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Ice Dams

By In Ice Dams On February 11, 2014

I’ve been seeing ice dams all over the Twin Cities, and I’ve heard from a number of homeowners who are having problems with ice dams right now.  I’ve written about ice dams extensively on this blog, so I’m putting together links to my three main blog posts on ice dams in one place.  The topics are how to prevent ice dams the right way, how to prevent ice dams from the outside if you can’t prevent them the right way, and how to get rid of ice dams.  I also have few more ice dam observations; file these under “advanced ice dam prevention”.

How To Prevent Ice Dams (the right way)

Ice dams form when snow is melted on the roof, then freezes again at the eaves.  The main reason the snow melts is because heat is getting to the roof decking from the house.  Stop the heat transfer, and you’ll probably stop the ice dams.  The main way to stop the heat transfer is to have air sealing performed in the attic.  The next step is to have insufficient insulation addressed.  Finally, if venting is improper, consider fixing it… but venting only plays a small role.  Ice dams are mostly about air leaks and insufficient insulation.  Click this link for more information about preventing ice dams the right way.

Anatomy of an ice dam

How To Prevent Ice Dams from the Exterior

Roof RakeIf you live in a 1-1/2 story home in Minnesota, you probably get ice dams.  There’s not much that can be done to prevent ice dams the right way at this style of house, short of gutting the upper level and framing down, or tearing the roof off and framing up.   Homes with vaulted ceilings and other inaccessible attic spaces can also be a real challenge.  In these cases, ice dams may need to be controlled from the exterior.  The standard way to do this is to get a roof rake and pull snow off the roof.  When this is not practical, roof de-icing cables can be used, but should be considered a last resort.  Click this link for more information about preventing ice dams from the exterior.

How To Remove Ice Dams (hire a pro)

There are plenty of hack methods for removing ice dams, so I tried ’em all out.  The methods I discuss involve an axe, ice pick, pantyhose, salt tablets, heat cables, a pressure washer, and even a blowtorch… just for fun.  I don’t recommend any of these though.  If ice dams need to be removed, hire a pro to steam them off.  Don’t let anyone near your roof with a pressure washer, or the shingles might end up like the ones shown below.

Hack Ice Dam Removal from pressure washer

Click this link for more information about how to remove ice dams.

A Few More Tips

Here are a few more tips on preventing ice dams.  These deal more with the design of a house than anything else.

Valleys Can’t Be Vented

Ventilation plays a small role when it comes to preventing ice dams, because vents can help to cool the roof temperature.  The problem with roof valleys is that they can’t be vented.  If I were to design my own house, it would certainly be a big boring box with a plain hip roof; no valleys.

Plain hip roof

Plain hip roof

Valleys Should Never Meet

Valleys can’t be vented, they have a lower slope than pitched roofs, and ice from two roof surfaces gets concentrated.  Ice dams are always the worst at valleys.  What happens when two valleys meet each other?  The potential for ice dams goes way up.  In my humble opinion, this is just plain stupid design when it comes to performance.

Valleys Meeting

Oh, and don’t get me started on what this means for water management during the summer… never mind, I already blogged about that: Have Your Builder Plan for Water Management.

Don’t vent fans through the roof

What happens when bath fans and kitchen fans terminate at the roof?  Snow melts when the fans run, of course.  This leads to water running down underneath the snow, then freezing again at the eave, or in some cases, right in the middle of the roof.

Bath fans at roof with ice dam

This can be a major contributor to ice dams, or in the case of the photo above, can be the sole cause of ice dams.  The way to avoid this is to have bath fans and kitchen fans terminate at walls, not roofs.  This also applies to clothes dryers; while it has become standard practice to put laundry rooms on the second floor in new construction homes and terminate the vent at the roof, I think this is a bad place to terminate the dryer duct.  It will melt a lot of snow, and there is usually no easy way to clean off the terminal.

Oh, and whatever you do, don’t place vent terminals for bath fans, kitchen fans, or clothes dryers in a place where the melted snow will pile up in a valley.  That’s almost a sure way to get ice dams, even if everything else is done properly.

Author: Reuben Saltzman, Structure Tech Home Inspections



About the Author


Reuben is a second generation home inspector with a passion for his work. He grew up remodeling homes and learning about carpentry since he was old enough to hold a hammer. Reuben has worked for Structure Tech since it was purchased by Neil in 1997, and is now co-owner and President of the company.


  • Bob Bylin, P.E. 3 YEARS AGO

    I have ME degrees from Iowa State and Stanford(MSME) and have studied snow accumulation on roof and problems with snow slides, ice dams and icicles for over 20 years. Bylin Engineered Systems has developed engineered retro-fit solutions for existing residential and commercial building roof problems. Over 9000 successful solutions to icicle/ice dam problems. Our local rep is Ron Faulkner -- 952-446-5574

  • Tara 3 YEARS AGO

    We live in a 1919, 1.5 story craftsman bungalo style home where the upstairs was converted into a bedroom. We purchaed the home in October 2013 and a brand new roof was installed with ridge venting. We got terrible ice dams this winter with one causing a leak. Because there is no longer an "attic" upstairs how can we prevent the ice dams?? Would re-insulating with a closed-cell spray foam help?

