Vinyl vs. Fiberglass Replacement Windows

A place to ask all your replacement window questions
Post Reply
Posts: 7
Joined: Sun Sep 03, 2006 7:09 pm

Vinyl vs. Fiberglass Replacement Windows

#1 Post by FiberglassVinyl » Sun Sep 03, 2006 9:03 pm

I am about to replace the original 55 year old steel frame single-pane windows in my house located in the southern end of the San Francisco Bay Area (sunnier and hotter than the city of SF in the summer, colder in the winter). I am trying to choose between vinyl and fiberglass replacement (Zbar, flush flange) windows. I plan to live here for the rest of my life (40+ years hopefully) and if possible would like to never have to replace the windows after this. I also want energy efficiency, but it seems both vinyl and fiberglass are about equal in that regard.

As far as I can tell, the reasons to eventually replace vinyl or fiberglass windows in the future are:

1. The windows become inoperable (won't open and close anymore).
2. They lose their energy efficiency -- IGU edge seals fail and argon (if included) escapes from IGU, or condensation forms inside IGU, corroding the Low-E coating; or vent windows no longer close tightly leading to air infiltration.
3. The frame material deteriorates with time and exposure to the elements becoming dull, chalky, discolored, cracked, etc. so as to lose its aesthetic appeal.
4. Window styles or technology evolves so the windows look dated or become significantly energy inefficient compared to modern technology (relative to current energy prices). This is the case on both counts for my current steel frame single-pane windows.

Other than #4, which is only a function of time, fiberglass seems to be a superior material to vinyl in all the other criteria:

1. Fiberglass' superior strength and thermal stability should help keep the windows operable for many years. Fiberglass frames and sashes won't expand as much and their strength will prevent bowing, both of which could make the windows difficult to open and close.
2. Although I've learned on this site that the spacer/edge seal is more important than frame material, it seems fiberglass' similar thermal coefficient relative to the glazing should reduce stress on the seal and help maintain its integrity. As I also learned here, a mitigating factor is
desiccant which keeps condensation from entering the IGU and ruining the Low-E coating even if the seal is compromised (although argon, if used, will escape).
3. The durability, stability, and strength of fiberglass should be superior to vinyl in maintaining the window's aesthetic appeal, plus fiberglass can be painted while vinyl cannot. Once vinyl deteriorates, there isn't anything you can do about it. Even though UPVC is much improved over the older vinyl windows that were installed years ago, I'm still worried what they'll look like in 15-20 years. In addition to all this, fiberglass should have larger sightlines than vinyl (greater even than Milgard Styleline, I believe), adding to their aesthetics.

If fiberglass and vinyl were equal in cost, the decision would be easy -- fiberglass. I have quotes for Milgard Ultra and Pella Impervia fiberglass that are 35% higher (installed) than Milgard Classic vinyl. This tells me that to get equal value fiberglass must last 35% longer than vinyl. For example, if vinyl lasts 20 years before needing replacement, fiberglass should last 27 years or more to achieve equal or greater value. This is where I have no clue. Is the extra cost of fiberglass worth it in terms of longevity? Also, what are the life expectanies of Milgard and Pella edge seals? I think Milgard (and Pella?) use aluminum spacers in their fiberglass windows, but Milgard uses intercept spacers in their vinyl windows. I'm not sure about the sealant materials.

To summarize, what would require the eventual replacement of vinyl and fiberglass windows and what is the life expectancy for vinyl and fiberglass in the moderate climate of the Bay Area? Any other consideration would be appreciated as well. Thank you.

Posts: 13
Joined: Thu Aug 31, 2006 9:01 pm
Location: Chicago-NW Sub

#2 Post by mike.windowguy » Mon Sep 04, 2006 12:40 am

Albeit, new technology, but Fiberglass won't rot, chip, or peal. It expands and contracts at the same rate as glass. Vinyl expands and contracts up to 14 times that of glass.

Plus, fiberglass looks much better.

Beer or Champagne budget?

Posts: 508
Joined: Tue Jan 04, 2005 5:06 pm
Location: Kentucky

#3 Post by JScott » Mon Sep 04, 2006 7:06 am

Milgard has been using fiberglass for 20 years. Not new technology. I know of no fiberglass window that has ever needed to be replaced. Milgard will cover labor and materials for seal failures of your glass and hardware for as long as you live in your home or as long as they are in business. The quality and performance of the Milgard is time tested and much greater than that of Impervia which is the newest player on the block. The Z-bar fin is the perfect installation approach to steel frames.

Posts: 7
Joined: Sun Sep 03, 2006 7:09 pm

Vinyl vs. Fiberglass Replacement Windows

#4 Post by FiberglassVinyl » Wed Sep 06, 2006 2:20 pm

I'm still wondering how long vinyl windows will last before needing replacement?

