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Musings of an Energy Nerd

Passivhaus Windows

Cold-climate builders look for the best available windows

European technology. One reason for the very low U-factors of many European windows: their frames include thermal breaks made of cork and insulating foam. This triple-glazed window is made by Optiwin, a manufacturer with plants in Austria and Germany.
Image Credit: Jesse Thompson, Kaplan Thompson Architects

UPDATED on June 11, 2013 with new information on European Passivhaus-certified windows available in the U.S.

German windows, like German cars, have a very solid reputation for high performance and durability. U.S. interest in German windows has grown in recent years, especially among Passivhaus builders, leading several U.S. importers to conclude that the time is ripe to offer German windows to North American customers.

Double glazing isn’t good enough

To meet the Passivhaus standard, cold-climate builders need a very good window. In central Europe, Passivhaus designers insist on triple-glazed windows with a maximum U-factor (in U.S. terms) of 0.14. That’s a standard that few U.S. windows can meet.

When I interviewed Dr. Wolfgang Feist in 2007, he told me, “The reason for the number which we now use in Europe is the comfort of the occupants. It is a functional definition. During the winter, the coldest surface temperature in the room will be the window. If you don’t have a radiator in your room, the difference between the surface temperature of the window and the mean surface temperature of the room should not be more than 3 degrees Celsius; that’s for comfort reasons.”

The colder the climate, the more important it is to use U-0.14 or better windows in a Passivhaus building — and not just for comfort. Low U-factor windows are necessary to meet the Passivhaus maximum annual heating energy standard of 15 kWh per square meter.

Calculating U-factors

The lower a window’s U-factor, the better it is at resisting heat flow. In the U.S., U-factors are calculated according to a standard established by the National Fenestration Rating Council (NRFC). The U-factor shown on the familiar NFRC labels is a whole-window rating that takes into account the different U-factors of the window’s frame, sash, edge of glass,…

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  1. Katrin | | #1

    North-American windows pull almost even
    Martin, awesome article on windows for PH applications! This is a great and very interesting topic and thanks for kicking it off in this forum.

    I like to add this for those PH designers of us who just can't afford the cost of European windows: Our experience has been that the overall performance of the fiberglass framed Canadian and US windows is almost as good as the German PH windows if you look at the overall systems design of PH! The reason here is that the overall frame area is much smaller. The frame U-value is much weaker than the glazing U-value. Therefore a window with less frame area performs overall better than one with a larger frame area (such as most of the European windows have, except the Pazen design which is a new level and class of its own, probably the best performing window out there as of right now). Also, PH takes the solar gain into account for the overall energy balance and more glass percentage yields higher total solar gains.

    I don't see that the European window is "mystical", it is excellent craftsmanship and a well thought through piece of PH technology designed to do what it needs to do (we sometimes joke in the office that PH windows are part of the mechanical system). The European windows excel by far in durability, strength, aesthetics, hardware quality, airtightness, watertightness and a well weighted SHGC. They definitely are built to last and worth it if the budget allows!

  2. GBA Editor
    Martin Holladay | | #2

    Solid engineering is not mystical
    Thanks! The "mystical aura" comment was a reference to the awestruck tone of Dehler-Seter's report about opening the shipping container full of its precious cargo (Mr. Müller's windows). I agree with you that, from all evidence I've assembled, the reputation of European windows is based on solid craftsmanship, not hocus-pocus.

  3. Stephen Thwaites | | #3

    Windows reflect Culture and Climate
    There are differences between European Tilt & Turn windows and North American Casements and Awnings that can affect market share more than their thermal characterisitcs. These differences reflect cultural and climatic norms.

    An obvious difference is the one swings in and the other swings out. Show an inswing window to the average North American and they say, "Why would i want that? - What do i do with my drapes?" Show an outswing window to the average European and they say " Why would i want that ? - How can i put Rollshutters on it?"

    Inswing Tilt & turn windows in general have 1 or maybe 2 tilt-in ventilation positions. In my view this is fine for a more moderate European climate.
    Outswing Casement windows can be opened any amount - up to 90 degrees. In my view this is better for the hotter and often more humid weather in much of North America.

    These are but two examples among many cultural and climatic issues that often trump thermal considerations.

