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What frames hold up best to high UV?
Last Post 03 Dec 2012 09:04 PM by jonr. 33 Replies. |
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LarryT
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| 07 Nov 2012 05:19 PM |
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Another question as I start working details on final design and going out for bids.
9000' heating dominated climate with large day/night temp swings and very cold winter temps. For me that will rule out vinyl. But very high UV as dry climate, lots of sun and high altitude. Aluminum clad wood or fiberglass? |
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Lbear
Veteran Member
Posts:2740
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| 07 Nov 2012 10:41 PM |
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Out of your options, the best frame would be fiberglass. Depending on your exposure, you will want windows with good DP Ratings because of the wind loads. At 9,000 feet you will see some insane wind speeds. 150 MPH gusts were common when I was at 8,000 feet in parts of Colorado during weather events. DP 60 or greater would be called for. Good Passive House planning with high SHGC windows will be well worth the investment. Get some modeling done by Passive House consultants. I know you ruled out PVC but it might be worth checking out Intus PVC triple pane windows. They have been installed all over Europe in high elevations and in the Mideast in extreme desert climates. American vinyl windows have forever poisoned the well of how people view vinyl windows but European or Canadian made vinyl/PVC are night and day difference in quality compared to anything US made. Sort of like when Ford and GM decided to design and install their own diesel engines in the 1980s. It was a complete disaster, they were all junk and they would grenade after a few miles. That forever has implanted in the minds of people and people look down at diesel engines. GM and Ford got smart and outsourced diesel engines and now they have 3rd party companies supply their diesels for their trucks.  The above is an Intus PVC Triple Pane Window that is steel reinforced. Compare that window profile to what you will find here in the States. |
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LarryT
New Member
Posts:84
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| 07 Nov 2012 11:55 PM |
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I've been told that 140 mph is possible where I'm situated. So i need to pay attention to DP.
We are taking advantage of excellent southern exposure with a number of large windows, and a three story staircase that has glass on the large southern face, but we do have a window wall in the great room that looks out over a fantastic 20 mile view of the valley below. That faces north and will reduce the gains from the other side somewhat.
Although one of the heated levels will have ICF for three sides, the other floors will not have much thermal mass. Until I run calcs, really a worry of mine at the moment is overheating in the summer because of the staircase window wall. So I may not go to a really high SHGC for those. Another thing I'll look at is provide operable windows top and bottom of that staircase to create a chimney effect in the summer to pull the heat out of that area.
It was a lot easier being clueless once upon a time. One never paid attention to these these, eh?
My concern with vinyl is simply the large daily temp swings especially in winter and the large coefficient of expansion for vinyl. But I'll check Intus' site for information. |
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Lbear
Veteran Member
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| 08 Nov 2012 03:38 AM |
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Posted By LarryT on 07 Nov 2012 11:55 PM
I've been told that 140 mph is possible where I'm situated. So i need to pay attention to DP.
My concern with vinyl is simply the large daily temp swings especially in winter and the large coefficient of expansion for vinyl. But I'll check Intus' site for information.
