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Yet another window question (YAWQ): Pella Impervia feedback?

TrueSouth | Posted in Green Products and Materials on


I’m building a house in central Oregon (zone 5). It’s a mostly passive solar design, with CMU shell construction that is insulated on the outside (my builder has a patented method to attach insulation to exterior of CMU walls) and this plus a mix of tile and concrete floors means I have a huge amount of thermal mass.

So we’re considering using Pella Impervia with their high SHGC “Natural Sun” glazing for five of the main south-facing 42″ x 112″ windows (Alpen and their better U-value is planned for the other 30+ windows).

Besides the higher SHGC offered by the Pella (Cardinal) glazing, the other benefit would be that Pella says a height of up to 112″ is doable, which is 16″ higher than most others. This taller size would make it tolerable for us to use these in place of expensive composite 2-tall (96″ over 30″) units for these five window locations. (Alpen’s price is surprisingly good for all other windows, it’s just the composite 2-high units that add a painful premium).

Before we pursue this mixed window approach, I thought I’d see if anyone had any new or updated feedback on Pella Impervia to share? I saw some comments from 2010 (I believe Riversong was specifying these in several houses then), but any updated endorsements, warnings, or regrets would be most appreciated! General web searches will convince one that Pella is just about the worst company ever and that I should count on some or all of the five windows leaking instantly, but I’m hoping that’s not really an accurate assessment…


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  1. wjrobinson | | #1

    Failed seals. I know that can happen. I have installed Pella and no problems to date. Actually have not seen a failed seal in a window I have installed for 3 decades including my own home. And if that happens most window companies have warranties.

    Be nice to hear how your home performs when completed.

  2. iLikeDirt | | #2

    Those are some huge windows. Have you calculated that the projected BTU gain from the higher SHGC on the Pellas will actually exceed the higher loss from the windows' lower U-values vs Alpen's windows?

  3. TrueSouth | | #3

    Thanks AJ.

    Nathaniel, good question. We did do the calcs and appear to come out ahead with the higher SHGC for those windows (which will be lined up in serial in the main living level of our split level). We have some large fir trees that will cast some shade so have a need to maximize glazing there, and a cliff to the west will limit some intake also (that plus the termal mass and long eaves appear to mitigate excessive summer heat risk).

    The kicker is that I'm planning to install an insulated curtain that is 20' wide x 12' tall and will come down automatically from a soffit each night in front of this window wall. It's two layers of UVR Poly with a 1/4" closed cell foam liner so won't be super high R-value but will also trap an air pocket and is enough to really shift the window calculation in favor of higher SHGC over U value. My builder normally installs an insulated garage door in front of his main window walls but my wife vetoed having that in the main living area so this hidden curtain roll solution is the compromise.

  4. TrueSouth | | #4

    I thought I'd post an update for anyone interested that we did go ahead with a mixed package of mostly Alpen windows but also seven Pella Impervia windows where we needed a window taller than 8' (five side by side in the main room) and where we didn't care about Alpen's better U factor and only wanted max SHGC (two very large windows in the "sun space" garage).

    In summary, I am extremely impressed with the Alpen windows. My installers commented even without me asking about how nice those were, all of them straight and true with quality metal flanges. They were happy I didn't buy all Pella windows -- those had a lot of bowing in the frames and the plastic flanges just slide right off, so were difficult to install and needed a lot of shimming to give the appearance of being square with the window trim. I needed windows closer to ~9.5 feet tall and Pella seems to be the only ones doing that in fiberglass, so I think I made the necessary choice there, but Alpen IMHO is really a superior window and I'm very glad I ran across them from prior posts on this site.

    Anyway, the build progresses now -- cavities spray foamed, 3" rigid insulation attached to perimeter of the CMU shell and ready for fiber cement siding now, and standing seam roof on awaiting PV install.


    1. Levanger | | #5

      Digging up an old one..... How are those Alpen's doing Dave? We are starting the window hunt for McCall, ID climate 6b and the Alpen's are on the short list. What series did you install?

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