Reuben Saltzman

Adding attic insulation? Read this first.

If you’ve considered adding attic insulation to your home this year, please read this first. Most homeowners go about re-insulating their attics all wrong. What’s far more important than simply adding attic insulation is to have air-sealing performed first. This is the labor-intensive part of an attic insulation job that unscrupulous insulation companies may not mention.

Not only is it important to seal attic bypasses before adding insulation, but it’s also the law here in Minnesota. Section 1322.0100 Supb. 3 of the 2015 Minnesota Residential Energy Code says that “Attic insulation shall not be installed unless accessible attic bypasses have been sealed. ” The Minnesota Department of Commerce even issued a press release in 2014 to help make this information known: “Beware the Insulation Contractor Who Does Not Include Air Sealing

Attic Bypasses

The Minnesota Energy Code says “An attic bypass is any air passageway between a conditioned space and an unconditioned attic.”

So what the heck is that? Just check out the images below. I think these all demonstrate attic bypasses quite nicely.

Bypass at furnace vent

attic bypass around plumbing vent

Bypass at plumbing vent

Attic bypass around furnace vent with fire stop

Bypasses at bore holes

Attic bypass around wires

Bypass at addition

Huge Attic bypass around furnace vent

attic bypass around recessed light

Attic - Air Leak

That last image was from a new construction pre-drywall inspection, and is a pretty common detail on new construction homes.

If a home was built before about 1991, there was probably no attempt to seal attic bypasses. After that, there’s a good chance that some of the larger attic bypasses have been sealed, but surely not all of them. To seal up most of these attic bypasses, an insulation company will pull the insulation away and use spray foam insulation to get everything perfectly airtight. Handy homeowners can do most of this work by crawling around in their attic with a can of foam insulation, but let me warn you, this is nasty work. I certainly don’t advise it.

For homeowners who insist on performing their own attic air sealing, I recommend downloading this guide from Building Science Corporation: Attic Air Sealing Guide. Also, please read this Building Envelope Guide from the Minnesota Department of Commerce.

Why attic bypasses matter

Attic bypasses are the driving force behind ice dams, as well as frost, moisture, and mold in the attic. If you eliminate all attic bypasses, you’ll probably eliminate all of these problems. That’s why it’s so important to address attic bypasses before doing anything else.

Sealing attic bypasses will also help to reduce energy bills and help with the comfort of your home. Many people mistakenly believe that replacing windows will achieve this, but this is largely due to overzealous window salespeople making outrageous claims. In reality, the biggest source of heat loss is through the attic, and the best return on investment is usually accomplished through air sealing and re-insulating the attic.

If insulation is added to an attic before addressing attic bypasses, it could potentially make the attic space much colder than it has ever been before. When this is done without eliminating the driving force behind frost in the attic, frost gets even worse.

Can you add too much attic insulation?

No, you can’t add too much insulation. Of course, that assumes all other things are equal, meaning you’re not doing anything stupid with your insulation like blocking the soffit vents or piling the insulation right up to the roof decking. Maybe. This also assumes that you’ve sealed your attic air leaks first. If you haven’t addressed attic air leaks, do not add insulation. First things first.

Why do I even address this question? Because I’ve seen warnings about excessive insulation leading to moisture issues in the attic, but that’s hogwash. Attic bypasses cause moisture problems, not insulation.

On the other hand, there’s no reason to go crazy with insulation. There is certainly a law of diminishing returns when it comes to attic insulation. You’ll get the most value out of the first few inches of insulation, and the increases drop off pretty rapidly after that. The current standard for new homes in Minnesota is R-49.

Where to begin

In next week’s post, we’ll discuss the importance of detailed home performance assessments, as well as the unintended consequences of blindly adding attic insulation.

Author: Reuben SaltzmanStructure Tech Home Inspections

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No responses to “Adding attic insulation? Read this first.”

  1. Adam Stetten
    January 16, 2018, 7:49 am

    I love this post! And I love that Minnesota made it code to execute attic air ceiling prior to adding attic insulation :-)!

    Keep up the good work you guys!

  2. Andrew
    January 16, 2018, 9:29 am

    I’m having spray foam insulation installed in my attic, does that perform the same activity as sealing the air bypasses? or do I still need to seal bypasses prior to installing the spray foam insulation?

    Another question I have is that I’ve got a typical one and a half story home which also has a front porch. The front porch was designed with a “cold roof” which supposedly vents to the attic. If we do spray foam (Hot Roof) in the attic but not the porch, does that have the potential to cause ice damming where the two meet?


  3. Reuben Saltzman
    January 16, 2018, 10:43 am

    Hi Andrew,

    If the spray foam is properly installed, yes. That will seal the attic bypasses.

    Assuming there’s enough insulation at the hot roof, there should be no concerns about that intersection. The cold roof would be no different from any other soffit.

  4. Andrew
    January 16, 2018, 11:32 am

    Thank you very much Reuben! That helps give me some additional piece of mind.

  5. Julianne
    January 16, 2018, 12:36 pm

    This is super helpful!! I need to know some good contractors for this exact thing.

    Suggestions please! I’m a newish homeowner and don’t know who’s good and reputable. I’m in Hamline-Midway neighborhood of St. Paul.

  6. Reuben Saltzman
    January 16, 2018, 1:11 pm

  7. charlie
    January 16, 2018, 4:45 pm

    We live in western Mich, weather somewhat the same as you. We seem to have plenty of insulation, but get huge ice on eaves. Do you have a way I can scan you some photos?
    Thanks Charlie

  8. Reuben Saltzman
    January 17, 2018, 5:13 am

    Hi Charlie, you could email photos to me at, but there’s really no need. You have ice dams. Check out this post for what to do, and be sure to follow the links:

  9. Tony in Saint Paul
    February 10, 2018, 7:20 pm

    A few years back I did some work in the 2nd floor bathroom of my 1959 1.5 story in Saint Paul and found that the interior wall running parallel to the roof joists had a 1/4″ gap straight into the attic (see At that time I did some inquiring online and found out that it was apparently a method used by some back then, but no old timers could recall the reason. A large amount of fiberglass insulation was installed in the attic before I bought the house: two thick layers laid perpendicular, which has remained largely undisturbed (except for where I found the 8″ bathroom fan was blowing straight into the attic, which I have since vented to the outside). After reading this and others of your articles, I realize I need to pull up all the batts and seal those gaps and other bypasses I will likely find in my poorly-insulated but otherwise well-built house. I doubt I can afford to have all this done by professionals, unfortunately. My question is: have you seen much of this in your inspections? If so, could I expect to find this gap above most of the walls? Thanks, great blog!

  10. Reuben Saltzman
    February 12, 2018, 1:29 pm

    Hi Tony,

    Yes, what you’re showing in the photo that you uploaded is typical for any old house; in fact, I know I have some similar issues in my 1998-built home, so it’s not exclusive to old houses. Yes, you can expect to find gaps like this above all of your walls. It’s not a guarantee they’ll be there, but it’s very possible.

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