Window4U (IL)
Posts: 1548
Joined: Thu Oct 07, 2004 8:46 am
Location: Sales and Installation in Chicagoland and Central Illinois

Re: Vinyl vs. Fiberglass Replacement Windows

#5 Post by Window4U (IL) » Wed Sep 06, 2006 4:12 pm

FiberglassVinyl wrote:I'm still wondering how long vinyl windows will last before needing replacement?
I've seen vinyl windows I put in 25 years ago (that have been washed regularly) that look and operate almost like the day I installed them. Not all vinyl windows will though.
The installation methods, the size of the window, the type of the window, the counterbalances used in the window (if doublehung) and the success of the spacer system all have their share to do with the longevity of the window.
That why it is important to research the components and find out what type window is best for the window openings you now have before you purchase.

Posts: 305
Joined: Mon Nov 15, 2004 4:52 am
Location: West Coast

#6 Post by earwax » Wed Sep 06, 2006 8:10 pm

I do not think that either option is a bad one. The companies that make fiberglass also make vinyl in a lot of cases. VInyl is cheaper and have less color options. It is less rigid. Vinyl is cheaper and is cheaper, and did I say that vinyl is cheaper?

House Doctor
Posts: 11
Joined: Sat Aug 26, 2006 7:38 pm

#7 Post by House Doctor » Sun Sep 10, 2006 9:40 am

Penny wise and Dollar dumb? If you're selling the house in 1-3 years go vinyl-- it's cheap & quick & good enough for the next owner. But if you're going to be stuck trying to sell it in 10 years or more; go with the fiberglass. They'll still look and work and perform like new even 10 or 20 years from now. The future buyer won't be subtracting the cost of a window replacement from your asking price. Fiberglass windows have fewer stress cracks & seal failures. (Actually, in all my years in the construction industry, I've NEVER seen a stress crack (or a seal failure) in ANY FIBERGLASS unit. That includes Milgard, Comfortline, Integrity, Infinity, and a couple from Canada. They're all built like a tank -- indestructable. (The Pella is brand new, so I'll withhold my opinion on that one.) Fiberglass also holds it's air-tightness better than Clad wood, and MUCH MUCH MUCH BETTER than vinyl (vinyl expands/contracts too much). A COUPLE CORRECTIONS: 1)Glass edge spacer is LESS improtant than frame material: just compare the price of re-glazing a fiberglass sash to the price of replacing the entire frame and both sash. (The most reliable glass spacer is Cardinal's Stainless--and its standard in all Marvin products like Infinity Fiberglass & Integrity) 2) DESSICANT does NOT prevent or even delay cloudiness if you have a seal failure, and ALL insulated windows have dessicant-- so it's not a deciding factor anyway. OTHER THOUGHTS: Dull or chalky appearance is equally likely on all (non-Kynar) windows: Vinyl, Alum clad, and fiberglass. The IMPORTANT difference is that ONLY fiberglass is paintable, at any time with any exterior acrylic latex--even after 20 years. (Paint won't stay stuck to vinyl or alum clad, but it sticks to fiberglass forever-- so the chalking problem of vinyl is no problem with fiberglass). I think you're overly optimistic to think that a vinyl window will last more than 10 years before developing problems. Even the #1-rated Milgard Classic Vinyl will look second-rate compared to a Milgard's own Fiberglass after about 8-12 years (I've worked with both). Think hard about when you'll be selling this place, and how many years you'll be paying for heat & a/c. The answer will become obvious.

Posts: 4
Joined: Mon Sep 11, 2006 8:24 am

#8 Post by Window_Guy » Mon Sep 11, 2006 8:38 am

Hey Doc,

Excuse me but any chance you could, like present some facts to back up these claims?
vinyl expands/contracts too much
I think you're overly optimistic to think that a vinyl window will last more than 10 years before developing problems

Your speaking to folks who need to make a relatively big decision here and while i'm sure everyone appreciates your love of fiberglass there is no factual basis for what your saying that I am aware of.

I live to learn as they say so i'm all ears to any factual data that supports your theory that a vinyl window will not last more than 10 years.


Posts: 7
Joined: Wed Apr 05, 2006 7:38 pm

#9 Post by jpmkam » Mon Sep 11, 2006 5:38 pm

Penny wise and Dollar dumb? If you're selling the house in 1-3 years go vinyl-- it's cheap & quick & good enough for the next owner. But if you're going to be stuck trying to sell it in 10 years or more; go with the fiberglass.
I live in a house with 15 year old vinyl windows and they look like the new (even in the windows facing W and NW). I find your claim about 3 years quite a stretch.

