Reuben's Home Inspection Blog


Thinking of adding more insulation to your attic? Read this first.

If you're tired of dealing with ice dams and you've decided to finally get your attic re-insulated, please read this first.  You might save yourself a lot of time and money.

Over the past two months, a large portion of my business has been ice dam inspections in Minnesota.   For most of these inspections, I was hired to determine the cause of the ice dams and to recommend a solution.

I feel extremely fortunate to have spent the past two months doing this.  During this time, I've dug through a ridiculous amount of insulation in attics.   I've come home with itching arms, neck, cheeks, and red eyes (I'm pretty sure fiberglass insulation was invented by a very evil person).  Most importantly, I've learned quite a bit about attics.

I'd like to share the complaints I've heard from homeowners, what I've learned, and what I've recommended.  My goal is to help homeowners benefit from my experience.

What I've Heard

I had more insulation added to my attic after last winter, but the ice dams are just as bad as they were last year, if not worse!

I heard versions of this statement over and over from frustrated homeowners.  Just adding more insulation typically won't fix ice dam problems.  I'll come back to this.

I just had a new roof installed, and the roofer said they laid down a rubber membrane going six feet up.  Obviously my roofer is a liar, because if they really had laid down a rubber membrane like they said, my roof wouldn't be leaking.

I've heard so many versions of this!  The 'rubber membrane' that everyone refers to is actually an underlayment that's commonly referred to as an ice and water shield.  This underlayment is required by the Minnesota State Building Code; it must be installed underneath the shingles and "extend from the eave's edge to a point at least 24 inches inside the exterior wall line of the building."  This stuff comes in a three foot roll, and roofers usually have to lay down two layers of it to get 24" inside the exterior wall line, so it's usually six feet.

Ice and water shield will not prevent roof leakage from ice dams. Ice dams can cause leaks above the underlayment, or even right through the underlayment; I've seen it happen.  According to Certainteed, the manufacturer of Winterguard underlayment, it "provides your first line of defense."  It's not a guarantee against leaks.

If you have ice dams and your roof leaks during the winter, don't blame your roofer.  I can almost guarantee you that it has nothing to do with the way your roof was installed.

Why do I live in Minnesota?

This last weekend was a great reminder of why we live in Minnesota.  The temperature shoots up to 40 degrees and it feels like summer is around the corner.

What I've Learned

Gutters don't cause ice dams. Ok, I always knew this, but I've noticed plenty of ice dams with no gutters this year.  Ice dams will show up whether gutters are installed or not.  I mention this because I actually heard a 'professional' guest on a local radio show say that gutters cause ice dams, and that homes without gutters won't get ice dams.  I'm sorry, but that just ain't true.  You should have seen me 'calmly' disagreeing with my radio when I heard this.

Ice dam with no gutters 3

Ventilation has little to do with ice dams. I'm sure I'll get plenty of indignant feedback for this blasphemous statement.  I've always been taught that you won't get ice dams if you have enough ventilation, and I even used to preach this myself.  This is a concept that is deeply ingrained in the minds of contractors, roofers, and home inspectors everywhere.

Nevertheless, from all of the houses I've been to, I've seen little to no relationship between attic ventilation and ice dams.  Sure, attic ventilation is required.  Attic ventilation will help to cool the attic space, which helps to cool the roof decking, which helps to prevent snow melt, which helps to prevent ice dams... but this is a very small part of the equation.

The Minnesota Department of Commerce lists attic ventilation as a non-solution to ice dams.  TheUniversity of Minnesota Extension says that "only small amounts of roof ventilation are needed to maintain uniform roof surface temperatures."

Adding more ventilation probably won't change your ice dam problems.  Shoveling the snow off your roof vents probably won't change your ice dam problems.

Adding more insulation to your attic probably won't fix your ice dam problems. As I mentioned at the beginning of this blog, I've been to a ridiculous number of houses this winter where insulation was added, but the problems didn't go away.

If an attic lacks insulation, it's probably an older attic.  Not always, but usually.  If it's an older attic, it's pretty much a guarantee that there are attic bypasses present.  Attic bypasses are passageways for warm air to get in to the attic, and they're the driving force behind ice dams.  In almost every home that I inspected this winter, attic bypasses were at the root of the ice dams, regardless of how much insulation was present.  Through the use of an infrared camera, I've learned that insulation can't make up for air leakage.

It doesn't matter how much insulation is present in an attic; if there are air leaks, warm air will pass through traditional insulation.  The images below help to illustrate this; this was a very small attic bypass, but it still shows up plain as day through 14" of loose fill fiberglass and another 4" of cellulose on top of that.  I have hundreds of image sequences just like this.

Attic bypass

Recessed lights are huge contributors to ice dams. I recently wrote about this in another blog - Recessed Lights Are Evil.

What I've Recommended

I've recommended the same thing over and over; seal the attic bypasses.  They're the main cause of the ice dams.  When insulation has already been added to an attic space, this becomes an extremely difficult, if not impossible chore.  To access and seal the attic bypasses, you first need to know where they are.  When they're buried under one to two feet of insulation... forget it.

An experienced insulation contractor might be good enough at their job to know where to look for most of the attic bypasses, and could spend their time digging through the insulation to find most of them, but without completely removing the existing insulation, there is no way to seal all of them.

In most cases, I've told homeowners that they can hire an experienced insulation contractor to seal up all of the attic bypasses that they can find, and to keep their fingers crossed.  This willprobably be enough to prevent leakage from ice dams again, and it will be a good repair, but not complete.  For a complete repair, all of the existing insulation needs to be removed so all of the attic bypasses can be located and sealed.

If you're going to have insulation added to your attic, be sure to seal the attic bypasses first.