Like I mentioned, 150MPH winds in such locations are common. I hope you are building the home out of ICF, Steel SIPs, SCIPs or something along those lines. A wood frames house will get racked with those types of wind and I've seen wood framed homes but they require double shear walls and even then ICF is 4 times stronger than a double sheared wall. A typical wood framed home with exterior OSB would not fare well in such conditions. As far as thermal expansion of PVC, that is correct, it does expand and contract more than fiberglass or wood. That is why companies like Intus created floating glazing units. While the PVC frames will expand at higher rates than the glazing, the glazing unit is allowed to move at its own pace. The triple pane glazing consists of three sealed panes of glass with two sealed spacers. The glazing unit then sits within the PVC frame but is allowed to move on its own as it has 2 gaskets (one on each side of the complete glazing unit) and the bottom portion has a floating seal (see picture). This allows the PVC frames to expand and contract at their own rates without damaging or interfering with the glazing unit. US Manufacturers will permanently attach the glazing unit to the PVC frame with either silicone or some type of double sided tape. When the PVC frames expand faster than the glazing unit, the seals rip and break, causing failure and leakage. Intus also installs galvanized steel "C" channels throughout the frames. They provide A LOT of rigidity and Intus windows have a DP rating of DP70. That is basically a commercial rating. Look at the picture I provided and see how robust the PVC channels are. This is not thin vinyl garbage, these are quality windows. Trust me on this, I have seen and spent a lot of time researching windows. Intus makes some awesome windows in both performance and strength. Air Infiltration (cfm/ft2) = < 0.03 U-Values = 0.14 - 0.18 They can produce large sizes. |
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LarryT
New Member
Posts:84
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| 08 Nov 2012 07:30 AM |
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Regarding method of construction, I'm using KAMA-EBBS. For the above grade stories. Steel frame inbedded in EPS. I'm using Icf for the two stories below that are daylight on front , but into the hillside on three sides. I'll rely on the engineer for bracing design,he is pretty conservative at least in all the foundation design, but he as already said that because of the limited amount of exposure in the prevailing wind direction, he doesn't see a big issue in getting it braced properly.
The floating glass sounds great - but what about where the frame contacts the exterior finish. I'm planning on using stucco, either real or EIFS, and worry about that seal and moisture egress? |
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Lbear
Veteran Member
Posts:2740
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| 08 Nov 2012 09:13 AM |
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Posted By LarryT on 08 Nov 2012 07:30 AM
The floating glass sounds great - but what about where the frame contacts the exterior finish. I'm planning on using stucco, either real or EIFS, and worry about that seal and moisture egress?
I was told that a casing bead
3/8" away from the window frame and then fill the void with backer rod and
sealant. If I were you I would use EIFS or a product like StuccoMax, there is less shrinkage and it is much stronger than typical stucco. As stucco always pulls back and shrinks. The casing bead is critical. It creates an expansion gap that lets the
framing and sheathing expand and contract without cracking the stucco or
the windows. The lack of a casing bead is especially bad as it can put a lot of
stress on vinyl window frames. A vinyl J-channel or with a product called E-Z Bead made just for
this purpose. In both cases, the bead is separated from the casing by a
3/8-inch space that gets filled with a rubberized caulk applied over a
flexible base. E-Z Bead has a built-in foam extrusion that serves as
that base, while J-channel requires the use of foam backer rod. Where two dissimilar surfaces meet, whether it's PVC, wood, aluminum, stucco, etc., you always have to take into consideration that each one will move at different rates. A flexible member should be placed between the two so that each can move and contract without permanently breaking the bond and opening to a large gap. Of course EZ Bead would only work if you are installing the window flush with the exterior wall. SEE VIDEO Intus windows do NOT have a nailing flange and are usually installed recessed within the window framing area. In which case the casing bead would be used. SEE VIDEO SEE VIDEO 2 |
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LarryT
New Member
Posts:84
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| 09 Nov 2012 12:22 AM |
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Lbear,
Thanks for all the information. Very enlightening and I'll look further into Intus when I go out for bids. In the one video, installing with foam, is that the only thing that holds the window in place? Or is it still screwed to the frame? The video didn't really explain |
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Lbear
Veteran Member
Posts:2740
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| 09 Nov 2012 12:36 AM |
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Posted By LarryT on 09 Nov 2012 12:22 AM
Lbear,
Thanks for all the information. Very enlightening and I'll look further into Intus when I go out for bids. In the one video, installing with foam, is that the only thing that holds the window in place? Or is it still screwed to the frame? The video didn't really explain
The Intus windows must be screwed to the window framing area with the brackets. I believe they call for two on each side, depending on window size. Fiberglass frames will have the least expansion but you have to look at all the variables; DP Ratings, energy #'s, price, size, availability, etc. when it comes to choosing windows. With high quality PVC like Intus, it's not the typical vinyl junk you see floating around stores like Lowe's and Home Depot. Cost wise, windows like Intus are actually less money than most US double pane windows. With the way our economy is going and energy costs expected to maybe even double in the next few years. The current ROI models are invalid because they take into account modern-day cheap/inexpensive electric and gas costs. If we see European type of energy costs, which many believe we will, making a home more energy efficient is a hedge against high energy costs. |
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LarryT
New Member
Posts:84
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| 11 Nov 2012 11:04 AM |
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As I will be running off of Propane, and 9000 degree days, I definitely am looking at cost effective efficiency. As I run Manual J, I'll look at running a couple different efficiency windows schemes and compare against current energy cost and make some assumptions about escalation in pricing. Whether we ever get to to European cost - much of that depends on politics. Much of the European cost, especially for motor fuel is the tax structure, not the cost of oil (which is the same as what is here). I'm not sure about heating fuels. It's good to see the current cost of propane is nearly half what is was a couple of years ago, but still twice what is was 10 years ago.
