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best way to do a corner window detail

Post in 'DIY and General non-hearth advice' started by RustyShackleford, Nov 29, 2012.

  1. RustyShackleford

    RustyShackleford Minister of Fire

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    On a room addition, I am doing a "corner window". I have framed a single opening that extends back from the corner of the room about 18" along BOTH of the walls that meet at the corner. It's open from about 3ft to 7ft above the floor. There is no sort of support or jack at the actual corner; I have done this with the assistance of a skilled professional carpenter, so everything is structurally sound (the headers that are cantilevered from the main part of each wall out 18" over the opening are designed properly). I will have two IGUs (custom-size pieces of insulated window glass) fabricated, each about 18" wide by 4ft tall, that will form the corner detail.

    The thing I can't figure out is what will happen where the two pieces of glass meet at the corner. I'm not too worried about structure, as each piece of glass will be firmly supported on the other 3 edges, nor am I much concerned about air leakage, as whatever I do will be caulked with something like silicon. But I am concerned about what will look best. The IGUs will be 3/4" thick, in order to have a 1/2" air space (for good thermal performance) and 3/16" tempered glass on the outer side (since the corner is so exposed to damage). So the spacer/seal bands along the edges will be visually significant. I can imagine three ways to do it. 1 - Just butt-joint one piece against the other. 2 - Have the two pieces meet on their inner corner (so the inner pieces of glass just touch) and caulk a 3/4 x 3/4" piece of trim in to square off the corner. 3 - Get what are known as "step glazed" IGUs, where the edge of the inner piece of glass is stepped back from the edge of the outer piece (some specified fraction of an inch along one side of each IGU); note this does not produce a smooth 45-degree bevel along the edge of the IGU, just a jagged approximation thereof. So I solicit thoughts on which of these options seems best, and possible additional strategies.

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  2. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    Interesting problem. I had to read your post twice to get the brain wrapped around it. Being in NC, I don't suppose you hafta worry about the frigid winters we get, so I guess cold penetration wouldn't be an issue.
    I'd try it with an aluminum 3/4" square tube that had the adjacent inner sides made like an F-channel...

    Rough drawing:
    ___
    I_I_
    I I
    So that the glass would actually be inserted into each "F" & give you a place to caulk....
  3. RustyShackleford

    RustyShackleford Minister of Fire

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    Screen Shot 2012-11-29 at 1.14.58 PM.png Thanks Daksy. No not that cold here, but winter-time comfort is still an issue certainly. Anyhow, whichever option I choose, I don't see cold penetration being significantly greater than with just a single flat window the same size - assuming I caulk that corner joint well, which I intend to.

    Your 'F' idea is neat, but I don't *think* I need something so complex. I think my idea of just letting the IGUs touch at their inner corners (see picture) will work ok and look cleaner. I just have to get a good silicon caulk seal between the trim piece and the edge of each IGU and I'm well sealed. I imagine just laying a thin bead of caulk on two faces of the trim and pressing it into place. I believe that the other 3 edges of each IGU being firmly held in place by being caulked into inner and outer "stops" will hold the panels firmly.
  4. DAKSY

    DAKSY Patriot Guard Rider Staff Member

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    I ju
    I was just thinking that the "F" would hide the caulk & give you nice "clean" edges, both inside & out. If the IGU has perfectly straight edges, & you're really sure handed with a blade, you can probably make it look good. Either way, post a pic. I'd like to see the finished product.
  5. RustyShackleford

    RustyShackleford Minister of Fire

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    If I can't make it look good, I could probably mill pieces of trim to cover the joint: L-shaped pieces that fit over the inside and/or the outside of the corner. Or pieces of aluminum angle iron (painted probably). Thanks for thinking on this ...
    DAKSY likes this.
  6. greg13

    greg13 Feeling the Heat

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    I would contact a window professional, or find plans for a sun room. The window pane edges would probably best be sealed with urethane sealer like Auto windshields use.
  7. woodgeek

    woodgeek Minister of Fire

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    I would def 'protect' the edges....as they fragile. Aluminum or stainless tube would have low expansion...could get square vinyl tube like for a railing but it might debond due to expansion/shrinkage??
  8. RustyShackleford

    RustyShackleford Minister of Fire

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    That's one thing I like about my option #2 (have them touch at the inside corner and fill the square gap with trim). The few folks I've talked with here use option #1 (the butt joint) but it seems to me like #2 would look better and protect the edges better.
  9. ironpony

    ironpony Minister of Fire

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    I would go with option 3, anything solid in the corner would bug me. I persoanlly would even consider single pane 3/8 tempered for this just to not have as visible a seam. kinda like my glass in the shower,maybe a 1/16 line. yes I know it would not be energy efficient but it would be a good trade off for me.
  10. RustyShackleford

    RustyShackleford Minister of Fire

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    There *will* be something in the corner, because there will be the seal along each edge of the two IGUs. I'm just trying to figure out how to make it least offensive.
    Funny you mention that. My neighbor, a carpenter, from whom I got this idea, wanted to do the same thing, but talked to the bldg inspector first and they were not going to allow it. He thought he could fight it by calculating the overall U-value of the room and showing it was efficient enough, but decided it wasn't worth the trouble. For me, I don't think it's worth it, because of the reduced comfort when seated near the window, which I foresee.

    Oh, and he butt-jointed his, but didn't seem to think it was definitely the way to go.
  11. ironpony

    ironpony Minister of Fire

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    the glass panels I have are mitered on the corners, when they are put in place a 1/16 gap is left, then caulked. looking thru the glass the seam almost disappears.
  12. RustyShackleford

    RustyShackleford Minister of Fire

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    When you say "glass panel", do you mean insulated units composed of two pieces of glass sealed with an air (or argon) space between them ?
  13. ironpony

    ironpony Minister of Fire

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    3/8 tempered
  14. RustyShackleford

    RustyShackleford Minister of Fire

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    I finished this a few months ago. I ended up going with option #2, except as drawn in the third post in this thread. I am very pleased with the way it looks.
  15. bmblank

    bmblank Minister of Fire

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    A b&b i stay at on occasion has something like this. To me it just looks like 1/2" Lexan with a butt joint in the corner. You can see the joint, buy its not overt or anything. I could see a mitered corner disappearing more.
  16. woodgeek

    woodgeek Minister of Fire

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    What material did you use, hollow vinyl, solid PVC, etc?
  17. save$

    save$ Minister of Fire

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    Can you post a picture? Thanks
  18. RustyShackleford

    RustyShackleford Minister of Fire

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    I used 1/2" thick IGUs (insulated glass unit), with regular squared-off edges, not the quasi-beveled ones I mentioned above.
  19. RustyShackleford

    RustyShackleford Minister of Fire

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    Yeah, I'll try to take one soon.
  20. woodgeek

    woodgeek Minister of Fire

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    But you put some 3/4" square stock on the corner, rather than butt/lap the glass? What stock?
  21. RustyShackleford

    RustyShackleford Minister of Fire

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    Sorry, I meant the IGUs are 3/4" thick. So the 3/4" stock squares-off the corner. I just used pressure-treated wood.

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