    Stephen Thwaites
    Thermotech Fiberglass Fenestration

  4. Coyo | | #4

    We can catch up
    Great article Martin.
    As windows and doors was one of our main weak points I spend a lot of time on this subject the last year - and visited with German Passiv Haus window manufactures after my trip to the conferences in Europe. It was very frustrating to see and explore all these cutting edge products and technologies in Germany and comparing them to what I have available back home in the States. I was very close in ordering in windows and doors from Germany for some of our Projects. My main concerns were costs and lead time and of course warranty and replacement. But in the end the deciding factor for me to not to go down this path was something else all together. I decided for myself that ordering windows from Germany was just not the solution. I believe in community, local business and the importance of ripple effect for the local economy. In a way one of the biggest lessons for me traveling through Europe and attending the Passiv Haus conferences and talking to many Architects, Builders and Manufactures was to take in there technologies and knowledge and to incorporate it in our climate and our constrains - BUT to nevertheless focus on working with our own community on improving what we do. And we really try hard to push that sense of "community" through to our clients - with great success.
    I approached our small local window manufactures and tried to sell them on the "Passiv Haus Window". And one of them was very interested and worked hard with us on their windows - and I am hoping to travel to Germany in the spring with the owner to explore ways to further incorporate their window technology. There is no reason for us not to build equally good windows here in our own community. And we are happily installing homegrown insulated Fiberglass Windows with German tilt and turn hardware, in swing, wide frames to be able to over insulated the frames on the outside with high performing Heat Mirror glazing on all our project now. The wide frames and the tilt-turn hardware allows us to over insulate the outside of the frames very well which results in a tremendous gain in installed U-Value. I highly recommend studying the Passiv Haus publication # 37 which was published last year (so far only in German) which is very eye opening about the importance of not just the window but also its placement in the wall assembly and over insulation level on the outside of the frame. Great Isothermal pictures and diagrams. We spend a lot of time, energy and money this year on figuring out the best means of incorporating this into our building practices. Anybody trying to build high efficient homes in cold climates should look into this IMO. and of course into insulated window shutters...
    Now Martin it's time to work on your Passiv Haus doors (airtight, multiple locking and R-40 performance) article...ever tried to find a high performance entry door? I completely gave up on that and we custom build them now in house.

  5. GBA Editor
    Martin Holladay | | #5

    A few questions
    Great post, Thorsten. A couple of questions and comments:

    1. What type of Heat Mirror glazing do you use? Are you able to order Heat Mirror glazing with a decent SHGC? The offerings of Serious Materials all seem to have low SHGC numbers and low VT.

    2. A while back, after reading about the German technique that you call "overinsulating the frames" — that is, covering the exterior of the window frames with rigid foam and exterior trim, in order to limit heat transfer through the frames — I went outside and looked at the exposed frames of the Thermotech windows I installed on my house. The width of the exposed window frame on the exterior of my house is only 3/4 inch — hardly enough to warrant an elaborate "overinsulation" detail. So I concluded that Canadian fiberglass frames are so narrow that the "overinsulation" detail developed in Germany is only necessary to solve a peculiarly German problem — namely the fact that they use wide (what some critics call "clunky") frame materials made out of wood glued to thermal breaks. The Canadian solution (use pultruded fiberglass, which is inherently stiff and structurally strong and therefore relatively narrow, and then fill the pultrusion with foam) obviates the need for the German "overinsulation" technique. Comments?

  6. dankolbert | | #6

    Great topic
    Thanks for raising the topic, Martin. We're relatively new to high-performance window and are trying to catch up. We used Thermo-Tech's on our last house and I think they're terrific units. My big concern with triple-glazed units in general is the hardware - on casement windows big enough to meet egress, there's a lot of weight torquing off the frame. I'm thinking about using more awning and less casements in the future.

    And Stephen's comments on culture are right on - would require something of a shift, although all my clients who see tilt-turn hardware always have an immediate and positive reaction, although so far the price tag has stopped all of them from actually buying them.