I've got floorplan finally printed out large enough to read window sizes and will start getting quotes soon. |
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Lee Dodge
Advanced Member
Posts:714
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| 11 Nov 2012 01:35 PM |
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Posted By LarryT on 07 Nov 2012 05:19 PM
Another question as I start working details on final design and going out for bids.
9000' heating dominated climate with large day/night temp swings and very cold winter temps. For me that will rule out vinyl. But very high UV as dry climate, lots of sun and high altitude. Aluminum clad wood or fiberglass?
Keeping in mind that "fiberglass" is glass strand reinforced plastic, conventional wisdom would rate windows for best to worst UV resistance as aluminum clad wood, fiberglass, and then vinyl. (Straight aluminum would be the best, but is probably not available.) For least thermal expansion, the rating would be fiberglass, aluminum clad wood, and then vinyl, as I understand it. Least cost is typically vinyl. Asthetic appeal is important, but personal. What type of windows are available, and that the subs are used to working with is sometimes a determining factor. And in your case, what is available for high altitudes is important. |
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Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
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LarryT
New Member
Posts:84
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| 12 Nov 2012 09:32 PM |
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Those two scales are what I was looking for in the original post. I assume all three could be made to work, just have to understand the characteristics of each and how to deal with those.
Lbear, you have eliminated all my concerns about being able to use PVC except - low temperature brittleness. Is there any information on that? |
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Lbear
Veteran Member
Posts:2740
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| 13 Nov 2012 05:15 AM |
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Posted By Lee Dodge on 11 Nov 2012 01:35 PM
Posted By LarryT on 07 Nov 2012 05:19 PM
Another question as I start working details on final design and going out for bids.
9000' heating dominated climate with large day/night temp swings and very cold winter temps. For me that will rule out vinyl. But very high UV as dry climate, lots of sun and high altitude. Aluminum clad wood or fiberglass?
Keeping in mind that "fiberglass" is glass strand reinforced plastic, conventional wisdom would rate windows for best to worst UV resistance as aluminum clad wood, fiberglass, and then vinyl. (Straight aluminum would be the best, but is probably not available.) For least thermal expansion, the rating would be fiberglass, aluminum clad wood, and then vinyl, as I understand it. Least cost is typically vinyl. Asthetic appeal is important, but personal. What type of windows are available, and that the subs are used to working with is sometimes a determining factor. And in your case, what is available for high altitudes is important.
