120 mph wind zone - impact glass windows

kritlynMay 9, 2006

We are building in a 120 mph wind zone, 1/2 mile from ocean. I am concerned about the cost of impact glass windows busting my budget. I have been told that impact glass windows can cost 2-3 times the cost of same window w/o impact glass. We are working w/ an architect who is sensitive to our budget and only going to use standard size windows. He has suggested that, although typically more expensive, Marvin's hurricane windows are a good choice. Any suggestions on how I might shop around for the best price for Marvin windows?

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I would suggest that you check out Marvin's web site and see what they list for local distributors in your area.

Distributors do have some control over how they set their own prices and depending on who you choose there can be huge differences between different ones.

Hurricane windows are expensive, but as a cost comparison if you were planning to use top-end windows anyway and then add shutters, then the cost of the upgrade to impact resistant is not that big of a stretch - and some studies have even shown the price differnce to be a wash.

Make sure that the windows are "impact resistant". There are folks who advertise "hurricane windows" that are not actually impact resistant - I am not suggesting that they are doing anything wrong, just that there are different classifications. If you order Marvin impact then you really are ordering the impact package.

I am going to drop a bit more info on these products...although I have posted versions of this next part a few times in the past, I believe that it will provide you with a bit more information than you will generally be able to get from a salesman or distributor.

This is not window company specific, but more of a quick primer on impact windows...hope it helps you some.

I don't generally discuss specific manufacturers, but I do have a few thoughts to share concerning impact windows and their performance...and maybe a couple comments on the systems used by a few different manufacturers...

Impact windows are made with laminated glass, upgraded hardware, upgraded frames and other components, and all sealed in place with some of the strongest silicone (or other) adhesives on the market.

Virtually all the major window manufacturers have impact products available. Some perform extremely well, others barely get by.

Laminated glass is simply two (or more) lites of glass bonded to a plastic interlayer for strength. Laminated glass is no stronger against breakage than is the glass it is made of. Let me say that again - laminated glass breaks as easily as the glass it is made of. I mention that because many folks have the mistaken impression that laminated glass / impact windows wont easily break. They will break, but the glass adheres to the plastic interlayer and keeps the envelope of the home closed.

There are four major food groups in the impact glass world (a few other minor ones as well) relating to the interlayers used to manufacture the laminates.

First we have PVB or Polyvinyl Butyral. This is the stuff that is in the windshield of your car. It is relatively soft and very flexible, yet it is also tough and doesnÂt tear easily. This is probably the most widely used product in the impact glass market since it does great when impacted. It stops whatever hits it and stretches to absorb the impact (such as a persons head in a car accident). PVB is a good product and is the choice for many manufacturers.

The second interlayer type is a hybrid of PVB with a layer of PET film between the PVB layers. This is a very tough product and it performs very nicely, but it can be a problem to manufacture and this product seems to be phasing out of the market  although a number of window companies still offer it.

The third type of interlayer is called SGP or Sentry Glass Plus. This is quite a bit different from PVB in that it is very stiff and very tough. It is becoming something of the product of choice in some of the toughest applications (including some bullet and bomb resistance applications). It is also a bit more expensive than PVB and may be overkill for some residential applications  but I think it is ultimately the best product on the market at this date.

SGP is also becoming the product of choice for a number of the wood window manufacturers, although vinyl folks donÂt seem to be using it quite as much yet, but SGP seems to be growing in the vinyl market as well. One reason it is a little behind in vinyl windows is because SGPÂs rigidity tends to transfer an impact force to the frame of the window rather than absorbing the impact as does PVB. Some (but not all) vinyl windows simply arenÂt strong enough to take that forceÂwhile some vinyl windows do quite well with SGP.

The fourth product line is the resin laminates  where a liquid resin is poured between two lites of glass and allowed to cure. I see liquid resin laminate as the "mom and pop shop" of laminated glass  although some larger manufacturers do use it. For the manufacturer it is cheap, it is easy, and it is an acceptable "mom and pop shop" product. Personally, I am not impressed with performance or longevityÂmy opinion only, but I wouldnÂt use it in my house.

Most window manufacturers buy their laminated glass from a laminated glass manufacturer (which does make sense!)Âbut a few laminate their ownÂsuch as PGT (whom you mentioned).

Among the major residential laminators (who are not window makers) are Cardinal, Old Castle, AFG, Arch Aluminum, Viracon and a few others. Of the bunch, Cardinal is almost entirely residential where the others mentioned are generally split between residential and commercial  most being primarily commercial.

