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How to improve insulation in the corners of the house?

seiyafan | Posted in General Questions on

I live in a 1987 bi-level house and recently a thermal scan showed some cold spots in the corners and between the walls and ceiling and floor (as in pictures attached). However those spots are very difficult to access from the attic due to the slope of the roof, on top of that the attic has blown-in cellulose installed a few years ago, so it’s almost impossible to navigate there for me. I am just curious if there is any method to improve insulation from inside the house instead of from the attic. Any other suggestions are very welcome! Thanks!

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  1. GBA Editor
    Martin Holladay | | #1

    These areas are, indeed, tricky. Here are a few points:

    1. It's always possible to remove drywall from the interior to see what's going on. If your house has sloppily installed fiberglass batts, removing the fiberglass at these cold spots and replacing the fiberglass with two-component spray foam will certainly reduce air leakage at these locations as well as improve the R-value. Remember, drywall repairs are cheap and easy.

    2. If your house has roof trusses or rafters that come close to the top plates of your exterior walls -- in other words, if your house doesn't have raised-heel trusses -- there may not be enough room between the top plate of your exterior wall and the underside of the roof sheathing for adequate R-value. This is a tough problem to fix. The only thorough solution is the "chainsaw retrofit" approach: lop off your roof overhangs, install rigid foam on the exterior side of your wall sheathing and roof sheathing, and then install new siding and roofing (along with scabbed-on overhangs). This is a tremendous amount of work, and it isn't cheap -- but it's the best solution.

  2. seiyafan | | #2

    Thanks! I will see what I can do. So there are no corner/side moldings that can provide some insulation benefits, right?

    Meanwhile I have another insulation question and it's about the front entrance door. Right now with the door bottom I can still feel cold air coming in, Are there products out there that can completely block air flow from the bottom of the door? like as tight as a window?

  3. Expert Member
    Dana Dorsett | | #3

    Corners are often framed such that there's a big uninsulated thermal bridge at the corners, but there is also high potential for air leaks on the exterior sheathing at the corners. Some you can do something about, others, not so much, depending on how it was framed, but you'll have to open up the wall to figure it out.

  4. charlie_sullivan | | #4

    Your proposal of insulated corner moldings sounded to me like a good idea, but then I found this old Q&A where Martin reports that it was tried and didn't work.

    I don't fully understand why it doesn't work, and perhaps it would be helpful in some ways, but it's been tried without good success.

  5. GBA Editor
    Martin Holladay | | #5

    Q. "So there are no corner/side moldings that can provide some insulation benefits, right?"

    A. For a thorough discussion of this issue, see this earlier Q&A thread: Interior insulated cornice for use under low-heel roof trusses?

  6. seiyafan | | #6

    It's good to see those issues have previously been discussed, even though the reality is a tough pill to swallow. No wonder it's important to do it right the first time!

    Any idea on the front entrance door issue? Right now I sealed the bottom of the door with tape (I can enter the house through garage door) to alleviate the air leak.

  7. GBA Editor
    Martin Holladay | | #7

    Here is a list of companies that manufacture or distribute weatherstripping for doors and windows:

    Accurate Metal Weatherstrip Co.
    725 South Fulton Ave.
    Mount Vernon, NY 10550

    AM Conservation Group
    2301 Charleston Regional Parkway
    Charleston, SC 29492
    [email protected]

    Architectural Resource Center
    557 Old Turnpike Road
    Northwood, NH 03261

    J & R Products, Inc.
    4695 East 200 North
    Craigville, IN 46731

    McMaster Carr

    Niagara Conservation
    45 Horsehill Rd.
    Cedar Knolls, NJ 07927

    P.O. Box 18966
    Memphis, TN 38141

    Resource Conservation Technology
    2633 North Calvert Street
    Baltimore, MD 21218

    Window Fur

    ZeroDraft / CanAm Building Envelope Specialists
    125 Traders Blvd. East, Unit #4
    Mississauga, ON L4Z 2H3

  8. seiyafan | | #8


    I have one more question (trying to keep everything in one place) on heat loss through windows. The two north facing windows in my garage are getting old and leaky so I sealed them with window films. Do you think there will be any noticeable difference if I installed curtain or shade over them? Right now there is nothing on the window (except the film). Three bedrooms are located directly above the garage. Although the garage is unheated, it's maintained at 50F-55F (when outside is 10F-25F) from the heat escaped from upstairs (8'' floor joist with R20 fiberglass). If putting curtains over them can make the garage warmer by a degree or two then I would not bother with it as it has no effect to the bedrooms.

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