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Mylar Storms

Discussion in 'Home Power and Microgeneration' started by j, Dec 4, 2012.

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  1. j

    j Guest

    An idea to pass along.

    I've been making indoor storms. These are made out of 1/2" (1/2" is
    about optimal air space) thick frames ripped from white pine 2 by stock.
    2x6's seem to be made out of better wood than 2x4's, so I've been using
    that. Half lap joints for the corners. Then, seal the wood.

    Spray contact cement on one side of the frame and plop it down on a
    sheet of mylar (I work on a glass top so I can cut with a blade right on
    top of the glass, quick and easy). Cut the mylar to size and repeat for
    the other side. 2 mil mylar works well (under $.20/SF), but 1 mil is
    half the price. The contact adhesive has some working time so you can
    pull any ripples out of the mylar using your fingers against the frame.

    My friends and myself have old double hung windows, so the frames sit
    against the window frame. What you wind up with is a poor mans triple
    glazed window. IR temp measurements come close to the insulated wall
    temps, the difference in room comfort is very noticeable. The U value is
    higher than I expected.

    Windows are dead clear, you may see some ripples at low angles at night,
    otherwise you can't tell they are there. Mylar needs to be inside as it
    deteriorates under UVB which ordinary glass blocks.

    Just thought I would pass this along. For roughly the cost of replacing
    one old school window you can get roughly the same thermal improvement
    for the whole house. And they look good!

    One mylar source:


  2. Bob F

    Bob F Guest

    Thanks for posting this. I am definately going to look into it.

    Do you have any problems with foggind of the outside glass windows due to
    leakage past the storms?
  3. Jim Wilkins

    Jim Wilkins Guest

    I made a set in 1981 and have mentioned them on a
    few times, generating no followup questions to fill in the details I
    intentionally omitted. I got the idea and the Mylar from John
    Stephenson who makes Warmlite camping gear and has played with Mylar
    film insulation since the 1950's.

    They work fine and most have survived without a tear. The window glass
    has kept UV from noticeably yellowing the film. The only maintenance
    has been replacing the closed cell weatherstripping that makes them a
    snug press fit in the window trim. Instead of cement I used
    double-stick tape and my wife and I stretched the plastic over the
    frame the same way theatre flats are covered with canvas, ie working
    from the centers toward the corners. Then we wrapped the edges with 2"
    clear packaging tape.

    Before covering the frames I stained them to match the windows so they
    practically disappear from inside. From outside the reflection of a
    few slight ripples shows at certain angles.

    On the exposed upwind side of the house I added retainers made from
    brass L hooks straightened, looped at the end and then bent 45 degrees
    in the center to make thumb latches, two per window.

    Infrared thermometer measurements of black tape on the plastic and the
    wall show only a few degrees difference when the outside temp is well
    below freezing. They seal the windows enough that winter-time humidity
    remains above 40%.

    It takes some cabinet-making skill to make invisible mortice and tenon
    corner joints. Ten of the eleven window frames I made would hold
    together without glue. The patio door frames were too big to stand
    upright on the table saw so I dowelled them, which has held up fine.

  4. Jim Wilkins

    Jim Wilkins Guest

    Mine fog if the closed-cell foam around them has worn, especially in
    the bathroom where the frame comes out frequently to vent after a
    shower. On other windows taping the frame to the window trim stops
    fogging, but marks up the trim a little.

    I made a similar frame with bird-proof acrylic sheet glazing to fit
    around and seal the air conditioner. It has doors on either side of
    the A/C so I don't have to align the frame, window and heavy A/C all
    at once. I place the A/C in the window, unlatch the doors and install
    the frame, close one door and push the A/C against it, then close the
    other one. One side could have been part of the solid frame but two
    identical doors aren't much more carpentry work than one.

  5. j

    j Guest

    I've installed them two ways, with a heavy felt cut from a cheap moving
    blanket from Northern Tool. Otherwise some clear packing tape ala USPS.
    I'm not in a climate where this is a problem but I had seen icing on a
    window, and that cleared up later. You can put in a little desiccant if
    you think this will be a problem.

    3M Type 45 spray contact cement is cheap and works about right. Give it
    about 90 seconds to dry. There is a long working time to pullout
    ripples, you'll get the hang of it quickly. Gluing the mylar goes fast,
    half the time is waiting to dry.

    Build one to check fit and then run the rest like a production line.
  6. j

    j Guest

    Very cool.
    That's a long life!

    The only maintenance
    I like that.

    The contact cement should give more latitude. I had tried double stick
    but it is hard to tug on the mylar.The contact slides until it sets. In
    fact you don't have to be that careful of getting out the ripples
    initially as they pull out easily after the mylar is on the frame.
    Same here.
    Same here, at least for as cold as we get! Seems like it works better
    than expected.

    They seal the windows enough that winter-time humidity
    Your skills trump mine. I cut half laps with a dado and a stop. Then
    pinned it together with a pin stapler while the glue set. Two half days
    to do up a dozen windows.

    Some of the pieces I've ripped have curved. What should I look for in
    feed stock? I think the pieces with tighter/closer grain curve more. I
    think the top grain is more critical than the edge grain. But I really
    don't know.

  7. Jim Wilkins

    Jim Wilkins Guest

    I've been a theatre set builder and thus practiced stretching the
    canvas. Since it's stapled before sizing it I could fix my beginner
    mistakes without wasting material. The glue seems easier.
    When I asked about the very large scrap pile I saw in a custom cabinet
    shop the owner said he simply bought extra and used whatever warped
    for firewood.

    I got the Southern Yellow Pine as strips trimmed off doors etc from a
    kitchen installer, and nowadays saw and plane my own furniture lumber
    from local high-quality old growth that dies or blows down.

    If you are limited to big box store wood you could buy extra, rip it
    slightly oversize and pile it up indoors to season. Most of the
    pressure-treated I've bought recently has dried pretty straight. I
    rebuilt the outer frames and sills of my windows with it.
  8. j

    j Guest

    I've given up on yellow pine. Everything I make is out of white pine, I
    haven't had too much trouble, but I do get the occasional errant piece.
    The white seems a good bit lighter too,I think not as strong, but strong

    I've got a good bit of 1 x 6 tongue and groove cypress (I bought a
    pallet Home Depot no longer wanted), it's my go to wood if the
    dimensions are suitable.

    The depot is not far and I can hang lumber out the car window and no one
    cares. I brought home some 12 footers once and they stuck out 5'. A bit
    too far for a comfortable drive home!

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