Reuben's Home Inspection Blog

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

February 15th, 2011 | 9 comments

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.  The University 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 either.

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 will probably 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 - EmailMaple Grove Home Inspections

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9 responses to “Thinking of adding more insulation to your attic? Read this first.”

  1. Jenn
    February 18, 2011, 2:26 pm

    We just had all of our insulation removed and the whole attic foamed. Will that seal everything?

  2. Reuben Saltzman
    February 18, 2011, 4:39 pm

    Jenn – yes, foam insulation does a fantastic job of sealing everything. You shouldn’t have anything to worry about, as long as the work was done right.

  3. Jim
    February 19, 2011, 10:30 am

    Hey Reuben, I am becoming a fan of your site.

    We have been getting quotes for a hot roof. The state of MN does not require the foam guys to be licensed so who knows what your getting.
    Quotes vary $1,200; none of the foamers have ever done one in Plymouth so they don’t know if there will be problems getting a permit

    I mentioned that the rafters could be extended out an inch or our foam board installed to increase R value in the dormer area. The one guy I asked about this had never heard of doing this!

  4. Reuben Saltzman
    February 19, 2011, 2:03 pm

    Thanks Jim!

    After the work is done, feel free to come back here and share your results. I’m sure other readers would be interested.

  5. Kenny
    February 20, 2011, 9:54 am

    Hi Reuben
    I work in a lumberyard and you are right about contractors preach about venting. When this doen not work they make up excuses.

  6. Todd Ness
    February 22, 2012, 8:21 am

    Great posts concerning heat loss in attic spaces, including attic bypasses such as chimney’s, wires, plumbing and recessed lighting. Reuben is correct… I have found in my practice that these attic bypasses are major contributions to heat loss which result in ice dams. Ventilation is also a key factor. Continuous venting along the soffit and ridge along with vent shoots in each rafter space gives you continuous natural convection air flow. Keep those soffit vents clear of paint, and debris. Replace them if necessary. Make sure your vent shoots are not damaged or pushed in plugging up your air flow. I have found many in attics that are not even functioning correctly because of this. I have installed custom fabricated ones for homeowners that are inexpensive to build and take care of that problem. Remember to fill those wire and plumbing bypasses etc. I also agree that just adding insulation on top of insulation is not the key. It is best to remove the insulation and find those bypasses if you can. It doesn’t take much for heat to excape from a small wire hole. Reubens post regarding recessed lights is a must read also. Build a box, get it air tight, Seal up all the joints. Then insulate properly on top of it. One more thing I would like to comment on is gutters. I have found ice dams on homes with and without gutters. If you are having the “Leaf Guard” type system installed, make sure these gutter systems are not installed too high. If the flat metal part is not in down plane with the roof or sitting up to high,the metal can actually freeze the water running off the roof creating an ice dam as well. If these are installed in plane with the roof it seems they work much better. I have found this to be true on some homes. Have you found any evidence of this in your practice Reuben? Keep up the great work and web site. Its a great source of information for homeowners.

  7. Reuben Saltzman
    February 23, 2012, 5:20 am

    Hi Todd, I’ve found that gutters can create a shelf for water and ice to build on, but I don’t think I’ve ever blamed the gutters for the ice dams.

    After this mild winter, I’m having a hard time remembering what an ice dam even is…

  8. Dan
    February 12, 2013, 8:22 am

    Regarding heat loss or bypasses
    What would you recommend if the kitchen and or room below has can lights that are installed in the attic?
    The light makers recommend a clearance space around the can lights to prevent fires etc.
    How can you prevent heat loss around these?

  9. Reuben Saltzman
    February 12, 2013, 11:58 am

    Dan – http://www.structuretech1.com/2011/02/recessed-lights-are-evil/

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