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Community and Q&A

Windows — Pretty Good or better in Western Colorado

Pat_Kiernan | Posted in Energy Efficiency and Durability on

I am looking for windows for a Pretty Good house I am preparing to build in Carbondale, CO at an elevation of about 6,200 feet. Climate zone is 6B. We get lots of sun here and large diurnal temperature swings, year round. I don’t know of any homes in town with air conditioning. I’m looking at Pretty Good insulation levels, R-5-10-20-40-60 and about 6 to 8% south facing glass with fairly low thermal mass — partial tile floors and 5/8 drywall. Windows on the north and west will be limited. I’ve heard that 4% overall operable glass is a reasonable target. My rooftop will have excellent exposure for PV.

Our access to window manufacturers is limited compared to more urban areas. One of the issues I’m running into at this altitude with manufacturers like Loewen, Marvin/Integrity, and Sierra Pacific is that they will either not offer Argon fill, or they will fill them with Argon but won’t guarantee the level of Argon fill. Apparently this is because the windows will “breathe’ through a capillary tube to compensate for altitude changes in transit. So an Argon fill on those terms would perform somewhere between air and argon fill levels. If the glazing units are sealed, bulging results that can lead to cracking, seal failures, or visual distortion.

I’d like U of 0.20 or better, VT of 0.5 and up, SHGC for south wall of 0.5 plus.

I’m not sure I’m prepared to spring for PassivHaus grade, but I’m open to suggestions. I haven’t been able to determine if Intus has a dealer that covers our area. There is a local Kneer-Sud representative. Zola has an office in Steamboat Springs, about 2.5 hours away.

Any personal experience with the merits and drawbacks of tilt & turn windows? It seems they could impose some awkward constraints on interior space adjacent to windows.

I’ve also been wondering about the wisdom of buying a high-tech, expensive windows from Europe and how potential warranty issues might be addressed — if the companies are still around!

I’ve tried to read all the excellent posts on glazing here. In one post, Martin wisely advised buying windows manufactured on your side of the Continental Divide to minimize issues associated with hauling windows over high mountain passes. My challenge is a climate/location/elevation specific issue.

GBA is a fantastic resource. Thanks to all of you who make it so!

Pat Kiernan

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  1. GBA Editor
    Martin Holladay | | #1

    Have you considered Alpen? They are in Colorado.

    Alpen Windows
    6268 Monarch Park Place
    Niwot, CO 80503

    Zola is also in Colorado.

    Zola Windows
    1104 Garfield Ave.
    Louisville, CO 80027

  2. Pat_Kiernan | | #2

    Thanks Martin. I've heard mixed reviews over the years on Alpen's various suspended film technologies -- innovative, but not always durable. I'll take a closer look at Zola.

  3. STEPHEN SHEEHY | | #3

    We have tilt-turn Intus windows. We found a good local distributor.

    We've found that you do need to think about furniture placement, but also keep in mind that a pretty good house will maintain an appropriate temperature and you may not use the turn function very often, even on days when you want them open. In addition, we were assuming we'd never use air conditioning, but the house is so easy and cheap to heat and cool that we did use A/C a fair amount in the summer (we're in Maine). The tilt function doesn't create any issues. You may use fixed glass in places where opening windows could interfere with furniture.

  4. Pat_Kiernan | | #4

    Thanks Stephen. Glad to hear they've worked for you. Your perspective on living with them is helpful as I select windows.

  5. onslow | | #5

    Mr. Kiernan,

    Please give Alpen a fair chance in your window selection. I recently built in south west-ish Colorado at 8000 feet and went through the same search for good windows. in the end I went with Alpen for my build.

    I too had read about the center film issues and came to realize most if not all were old posts or old news remembered. The Serious Windows period episodes seemed to be more related to issues other than the film or glass. The company is back in order I think. I can attest that the films in our windows are flawless. The performance is excellent and it is quite true that sitting next to a window on a subzero day doesn't suck the warmth out of you. The air sealing is phenomenal in the casements.

    As you found, Marvin/Integrity wouldn't allow for argon over a certain altitude and Sierra Pacific was only available with air if delivered here in Colorado if I remember correctly. The cost over Marvin was trivial and Sierra Pacific didn't come close for U value. We have an average U under .19 for all windows with the fixed being the dominant glass area and rated at .15 My particular design called for low SHGC in all windows to avoid summer heat gain. This will be our first summer living in the house so I can only judge the heat gain in our one over glazed room which is working as intended so far.

    If your location is as windy as ours can be, then go with more fixed than you might think. Our neighbors warned us of their mistake and we went with required code for opening plus a few more. Best advice we got. Also note available flange styles that make the windows more "normal" and easier to coordinate with exterior finishes.

