Impact Windows and Leakage (LONG)

runninginplaceJuly 5, 2012

Trying to decide on window replacements for my home, located in Miami FL. The choice is between installing regular non-impact windows with accordion shutters, or installng impact windows alone.

My husband is convinced, based on one neighbor's anecdotal experience, that impact windows leak. As 'proof' he requested a sample impact window from a salesman, and upon its delivery he tested it (a single hung style) by laying it horizontally on top of two cinder blocks and using a garden hose to pour water until a thin stream came out the side. He then concluded it was leaky, and therefore impact windows do not work.

As you can probably tell, I'm dubious about this. The salesman responded to the test by saying that ANY window will leak under those conditions, which actually makes sense given that windows are not meant to be bowls. Salesman said the weather stripping is what was letting water through.

I've been scouring this forum and reading past discussions but haven't seen this particular issue addressed. To the experts on this board, any knowledgeable insight or guidance is appreciated. I am having trouble believing that PGT and other manufacturers are knowingly selling thousands of windows that are defective and which leak worse than the 'old fashioned' non impact windows.

Another major factor in the decision: in my price estimates so far, installing non impact windows and accordion shutters will cost approximately 50% more than doing impact windows alone. Something that is definitely swaying my inclination! However if experts say that non-impact window and shutters are the best option I am willing to consider that. I hope and pray this window installation will last us for several decades of Florida storms.


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The issue your speaking of has ever been addressed because in my almost 30 yrs in the window and door business I have have never heard of someone thinking that that is a way to test a window for water infiltration. While I am not familiar with PGT I can assure you that all window Impact or not will leak using that testing method. And that does not mean they will leak water or even air if they are a quality product with a quality installation.

    Bookmark   July 5, 2012 at 8:40PM
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Windows on Washington

While it is not the norm, the salesperson is 100% correct in that every window will leak under those conditions.

Windows are not designed to be bowls in correct. I would encourage your husband to look up the criteria and testing of windows. It will make more sense after that.

Here is something that I copied and kept from Oberon. It summarizes quite a few questions for you.

In terms of which route to go, some might recommend impact windows and the storm shutters if you really want to protect the home. Some of the benefit of the impact windows is that you need not be home to "activate or pull down" the windows because they are always in place.

Here is what Oberon say....

