GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Vinyl versus fiberglass windows? Pro and con

| Posted in Green Products and Materials on

I am looking at several windows manufacturers for my project in Searsport Maine on near the ocean. I have looked at Intus uPVC windows, Fibertec Fiberglass windows and waiting on other quotes such as Marvin Integrity Fiberglass windows. I am trying to maintain a tight building envelope so the windows will be casement or tilt and turn. Any advice on these materials for windows? Pros and cons would help. Also should I consider other types? I am near the ocean and must take marine conditions in to consideration.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Fiberglass windows are generally more expensive than vinyl but are considered higher quality. The coefficient of thermal expansion of fiberglass is less than vinyl, and is closely matched to the coefficient of thermal expansion for glass -- that's a plus for fiberglass. Fiberglass isn't as soft, and will probably last longer. Fiberglass is structurally stronger, and has no need of steel inserts inside the hollow profiles (often used for larger vinyl windows).

  2. Tom_Maine | | #2

    Do you think that for a house that is trying to get the most efficient windows and tighest envolope that I should primarly concentrate on Fiberglass? Since my house will be close to the ocean I need something that will hold up to moisture and salt air without any degradation. I am also trying to get my ACH as low as possible but do not have an unlimited buget for windows. I found the Fibertec windows to be good. Should I look at any other manufaturers of fiberglass windows or any other material?

  3. Matthew Nolette - So Maine CZ 6A | | #3


    Caught your request for my opinion in the other thread. Martin answered your question but I think this is the consultation you're looking for.

    We chose Intus primarily on a performance-to-value basis. The Eforte PassivHaus uPVC have 0.106 U-value and .62 SHGC on the South and 0.088 U on the N, W, & E faces. By contrast Fibertec's best listed glazing for Southern faces is 0.16 U and 0.43 SHGC and the lowest U-value is 0.15. I can't locate specific U-value on Fibertec's frame but it's foam filled so I expect it's around 0.125 or better where the Intus frame is 0.167. Infiltration favors Fibertec but only by the narrowest of margins; the Eforte frame is PH-certified after all. Intus was notably less expensive but that's going to vary by supplier; Maine Green Building Supply is excellent but I assume you're talking to them already (Tell Jason I said, 'Hello.')

    The .62 SHGC on .106 U is a big win.

    For what it's worth, I was also very pleasantly surprised how reasonable the cost for upgrading the hardware finish was with Intus; particularly compared to Marvin.

  4. Tom_Maine | | #4


    I will tell Jason you said HI the next time I speak with them. I have been speaking with Alba but getting the emails from Jason. I was really impressed with the price on the Eforte PassiveHaus uPVC prices. I am just worried about the durability of the uPVC (Vinyl) to the coastal Maine climate.

    Do you know what the Intus translate into for whole window U value?

  5. GBA Editor
    Martin Holladay | | #5

    Q. "Do you think that for a house that is trying to get the most efficient windows and tighest envolope that I should primarly concentrate on fiberglass?"

    A. Yes, if those are your criteria. (Your question didn't mention cost.)

    Q. "Since my house will be close to the ocean I need something that will hold up to moisture and salt air without any degradation."

    A. Both vinyl and fiberglass hold up well to salty ocean air. But by all means, avoid windows with aluminum cladding.

    Q. "I do not have an unlimited buget for windows."

    A. Well, if you are worried about the cost, vinyl is cheaper.

  6. Karlyn K | | #6

    In case you were still looking for Fibertec's U-values, here's a link to the casement window's energy ratings and like you said, shows U values as low as 0.15:

  7. Brian P | | #7

    Another brand to consider would be Alpen:

    Distributed by Pinnacle in Hallowell, ME:

    We're using them for our house in north-central New Hampshire.


  8. Scott Kearney | | #8

    Tom you might want to take a look at UPVC windows along with Fiberglass. Fiberglass windows are mechanically fastened together while UPVC is generally fusion welded on all corners . UPVC windows are widely accepted as the window of choice in Europe when trying to achieve energy efficiency and low maintenance and are quickly gaining traction in the US. Here is a link to Kohltech windows made in Nova Scotia Canada Their windows and doors are made for the Canadian Maritime environment. Hope this helps!

  9. Roger Berry | | #9

    Just a heads up on being certain whether the values you are finding are metric or US. The value of .088 is a common value I have seen associated with European window choices I have looked at in the past. I can't remember the rule for conversion, but you will find that once converted, the values are similar to the best US units. Martin can chime in on the fine points of the whole window issue and perhaps provide the link to prior discussions of Euro vs US ratings.