  6. Pat_Kiernan | | #6

    Thanks for the encouragement to give Alpen another look, Mr. Berry, It's good to hear that you are enjoying your Alpen windows. Those are great U values. What allowed you to feel confident to move past the previous concerns and go for the Alpen? I gather that your installation was fairly recent. I'm not in a very windy area, and I welcome your advice not to overdo the operable windows.

  7. jackofalltrades777 | | #7

    Zola Windows are made in Poland so they would require breather tubes. Alpen Windows are made in Colorado but they still put in breather tubes because elevation levels are all over the place during transport to site. So breather tubes will be a must no matter who you go with.

    I wouldn't worry about losing Argon gas. It's insignificant since Argon gas only bumps the U-Value by a half a point to maybe a whole point. So instead of 0.15 it will be 0.16

    European tilt & turn windows are awesome pieces of engineering. Have you see a window like Intus Windows? They are built like a bank vault.

  8. BillDietze | | #8

    Zola offers an option that allows for an argon fill. When I wrote to Zola to ask about breather tubes in their windows, they sent me a pdf explaining why the don't use them. From that pdf:

    "A partial vacuum will be pulled on the glazing units at the production facility - giving the glass a very slight concave appearance. How much vacuum depends on each project’s specific elevation, and the average yearly temperature. As your windows travel from sea-level to high altitudes the pressure will equalize, and the glass will gradually go from concave to flat."

    Further on they state:

    "Zola has three approaches of tempering protection for its customer’s projects in high altitude:
    1. Projects between 2,600 and 5,000 feet receive Zola’s Altimeter Pressurization System (discussed above). Tempering of the glass is done only where required by code.
    2. Projects above 5,000 feet receive Zola’s Altimeter Pressurization System as well as tempering of all triple and quad glazed assemblies within a project.
    3. Projects over 7,500 feet receive Zola’s Altimeter Pressurization System as well as tempering of all the glass within a project in double, triple, and quad glazed assemblies."

    And finally, under "Cost Associations":

    "Altimeters: Zola’s Altimeter Pressurization Systems are priced at $39.00 each. Double pane glazing assemblies require only one altimeter per glazing unit, whether it’s a window or a door, because there is only one glazing cavity. Triple pane glazing assemblies require two altimeters, because they have two glazing cavities (each separated by the middle pane of glass). Quad assemblies require three altimeters."

  9. onslow | | #9

    Mr. Kiernan, I looked up Carbondale and it seems that we are maybe 100 miles apart as the crow flies. I would be glad to show you the windows and discuss the choice with you in more detail if you wish. Perhaps Mr. Holloday can facilitate getting my email to you. I would share on this forum except some of my observations might fall into the "one person's view" category.

    I did a lot of research and calling over more than three years as I stumbled through the design and build process and honestly the final decision was based on a combination of faith and trust in the representative I used to order the windows. The windows arrived packed in amazing crating with the little poly balloons used to equalize the internal pressure for the trip over the Eisenhower Pass. My memory of the argon's thermal value was much greater than noted in previous comments, but I can't find any definitive sources to back up my memory.

    I did give very serious consideration to the Zola at the time, but the long lead time with the risk of a shipping delay made me remove them from consideration. In light of the details provided by Mr. Dietze, I wonder how they get over the Pass without tempering everything regardless of installed altitude.

    In any case, I remember there were problems with Hurd way back almost 30 years ago that still get mentioned. Also, someone that had seal incompatibility issues about 10 years back. Perhaps I am gambling and don't know it, but the weight of all glass triple glaze is substantial and I have boxed outie windows which pretty much required a less beefy window. The extreme sun load we have here also lead me to go with the pultrusion frames over PVC as the house we moved from (with PVC) had a lot of sun stress after only 12 years.

  10. GBA Editor
    Martin Holladay | | #10

    Bill and Pat,
    If you want to get in touch with each other by email, let me know. My email address is:
    martin [at] greenbuildingadvisor [dot] com

  11. BillDietze | | #11


    I would gladly hear your "one person's view". I haven't bought windows yet but hope to next year in the San Juan Mountains SW of Carbondale. As for the passes, the Zola folks take into account the highest pass elevation one the way to the site and (somehow) take that into consideration. From the Zola Brochure:

    "We use three crucial numbers, specific to the building site, to custom dial the pressure for your glass: 1) your project’s elevation, 2) the average yearly temperature at your project’s site (NOT the average high!), and 3) the highest altitude your project will experience while being delivered (over specific mountain passes for example)."

    I'm not making any recommendation of Zola as I have only read their sales material! Just trying to get the options available disseminated.

  12. lesse | | #12


    Watch out with gas filled IG see my story down below,
    I have very bad experience with HEAT MIRROR film 193 of my IG glass panes gone concave because the sealant that Eastman recommends does not handel Krypton gas see the full problem on Eastman does not even react to my emails and ECO Insulating Glass Inc. does not want to take responsibility.

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