Posts: 305
Joined: Mon Nov 15, 2004 4:52 am
Location: West Coast

#10 Post by earwax » Mon Sep 11, 2006 7:46 pm

Doc: I do not mean to be rude, but most of your post that I have read sound like regurgitated sales pitches from poor sales people. Scare tactics and false information. Where did you learn all your information? You manufacturing knowledge is poor, your sales information if even less impressive and you knowledge of window materials is putrid. Makes me nervous to think people might listen to your nonsense.

Vinyl is a durable product, it has stood the test of time. (Over twenty years for most the large manufacturers) Fiberglass is the newer technology for the mass producers. I would be more unsure about the fiberglass windows and the mitred corners than a fusion welded vinyl window.

Glass.......Where did you get the facts about the different spacers. Glass edge spacer is LESS important than frame material. Do you believe that the material of the frame plays a large role in seal failures?

Vinyl expansion and contraction. GIVE ME A BREAK. RIDE A DIFFERENT HORSE. THAT ONE IS DEAD. The expansion on vinyl is so minimal, you will most likely never, never, I mean, NEVER see a problem because of this. Unless you live in Arizona and put the windows facing south west, no cover and paint the windows bronze. You might see the breakdown of the vinyl integrity. You have to get the window to 160 for the PVC to become pliable.

House Doctor
Posts: 11
Joined: Sat Aug 26, 2006 7:38 pm

#11 Post by House Doctor » Mon Sep 11, 2006 9:18 pm

O:K, all you vinyl salesmen, you asked for it; First of all, let me say that I do use vinyl windows from time to time, and I’ll be the first to admit they have their place. But to suggest that they’re ALWAYS the best choice for EVERYBODY, and that they’ll work just as good as fiberglass in any situation, is just not facing reality. I’ve added coments in parantheses and shown deletions with …. Dots. If you want to read the whole articles just go to the sites I’ve listed. Here’s what a quick 10 minute surf through the internet turned up; and believe me, it’s the tip of the iceburg:

• “The life expectancy of a fiberglass window exceeds all other traditional materials.
• Vinyl..................15 years
• Aluminum............20 years
• Wood................25 years
• Fiberglass...........40 years”
“Fiberglass expands and contracts at similar rate as glass (1/7th rate of vinyl)”
• “ (Fiberglass) has Less torsion and stress between glass and frame in cold weather (than vinyl, and also…)
o Reduced air leakage
o Decreased stress on locking mechanisms”

“Since vinyl has a higher coefficient of expansion than either wood or aluminum, vinyl window frame profiles should be designed and assembled to eliminate excessive movement caused by thermal cycles. … Large hollow chambers within the (vinyl) frame can allow unwanted heat transfer through convection currents.

fiberglass frames are dimensionally stable and achieve good insulating value … and can be filled with insulation for higher thermal performance. The strength of fiberglass allows manufacturers to maintain the same sight lines as aluminum windows while achieving significantly lower U-factors. The low coefficient of thermal expansion maintains seal integrity and minimizes warpage or leakage in high inside/outside temperature differentials. Fiberglass pultrusions have a higher heat deflection temperature than vinyl, permitting the use of dark colors unlike other thermoplastic extrusions. They can be painted, powder coated, or finished with coextruded acrylic resin.”

“Pultruded fiberglass is virtually impervious to moisture (it has a moisture migration rate of 0.17 percent)
Stability over temperature extremes
(Fiberglass) Pultrusion, like glass, has a very low coefficient of thermal expansion/contraction (3.8 x 106 in/in oF). It does not distort in the extreme hot or cold temperatures to which window frames are subjected. Window frames of (fiberglass) pultrusion hold their original shape, are impervious to temperature changes, and maintain their initial air infiltration rates” SOURCE:

Fiberglass has been around for a long time... it has an excellent record for durability. Fiberglass is strong, so hollow parts can be made without the stiffeners required for vinyl. This allows manufacturers to produce higher efficiency windows by filling voids with insulation. In fact, insulated fiberglass windows are even more energy efficient than those made from solid wood. You can paint fiberglass windows, but they won't deteriorate if the finish wears away. ( ON THE OTHER HAND) : Vinyl windows are inexpensive… They often look chunkier than wood or metal windows because vinyl isn't strong enough …. . The other problem is that the texture is unmistakably plastic. You can't paint them… Vinyl Windows: Then and Now: Early vinyl windows had problems with thermal expansion. When temperatures changed, the vinyl sash would expand or contract at a very different rate from the glass. As a result, the window fit poorly, leaked, or cracked. Such problems have been on the decline, but… SOURCE: The truth is that currently the projects I’m working on use vinyl about 30% of the time; Clad wood probably 25%, Fiberglass about 35%, and Aluminum about 10%. But as fiberglass is coming down to earth on cost, it is increasingly becoming the choice of more and more people. And I really don’t see that changing. But who knows, mabey you know something I don’t. That’s why I give my clients a whole lot of information and let them make their own decisions. I get paid the same flat fee no mater WHAT kind of window goes on the project. As long as they’re still a good reference in 15 years; I’m happy.