    • Reuben Saltzman 3 YEARS AGO

      @Tara - you can prevent the ice dams by removing snow from your roof. http://www.structuretech1.com/2013/03/how-to-prevent-ice-dams-from-the-exterior/ Sure, re-insulating with a closed-cell spray foam would help, but you'll probably need to gut the upper level and change your roof to hot roof. You'll need to frame out the old 2x4s as well, because the cavity provided by 2x4s isn't enough. It's a huge project. Most people decide it's easier to just pull the snow off the roof. http://www.structuretech1.com/2010/05/one-and-one-half-story-houses/

  • Mark 3 YEARS AGO

    Reuben - What are the best options to air seal the attic space? Seems like it would be to remove the existing insulation and put down an inch or two of foam everywhere and then insulate on top. Others?

  • Rachel 3 YEARS AGO

    Reuben, thank you..(last) follow up question. Would a poor roofing job make it easier for water to enter the house if we did have ice dams (now we know that are not caused by roofing repairs) TIA!!

    • Reuben Saltzman 3 YEARS AGO

      @Rachel - if eave protection (ice & water shield) wasn't installed, it would certainly make it easier for ice dams to cause leakage, but installing the ice shield is a very basic requirement that all roofers know about. It's not too likely that your roofer forgot to do this.

  • Rachel 3 YEARS AGO

    Last year we had our roof replaced due to some hail and storm damage, now this year we have water damage in an area we've never had water leaking prior to the roof being replaced. Can ice dams form from a poorly done roofing job? There is no attic over nor vent(s) in this area.

    • Reuben Saltzman 3 YEARS AGO

      @Rachel - No, a bad roofing job won't cause ice dams.

  • John 3 YEARS AGO

    I have a fourplex with a flat, gently sloping roof towards the rear of the building. There is about 2 feet of snow over the entire roof. Across the back 10 feet of the building is the back staircase. The gutter is frozen solid and there are a couple of leaks when it gets warmer. I am thinking if the gutter wasn't there, all across the back, the ice wouldn't build up on the back 10 feet of the building. What should I do?

    • Reuben Saltzman 3 YEARS AGO

      @John - I recommend fixing what's causing the snow to melt.

  • Nervous Cat 3 YEARS AGO

    Got any advice for condo owners regarding ice dams? We have no control over the exterior maintenance.

    • Reuben Saltzman 3 YEARS AGO

      @Nervous Cat - the advice is all the same. If your association isn't doing anything about it, make some noise.

  • Shahna 3 YEARS AGO

    @Reuben. Thanks for the link to your posting about weight of accumulated snow on the roof. That is exactly what I was looking for! We have problems with ice dams too, even after better insulation (one reason to hate cathedral ceilings and barely 10" of attic space to work with), but thanks to your tips we've been able to keep them under control.

  • Greg 3 YEARS AGO

    Reuben, Thanks for the follow-up. I was wondering how a steel roof would help against ice dams. I know it would keep water from backing up through the roof, since there's no shingles for water to sneak back underneath. However, would the roof also help keep the ice from even piling up along the edges?

    • Reuben Saltzman 3 YEARS AGO

      @Greg - the main purpose of the steel roof would be to prevent water leakage, but like you said, it could also help to prevent the formation of ice dams in the first place, because it's much easier for snow to slide off.

  • Shahna 3 YEARS AGO

    Can you comment on when it's time to remove snow from roofs? We have 2 foot drifts on one side of our roof (4/12 pitch) and about 1 foot deep snow on the other side. With the warmer temperatures coming, I heard on the news this morning that it won't necessarily get rid of any of the snow, just make it compact more. And there is more snow forecast for Thursday. Thanks!

  • Greg 3 YEARS AGO

    Reuben, Thanks for another informative and interesting post. I really enjoy them. My newly purchased (September of 2013) 1940s home has had multiple additions and as a result the roofline has a couple of valleys that meet at different angles. I have already had to contact Mr. Kuhl's company regarding ice dam issues and the resulting need for better insulation. Beyond being totally screwed or doing a completely new roof to fix this, are there any other tips or products that can help those of us afflicted with these valleys? Is there a particular roof rake that may be helpful? How about a product like the IceFree Valley Panel from some company called Engineered Roof Deicing?

    • Reuben Saltzman 3 YEARS AGO

      @Greg - I hadn't even seen the IceFree Valley Panel until I googled it. Looks like a neat product. I've seen a number of similar roof de-icing products; they all work the same way. The one thing I didn't mention as an option would be to have a waterproof material installed at the roof, such as an epdm membrane or a steel roof. Those are very effective.



    • Reuben Saltzman 3 YEARS AGO

      No, insulation should only be applied to the ceiling. The only time insulation should be applied directly to the underside of a roof deck is when it's a hot roof, and in those cases, it gets tricky.

  • Nicholas 3 YEARS AGO

    I see that you recommend not venting through the roof of a house. How would you recommend installing exhaust fans in a house with a hip roof?

    • Reuben Saltzman 3 YEARS AGO

      Great question. I'd still vent the fans through the roof; while it's preferable to vent the fans through the sidewall, it's not terrible to vent fans through the roof.