional steps to make that steep sloped roof perform more like a low sloped roof.

Think of a rain coat. A rain coat keeps you dry when you’re standing in the rain. But what if you jump in the ocean?

When water backs up due to an ice dam blocking drainage, most steep slope roofing is about as effective as a rain coat in the ocean.

What we need for the ocean is a submarine.

How to stop ice dam roof leaks

Ok, you’ve read this far (or maybe jumped ahead) and here’s what you’ve been waiting for: how to stop ice dam roof leaks.

Solving ice dam leak problems boils down to two things:

  1. stop ice dams from forming
  2. keep the water out when ice dams do form

Simple right?

How do we stop ice dams from forming, and how do we keep the water out when ice dams do form?

Read on…

Stop Ice Dams From Forming

To stop ice dams from forming we need to keep the roof cold. There are several key strategies2 to keeping the roof cold, including:

  • improve ventilation
  • improve insulation
  • improve air sealing
  • eliminate heat sources

In an ideal world every steep sloped roof would have ample ventilation and ample insulation. In the real world one or both is often constrained. So it’s usually a process of trying to improve each to the greatest extent practical. Adding insulation and improving ventilation are cornerstones of fixing ice dam leaks.

A less-often talked about component to solving ice dam leaks is reducing air leakage. Uncontrolled air leakage from conditioned parts of a home into places that are supposed to be unconditioned can short circuit the best intended blanket of insulation.

Heat sources in the attic (like ducts or furnaces) are also problematic. Just don’t do it. If they’re already there, you probably want to make the attic “indoors” and stop trying to roll the boulder uphill.

This business of indoors and outdoors is important. Understanding where the line is between indoors and outdoors is critical to properly implementing the strategies above.

Stop Roof Leaks

You can do everything described above to stop ice dams from forming and there will still come a day, if you live in a cold climate, that ice dams will be there. Nature is persistent.

So, when ice dams form, the roof needs to be ready to keep the water out.

Folks have written about how to do this. Basically: build it like a submarine, not a rain coat (i.e. make it waterproof). Use good quality self-adhering membrane underlayment, use the right amount of it, and install it carefully.

Ready for More?

This post is about 1,000 words… all about ice dams… and we’re barely scratching the surface. Want to learn more? Let me know what questions you have in the comments below. I’d love to address your question in a future post.

If you’re struggling with ice dam roof leaks at a property you own or manage – give me a shout. I’d love to help.

  1. Like the two houses pictured in this post (red house photo by NeONBRAND on Unsplash and white house photo by Amber Kipp on Unsplash). 


  1. For the purposes of this post, I’m not going to differentiate between traditional vented attics and “compact” roof assemblies where the ceiling is installed directly to the bottom of the roof. While the specific tactics to reduce ice dam formation vary between these types of systems, the strategies are generally the same. We can talk more about tactics in a future post. 

Leave a Reply