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.

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.

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.