  7. Coyo | | #7

    Overinsulation hiding clunky windows? Not really...
    Martin, in my experience the weakest point in the window assembly is it's installation gap. In our extreme cold climate this is where I seen the most issues. If one takes a thermal images on the installed (high performing) window it is pretty revealing on how heat loss occurs in the installation gap - which on average is spray foamed. I experimented quite a bit with this "problem" for the last two years and tried different solutions on improving installation of the windows. When I got my hands on the study performed by the Passiv Haus institute in Darmstad about just this topic last fall I found a lot of my findings about this being studied and monitored by them for a long time, this paper is a wealth of knowledge on how to go about improving the installed U-Value of windows. This study is worth the money - even if you can't read German as it is full of Isothermal images which are pretty self explaining - but nevertheless of course as with anything Passiv Haus it really, really helps if you can read and understand German. "Overinsulation" of the window frames on the outside isn't about hiding clunky window frames. It is about addressing the weak point in the assembly, the installation gap. And no matter how good of a window you install - this is always the case - and a problem. When you looked at your Thermotech window frame on the outside you concluded correctly that there isn't anything to over insulate. You are looking at a casement window, one which your outside-exposed window frame is hardly providing anything to be able to detail this. If you look on the inside it is a different story all together, you will see quite a bit of extra frame width. That is the nature of the window type. To be able to detail the exterior and eliminate the weak point of the installation gap you need a tilt-turn window which swings in and has the wider frame part on the outside. With the insulated Fiberglass frames we use we can "over insulate" the outside frames by 1-1/2" - in our case with six inches of EPS on our REMOTE walls. The windows is placed in the center of the wall assembly and we build window buck extensions to finish of the outside. And of course everything is flashed, waterproofed and air sealed. The window is installed from the inside and can be replaced still fairly easy at a later point if the need arises without having to tear down the exterior siding-which was one of my primary goals when I worked on the details for this. With the heavy windows we use it makes the installation also a lot easier and safer. Lots of detailing and extra work - is it worth it? I absolutely believe so - and will carefully study and monitor this winter on how much gain we are seeing from this new detailing. One big lesson learned on my path to build high efficient homes is that it is in the details which in the end makes the sum of all its parts to build truly efficient homes.

    Side note - I don't dictate my clients which direction we go on windows for their home but I provide them with a lot of information via our "Homeowner selection guide" to give them the knowledge they need to make an informed decision. Every client has opted to spend the about 30% increase in money to go Tilt-Turn, overinsulated "Passiv" window option.

  8. furniturefarmer | | #8

    Heat Mirror high-gain glass units
    Serious makes a glazing unit with a SHGC of .517 and a COG U-value of .143. We were able to spec this for most of our southern glazing on a couple recent projects, but for some reason they do not to offer it in any of their standard lines.

  9. Kori Fox | | #9

    We Can Catch Up
    I work for Medallion Industries in Portland OR. We are a window, door, and millwork distributer and have been in business for 39 years. My job has become solely focused on Green Building Materials. I have recently aquired for our company the distributorship of the Serious Window in our area. I got educated on this product while working with a local builder who is on track to build the PH certified house in our area. I have done months of research on windows and doors. The Serious 925 series window is being used with a custom glass package (they are willing to do this for certain sized orders).

    The problem we are left with (of course) are the doors. We have quoted Internorm because they are PH certified and meet the requirements. But for all of the reasons you mentioned no one is thrilled with this as an option. You stated that you are making your own door in house and I would like to ask you for more information. Is this something you are willing to entertain selling to others? Where are you located? I have numerous questions and would like the opportunity to talk with you. I don't know the best way to get contact information to you or from you. I look forward to hearing from you. Thank you!!

  10. Stephen Thwaites | | #10

    Certifying North American Windows to the PH Stnd

    As i understand the requirements for PH windows, there are at least two reasons why North American Windows have a tough time becoming PH windows.

    1.Standard size
    The standard size for a PH window is 1230mm x 1470mm. This can be done with one sash with Inswing European Tilt and Turn hardware. Filling this size opening with Outswing North American Casement hardware requires two casements with a post between them. This extra framing increases Uwindow making it very difficult the PH window U requirement of 0.80 W/m^2K (0.14 Btu/ft^2F)

    2.U calculated for Smaller Delta T
    As I understand it, in Europe U is based a 0C (32F) outdoor temperature and a 20C (68F) indoor temperature. In North America U is based on -18C ( 0F) outdoor temperature and a 21C ( 70F) indoor temperature. While most materials don't change their insulating properties over this temperature range, gases can. As a result in Europe the optimal air/gas space is 16mm, while in North America the optimal air/gas space is 12.5mm. North American windows with optimal spacing between panes, when evaluated to European norms are sub-optimal. (The reverse is not true).

    ((As an aside there are strong arguments for following Europe on this temperature issue. In North America the -18C ( 0F) outdoor temperature to calculate Uwindow was adopted to size heating equipment. Given that;
    - heating systems are routinely obscenely over sized
    - most homes in North America only rarely experience -18C ( 0F) wintertime temperatures
    - Uwindow's role in predicting seasonal energy use is more important, than is role in sizing heating systems
    there is a strong argument that the delta T used to calculate Uwindow should be decreased to something that represents typical rather than extreme conditions - more like what is used in Europe.))

  11. jimblodgett | | #11

    Serious Misinformation?
    I recently met with a Serious rep and have company literature in my hand that claims a couple glazing options for the 925 series.

