Water Tightness and Wind Load Resistance (DP ratings)

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msbriggs
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Water Tightness and Wind Load Resistance (DP ratings)

#1 Post by msbriggs »

In comparing the two windows that I've finalized my choice for my sunroom to, most criteria are similar (U-factor, SHGC, air infiltration), but there are significant differences in the listed water tightness and wind load resistance ratings. The Fibertec double-hungs are listed at DP30 for both (see http://www.fibertec.com/pictures/produc ... fo_251.pdf), which apparently means no water resistance at 4.5 psf and some minimal amount of deflection at +/- 45 psf (wind load resistance). The Inlines, on the other hand, are listed at DP80 for water and DP55 for wind - corresponding to no water leakage at 12 psf and no deformation at 82.5 psf.

How meaningful are these ratings? What surprises me, is that I would think the better ratings of the Inline double-hungs on the water resistance and wind loading would translate into a better air infiltration rating - but the Fibertec has a slightly better air infiltration rating (0.1 CFM/ft^2 compared to 0.12).

So - should I make anything of the DP ratings? Or focus on U-factor, SHGC, and air infiltration?

Thanks.

Skydawggy.
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#2 Post by Skydawggy. »

Would you like a knife or an ax to split that hair with? :lol:

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HomeSealed
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#3 Post by HomeSealed »

I agree, that difference in AI is negligible, although neither one is great. The difference in DP rating sounds like a window with some type of reinforcement vs one with none. I don't know all that much about your two choices, however based on the ratings alone, the Inline is a better choice.

msbriggs
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#4 Post by msbriggs »

HomeSealed wrote:I agree, that difference in AI is negligible, although neither one is great. The difference in DP rating sounds like a window with some type of reinforcement vs one with none. I don't know all that much about your two choices, however based on the ratings alone, the Inline is a better choice.
For double-hung windows, aren't AIs of around 0.1 pretty good? Sure, with picture windows or casements you can get a good deal lower, but for double-hungs I would think a 0.1 is good. For example, the Marvin Infinities that I put in the rest of our house have an AI of 0.27.

On the DP rating - is that mostly only going to be important as far as the window's ability to withstand very high winds and driven rain? Or is a lower DP rating indicative of a window being weaker in ways that would affect its energy efficiency?

Where I live (New Hampshire), we very rarely have wind gusts anywhere near the DP30 rating test speed (which is something like 130 mph). So, I'm not concerned about windows being able to survive very high winds intact - my concern is with energy efficiency.

Thanks,
Mike

TLHWINDOW
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#5 Post by TLHWINDOW »

DP is were the window begins to fail at certian pressures or "wind speeds".

Failing typically means allowing air/water in. So if you live in an area that can get winds of 100mph (like florida) often, you want a higher DP to allow for it.

msbriggs
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#6 Post by msbriggs »

Ah, ok. Hmmm... it's been a lonnng time since we've had 100 mph winds, but we did have a storm this spring with 70 mph gusts and driven rain. The structural loading may not be as much of an issue up here as the water resistance due to wind driven rain. For that reason, the higher DP rating might be very nice.

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HomeSealed
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#7 Post by HomeSealed »

Yes, that is technically what the DP rating shows, however IMO, it really shows the structural soundness of the product. A window with a better DP rating will either have a stronger extrusion or some type of reinforcement(or both), either of which are going to help your window sustain a higher level of performance for a longer period of time... In terms of AI, .1 is pretty decent, however you can find Dh's with AI ratings of .08, .06, and even lower. The general rule is that anything under .2 is fair, however not great.

buddy11
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#8 Post by buddy11 »

I challenge anyone to show me a tangible difference, one that equates to a difference in energy savings between a .27 and a .01. Any takers?????
Ok my .27 :lol: Integrity's leak no neglible air. I live on a plain with no trees and a prevailing wind. They're as airtight as any window I've owned. They're DP rating is 30. Last week, I powerwashed the back of my house. I sprayed the windows directly with 2500 psi. Not a drop of water came in, Zero.

So to answer your question a DP 80 is great if you live in a hurricane zone. Outside of that it's useless. A DP 30 is more than adequate.

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HomeSealed
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#9 Post by HomeSealed »

Whoa, .27 AI and DP30 .... Sounds like the Excalibur! :lol:........J/k, I should have clarified, I was referring more to vinyl products as IMO, they need the extra strength to maintain performance over time. I just noticed that the products you are looking at are fiberglass. :wink:

msbriggs
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#10 Post by msbriggs »

HomeSealed wrote:Whoa, .27 AI and DP30 .... Sounds like the Excalibur! :lol:........J/k, I should have clarified, I was referring more to vinyl products as IMO, they need the extra strength to maintain performance over time. I just noticed that the products you are looking at are fiberglass. :wink:
So does that mean I shouldn't care much about the DP ratings since these are fiberglass windows?

Ga! Can't make up my mind between these two!

fenestrationman
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#11 Post by fenestrationman »

Design pressure is a direct relationship to your windzone.

90 mph - dp21
100 mph - dp26
110 mph - dp31
120 mph - dp37
130 mph - dp43
140 mph - dp50

Regards,

buddy11
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#12 Post by buddy11 »

fenestrationman wrote:Design pressure is a direct relationship to your windzone.

90 mph - dp21
100 mph - dp26
110 mph - dp31
120 mph - dp37
130 mph - dp43
140 mph - dp50

Regards,

Finally some legimate data...

Thank you!

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Windows on Washington
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#13 Post by Windows on Washington »


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HomeSealed
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#14 Post by HomeSealed »

msbrigs, are you legitimately concerned with the windspeeds etc, or are you just looking for which product is superior? The fact is, the design pressure ratings do give some indication as to the strength of a particular product. The AI ratings are clearly important for the performance and energy efficiency. Can you get a product with ratings that are overkill for your application? Sure, but that doesn't change the fact -that it is- in fact, a better rating. I don't sell any of the products that you are considering so I have no vested interest one way or another, but if price is not a factor, I'd choose the product with better ratings 100% of the time. That being said, obviously there are many other factors involved in a window purchase so be very careful not to give this issue too much weight in your decision.

msbriggs
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Re: Water Tightness and Wind Load Resistance (DP ratings)

#15 Post by msbriggs »

HomeSealed wrote:msbrigs, are you legitimately concerned with the windspeeds etc, or are you just looking for which product is superior?
My bigger concern is which is an overall better quality window. The structural loading rating doesn't concern me much - the water resistance could be an issue though (for example, a storm a few months ago that had 70 mph gusts during a strong rain storm. I should say though that the Infinity windows held up fine, and they are only DP30).
The fact is, the design pressure ratings do give some indication as to the strength of a particular product. The AI ratings are clearly important for the performance and energy efficiency. Can you get a product with ratings that are overkill for your application? Sure, but that doesn't change the fact -that it is- in fact, a better rating. I don't sell any of the products that you are considering so I have no vested interest one way or another, but if price is not a factor, I'd choose the product with better ratings 100% of the time. That being said, obviously there are many other factors involved in a window purchase so be very careful not to give this issue too much weight in your decision.
THanks, that definitely helps.

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