As a window company, PGT laminates most of their own glass and they are very good at it. They also outsource some laminated glass as well. Simonton currently buys their laminated glass from one (or more) of the vendors that I mentioned, but I believe that they are in the process of building their own line.

PGT is primarily an aluminum window manufacturer. Their windows have done very well in the past few Florida storm seasons. I believe that they are by far the largest seller of impact windows in the southeast (and probably everywhere else) Â but thatÂs a guess.

When buying IG (dual pane) windows, some manufacturers place the laminate to the exterior, and some to the interior. This is often based on how the window is glazed. The manufacturer wants to seal the laminated glass to the strongest component of the window / sash. Generally this is the "fixed" stop versus the removable stop.

If the window sash is "internally glazed" meaning that the removable stop is interior, then the laminate will be the exterior lite. If the window is "externally glazed" meaning that the removable stop is external, then the laminated glass is likely the inboard lite.

This isnÂt 100% though. Some manufacturers prefer one version to another for other reasons  such as keeping the laminated lite inboard to stop broken glass from coming into the home when the "other" lite is broken. If the non-laminate is to the interior and the laminate is impacted, then that other lite will break and the glass shards will be inside the homeÂpotentially violently. This can be avoided by placing the lami inboard.

    Bookmark   May 11, 2006 at 8:02PM
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The impact glass equipped windows also offer the benefit of being in place 24/7. As long as the window is shut and locked, it's ready. Shutters, storm panels, etc., all require someone to do something in order to protect the house.
The reason for the protection, however, is to protect the envelope of the house. During a storm, if a window or door is breached (broken), the interior of the building can pressurize. The pressure has to go somewhere, and that usually means the roof blows off, rendering the entire home, and it's contents, a complete loss.
The insurance companies pushed through the new International Building Codes, which address the hurricane prone areas, and many companies have stopped insuring properties in coastal areas. Others charge insane deductibles for storm damage. I had a customer in Rhode Island that actually received a discount on insurance for using Andersen's StormWatch units.
But these windows have to address more than just impacts. Design Pressure ratings, which deal with air & water infiltration, structural loads, and such, are another big factor. Hurricane or StormWatch units are usually in the area of DP+50/-65.
One thing to be aware of, is the modifications some windows get in order to meet the codes. Brackets, installation clips, and higher stops are sometimes added to increase performance.
Double hungs typically require more modifications that casements, which are stronger by design.
Be sure to view samples. Don't buy anything sight unseen.
There are a few companies that offer some decent products, so I'd look into a couple of them. At least this way you'll have some options.

    Bookmark   May 12, 2006 at 12:01AM
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Interesting .. I'm building in 120mph wind zone .. and do not have to have special glss unless it is within 4' of an exterior corner.

    Bookmark   May 12, 2006 at 2:43PM
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That is interesting. As I understand the code, the Design Pressure Requirements of a window can be different, depending on which zone they are in (Zone 4 is mid wall, Zone 5 is within 4' of an exterior corner. Zone 5 having a higher requirement), but opening protection was required for all units in any wind zone 120 and up. That is how the code is written. HOWEVER, and that's a big however, each state, and in some cases individual towns/cities, have the ability to adopt which ever parts of the codes they wish to. They can also modify the code to suit their liking.
So as long as the local building inspector has approved it, and the insurance company is aware of the change to the code and approved, you are all set. I would make a call to your insurance company and check on their requirements. Just because the town/state accepts the lesser requirement, does not mean the insurance company will. Find out now before anything happens. The last thing you want is to have a claim rejected because you weren't fully protected.
I had a homeowner in Massachusetts, with no requirement for opening protection, get turned down for coverage on a very large and expensive home ($2M) on the coast because the company wouldn't insure a coastal property without some form of opening protection.
Cover your assets!!!

    Bookmark   May 12, 2006 at 8:50PM
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As Mike pointed out, there are a number of conflicting and overlapping code issues involved. For example, Kritlyn's orginal question concerned impact glass.

Technically, impact glass isn't actually required anywhere. A homeowner can use shutters or even plywood (with certain requirements/restrictions for plywood) and not need impact glass.

Windzone requirements specific to impact glass are spelled out in ASTM E1996-05 and include several levels of protection required anywhere from a garden shed to "essential" structures such as hospitals, schools, police and fire stations.

