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Looking for a window resource

Michael Schonlau | Posted in Green Products and Materials on

I’m researching windows for our new home and don’t feel “equipped” to respond intelligently when talking to suppliers/contractors who don’t necessarily agree with my ideas. Our home is a passive solar design and we hope to build the structure close to Passive House specifications.

Here are some of the questions/comments I have heard:

-“Why not go with Andersen, Marvin, or Pella? They have local sales and service…”
I’ve been looking at Serious and Thermotech (triple-glazed, thermally-broken frames, higher SHGC values while keeping u-values low). I don’t see anything about thermally-broken frames on the Andersen/Marvin/Pella websites and the SHGC/U-value combinations don’t look good for my south-facing windows.

-“I wouldn’t worry about a few tenths [maybe he meant hundredths?] in the u-value”
What research can I use to show that these numbers do make “significant differences?

-“Most window frames are built and insulated the same way – just using different materials”
I think I’ve learned enough to know this isn’t true. Can someone tell me what advantages a thermally-broken window has over a not-thermally-broken window? How can I quantify the difference? Is there a resource out there that illustrates different window constructions?

-Regarding frames: “Fibrex (composite) is better than fiberglass and aluminum and vinyl are OK”
Does anyone know anything about Fibrex or other composite frame materials?

-“Triple glazing doesn’t make sense in our area [Omaha, NE]”
Is there some kind of cost-benefit research out there to support triple glazing vs double?

Again, thanks in advance for your feedback.

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Replies

  1. Andy Ault, CLC | | #1

    Michael - I would suggest that perhaps you're approaching this task from the wrong frame-of-reference. Specifically, rather than looking for data/research you can use to "prove to" or "convince" your builder that what you want makes sense, instead, you need to be looking for a NEW builder that doesn't need convincing. There are plenty of green-minded practitioners these days who will be all-too happy to work with you to accomplish your goals. From your comments, it seems like you haven't found that company yet because they all want to do what they've always done (otherwise you wouldn't be getting those lame responses).

    Depending on your market, you should look at either the local NAHB (Nat'l Assoc of Homebuilders) chapter or the local NARI (Nat'l Assoc of the Remodeling Industry) chapter. Some markets have both and some are only large enough to support one-or-the-other. Both of these trade associations have green professional designations which their members can take classes and pass tests to attain. Any contractor who takes the time to belong to one of these associations in the first place will almost always be a cut above. And then the ones from that self-selecting group who have gone a step further to get the additional training and certification are going to be the kind of company you want to work with.

    It can be pretty easy to screw up any construction. It can be even easier to screw up green construction if someone doesn't truly understand the building dynamics they're tinkering with. You don't really want to be that guy's Guinea pig. FIRST, find someone who can demonstrate to you that they are more than skin-deep when it comes to green building. Someone who makes it clear that they want to partner with you and approach your project from a "building as an integrated system" approach ... not simply a "building as a job" approach. THEN worry about selecting the proper materials, methods, etc.

  2. Kristina Thompson | | #2

    Hahaha! I live in the Omaha area as well, and had a number of contractors try to talk my out of my plan to replace our old windows with triple-pane krypton gas-filled. We went with the triple-pane and never looked back. Not too happy that Schuco left the industry the year after, but after five years I am still very pleased with the windows.

    Yes, there are methods of analysis which can be applied. Actually, a whole slew of them. There's a program available on the web called Window5 by LBNL that enables you to model your window (the U-value on your glass can be severely compromised by the frame, so yes, a thermal break is very important!) and there exist methods to quantify your heat loss through various parts of your building envelope. The thermal break is very important because without it, depending on what your thermal "bridge" is, you may be providing heat with a mini expressway to travel into or out of of your structure. Of course, the direction it travels will always be to your disadvantage!

    If you like, I could take a closer look at your passive solar home design and your window selections and do some limited analysis. I am an architectural engineering student at UNO's Peter Kiewit Institute and one of the classes in my enrollment requires me to do a case study or other topic on sustainable ("green") design once per week. Your analysis would fit very nicely into my coursework, and would give you some technical ammunition to use in discussion with your builders, to help give you the resolve and comprehension to stand your ground.

  3. Paul McGovern | | #3

    Michael, I like your approach so long as you are being equally diligent in evaluating the other components of the building envelope. Windows & doors are but one important component with Insulation, tightness of the envelope, bulk water & water vapor management, controlled mechanical ventilation, safe & efficient combustion appliance, engineered lumber & advanced framing techniques & a properly sized & sealed HVAC system. All components must be compatible with and complimentary too, the others.
    Regarding the windows, a "thermal break" is especially important in climate zones that experience temperature extremes as it resists conduction through the frame. It provides a "break", a gasket of sorts made up of a less conductive materials, that greatly reduces thermal bridging.
    The "U" value is important everywhere except the most consistently mild climates as that represents the amount of thermal conduction the sash will alow. "U" value is the inverse of "R" value. (.25 U = 4 R)
    Solar Heat Gain Co-efficient involves the amount of radiant heat tranfer allowed. If you are building a passive solar home, you may find that in some areas of your home, a low SHGC may be counterproductive as it will restrict the flow of energy to the designed areas.
    Window selection is climate specific ... and often times, it is preferable to use differently classified windows in different areas. Windows are so much more than light & view.
    A recent Georgia Tech study concluded that the cost of upgrading windows and envelope tightness are offset by reduced load requirements ... lower loads = less capacity = net neutral.
    Build tight & ventilate right!