    One option claims "U-factor: 0.11, VT: 0.38, SHGC: 0.22"

    The other "U-factor: 0.14, VT: 0.57, SHGC: 0.42"

    These are supposedly NFRC certified numbers.

    Am I mistaken to believe their literature?

  12. GBA Editor
    Martin Holladay | | #12

    I don't doubt the Serious Materials literature
    As far as I know, the information you have is correct.

    1. Option one has a very low SHGC -- certainly too low to use on the south elevation of a cold-climate house, in my opinion.

    2. Option two is only available as a fixed (non-operable) window, although it's a good compromise for anyone who doesn't need the window to open. If you want an operable window similar to this option, the numbers change: a casement window with the same glazing option is U-0.17 and a SHGC of 0.33 -- not much solar gain there. Thermotech offers a triple-glazed casement that is U-0.19 and has a SHGC of 0.42 -- much better on the SHGC.

  13. Kori Fox | | #13

    Serious Literature
    There are other customizable options through Serious for PH.

  14. Stephen Thwaites | | #14

    Window insulation is only Half the Story

    European PH windows insulate well – better than nearly any North American window.

    However, as Martin points out, PH windows don't insulate quite as well when evaluated to North American standards. When I put a typical 1st generation PH window into North American software, with North American outdoor-indoor temp. differences, pyrolytic solar gain low-e and Tilt & Turn sizing I got a different U window than reported in Europe. Instead of getting Uwindow of 0.80 (0.14), I got a Uwindow of 0.90 (0.16). In comparison, an insulated fglass casement with similar glass has a Uwindow of 1.08 (0.19)

    In the end this doesn't matter, because the PHPP software evaluates each window based on its actual size – which can be especially important for smaller windows w/ metal spacers. Additionally the PHPP software uses 'European data', not NFRC data. Although arguably, PH windows should at least 'astericize' non-NFRC U's in when marketing in North America.

    But insulating capability is half or less of the cold climate window story. To drive this point home with the Canadian ER (the Energy Rating includes the effects of losses and gains); the better insulating PH Tilt & Turn of the previous paragraph has an ER of + 40. While the poorer insulating fglass casement has an ER of + 41. In other words slim frames don't need to insulate as well as bulky frames to reach a given energy performance. Note the the newest version of the ER assumes a 20% reduction in solar gain due to shading, so the difference would be slightly greater on an unshaded window.

    The solar gain advantage of North American windows is even larger when it comes to fixed windows. Often the fixed version of a PH window can be as bulky as its operable counterpart. Typically North American Fixed windows are at least half as bulky as PH fixed windows.

    The bulkiness of PH windows is not that much of a drawback in relatively cloudy Europe. However northern North America while colder than Europe, is also sunnier.

    All this gets sorted out in the PHPP software. To the European trained eye North American windows look obviously inefficient. But as Katrin says, they produce surprisingly good results when input into the PHPP spreadsheets. It's there that their solar gain advantage can really shine – so to speak.

  15. Graham Irwin | | #15

    Rocky Mountain High???
    Nice article, Martin. I have two comments to add:

    1) I spoke with Robert Clarke of Serious (Alpenglass) Windows and he stated that their full palette of 200,000+ glazing configurations was available. I don't know how long this custom service will be around, but the stated values in the literature were irrelevant.

    2) As I understand it anecdotally, attempting to transport windows over the Rocky Mountains requires that there be a pressure equalizing tube installed and that eliminates the option of any special gas fill. It seems that those of us West of the continental divide have to get windows manufactured on this side or shipped via the Panama canal. People here seem to be going for German/Austrian windows since the air tightness is known (NFRC lists air tightness as an OPTIONAL rating!!!) We are also holding out hope for Serious Windows on some projects, but yet to install any...

  16. AdrienneBurt | | #16

    Ongoing discussion
    I think this is a really interesting discussion in the comments- from my recent experience it has been hard to find a forum or discussion about efficient windows. As more options become available to us throughout the US, it would be nice to have a forum on this site to talk about our projects using these windows. Specifically, I would like to see pictures of installations (as an aside- why are so many pictures on window manufacturers websites so awful???), information on local distributors (it's surprisingly hard to find this information, especially if you are in a rural area), and even a place for manufacturers to share news.

    Perhaps this kind of forum already exists somewhere, but I would love to see it here because I trust Martin and his colleagues to add their two cents and a dose of reality.

  17. GBA Editor
    Martin Holladay | | #17

    Welcome, Adrienne
    Please consider this YOUR forum — to contribute your questions and comments on windows. Glad it's useful. It will continue to stay active as long as readers keep posting here.

    It's always possible to start a new thread in our Q&A section as well. We're delighted when these resources are used.

