# dp rating



## goldmoon (Aug 16, 2012)

I live in Maryland (downtown area) - 9th flr (historic Belvedere built in 1903). I need to replace windows (currently aluminum -plan to switch to vinyl). NO ONE can tell me the required dp rating! Can you help? I'm thinking at least 50 but some tell me 50 is overkill and others tell me it should be at least 55 or 65. There are no high tress and very few other high-rises in the area.


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## joecaption (Nov 30, 2011)

http://mypermitnow.org/documents/permit/DP-Rating-chart-for-windows.pdf

Just ask your local building dept. what they require.


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## oberon (Apr 29, 2006)

goldmoon said:


> I live in Maryland (downtown area) - 9th flr (historic Belvedere built in 1903). I need to replace windows (currently aluminum -plan to switch to vinyl). NO ONE can tell me the required dp rating! Can you help? I'm thinking at least 50 but some tell me 50 is overkill and others tell me it should be at least 55 or 65. There are no high tress and very few other high-rises in the area.


How close are you to the coast and just curious but how did you come up with a DP50...I agree with whoever suggested it was overkill. At DP65 you are getting into South Florida and Gulf coast 150(+)mph windzone requirements.

Even if you are on the coast, Maryland is in a 110mph windzone which is equal to right about 30psf. DP is given in psf, so DP30 should be more than adequate. 

I never heard of a required DP for Maryland, I am curious when and where the requirement for a minimum DP came from?


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## JackOfAllTrades (Jan 8, 2008)

It depends on local wind loads but if I were you, go with the better DP rating, as you will eventually get a high wind driven rain event and you will wish you had the better DP rated windows. A good thunderstorm with 60MPH winds and wind drive rain will cause that window to leak.

I would *NOT *go with a window that only had a DP30 rating, unless you were putting that window in a dog house. :jester: That tells me that window manufacturer is using some pretty flimsy materials in that window.

The windows I am getting have a standard DP70 rating, that is their lowest rating for a residential window, they don't make anything lower. When you see the quality of their frames and seals, you know why. Do I need a DP70? No but price wise there is no difference and why not get the better window?


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## Windows on Wash (Aug 30, 2011)

Jack,

Is that those innotech you were talking about previously?


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## JackOfAllTrades (Jan 8, 2008)

Windows on Wash said:


> Jack,
> 
> Is that those innotech you were talking about previously?


I was referring to the Intus uPVC triple pane window. They have a DP70 rating.


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## Windows on Wash (Aug 30, 2011)

JackOfAllTrades said:


> I was referring to the Intus uPVC triple pane window. They have a DP70 rating.


I meant to Intus.

Innotech was the one that Oberon has talked about before.


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## JackOfAllTrades (Jan 8, 2008)

Windows on Wash said:


> I meant to Intus.
> 
> Innotech was the one that Oberon has talked about before.



Innotech makes some awesome windows as well. I would recommend both of them. 

In my opinion, any window that only has a DP30 rating should be avoided for a home. How cheap the materials and poorly engineered does a window have to be to only get a DP30 rating? I've seen DP30 rated windows leak like crazy in 40MPH rain driven winds. 

A properly engineered window with high quality materials like Innotech or Intus gets DP70 ratings because the windows are built correctly from the get-go.


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## oberon (Apr 29, 2006)

A DP 30 rating is equivalent to a 110mph wind. A window with a DP 30 is structurally tested at 150% of DP or 45psf, which is equivalent to right about a 135mph wind. The relationship between DP and mph is not linear so that DP 60 is not 220mph – it’s actually right about 155mph. So while the DP number (30 to 60) is a 100% increase, actual wind speed pressure performance improvement is 41%. Still a significant improvement, but not as good as people may assume based on the change from DP 30 to DP 60.

Saying_"...as you will eventually get a high wind driven rain event and you will wish you had the better DP rated windows. A good thunderstorm with 60MPH winds and wind drive rain will cause that window to leak."_, is incorrect. 

To quote *AAMA/WDMA/CSA 101/I.S.2/A440-08, NAFS – North American Fenestration Standard/ Specification for windows, doors, and skylights *(where DP ratings come from): *"...design pressure (DP) and structural test pressure are strictly structural qualifications, irrespective of the results of any air leakage resistance testing or water penetration resistance testing." *

DP covers expected structural performance, specifically wind pressure per ASTM E1300, or snow load if you are dealing with skylights. Air and water infiltration performance is separate from DP. Air and water are rated as part of PG or Performance Grade.

For computation purposes, the minimum requirement for water infiltration is 15% of DP. While water infiltration resistance can be much better than 15%, the DP rating won’t reflect it. 

To suggest that a window with DP 30 is made of flimsy or substandard materials is faulty since it doesn’t address how DP is determined. Want to change a DP 30 to a DP 50? Then change the glass from 3mm annealed to 3mm tempered, or simply use thicker glass, it’ll accomplish the same thing. 