That is an often overlooked point; that fiberglass is plastic based. Each material has it's pros and cons and for fiberglass its "kryptonite" is UV. That is why fiberglass windows MUST be painted, and all come painted from the factory. If you took an unpainted raw fiberglass window frame and exposed it to natural UV, the resins within the fiberglass would being to fail and the fiberglass unit would begin to disintegrate and the frame would fall apart. Over time if the paint begins to fade or chip away on the exterior of a fiberglass window, it MUST be repainted to protect the resins from UV damage. If this is not done, the fiberglass frame will begin to fail due to the UV damage. So there is a maintenance issue with fiberglass. They will eventually require repainting, not just for aesthetics, but to protect the fiberglass resins from UV damage. Devil is in the details, per manufacturer, "fiberglass will not degrade when painted."The other "con" with fiberglass is that the corners are NOT welded together like a quality PVC window would be. This is a potential weak spot in fiberglass windows. Fiberglass windows are mechanically fastened in the corner, usually with brackets. This plays a role in window frame strength, squareness, and potential air and water leaks. Some claim that all mechanically fastened window corners, including fiberglass windows, will eventually leak in the corners. A sort of marketing "gimmick" I found recently with fiberglass windows is their "strength" claims they make. They claim it is 8x stronger than vinyl but they are referring to its tensile strength. Or how much force it would take to deform a lineal if you grabbed each corner and attempted to pull it apart. A window will never see that type of stress where tensile strength is put to the test. The glazing is what gives a lot of the strength to fiberglass window frames. If you remove the glazing from the fiberglass frame, you can easily flex the corners with your bare hands because of them being mechanically fastened. Lastly, PVC is actually a much better insulator than pultruded fiberglass. A fiberglass window frame will transfer 3-4 times as much cold or heat over a PVC window frame. When you look at heat loss in BTU's per hour for window frames; wood has a value of 1.2, PVC is 1.4, fiberglass is 4.8 Fiberglass is a good product for window frames. No denying that. It has the lowest thermal expansion rates out of any window material and it is decently strong but it has its drawbacks also. The biggest being UV damage if the exterior frames are not properly painted. The other being the non-welded corners. |
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Lbear
Veteran Member
Posts:2740
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| 15 Nov 2012 02:38 AM |
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Posted By LarryT on 12 Nov 2012 09:32 PM
Those two scales are what I was looking for in the original post. I assume all three could be made to work, just have to understand the characteristics of each and how to deal with those.
Lbear, you have eliminated all my concerns about being able to use PVC except - low temperature brittleness. Is there any information on that?
The windows have been tested from -4 F to 140 F with no
problems. The product has been installed in cold environments like Russia and Northern Europe and they stated that there has been no breaking due to the cold itself. With their thicker PVC profiles, I don't think you will have any problems.
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Lbear
Veteran Member
Posts:2740
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| 29 Nov 2012 01:48 AM |
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Intus now utilizes a special pigment in their Titanium Plus color line. It basically infuses 3 layers of a special pigment which has a base foil with metallic pigments into the PVC frames. These metallic pigments reflect the sun light and UV to reduce thermal absorption and heating. Inoutic in Germany has designed this new paint technology and is incorporating it into their PVC window frames.
The frames resemble a contemporary/modern appearance and are grey aluminum in color but are actually PVC. They make a white aluminum and dark aluminum color also. I am trying to find out how much of a reflectivity they have, in terms of how a cool roof would have an actual LRV rating.
This really should help the PVC frames stay cooler, provide suburb UV protection, and protect the PVC's longevity. Sort of a "cool roof" technology but for your window frames.