  18. jimblodgett | | #18

    Hey Kori,
    You said "There are other customizable options through Serious for PH." I'd sure like to hear about them Kori. I'm in Western Washington. Is there some way we can talk?

    What about the elevation change issue that Graham Irwin mentioned. My understanding was that the expansion bulbs were added to windows to deal with the altitude change/expansion/contraction issues. Do you have any information regarding that?

  19. Kori Fox | | #19

    I would love to talk and/or meet. I am going to go out on a limb here and post my email (hoping for no spam). [email protected]

    Regarding the breather tubes, yes they have an expansion bulb on the end of the tube. As the gas is pushed out during expansion it is captured in the bulb. Upon arrival to our facility we compress the bulb to push the gas back into the unit, then close the breather tube.

  20. Coyo | | #20

    Heat mirror SHGC/Passiv Doors
    Martin - regarding the heat mirror question - we use HM TC88 with a U-Factor - 0.15 and a
    SHGC - 0.51. Southwall has many different variations on the glazing...and it is more a matter of specifying out what you want exactly then just going with the standard offering which often makes no sense for individual projects, circumstance and climate. And south and north facing windows shouldn't be glazed the same IMO.

    Kori - sorry for not getting back to you regarding the Passiv doors. Time is very sparse with lots of Projects in the Pipeline and winter around the corner here in Alaska. I will email you with contact info and see if I can get you some more information.

  21. GBA Editor
    Martin Holladay | | #21

    Great specs
    Those specs are so good that I have to assume that they are glazing-only specs, not whole-window specs. Am I guessing correctly?

  22. Mark Siddall | | #22

    PassivHaus Windows for all climates

    First off great article – this one had passed me by until now. Comments are as follows:

    I disagree that there is “redundant weatherstripping” the double seals ensure the thermal perfomance of the frame (assisting U-value, preventing air leakage and protecting against wear and tear)

    On Heat Mirror – The psi-value at the spacer bar has been rather poor in the past I’m not sure whether this has been addressed but it is something to keep an eye on. As noted the g-value of Heat Mirror is generally quire poor (as far as I know HM55 is the exception to the rule).

    Finally I thought that this link may be illuminating. It’s a paper that I worked on with Danny Havey from Toronto Uni. For the first half we looked at the PassivHaus comfort requirement of a maximum 3C difference in surface temps and calculated the U-value required for a range of external temperature conditions. This allows climate sensitive design and specification.

    NOTE: Value engineering may suggest in some climates / economic conditions (such as those in the UK) that it is more cost effective to specify a better glazing U-value. The result being that the requirements for the opaque building fabric becomes less onerous.


  23. Kori Fox | | #23

    Passive House Specs
    Serious Materials has just released a new piece of literature for Passive House. It gives all of the measurements needed for the PHPP software. These are the American Passive House measurements.

  24. Jesse Thompson | | #24

    Serious PHPP numbers

    Link please?

  25. Kori Fox | | #25

    This is brand new literature and I only have it as a pdf. Here is a link to our website and specifically the SeriousWindow page you can contact me through this page or email me directly at

  26. Kori Fox | | #26

    I made a mistake on my email
    I made a mistake on my email address [email protected]

  27. GBA Editor
    Martin Holladay | | #27

    More from Serious Materials
    Serious Materials has just issued more window information tailored for Passivhaus designers.

    Check it out:
    A Web page called "Serious Windows for Passive House."

    A pdf document also called "Serious Windows for Passive House."

  28. GBA Editor
    Martin Holladay | | #28

    More on Passivhaus windows
    For another perspective on Passivhaus windows, check out this blog entry:

  29. GBA Editor
    Martin Holladay | | #29

    One more distributor
    According to Bernie Wolf, a representative at European Windows in Gainesville, Georgia, Heinzmann vinyl windows (manufactured in Germany) are Passivhaus certified.

    The U.S. distributor for Heinmann windows is:

    European Windows
    3315 Dawsonville Highway
    Gainesville, GA 30506
    Fax: 770-287-9828

  30. GBA Editor
    Martin Holladay | | #30

    Well, maybe Heinzmann windows aren't certified...
    After checking with Katrin Klingenberg, I have learned that Heinzman windows are NOT listed on the Passivhaus Institut Web site as certified windows. I will investigate why Bernie Wolf told me otherwise.

    Katrin also provided further interesting information: two other Passivhaus-certified window brands -- Silber and Bieber -- are not being distributed in North America.