DP and Impact Window Discussion

The DP rating of a window or door is based on laboratory pressure testing in pounds per square foot or psf.
Air, water, structural is a three-part test that determines much about a window's overall performance. Air infiltration is the first phase, water penetration is next, and structural is the third part of the test.
Windows are tested for air infiltration simulating a 25mph wind or a 1.56PSF pressure load - air infiltration is treated separately from both water infiltration and structural and it is independent of the design pressure of the unit. Said again - the air infiltration rate in a window is not based on the design pressure rating of the unit.
Both water penetration and structural testing, on the other hand, are based on the window DP rating. Water infiltration is tested at 15% of the design pressure and structural is tested at 150% of DP rating.
What this means is that a window with a DP30 is tested for water infiltration at 4.5psf (15% of 30psf) while a window with a DP40 is tested at 6psf (15% of 40).
A window with a DP30 rating should be able to keep out rain when it�s driven by 42mph winds and a window with a DP40 should be able to keep out rain when driven by 49mph while water infiltration is DP related - and air infiltration is not - the nature of air and water infiltration is different.
The structural rating of a window is as much about the glass as it is about the frame and sash system. In order to get a higher DP rating the window manufacturer has to consider the thickness and possible heat-strengthening (or tempering) of the glass as well as the use of higher-end hardware and good quality sealants in the frame and sash system.
But, interestingly, there is nothing in the structural rating that specifically requires that the unit be air-tight. A window can leak air like a sieve and still achieve an excellent DP rating. Likewise a window that is sealed tightly can have a lower DP rating but excellent air infiltration numbers. Obviously there are also many units that have both excellent air infiltration numbers and a satisfactory DP rating (relating to both structural strength and water infiltration).
Simply stated, the relationship between DP and windspeed is -- "the ratios of the design pressures in psf are the square of the ratios of the wind-speeds in mph".
A window with a DP30 is rated to a pressure level equivalent to a 110mph windspeed, but it is tested (for structural) at a pressure equivalent to 164mph.
A window with a DP40 is rated to a pressure level equivalent to a 127mph windspeed, but it is tested (for structural) at a pressure equivalent to 190mph.
So what does the DP50 in the "hurricane resistant windows" actually mean? Not much really. Certainly a DP50 is acceptable in many circumstances, but "hurricane resistant windows" is pretty much meaningless in that the window isn't impact rated - meaning that in the event of a major storm you would still have to either use shutters or plywood to protect your home.
Impact (or "hurricane") 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 won�t 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 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 doesn�t 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.
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 can be more than 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 has become the product of choice for a number of the wood window manufacturers. Although vinyl folks don�t seem to be using it quite as much yet, SGP does seem to be growing in the vinyl market as well. I suspect that one reason SGP is a little behind in vinyl windows is because SGP�s rigidity tends to transfer the impact force to the frame of the window rather than absorbing the impact in the glass as does PVB. While the best vinyl windows can handle the force of an impact when using SGP as the laminate interlayer, not all vinyl windows are strong enough to take that force.
As a rule, aluminum windows tend to be pretty strong and can generally use any of the mentioned interlayer laminates.
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.
Impact rated windows - or to answer your question - Dade County Approved windows are tested to the same air, water, and structural testing that I mentioned earlier, but in addition they are required to twice successfully stop an 8', 9lb 2x4 that is fired at the window at 50fps.
If the impact window is able to stop the 2x4 - without penetration of the glazing - then the unit is subjected to 9000 high and low pressure cycles at up to 100% of the DP rating.
If the window manages to stop the two 2x4 impacts, and manages to successfully complete the 9000 pressure cycles, it still has to operate in order to successfully pass the entire testing sequence and get the Miami Dade Approval.
There are several advantages to using impact glass rather than shutters � not having to travel for hours to protect your home if you happen to be away for some reason is certainly a huge one � but beyond that:
First, and best (and restating), they are passive protection�you don't have to do a thing to protect your house if a storm is coming. If you are out-of-town, the house is protected.

Second, (and re-restating) they are passive protection...not just from storms, but also from unfriendly people who might want to enter your home when you are not there. Imagine trying to break thru a window or door that has been designed and built to withstand winds of over 150mph and at the same time to withstand impacts from a 2x4 projectile that turns plywood into kindling. Burglars look elsewhere.
Laminated glass, used in impact windows, blocks 99% of UV light from entering your home and also acts as a significant sound barrier as well. Homes that are near airports that are remodeled for soundproofing are retrofitted with laminated glass for that reason. But, those homes generally use a much thinner version than is used for impact resistance.
Unfortunately, looting is sometimes a problem after a major storm, and again that passive protection that impact windows gives you will help keep your belongings in your home long after the storm. The folks who do the deed are going to look at the homes that don't have that sort of protection.
Also, those folks who use shutters or plywood to protect their homes are going to be living in a windowless cave as long as they are in the house with the coverings in place. Folks with impact windows don't have to do that.
From a cost versus value comparison, IF you are planning to replace your windows anyway and you are planning to go with higher-end windows, then replacing your existing windows with impact units is cost-competitive with getting impact shutters.
If you are not planning to replace your windows - except to install impact units - then the cost of window replacement can be significantly more than the cost of installing shutters.

    Bookmark   July 6, 2012 at 11:36AM
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Thank you for the feedback--and for the very helpful information. Now that I have some data I can evaluate, and explain, in a more logical manner.

I'm probably going with the impact windows. I just won't install them horizontally and aim a garden hose at them daily!

    Bookmark   July 7, 2012 at 9:04AM
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Windows on Washington


Well said.

Good luck with the project and go easy on your husband. We try to be experts in all things but fall short some times.

    Bookmark   July 7, 2012 at 10:09AM
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