  10. Tom_Maine | | #10

    Thanks Everybody. This is really some good information. I reviewed the Intus quote and it said Ug=.088 Btu/hr sq.ft F. I am not sure if that Ug is the Center of Glass or whole window assemply. My feeling is that it is just Center of Glass. That U value would roughly translate to an R value of 11.4. Reviewing the Fibertec windows, I spoke with the rep and he said if the quoted window had a Hard Coat, it would have a U value for total window of .21 which is what was listed on Karlyn's post with the link. The rep said that if it had the Soft coat the Total window U value would be .15. I have gone out to the site to look at the stated U values of different windows. It is a good source to use.

  11. Greg Smith | | #11

    Euro U-values versus North American U-values has definitely been addressed a few times on GBA. From my perspective, a fun discussion all around.

    Anytime someone is discussing window energy performance, especially when comparing across the pond, it is very important to separate whole window performance from glass-only numbers. It is equally important to remember that trying to directly compare converted Euro performance numbers with NFRC derived performance numbers is better left for another day.

    All that said, it is also certainly possible to achieve something very close to .088 center-of-glass in a more or less standard triple pane IG unit, even when testing to NFRC criteria.

    Leaving aside the differences in test methods (and philosophy), and U-value conversions for the moment, a triple pane IGU fabricated using 3.0mm float glass, Cardinal LoE-366, triple silver coating on glass surfaces 2 and 4, Cardinal I89 on surface 6, 1/2" airspace, and 95% krypton fill, will have a center-of-glass U value of .092 - again to NFRC test criteria - calculated using LBNL Windows 7.1.

    Not quite .088, but once again direct comparisons between NFRC and Euro is ultimately a rather futile pursuit.

    If we substitute argon for krypton, which is a good idea for a variety of reasons, then U-value is .106, which by any measure that I can think of is a performance number that very few are likely to complain about. As has been said here in the past, the difference of a few hundredth's of a percent at this level is bragging rights more than perfomance differences.

    I do think that the ".62 SHGC on .106 U" benefits a lot in the conversion from Euro to NFRC, though. Meaning absolutely no disrespect to anyone anywhere, I would really like to know how the window company arrived at those numbers in a triple configuration.

    Heck, there is a window being made in Poland that has a claimed R-38 (and made it to a GBA blog - unfortunately I don't remember who bloged it, and I couldn't find it to link here). Although I can't imagine either the cost or the potential probems associated with manufacture and longevity, it is still a very interesting concept.



  12. Greg Smith | | #12


    Without looking at Fibertech's website or NFRC site, I am going to guess that the U value difference may be because they are using a high solar heat gain hard coat (possibly Pilkington energy Advantage?) versus a low or moderate solar heat gain softcoat.

    That would account for the U value change, but it would also affect SHGC as well between the two options.

    There are softcoat high solar heat gain coatings as well, but Canadian companies tend to rely on hardcoats a good bit more as a general rule (with some exceptions) when they want higher solar heat gain.

    (I really have to learn to review spelling BEFORE hitting the "post" button)


  13. Tom_Maine | | #13


    That is some really good information. It is funny that you mentioned the window from Poland. I saw that as well. I found it a little too hard to believe and figured that it would be way out of my budget range. I am going to talk with the Intus distributer again about the whole window U value. For some reason I think I asked what the whole window U value was and I thought he said .21, but I need to call back and confirm.

  14. Tom_Maine | | #14


    I spoke with the Intus dealer and asked about the difference in the Euro versus North American calculation of the U value. He said that the owner was surprised by the U values and asked the manufacturer to clarify. The dealer claims that the Whole Window U value is .12 . Also while I was on the phone with them I walked them through the site to check what their U values would be as measured using the NFRC method. The lowest they had listed for Intus was U .17. So they are going to look into it some more. All I know is that the it is triple pane with "premier glass 4mm / 20 mm Argon/4 mm/18 mm argon/4 mm. As for Fibertec they are using a combination of window types some that have the hard coat which they claim is whole window U = .21 and the soft coat is whole window U = .15. These numbers seem a little more realistic to me than what I am hearing from the other.

  15. Greg Smith | | #15

    Good morning Tom,

    Those numbers do make a lot more sense (IMO).

    Anytime I see a U value claim better that U.15 in a triple pane I become a little skeptical. Not saying it can't be done, but...curious as to how.

  16. Peter L | | #16

    The best bang-for-buck window will be Intus uPVC windows. They would perform flawlessly in a high-wind and salt air area. The hardware is stainless steel or galvanized steel. Intus makes the tilt & turn and they have multiple locking dowels so they lock and seal like a bank vault door. The air infiltration rating on them is <0.03 cfm/ft². They also have a DP (design pressure) rating of DP70 so they are good to 200MPH. They actually just got their windows hurricane approved by Miami-Dade. Best thing to do is price it out and compare the specs. Truth is in the numbers.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |