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Sealing windows

| Posted in Construction Techniques on August 5, 2002 02:53am

I need to seal windows on a log home.  The builder failed to properly seal the window flanges to the buck faces, or to flash the bucks first.  However, I’ve worked to seal the outside flanges with caulk and an adhesive-back durable membrane.  This has been pretty successful, except for a couple of windows for which the window opening was too big and great amounts of caulk were the builder’s answer.

From the inside I’ve removed the caulk, fiberglass insulation and occasional foam sill sealer to expose the window flange.  I’m planning on laying a bead of low-expansion foam along the flange, where the tube can reach, and then filling the remainder with sill sealer.  In all other areas (where I can’t see the flange or reach the flange) I was planning on using foam sill sealer, rather than fiber insulation.  My thinking is that the foam will help seal out any moisture, and the sill sealer will be less likely to retain any moisture that would tend to rot the wood.

Does this make sense?  Are there better options?  thanks for any feedback. 

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Replies

  1. IronHelix | Aug 07, 2002 01:27pm | #1

    Many window manufacturers express concern and caution about using foam in the jamb perimeter because:

    a. All foam expands, some a lot more than others. How else can you get so much volume out a small can? Thick applications in a closed area allow the top layer to dry first, encapsulating the remaining unset foam.  As the remaining foam finishes  setting it can push the jambs out of shape and render the window inoperable.

    My neighbor bought a log cabin package installed and had the same problem. I sold him the windows and had a callback because he said they were very difficult to operate.  His DIY quick fix for a sloppy frame job was foam. The lack of attention to detail and this foam have cost him the replacement of about half of his windows in a 10 year period.

    b. Select a foam that is waterproof when set.  If there is a leak in your window installation and the foam absorbs the water, then your window frame will be continually subjected to moisture and will rot from within the wall.

    Be very selective with the foam you choose, if you have to use one.

    The recomendations I see are for use of fiberglass lightly fitted into the perimeter of the rough opening and appropriate shimming to support the windows load and to keep plumb and level in the opening.

    The proper installation of the exterior flashings and rough opening wraps are the primary defense against water leakage and susequent rot.

    Think like water..................................................Iron Helix

    1. Edgar76b | Aug 07, 2002 04:12pm | #2

      "My neighbor bought a log cabin package installed and had the same problem. I sold him the windows and had a callback because he said they were very difficult to operate." -Iron helix, I have no idea about this ,but I am wondering. If the End grain of each log is in the window opening. Will the expansion and constration of the log push slightly on the window frame too?

       "I was born in the country, razed in the city, I'm a natural born shaker from my hips to the ground" 

  2. Edgar76b | Aug 07, 2002 04:22pm | #3

    They make a low expansion window and door foam, but is that really you problem. I don't see how you can use a nailflang on a log wall.

    What kind of windows?

    I would build a frame around the windows, to the wall width ( to eliminate the need for extension jambs ) and anchor it at a few places. then you can chink it ,outside.

    You might need to use smaller windows or make bigger rough openings. which is after the fact i know , but maybe that is how it should have been done.

    If you set the right jamb width you can set casing on the outside and the inside. it will float over the high points on the log.

     like I said I don't know much about log construction , but wouldn't that keep it weatherproof?

    "I was born in the country, razed in the city, I'm a natural born shaker from my hips to the ground" 

    1. Piffin | Aug 07, 2002 08:44pm | #4

      Log homes are built with buck frames to set the windows and doors into. They are made of four two bys to make a frame the interior of which is the size required for the rough openning. The window flange is nailed to it. There is also a channel tongue on the legs of it which fit a dao into the logs. This forms a slip joint to allow the logs to settle and keeps the frame from falling out. Exterior and interior trims can be nailed to the buck frame.

      The log ends thus do not meet the window frame. Lumber does not expand/contract lengthwise in any event.

      There are urethene foams specifically formulated for log homes that should be ideal for this. A search will eventually lead you to a supplier. Similar foams are used for synthetic chinking that is flexible, sticks well, accepts a trowel finish, is waterproof, and looks just like old mortar chinking sans cracks.

      If you don't find such a product, a low expabsion can spray foam if carefully and modestly applied should do the job for you. Good luck.Excellence is its own reward!

  3. Edgar76b | Aug 12, 2002 06:04pm | #5

    http://www.doityourself.com/to/sashcosealants.htm

    http://www.dow.com/greatstuff/index.htm

    "I was born in the country, razed in the city, I'm a natural born shaker from my hips to the ground" 

  4. Gabe | Aug 12, 2002 06:25pm | #6

    Do not try to foam in any opennings in a log home until a couple of years has passed.

    The foam is also an adhesive and will cause damage to the more delicate windows during settling.

    Use only FG to seal around the windows and cover with casing and tack only and finish off with a latex caulking for now.

    Gabe

    1. lechel | Aug 12, 2002 07:08pm | #7

      Gabe, thanks for replying.  The shell of the house, with windows, was completed in 1999.  What is FG?

      1. Gabe | Aug 12, 2002 07:38pm | #8

        Fibre Glass insulation.

        She's pretty well settled now but will continue to settle at a much reduced pace. Check the space over the windows and doors to make sure that the space is clear and the logs are not touching the window frames. Use FG on the top and foam on the sides and bottom. Nail the trim well to the window frames and lightly onto the logs.

        Gabe

        1. Piffin | Aug 13, 2002 05:11am | #9

          Gabe, if buck frames are uysed then settling is between logs and buck. window to buck sealing is same as regular framing. That is the purpose of frame bucks - to prevent settling from creating stress problems in windows and doors.

          Excellence is its own reward!

          1. Gabe | Aug 13, 2002 03:05pm | #10

            Point well taken if there was space between the buck frame and the log.

            A lot of log homes have rough framed 2 x's on the sides with a gap for settling at the top. The frame is there for ease of window or door installation more than anything else.

            Hard to say for certain, it depends on the builder.

            I've done a dozen or so pre-fab log homes but only one traditional so I'm limited on variety of types.

            Gabe

          2. Piffin | Aug 13, 2002 11:47pm | #11

            One of the beauties of alternative style construction techniques is that it alows an infinite degree of creativity to be applied, along with an infinite potential for mistakes.

            ;)Excellence is its own reward!

          3. dIrishInMe | Aug 13, 2002 11:52pm | #12

            Backer rod - that's the ticket, once the exterior is sealed:

            IMO the best product, used as an alternative to fiberglass is backer rod.  It comes in large spools, in a variety of sizes, and is kind of like foam spaghetti.  it's advantage is that is seals really well against air infiltration - far better than fiberglass.

            Here is a coupla links I got form a quick web search:

            http://www.grandrapids-mn.com/~loghelp/loghomesupply/backerod.html

            http://www.bayindustries.com/backerrod/

            Matt

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