Structural rating when dealing with DP, comes down to excessive glass deflection or a potential crack; nothing to do with either air or water penetration or anything suggesting catastrophic failure. 

The very best sash/frame in the world with thinner glass is not going to have a DP as high as an average frame/sash with tempered or thicker glass – that’s how DP actually works. Obviously a thicker and stiffer frame sash with tempered or thicker glass is an advantage when testing to higher DP ratings because it is going to deflect less under pressure. 

Again to quote *AAMA/WDMA/CSA 101/I.S.2/A440-08: **“*_*30 psf (1,440 Pa) for the new CW class (commonly used in low- and mid-rise buildings where larger sizes, higher loading requirements, limits on deflection and heavier use are expected)”.* _That doesn’t sound like something that rates being used for a dog house.


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## oberon (Apr 29, 2006)

Windows on Wash said:


> I meant to Intus.
> 
> Innotech was the one that Oberon has talked about before.


Innotech windows are manufactured near Vancouver, BC. They use German hardware and extrusions (Kommerling), but the IG's come from Cardinal.

The windows I installed in my daughter's house were DP 100, U.17, and .003cfm. They are tilt/turn triples with 4mm glass enclosing 3mm middle lite. LoE on surface 2 and 5.

Keeping in mind that Euro window U-values are computed differently than are North American (NFRC), a Euro window U.14 rating (assuming that the U.14 was converted directly from Euro W/m²k), is about 20% better than it would be if calculated using NFRC procedure. So Euro U.14 is pretty close to NFRC U.17, which is still a heck of a good number in any event.

There is no intent by anyone to deceive or to mislead, it's simply a matter of computing the performance differently.


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## JackOfAllTrades (Jan 8, 2008)

oberon said:


> Innotech windows are manufactured near Vancouver, BC. They use German hardware and extrusions (Kommerling), but the IG's come from Cardinal.
> 
> The windows I installed in my daughter's house were DP 100, U.17, and .003cfm. They are tilt/turn triples with 4mm glass enclosing 3mm middle lite. LoE on surface 2 and 5.


Are Intus windows on-par with Innotech? I believe they use the same glass thickness for both.


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## JackOfAllTrades (Jan 8, 2008)

oberon said:


> A DP 30 rating is equivalent to a 110mph wind. A window with a DP 30 is structurally tested at 150% of DP or 45psf, which is equivalent to right about a 135mph wind. The relationship between DP and mph is not linear so that DP 60 is not 220mph – it’s actually right about 155mph. So while the DP number (30 to 60) is a 100% increase, actual wind speed pressure performance improvement is 41%. Still a significant improvement, but not as good as people may assume based on the change from DP 30 to DP 60.
> Saying_"...as you will eventually get a high wind driven rain event and you will wish you had the better DP rated windows. A good thunderstorm with 60MPH winds and wind drive rain will cause that window to leak."_, is incorrect.



As you touched on, windows are tested for air infiltration and are treated *separately* from both water infiltration and structural. Water infiltration is tested at 15% of the design pressure and structural is tested at 150% of DP rating. That means 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 its driven by a max 42mph wind and a window with a DP40 should be able to keep out rain when driven by 49mph max winds. A DP50 is good for 54MPH. A DP60 is good for 59MPH and a *DP70 is good for 65MPH* wind driven rain. 

I say with confidence that a *DP 30 window* *will leak water* in a wind driven rain event of 40MPH. I've seen it numerous times before and my current windows are DP30 and they leak in high wind driven rains of 40MPH. Go on any forums/sites that people talk about windows and read all the complaints about water leaking inside the home during 40MPH winds and 95% of the time the window is rated DP30. 

The fact is they* WILL NOT *stand behind there product when it comes to water infiltration in wind driven events. All they will say is that the water came in at the time that surpassed their DP30 rating (45MPH+ gust) and there is nothing you can do to prove them different, *warranty DENIED. *

A window can leak air like crazy but still achieve an excellent DP rating. Intus Windows achieve an air infiltration rate of 0.03 cfm which is excellent. Water infiltration is DP related but air infiltration is not.

In the end why not spend a few bucks more and get a window that has been engineered and tested to withstand higher parameters?


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## Windows on Wash (Aug 30, 2011)

Jack,

I think you will find that Oberon would always spend a few bucks more and get the better window.

I think he is just trying to make the point that a DP-30 is still far better than what is in most peoples homes.


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## oberon (Apr 29, 2006)

JackOfAllTrades said:


> Are Intus windows on-par with Innotech? I believe they use the same glass thickness for both.


I have never worked with Intus, and haven't seen one of their units in person, but based on what I have read and based on what I have heard, they are a darn good window.

When I saw the pictures you first posted I asked if they were Innotech because the profile looked identical to the Innotech.

My guess is that they are very much on a par.

My other guess is that you made a great call on those windows.


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