  4. GBA Editor
    Martin Holladay | | #4

    Paul,
    Could you provide a link or more information on the Georgia Tech study? I assume the study shows that the incremental cost of high-performance windows is a cost-effective investment when buying windows for new construction. That is very different, of course, from saying that it is cost-effective to invest in replacement windows for an existing house -- something that isn't true.

  5. David Meiland | | #5

    Andersen/Marvin/Pella websites and the SHGC/U-value combinations don't look good for my south-facing windows

    Most window manufacturers have "standard" glazing for most windows they sell, with low U-factor and SHGC, such as Cardinal's 272 low-e coating. That's what you're seeing on those sites. Whoever you buy from should be easily able to offer low U and high SHGC, such as Cardinal 179 or similar. You have to ask to get these options, and the salespeople who sell the major lines rarely get asked.

    What research can I use to show that these numbers do make "significant differences?

    It's not research so much as a software energy model of the proposed house that includes all of the windows, their individual performance characteristics, locations, orientations, shading, etc. Are you or your designer using anything like that to plan the house? I would talk to Kristina above and see what she proposes.

    what advantages a thermally-broken window has over a not-thermally-broken window? How can I quantify the difference?

    Again, it's the energy model of the house and the NFRC unit U-factors of the windows.

    Does anyone know anything about Fibrex or other composite frame materials?

    An insulated Fibrex frame is probably going to be an excellent performer.

  6. Michael Schonlau | | #6

    Andy - I should have mentioned that the builder I'm working with is open-minded about building this way - just inexperienced. He is very detail-oriented, but is young and hasn't built many homes that approach the energy efficiency levels we hope to achieve. He is the not one who asked me those questions. I am just trying to educate myself more, so I can be more involved and know more about what will likely the biggest investment of my lifetime. If I can back up my proposed design with good research and data, that will help my builder and I convince/educate subs that building thicker walls, paying closer attention to air sealing, and investing in better windows make sense.

    Kristina - I look forward to speaking with you. I think I might know one of your professors (Avery?). You can contact me at schonlau at gmail dot-com.

  7. Riversong | | #7

    Michael,

    You and the recalcitrant suppliers/contractors may both be right.

    Pella now has a high SHGC LowE argon double glazing option in both their Proline and their new Impervia fiberglass window line (which offers optional foam fill for slightly lower U).

    I have a house going up right now in VT that I designed to be super-insulated and passive solar and, comparing the Pella options with Serious and Thermotech and Accurate Dorwin triple-glazed units, the Pella's came out way ahead in bang for the buck.

    The savings from the more expensive triple-glazed windows had payback periods of 30 to 70 years.

  8. David Meiland | | #8

    Robert, what were your projections for future energy costs for that house?

  9. Riversong | | #9

    David,

    I was using today's fuel prices. I don't predict the future, since the world-as-we-know-it will end in 2012.

    I also chose Pella because of their quality, their delivery time, their warranty, their product support, and their factory service.

  10. Paul McGovern | | #10

    Martin .... thanks for the clarification ... the Georgia Tech study was referring specifically to new construction ... Regarding retrofits, it is my belief that you air-seal first, and everything else is second. Must look for info on the study & will post tomorrow

  11. Kevin Dickson, MSME | | #11

    Robert,

    Thanks for the info on the Pella high SHGC windows! Now, are you recommending an insulated shade for those double glazed windows, like Window Quilts? (https://www.greenbuildingadvisor.com/product-guide/prod/high-performance-insulated-shades)

    And doesn't Pella have between-the-glass shades? is that worth considering?

    I know homeowners can't be trusted to use shades correctly, but this is for my own mountain home in a location with over 11,000 DD/yr. An R-4 window with an R-5 shade would be pretty good for the those north facing windows, and the big south facing windows at night.

  12. GBA Editor
    Martin Holladay | | #12

    Kevin,
    For a home in the mountains, at a location with 11,000 heating-degree days, I wouldn't consider anything less than triple glazing -- for comfort as well as energy savings.

  13. Riversong | | #13

    Kevin,

    I would have to agree with Martin that, in a climate as severe as yours, triple-glazing should be the standard. However, if you can't find good high SHGC triple glazed windows at an affordable price, then the solar double glazed units with Window Quilts might be a reasonable alternative (though I haven't priced out the quilts and don't know if that would bring the unit price up to triple glazed levels).

    But sealed, insulated, lowE quilts, like Window Quilt or the now defunct Comfort Shade (that was made by my neighbor in the 80s and may get revived), are the only window insulators worth considering. Window Quilt's brochure, however, offers only an R-3.69 advantage when used with lowE double-glazing, probably because the lowE advantage is already built into the windows and the lowE film in the quilt doesn't offer anything additional).

    You'd have to do some energy analysis with good passive solar modeling software to determine the relative benefit of each option.

    You might consider high SHGC double-glazed windows with quilts on the south facade and lower gain triples on the other faces. But, in hilly snow country, there's available solar gain from all directions because of diffused light reflected by the snow.

    Regardless of the number of glass layers (or suspended films), the goal is to minimize whole window U-value and maximize SHGC for all units, and use other strategies - such as thermal mass, open floor plans, insulating shades, etc. - to optimize the balance between free solar gain and conductive losses.

    By the way, I don't believe the more expensive Pella Designer and Architect lines, with between-the-glass options, offers the new high SHGC glass.

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