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windowrookie
Basic Member
Posts:104
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| 30 Nov 2012 05:52 PM |
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LBear Every fiberglass manufacturer has a lifetime warranty on the adhesion of the paint. Which means you never have to paint them and only if you want to. The
paint will remain on the substrate as long as the substrate is around...Foiled/painted vinyl, the maximum warranty I've seen is 12 years on adhesion. Most fiberglass companies offer AAMA 623, 624 and 625 certified paints which can equate to up to 10 years no fading depending on the selection of the paint. However everything fades regardless of the coating, just some last longer than others. Every vinyl warranty I have ever read excludes warranty on fading... Fiberglass windows have a 38% longer useful life expectancy than vinyl. ( Life cycle assessment of windows for the North
American residential market: Case study” by the University of British
Columbia. Scandinavian Journal of Forest Research, 2008.). Therefore with such terrible corners and paint why do they outlast a vinyl window that badly????? According to Marvins website fiberglass 833% less expansion than vinyl, (btw take it up with Marvin). Your comment that vinyl window corners are fused translated is that as you add heat to vinyl and it melts....Does that mean in the hot sun of Arizona there will be even more expansion of a vinyl window and further shortening its life cycle? Why the steel and now fiberglass reinforcements in PVC, fiberglass only has tensile strength right? Your quote "Lastly, PVC is actually a much better insulator than pultruded
fiberglass. A fiberglass window frame will transfer 3-4 times as much
cold or heat over a PVC window frame. When you look at heat loss in
BTU's per hour for window frames; wood has a value of 1.2, PVC is 1.4,
fiberglass is 4.8"
1. Vinyl is a better insulator, true. But fiberglass is engineered to have less mass and less thermal bridging therefore making up for the higher conductivity. If this was true then the U value of a PVC window would be tremendously lower than a similar fiberglass window using the same glass right? That same argument can be made with 62 thouPVC versus 70 thou PVC. Thinner vinyl is certainly more energy efficient than thicker vinyl but will not last nearly as long. Fiberglass pultrusions can range from 72 thou all the way to about 95. Your comment is certainly misleading because that would mean you only sell windows without glass, right? Or do you? My test results state that fiberglass is 2 BTU(ASTM). 2. Source please. LBear, you danced around the subject of UV and played the fear mongering game like a 1970's tin man. So please provide us with factual information about the fading of vinyl and thermal performance. Looking forward to your response. And by the way, fiberglass windows are in the Antarctic... 
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Lbear
Veteran Member
Posts:2740
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| 30 Nov 2012 09:25 PM |
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Posted By windowrookie on 30 Nov 2012 05:52 PM
LBear
Every fiberglass manufacturer has a lifetime warranty on the adhesion of the paint. Which means you never have to paint them and only if you want to. The
paint will remain on the substrate as long as the substrate is around...Foiled/painted vinyl, the maximum warranty I've seen is 12 years on adhesion.
Most fiberglass companies offer AAMA 623, 624 and 625 certified paints which can equate to up to 10 years no fading depending on the selection of the paint. However everything fades regardless of the coating, just some last longer than others.
I am not knocking fiberglass, it is a great window frame but like
anything in life & building materials, there is nothing perfect and everything has some sort
of drawback. There is no doubt that PVC has greater thermal expansion
rates than fiberglass. One cannot compare US made PVC windows vs European/Canadian PVC windows, it's a night and day difference. Thicker profiles and steel reinforcement is what Intus and other quality PVC manufacturers use. Fiberglass and PVC are both plastic based. Direct
UV on fiberglass will result in the loss of physical strength through
degradation of the resin-glass bond. Manufacturers must protect the
fiberglass by placing a paint/resin-rich protective layer between the
structural fiberglass and the outer surface. Marvin Fiberglass windows had the worst AI rating of any window I bid out: Marvin Ultrex IssuesThat's news to me that every fiberglass window manufacturer has a "lifetime warranty" on paint. All the major manufacturers I spoke to offer a limited warranty. One only needs to read the numerous fine print paragraphs in "Lifetime Warranties" to realize that in the end you are truly on your own for the most part. Plenty of real life examples out there of Lifetime Warranties by big name companies like Pella where the customer is basically SOL, even when a legit warranty claim arises. This applies for all window types; fiberglass, wood, aluminum, PVC. (See above video link) Regarding Marvin, as I mentioned before, their fiberglass windows were not strong enough