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 21 commentsReuben Saltzman • February 15 2011 05:52AM


Geez Reubs!  Go to bed!  I mean, hey, great blog!  You are right about those pesky bypasses.

Solution?  Dryer lint!  Yep, each time you clean that dryer screen, place it carefully around any of your bypasses.  When done you will notice a huge difference in the ice dam problem.

So, take your dam lint, put it around the dam bypasses to stop the dam heat from escaping from the dam living space into the dam attic causing the dam snow (when it melts when the dam summer comes at 40F) to melt and refreeze into dam ice.  It's the dryer lint that's damming the dams my friend!

R-value of dryer lint?  2.4/inch.  That should be dam accurate.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

Very interesting, I had not heard or read of bypasses and I was SURE gutters played a part.  Good information, thank you.

Posted by Brin Realty Associates Team At Bean Group, Amherst NH homes and Southern NH real estate (Bean Group | Brin Realty Associates) over 8 years ago

Jay - dryer lint, huh?  That sounds like a dam good idea!  I wonder how Billie Jays would sell that...

Rene - thanks, it seems that attic bypasses are a foriegn word to most homeowners.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Wow, I had No idea! The more I learn, the more inclined I am to have a home inspection on my own home. I am glad that we don't have those ice dams.

Posted by Renée Montgomery, Northern Virginia Real Estate (Century 21 New Millennium) over 8 years ago

Reuben, Great info!  We've heard of ice dams causing damage here, so always good to have more knowledge on the problem.

Posted by Liz and Bill Spear, RE/MAX Elite Warren County OH (Cincinnati/Dayton) (RE/MAX Elite 513.520.5305 over 8 years ago

Renee - I'm glad you don't have to deal with them too!

Liz and Bill - if you know of anyone trying to fix their problems, please pass this along.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

Hi Reuben - Thanks - this is really clear an well-written. I understand quite a bit more now about ice dams and what causes them. I hit Suggest.

Posted by Judy Klem, Home Staging, Senior Move Management, Fairfield/New Haven counties (Transition Stage LLC) over 8 years ago

Hi Reuben, lots of info, great post.

Clint McKie

Posted by Clint Mckie, Desert Sun Home, Comm. Inspection 1-575-706-5586 (Desert Sun Home, commercial Inspections) over 8 years ago

Hi Reuben,

Another great post to illustrate there is more than one way to create an ice dam. Just when it seems to make sense to live in the South and avoid all this, we have a winter like this one where everyone takes a chilly hit.

Posted by John McCarthy, Realtor - Seacoast NH (Bean Group Portsmouth NH) over 8 years ago


Excellent information. We have a lot of cold weather and ice in Canada too.


Posted by Brian Madigan, LL.B., Broker (RE/MAX West Realty Inc., Brokerage (Toronto)) over 8 years ago

Wow, I've never even heard of ice dams.  Impressive blog.

Posted by Wade Mattingly (WEICHERT Realtors--Bluegrass Living) over 8 years ago

Another great post Reuben. As inspectors we have to remind ourselves that the public doesn't know what we know. We see it all the time, sometimes daily. Myths = mistakes.

I liked Jay's 'dam' dryer lint. Navel lint would work in a pinch.

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) over 8 years ago

I have seen it!  Many times actually!

Oh, that roof you are on in your avatar is too steep to be playing on.  I fell off of one 14 years ago and shattered everything on the left side on the deck below.  Still a big, big problem.

Don't think it can't happen to you.  I was running marathons at the time and in great shape.  One slight mishap and boom.

LOVE Robert's pinch comment!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

Reuben, nice summary.  I've been following your writing about this during this winter and found the topic extremely interesting.

Maybe the could remove all the insulation and spray in icynene that Jay talked about in his blog?  It seemed to keep a great seal on the heat transfer, and I'm sure would effectively close all attic bypasses.

Which reminds me, attic bypass sounds like a road around the heavily trafficked attic.  :D

Posted by Jeremy Wrenn, C.O.O., Winslow Homes (Winslow Homes) over 8 years ago

Reuben, right on---stopping air movement is key---and of course inadequate insulation coverage/thickness.  This can be very difficult in older homes and mismanaged in newer homes.  Something as simple as missing insulation and weather-stripping on attic access hatches can be huge.  That said the "type" of insulation is important to.  Batt type insulation should flat out not be allowed in attics in my opinion and using types that eliminate air movement is essential.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 8 years ago

Uninsulated top plates which you will find in almost every home I believe are one of the biggest contributers to this problem.

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 8 years ago

Judy - thanks! I'm glad I could help.

Clint - thank you.

John - this has been one nasty winter, hasn't it?

Brian - the problems with ice and snow have gotta be worse for you than me :)

Wade - I hope you never have to deal with this stuff.

Robert - navel lint, ha!  Pocket lint would probably work too.

Jay - don't worry, I wasn't playing on that roof; I was carefully perched atop a ridge.  I know it could happen to me, and I'm always very careful.  I find myself taking less and less risks.

Jeremy - thanks.  I know you guys had some ridiculous snow this year.

Charles - I completely agree with you, fiberglass batts are garbage.  They cost more, they do a terrible job of insulating, they're impossible to install right... what's the benefit?  

James - agreed.  Foaming the tops of wall plates on older houses is definitely the best way to go.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago

What Jim said!  Spoken like a true thermographer!  Until IR nobody really saw how much heat loss comes from there!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 8 years ago

Jay - exactly.  That's the one area in an attic where soffit vents are pretty good at masking the effects of heat loss.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago


Great blog and comments from the big boys of inspection biz. Love the lint idea.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 8 years ago

Thanks Donald.  The dryer lint is all about being green.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 8 years ago