    Bieber windows are manufactured in Waldhambach, France. They are distributed by:
    Bieber Architectural Windows
    15773 Gateway
    Tustin, CA 92780

    Silber windows are manufactured in Mistelbach, Austria. They are distributed by:
    Red Cougar Enterprises
    P.O. Box 1507
    Cochrane, Alberta T4C 1B4

    Thanks, Katrin, for the very useful information.

  31. GBA Editor
    Martin Holladay | | #31

    Heinzmann windows
    According to Bernie Wolf, Henizmann vinyl windows are manufactured in Germany using Veka vinyl extrusions. These Veka frames have obtained Passivhaus certification.

    So, it appears that (as long as the appropriate glazing is specified) Heinzmann windows with Veka extrusions meet Passivhaus requirements.

    For more information on Heinzmann Windows, contact:
    Bernie Wolf
    European Windows
    Gainesville, GA 30506
    [email protected]

    I have updated the article above to include Bieber, Heinzmann, and Silber windows.

  32. Stewart Rohrer | | #32

    North American Fibreglass Frames
    I find it curious that the installation gap/heat loss issue is still not being addressed adequately by North American fibreglass frame manufacturers. This issue has been with us ever since windows have moved from in-house framed window panes to discrete framed (aluminum, vinyl, fibreglass, etc) window units set into rough openings - a long time I would think. Why can't integral insulated extensions be incorporated into casement /out opening window fibreglass frames so that the issue of exterior insulation to installation gap can be addressed without having to resort to the more expensive inward opening tilt/turn windows. As a roofer, I also do not understand why frames are lacking integrated flashing attachments that would allow flashing overlap similar to the interlocking roof systems. Depending totally on seals for a watertight seal in an area of heavy horizontal rain doesn't seem particularly appealing to me - water needs to flow naturally away with the seal only acting as backup. Thorsten Chlupp is definitely on the right track in dealing with the installation gap but we really need the window frame manufacturers to step up to the plate to address the window frame to rough opening interface in a more responsible manner. If such a manufacturer already exists, please let me know who they are.

  33. Scott | | #33

    Sustianbility and High Efficiency Windows
    I wanted to add my small part here. As I read the about the construction of the windows and the way every one was smitten by the true craftsmanship of these products . I was struck by the same methods we employ as do the German Window Manufacture. We offer sustainable wood cases for both our entry doors and windows made from Exotic Northern Cedar. The wood is harvest from the floor of the forest as it is mostly impervious to mother natures decay. Our warranty is the best in the business because we build our products to last and of course we stand behind our work. Frankly we have been building doors and windows like this for nearly a century here in the US. Just as the Germans have been building quality products for the last century. I agree the Germans build some beautiful pieces but we can build to the same standards of any other country in the World. In fact we can build better with the resources we have in the US. Most companies choose not to do this. I can tell you from experience. Customers still find products made to last generations extremely desirable.

  34. GBA Editor
    Martin Holladay | | #34

    Sorry, Scott
    I don't see any information at all on your Web site about energy performance, so I'm afraid I don't see how your thoughts are relevant. The Passivhaus Institut has established criteria for Passivhaus doors — as far as I can determine, the overall door assembly must have a U.S. U-factor of 0.14 or lower (metric U-factor of 0.8 or lower). So door manufacturers who are interested in meeting the Passivhaus market have their goal set out for them.

    It's a challenging goal. When Passivhaus builders are shopping for doors, they want information on U-factor and infiltration rates.

  35. hejdoe | | #35

    Thanks for all your postings and links. Just a small correction on an address you give for a Canadian Silber distributor:

    Red Cougar Enterprises
    P.O. Box 1507
    Cochrne, Alberta T4C 1B4

    The town is Cochrane, not Cochrne. It's a short drive West of Calgary


  36. GBA Editor
    Martin Holladay | | #36

    Corrections made
    Thanks. I have made the corrections.

  37. Larry Martin | | #37

    Unilux Windows
    To acquire the Unilux Windows, call the correct phone number for Hawkeye Windows & Doors, Inc at 319-232-3220 or 800-701-3220. We have be been German window dealers since 1998.

  38. GBA Editor
    Martin Holladay | | #38

    Unilux contact information
    Thanks for the correction. Anyone interested in Unilux windows can also contact George Wright, the national sales manager for Unilux. George Wright lives in Florida. His contact information:
    George Wright
    Cell phone: 850-419-2962
    george.wright [at]

  39. Custom Doors | | #39

    Why can't integral insulated extensions be incorporated into casement /out opening window fibreglass frames so that the issue of exterior insulation to installation gap can be addressed without having to resort to the more expensive inward opening tilt/turn windows. As a roofer, I also do not understand why frames are lacking integrated flashing attachments that would allow flashing overlap similar to the interlocking roof systems.