to be used in my building design. Marvin engineers told me that fiberglass frames have limitations and they cannot produce certain window sizes. They even admitted that the corners in fiberglass windows can be a weak point because they are merely screwed together and if they get tweaked, it can cause a leak issue in the corners. Only the Canadian fiberglass manufacturers are able to produce the larger sizes but even then they are limited and cannot produce the same size I can easily get with Intus PVC. In the end, the highest DP Rating was the Intus PVC and then the Canadian fiberglass manufacturers. The lowest DP Rating was with Marvin fiberglass. In the end, window design choice should be based on climate location and building application. I think US made fiberglass are OK but better fiberglass windows are made in Canada. If one wants PVC, European manufacturers lead the way and Canadian are right behind. I would stay COMPLETELY away from U.S. made PVC windows. |
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windowrookie
Basic Member
Posts:104
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| 30 Nov 2012 10:08 PM |
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What????Of course you were bashing fiberglass. Nice way to try to retract. You said paint, corners and thermal.... No need to educate me on Fiberglass and paint, I've been around enough. Fiberglass is coated because they want a nice surface finish. UV stabilizers and pigment( if needed) can be added in the pultrusion along with veil but the finish doesn't cut it(ladder rails). Therefore how do you sell a premium product that looks 2nd rate. And so what if I has to be painted. In the past vinyl couldn't be painted and now they do, so who cares. The biggest being UV damage if the exterior frames are not properly painted. The other being the non-welded corners. . You said this not me. A fiberglass window frame will transfer 3-4 times as much cold or heat over a PVC window frame. You said this not me. How can that be misconstrued as anything but non sense at a cheap shot. Am I missing something? I am not here to lecture but I have heard all the baloney every sales person has ever thrown. If you want to talk numbers and facts super, if you want to mislead then don't waste your time. People here are very intelligent and see through the smoke and mirrors. fiberglass its "kryptonite" is UV. A sort of marketing "gimmick" I found recently with fiberglass windows is their "strength" claims they make. O.k. I believe you, you were not mocking fiberglass... Can you send me the source on the thermal numbers of 4.8 for fiberglass please. And by the way, Marvin is a totally different thread.... |
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Lbear
Veteran Member
Posts:2740
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| 01 Dec 2012 01:36 AM |
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Posted By windowrookie on 30 Nov 2012 10:08 PM
How can that be misconstrued as anything but non sense at a cheap shot. Am I missing something?
I am not here to lecture but I have heard all the baloney every sales person has ever thrown. If you want to talk numbers and facts super, if you want to mislead then don't waste your time. People here are very intelligent and see through the smoke and mirrors.
Look, apparently windows are your hot topic. Your forum name makes that apparent. I discuss a wide range of topics on this forum, as seen by my 1,000+ posts. You focus on windows, I get it. I don't sell windows, you do. Fiberglass frames are a great product but one has to look at the total package. You can have a fiberglass frame but if it leaks air like crazy, it's a horrible product. Did you even bother to look at the video? If they developed a fiberglass frame that got a DP70 rating, can hold triple pane glass, has a air leakage rate of <0.03, and can be made in large sizes, has U-Values < 0.20, all at a reasonable price, then you will have a top notch window product. Unfortunately, currently no such fiberglass window exists in the US market. There is a Canadian company that does make top notch fiberglass windows but the price is very high and will be out of reach for most consumers. Until such a fiberglass window is manufactured and at a reasonable price, one has to find other options. If one is dead set on buying fiberglass frames from Marvin, then you have to compromise and deal with windows that leak a lot of air, get average energy ratings and have low DP 30 ratings. If you live in an area with little to no wind, surrounded by wind breaks, then maybe DP ratings are not that important. |
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Lee Dodge
Advanced Member
Posts:714
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| 01 Dec 2012 01:58 PM |
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Posted By Lbear on 01 Dec 2012 01:36 AM
...snip...
If they developed a fiberglass frame that got a DP70 rating...
...snip...
If one is dead set on buying fiberglass frames from Marvin, then you have to compromise and deal with windows that leak a lot of air, get average energy ratings and have low DP 30 ratings. If you live in an area with little to no wind, surrounded by wind breaks, then maybe DP ratings are not that important.