Within the windzone guidelines are levels of testing for the different types of structures within the specific windzones. It isn't particularly complex, but it is involved. The specific requirements do separate roof windows from vertical windows for example and also windows that are above and below 30'. As Mike pointed out, local codes can become much more (or less) restrictive and much more specific.

Design Pressure, or DP, requirements also vary by location and windzone. DP is NOT necessarily indicative of an impact product. That is why some manufacturers can get away with saying they sell "hurricane" windows that are not impact resistant - they have met windload Design Pressure requirements, but remember that that window isn't specifically protected from the neighbor's flying lawn furniture in the event of a storm. It will require something to protect it from an impact.

DP ratings do apply to specific windspeeds and as such may be mandated in certain areas. Often, the requirement is specified by the architect or engineer designing the home or the protection for the home...and it is quite possible to have different requirements for windows in the same house based on orientation and location (such as near a corner).

    Bookmark   May 13, 2006 at 10:07PM
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I bumped this up to ask a follow-up question. We are renovating an oceanfront property, and trying to decide whether we need Stormwatch windows anywhere.

I think my property's windows are more vulnerable to years of salt air and wind whipping at them than to possible hurricane damage. As I understand it, Stormwatch windows are not any better in than regular windows in keeping out a regular thunderstorm - installation is the most important thing to ensure that there are no leaks, etc. correct?

I have NO requirement by my insurance company to have Stormwatch type windows. The house is 30+ years old and has withstood a number of storms with no real problems except some minor leakage in the last few years that I attribute to poor upkeep and maintenance (we just bought it last fall).

I have had a contractor tell me that while a Stormwatch window may withstand a 2x4 coming at it, he is not sure the siding and drywall framing in between the windows could withstand it!

The biggest risks I have heard about on this NJ barrier island is from flooding in 1962, or lightning storms. I cannot find any good info on losses due to window damage.

I am tempted to just install Stormwatch on perhaps the Northeast corner window and put regular windows elsewhere. Any feedback?

    Bookmark   June 6, 2007 at 5:32PM
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OK Oberon, I got your message about the different types of interlayers, and that in your opinion SGP is the best product on the market. Do you know which manufacturers use this type of interlayer? Does PGT?

    Bookmark   September 7, 2007 at 11:39AM
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Hi Tasha,

There are MANY window manufacturers who offer impact windows, PGT being one of them. Many have a variety of interlayers available - including SGP.

Actually, when I reread my post on this thread I did an "oops" about mentioning PGT at all simply because I had apparently copy/pasted from another post that I must have done around the same time - mentioning PGT even when the original question didn't.

Does PGT offer SGP? Trying to remember...I think that they do, but don't quote me on that one.

What is your specific application, if I may ask?

    Bookmark   September 8, 2007 at 10:43PM
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Bumping up to get clarification on sound insulation qualities between SGP vs PVB. Oberon, my understanding is that windows with a PVB interlayer will perform much better in OITC and STC tests than one with a SGP interlayer, mostly because of the fact that PVB is "soft" and pliable, vs SGP which is "hard" and rigid. Thus SGP does a better job of protecting the interior from fast flying objects hitting the glass and penetrating it vs PVB which is softer and could stretch more easily to its breaking point upon impact.

Am I correct with these assumptions? I've looked all over the web to find STC and OITC test results for laminated glass w/SGP interlayer but have not found anything. If you have an online resource, please let me know. Thanks again.

    Bookmark   April 22, 2009 at 6:27PM
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SGP is not specifically intended to be used for sound attenuation, unlike PVB.

There are sound attenuation PVB interlayers on the market as well that are an improvement over regular PVB at blocking unwanted noise.

The overall STC improvement over regular PVB is only about 1 or 2 points, but there are improvements at specific frequencies that would be noticeable beyond the overall STC (or OITC).

    Bookmark   April 24, 2009 at 8:19PM
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I am working on a prototype affordable home design that can withstand windloads up to category EF-4 tornados.
(205 mph) A national magazine has shown an interest in publishing it.
I need information about the ultimate impact strength of impact glass. All I can find is Miami-Dade 9 lb. 2x4 at 34 mph. Texas Tech testing for 250 mph shows failure.(15 lb.2x4 at 100 mph) I'm trying to find the failure point.
Can you point me in the right direction? Would you be interested in participating in the article?

    Bookmark   November 27, 2011 at 7:20AM
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