  40. Don Overland | | #40

    Hardtime (Series?) triple-glazed-iNLINE windows for $40 or $50
    I am having a hard time finding which (series/spec?) for triple-glazed-iNLINE windows that are as low as $40 or $50 a square foot according to Jesse Thompson in your article. For Dan Lolbert I agree that there is a lot of weight torquiring off the frame. I ran into that problem in 1981 when we didn't have low-e, at that time, so we went with 4-panes of glass and are cranking hardware would fail too. We were building superinsulated home at the time. Awnings help with that problem and for egress we were force to switch to 6 panel (no lite) entry doors with aluminum self/storing storm doors. I hope this will help with the door problem. Steel or aluminum that are multi-vent storm doors are the only way to go otherwise it get too hot for other storm doors. Others wil be asking about the windows because of FHB #210 and in the future FHB #213. Nice blog you have Martin and GreenBuildingAdvisor. Thanks again for the help, Don from WI

  41. Teresa Grabill | | #41

    North American Windows
    There are several high end windows manufactures in the USA one of them being Grabill Windows made right here in the USA that can meet U-Values of .28 in a double glazed window and better for triple glazing. These products give the architect design freedom which is not always possible with a standard window product made oversees on CNC machines.
    Doing business in the USA has many advantages. Attention to detail, personalized service and great warranties are offered. There are long lead times and language barriers when purchasing oversees. I am sure the German windows you described are very nice but give the American market another look.

  42. GBA Editor
    Martin Holladay | | #42

    U-0.28 is not that great
    Many builders are aiming for windows with U-factors lower than 0.20, so U-0.28 isn't that impressive.

  43. Brian O' Hanlon | | #43

    Thanks for the article
    Just the kind of article I was looking for at the moment in fact. When I get a chance to read it, I must offer whatever comments or observations I can. I saw your link to this article from one of the GBA Q&A items on windows.

    I think it is a neat trick in GBA web site, the way you fellows provide links to 'other related content' and so forth. It is most useful. I was listening to Chris and Phil's podcast in Design Matters blog last night, and their podcast had links to various other GBA content. Most useful feature, I must say.

    Thanks again, B.

  44. Brian O' Hanlon | | #44

    Thinking about the envelope
    In terms of thinking about the construction envelope, I think we will begin to demand a lot more of these kinds of graphic presentations from architectural consultants in the future.

    It is the only way to coordinate the efforts of multiple 'gangs', installing different parts of the puzzle on a building program on site.

  45. Graham Irwin | | #45

    Serious Windows PHPP values
    Converting US manufacturer NFRC performance data to PHPP compatible inputs is a challenging task. I have taken a stab at it and detailed it here:

    I'd welcome insight.

  46. Tomas Kocis | | #46

    PH Windows Ug-10, SHGC of 0.6, VT of 0.74
    I would like to contribute with our specs for windows that we import from Europe.
    We started to import European PVC Schuco windows for passive house projects.
    We offer PH Certified windows with the following glazing specs:

    1. Ug-0.105, SHGC of 0.5, VT of 0.71 (Btu (th)/hour/square foot/°F)
    2. Ug-0.105, SHGC of 0.6, VT of 0.74 (Btu (th)/hour/square foot/°F)

    I am happy to answer any questions here or you can contact me directly at [email protected]

  47. mchelnov | | #47

    US fabricated windows comparable to Fibertec and Inline
    For those who are looking for US made windows with pretty good numbers, you might want to look at Soft Lite windows listed on NFRC as SLL-A-33-00044-00001 and SLL-A-33-00046-00001. they have NFRC U and SHGC values that are comparable to Inline or Fibertec. These are vinyl insulated frame windows . I checked out a condominium installation of these windows (actually their slightly less robust predecessors) that is 12 years old and they are holding up very well. Soft Lite developped the glazing for us to approach Passive house specs. Soft Lite is a replacement window manufacturer with a passion for high efficiency .

  48. GBA Editor
    Martin Holladay | | #48

    Response to Michael
    Using krypton, which is much more expensive than argon, the SLL-A-33-00044-00001 achieves U-0.19 -- not quite as good as Thermotech triple-glazed casements with argon, which achieve 0.17.

  49. Michael Chelnov | | #49

    Response to Martin
    It's true, they are not quite as good as Thermotech....but I have found them to be easier on the pocketbook . For those who want to build according to the passive house standard, but are on a tight budget...I would recommend taking a look.... From what I can tell they are a very good step in the direction of making Passive house construction more accessible.