1. When you say that they "leak a lot of air," what is the measured, published leakage rate for these windows?
2. Why do you equate high DP ratings with high quality windows? In my opinion, high DP ratings are important in hurricane-prone areas or on mountain tops, but I, personally, have never had any windows blown out simply by wind force. Have you? Footballs, yes; wind force, no. |
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Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
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Lbear
Veteran Member
Posts:2740
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| 02 Dec 2012 03:14 AM |
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Posted By Lee Dodge on 01 Dec 2012 01:58 PM
1. When you say that they "leak a lot of air," what is the measured, published leakage rate for these windows?
2. Why do you equate high DP ratings with high quality windows? In my opinion, high DP ratings are important in hurricane-prone areas or on mountain tops, but I, personally, have never had any windows blown out simply by wind force. Have you? Footballs, yes; wind force, no.
I recommend viewing the video, posted in 2012: Marvin Ultrex
Posted By kdupuis on 11 Nov 2010 11:14 AM
I just installed 9 Marvin Integrity doublehungs in a new addition. I've
had the same experience as did rbrais. There is considerable air leak
on each side where the sashes meet. In fact, I can see daylight coming
in from outside on every window. There is a gap in the weather strip.
It's the same on each window, so it's not one bad window. These windows
were installed properly. They are all square, level and plumb. The
sashes work fine. Fortunately for me I advised against them, but the
customer insisted on them, so I'm off the hook. However, it's
frustrating to take the time, care and expense to build a superior
thermal envelope only to have 18 air leaks courtesy of Marvin. I've
installed cheap vinyl doublehungs that are more air tight than these.
IMO fiberglass is the way to go, but that doesn't mean all fiberglass
windows are made well.
1 - As far as the published air rating for the Marvin fiberglass windows, Marvin Ultrex rating is the bare code minimum at 0.30. As shown in the above window, and as referenced in the above post, this is a common problem with these windows. During winter with the cold air leaks coming in through the window and hitting the warm air of the home, you will get condensation and the subsequent problems shown. Why install leaky windows in the first place? It totally defeats the purpose of having an energy efficient home. Quality window manufacturers can get AI numbers as low as 0.03 or lower. 2 - DP Ratings are more than a window simply experiencing a catastrophic "blowing out" in a hurricane or high-wind storm. DP Ratings show the entire quality and strength of a window. A higher DP value indicates a windows ability to withstand greater wind, water and structural loads. Then you have negative and positive forces on the window based on location on the homes wall, elevations, roof edge locations, wall corners, etc. Windows can experience higher pressures over what the outside wind speed is actually at. Most homeowners/builders do not even calculate these pressures as most are not even aware that such pressures even exist in a home. Therefore they are not taken into account until the window experiences failures in minor wind driven rain events. A window that has a DP30 rating means that it is only capable of keeping out wind driven rain up to around 40MPH (water/air testing is done at 15% of the 30psf rating). In the real world that means if the window is placed in an area of the home that has moderate positive and negative pressures, a simple 30MPH wind driven rain storm will most likely make that window experience water leakage. Even without the rain, a simple 30MPH wind can cause a DP30 rated window to leak air, irregardless of its AI rating. So while a DP30 rated window is rated that it will not fail structurally up to 110MPH winds. It is only rated for wind driven rain events up to 40MPH and that is not considering positive and negative pressures that are found throughout a homes wall area. That means it most likely will leak air and rain when the outside wind is at 30MPH or greater. A DP70 ratings shows that the window is engineered to structurally withstand wind loads of 170MPH (blowout) but more importantly it will not leak water in wind driven rain events up to 65MPH. I would not put a DP30 rated window on a home, no matter where it was situated. It's just too low of a rating when it comes to wind and air leakage. These values are calculated from the Ensewiler Formula, P = .002496
V2, where V = Wind Velocity in MPH and P = the Differential Pressure
across the window in Pounds per Square Foot (PSF).The equation assumes
the direction of wind is perpendicular to the window and there are no
effects from surrounding terrain or the shape of the building in which
it is installed. Positive (+) pressures act inward and Negative (-)
pressures act outward on the window.
An easier way to perform this calculation would be as follows:
Square Root of PSF X 20.016 (e.g. 15 Sq.Rt. = 3.87 X 20.016 = 77.52)
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