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“Pretty good house” window choices

Alok Khuntia | Posted in Green Building Techniques on

Hi, we are in the design stage of a high efficiency retrofit and addition to an 1888 Victorian house in the Chicago suburbs. Our architect and his preferred builder are leading many of the Passive house projects in the area and are very interested in getting our project to approach those standards. Although i think it would be very cool as well, i am finding that the technical approaches and costs simply don’t justify the benefits. In doing my own research, i am leaning towards designing for “pretty good” near net-zero instead of near-passive. The house is registered as historical in the community so we will not be able to replace the entire existing siding which means the superinsulation expenses would much higher than other projects.

i have two specific questions now…

1) is a double pane window like a Zola Classic Wood (instead of triple pane Thermo Wood) appropriate for a house that is targeting 2 air changes per hour as opposed to 0.6 for PH?
2) in my own pre-bid financial modeling, i am estimating $75/sf installed price for triple pane and $62 for double pane… is this reasonable?

thanks for any guidance you can provide. I

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Replies

  1. Aj Builder, Upstate NY Zone 6a | | #1

    Amok, to me the long term smart choice is to buy the more expensive windows this one time. Expensive counters and fixtures can be upgraded much more readily over the years. Windows should be a forever choice.

  2. Stephen Sheehy | | #2

    Using fixed windows in some locations instead of opening ones can save a lot of money and may even be a bit more energy efficient.

  3. Alok Khuntia | | #3

    Thanks for these comments and i agree entirely with both of you. My dilemma is simply a practical cost benefit question. I could buy the BEST and pay $100+/sf or buy something less expensive. I feel like the best value will be to match the window performance to the realistic whole house performance that i am aiming for. If the windows will be the weakest link in my house envelope then i guess i should get the best i can afford but if the there is a less expensive option that will still allow me to achieve my desired performance, i would like to find that.

    Zola has a comparison chart that i was using as a reference. http://www.zolawindows.com/passivehousewindowsperformance/

    i am trying to decide what the dollar value is to me for the extra 2 r-value of the high end windows. Per the chart, i think even the mid line window is still a high quality lifetime window.

    thanks again.

  4. Dan Kolbert | | #4

    Is there an energy model? It should be pretty easy to compare the performance numbers.

  5. Alok Khuntia | | #5

    pardon my ignorance, i am the homeowner and have only been doing research for a few months in the building science arena. are you asking if there is an energy model of my project (the house)? the answer is 'not yet' to that as we are primarily at the concept stage for the structures.

    Are there any rules of them like you only need the r-7+ windows for true passive house? or in general the best bang for your buck is around r-5?

  6. Nate G | | #6

    Alok, as you will soon discover, it is virtually impossible to determine what windows are "cost effective." The marginal energy savings of improves windows can only be determined through energy modeling software, using the actual prices you'll pay for your utilities. The task is confounded by the great difficulty of actually determining the prices of the windows. Finally, for any retrofit, new windows are almost never cost-effective, and the "almost" becomes more of an "ever ever ever" the more money you pay. So don't think about saving money, because you won't live long enough to see it. Think about other things instead:

    My recommendations:
    1. Determine your aesthetic goals. Since this is a historic retrofit, that's important. So no vinyl.
    2. Determine your functional goals. Do they need to be double-hung? That eliminates a lot of the pricey Euro windows, most of which are casements or tilt-turns. Can they be fixed windows? That saves money.
    3. Determine longevity goals. If long life is desired, go for fiberglass or aluminum-clad wood. No vinyl or exterior wood.
    4. Determine climate-specific requirements. Chicago is cold and wet. That means condensation on the inside of the windows if they don't insulate well enough. That means triple-pane is a virtual necessity unless you're willing to live with interior condensation or keeping the indoor humidity very low, most likely with a dehumidifier.

    Zola doesn't sell double-hung windows, so if that's what you need, you'll have to look elsewhere. You may have difficulty finding an adequate clad wood triple pane double hung window. A quick web search shows that Loewen makes these, and according to their website they've got a dealer in Chicago too.

  7. Alok Khuntia | | #7

    Nathaniel, thanks for that practical advice. We are actually going to be pulling out early 2000s cheap vinyl double windows but we have never had condensation issues. Is that expected? is it because our house is so leaky now? We previously lived in an 1898 victorian for 13 years which also contained cheap double pane vinyl windows and never had condensation issues. That house was modestly rehabbed and i imagine was at near 'to-code' specs. I am actually quite a bit concerned about over tightening this house with the retrofit and introducing condensation problems that haven't existed in 127 years. For that reason, I DON'T want a vapor barrier and I don't want to attempt superinsulation --- just pretty good above code insulation.

    For me, aesthetics are the most important thing and I am leaning towards an all wood window. My rationale for exterior wood is that it looks better (to me) and i will have to maintain the painted siding anyway on a regular basis so i can just as easily maintain the windows. Zola does have a Historic line faux double hung that looked cool to me but i am not especially attached to that brand. It is just a brand recommended by the architect for quality at a fair price. I will definitely look into the Loewen though.

    Thanks again.

  8. Nate G | | #8

    Yes, it is absolutely because your house is so leaky now. It's the Old House Disease: leakiness was almost built into the design, and contributed greatly to the houses' durability at the expense of comfort and heating bills. When you tighten them up, you solve those problems, but can introduce others. It's important that your builder/architect/passivehaus consultant is familiar with the particular challenges of historic retrofits.

    Double pane will be fine as long as you keep the interior moisture load low. Triple pane will allow you to maintain a higher level of wintertime indoor humidity without causing condensation, which is more comfortable to some. depends on your preferences. I live in the high desert and find that about 30% wintertime humidity is perfectly comfortable to me, and I never have condensation on my double-pane vinyl windows.

  9. Alok Khuntia | | #9

    You've got me leaning towards triple pane... I had discounted the likelihood of condensation previously. Thanks for the advice.

  10. GBA Editor
    Martin Holladay | | #10

    Alok,
    I think that it is safe to say that Nathaniel is overstating the case for triple-glazed windows. While triple-glazed windows reduce energy costs and are more comfortable to sit beside on cold nights, they are not necessary in most homes to prevent condensation problems. The vast majority of cold-climate homes in the U.S. have double-glazed windows, not triple glazed windows, and the condensation issues in these homes, if any, are mostly minor.

    For more information on window payback, you may want to read Study Shows That Expensive Windows Yield Meager Energy Returns.

    You may also want to read about David Posluszny's approach to window purchasing decisions: "The windows have a U-factor of 0.29. I would have preferred windows with a lower U-factor, but I bought the windows inexpensively as odd-lots. Prior to purchasing them I ran some heat load calculations. My home is heated with electricity produced by a solar array. I had to purchase all the solar panels to make the electricity for the heat. After my heat-loss calculations, I found that the extra solar panels were less expensive than windows with lower U-factors."

  11. Alok Khuntia | | #11

    Thanks for the links Martin. I will check them out. My initial intention with moving away from super insulation and triple glazing was to put some of the money towards a larger pv array.

  12. Aj Builder, Upstate NY Zone 6a | | #12

    Buy the Windows with no intention of them needing to be upgraded.

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