Posts: 508
Joined: Tue Jan 04, 2005 5:06 pm
Location: Kentucky

#12 Post by JScott » Tue Sep 12, 2006 12:00 am

House Doctor,
Very good perspective. 8)
Last edited by JScott on Wed Sep 13, 2006 11:02 pm, edited 1 time in total.

Posts: 305
Joined: Mon Nov 15, 2004 4:52 am
Location: West Coast

#13 Post by earwax » Tue Sep 12, 2006 12:40 am

Man....I fell like we have all read this same thread before.

I like Fiberglass windows. I have nothing against them. They are easy to make, costly to buy and look and operate well. Doc, I think we can agree to disagree on some things. The reason why I do not like the way your information is presented, is, it has strong bias. You quote fiberglass window company websites. Look up life expectancy of vinyl windows. Most of the web sites have 20-30 years listed as the life expectancy.

If you statistics are correct, why does vinyl always have a better warranty than wood....and the same as vinyl. (if sold by a company that sell vinyl and fiberglass. Marvin only has a 10 year warranty on the fiberglass...why?) If the glass holds up better in fiberglass, than why only a 20 year warranty? I am not saying that vinyl is better. Fiberglass has much better structural properties. The thermal properties are better too. (though not worth the cost upgrade of a fiberglass window) They can be painted. That is why I would sell them. They can be painted where vinyl is painted against most manufactures suggestions. They are usually extruded a shade of light brown or white. Vinyl usually has at least a 20 year warranty from a poor warranty to a lifetime warranty. On the West Coast, if you do no have a lifetime warranty on the vinyl and at least a 20 year non prorated glass for vinyl, good luck selling the window. The contraction and expansion of vinyl described by fiberglass sales people makes it sound like glass is crushed by shrinking frames and then pops out by expanding frames. Post a picture of a home or IG damaged by contraction and expansion of a decent vinyl window. That would put that discussion to bed and I will concede your argument. I have yet to see one.

Again, fiberglass is a good product. Structurally, I do not like mitered corner. They can break, pull apart etc. (I think of aluminum mitred corners, and see them after years allowing water. Not says fiberglass will, but I can envision it)

JScott: I saw the movie, good movie. Greenpeace does a good job in making sure our environment is protected. :oops: If that is the reason not to sell a good window are a good price and start forcing consumers to buy other types of windows, we should all install wood window. Wouldn't you think? It is a renewable source and is much more eco friendly than Fiberglas.

All kidding and sarcasm aside, all window types have their place. I just get sick of people saying one is better than the other using bad facts (or blown out of proportion facts) that amount to scare tactics for sales people to steer them toward one window.

House Doctor
Posts: 11
Joined: Sat Aug 26, 2006 7:38 pm

#14 Post by House Doctor » Tue Sep 12, 2006 7:03 am

I've seen a lot of welded corners crack right at the weld ( Expecially in HURD vinyl windows ) I've NEVER seen a keyed and screwed joint come apart on a clad wood or fiberglass or commercial aluminum window--ever. As far as warranty, vinyl windows are like Hyundai cars. Both decent products. Vinyl usually has a longer warranty than fiberglass or clad wood. And vinyl is cheaper. Hyundai has a longer warranty than Mercedes or Lexus. And Hyundai is cheaper. Is this because higher quality products always have longer warranties? Or is it more of a marketing decision? I'll bet you know the answer. Thanks for the rigerous banter. Hasta Luego.

Posts: 1011
Joined: Fri Oct 08, 2004 7:26 am
Location: Houston, TX

#15 Post by Randy » Tue Sep 12, 2006 7:56 am

Interesting post, and very reminiscent of some previous posts, debating the merits of fiberglass vs. vinyl.

I have sold many Milgard Ultra fiberglass windows, and some Comfort Line windows as well. Both products have some major issues to resolve before I would sell them again. Although I have never carried the Marvin Infinity or Integrity, both Milgard and Comfortline have been making fiberglass windows far longer and have yet to get their complete act together, so somehow I doubt that Marvin, or Pella for that matter, has managed to pull off a perfect product in their very short time producing fiberglass windows.

To the House Doctor; in your post which was to back up some of your previous claims, you did not address the statement you made which said "The most reliable glass spacer is Cardinal's Stainless....". Where did you get that information? Let me guess, the Cardinal Glass website.

Fiberglass windows have great potential, and very well may be the future of window construction. However, in my opinion, they have a long way to go before I would highly recommend them to my customers. As with most consumer items, the people who purchase early pay an inflated price to cover the cost of development, and eventually the price settles down to an affordable alternative for the masses.

Post Reply