  50. Michael Chelnov | | #50

    I was reading your great interview with Dr Feist, and his simple "you don't have to buy windows from Europe " attitude inspired me to mention this up and coming window manufacturer. The performance numbers are close..the quality is good, and they are competitively priced.

  51. GBA Editor
    Martin Holladay | | #51

    More information
    Check out an interesting article, Windows for North American Passive Houses, in the Fall 2010 issue of the Efficient Windows Collaborative newsletter.

  52. Kevin Stamm | | #52

    choosing windows
    I've seen the damage done and the drug is water. For me the first thing I look at in a window is water management, if something starts leaking, ooh say in a corner, where does the water go? There has to be a weep system to get the inevitable water down and out, it can't sit in the frame and rot it if wood or cause mischief was glazing seals. Does one expect the caulking on the glazing to sash joint or the corners of the sash to last forever? I look at corner samples I just wish it was easier to see them from all the world over choices brought up in these blogs. Choose a window first on durability then crunch all those U and SHGC #'s . Would like to hear from someone who has looked at a lot of corner samples w/ this goal and would like to see this as part of window "rating system" Kevin Stamm

  53. QuVZ3VkZxC | | #53

    Passiv Haus publication # 37 ?
    New to this blog. Great discussion. Where can I linked to the publication, Passiv Haus publication # 37, mentioned by Thorsten Chlupp?
    We are looking for high-performing Entry Doors; any ideas?
    thanks, Tim

  54. GBA Editor
    Martin Holladay | | #54

    Response to Tim Koelle
    I think this is the document that Thorsten was talking about:

    How's your German?

  55. user-1147398 | | #55

    Part of being green - produce locally
    Thank you for an excellent article and what a great resource to not just the products but the knowledge!

    And part of being green is the source locally as much as possible to avoid transportation footprints. We don't live in an isolated world; trade and exchange among countries and communities are important. Yet, we can surely find benefits in job creations and carbon footprint reduction by building these European windows and doors right here in North America.

    Since 2010, I am part of a few small business owners who have been bringing the technologies and education in North America. The Alpine Technical Workshops(c) teaches the production and construction method of German-style wooden tilt-and-turn window and lift-and-slide doors, from preparing blank stocks to profiling, from glue-up to hardware construction, and from glass to gasket installation. This small business caters to mostly other smaller to medium size shops all around North America. Before any woodworker invests in the machines and tooling on these products, a few of them likes to come to our live workshop in Colorado to experience it first hand on how it works and study to business opportunities before expanding their current shop products.

    Again, I am glad to see more community building articles like this one as it shares knowledge and products that move our business and desires to be greener forward. And it's a bonus that manufacturing locally in each community (or at least right here in North America) produces more jobs and business opportunities.

  56. jpstaub | | #56

    Buyer beware
    For those interested in certified Passive House components this is an excellent link:

    The above link is a primary source for up-to-date information on who's making what Passive House International certified component where. Hint: Northwin of Canada has a certified window frame.

    Based on my own hunt for Passive House windows the best piece of advice I can give is to ask for a THERM file for the window. If the company doesn't have a THERM file and you can't make one yourself based on company supplied information you might as well buy more "expensive" windows for all the time/money you'll spend to verify that "cheaper" so called "Passive House" windows will perform as advertised. If verification isn't your bag then Passive House isn't really either.

    Full disclosure: I am not affiliated with any Passive House agency, group, or manufacturer. I am developing a Passive House and the marketing tactics that have been deployed to secure market share make the process unnecessarily challenging.

    Jake Staub

  57. GBA Editor
    Martin Holladay | | #57

    Response to Jacob Staub
    Thanks for the useful advice.

    I'll leave it to the readers to determine whether the high hurdles that North American Passivhaus designers face when choosing windows are due to useful criteria set by the Passivhaus Institut in Darmstadt -- hurdles which assure quality and performance -- or are due instead to an obsession with paperwork that is unjustified by results.

  58. Casshua | | #58

    Passivehaus windows
    Canadian Manufacturers have made significant progress in matching style and performance of European windows. See the people at - they make a very good fiberglass window and offer doors as well.

  59. Chris_Alpine_Workshops | | #59

    New window in US certified by Passive House Institute
    Casagrande Woodworks Inc. has received the first Passive House Institute (PHI)’s window frame certification in the United States for its window called Synergist. This window has a thermal transmittance (Uw) of 0.79 W/(m2K) with Passive House Efficiency Class A (advanced component). Synergist is also the only PHI-certified solid all wood, out-swing casement window in the world and will be manufactured by Casagrande Woodworks in California later in July 2013.

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