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Glazed curtain wall allowed?

Codegeek

Codegeek

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Jun 17, 2011
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Kansas
With the limitations in the IECC for fenestrations to a maximum of 40%, how does one design a glazed curtain wall? Would that be where Table 402.1.2 comes into play that if the entire assembly gets a U factor of less than that Table then it’s permitted? If not Table 402.1.2, then where is the language that would allow the glazed curtain wall? Or would a glazed curtain wall even be permitted under the 2012 IECC?

What purpose does Table 402.1.2 serve if it's not for a glazed curtain wall application? I'm not sure I understand when it would be used.
 
I'm not in the 2012 IECC and after taking a peep they redesigned the entire code again (they must enjoy screwing with designers, inspectors and builders) and added a bit more detail. Anyhow a building can be designed with 41% glazing or more, think Vegas strip casino's and hotels. The design would have to be on the lines of Total UA, Total Building Performance, ComCheck or ASHRAE 90.1
 
ComCheck will tell you in the analysis report that the glazing is limited to 40 percent. So I'm still in a quandary as to how a glazed curtain wall building can be done.
 
It is all see thru glass or is over 60% glass siding backed by insulation of some type?

UA method or energy budget method--Ie gold plate the glass to get almost no solar heat gain in desert climate where cooling is a big issue--although this can create a problem for the neighbors by putting additional solar gain on their building, car, etc. or wehn the building is concave can fry those at the pool below.
 
Builder Bob, yes, ComCheck lets you perform trade offs. However, the report still comes out with an error message if you exceed the 40% glazing factor.
 
Frank, it's not a specific type of glass. I've been asked by some folks in our office to see what impact the 2012 IECC would have on a glazed building hence the post.
 
Even with the error message about the glazing, does the report still state at the end ( building, mechanical, and electrical components completed), that the building does or does not meet the energy code?

Comcheck requires completion of all portions to determine compliance, otherwise it is going to throw a flag up when you finish one portion since other trade offs may have been used in mechanical and electrical areas of COMCHECK.
 
Well, it won't let me "reply with quote", so anyhow...

Builder Bob, yes it says the building exceeds the code requirements, but still says the glazing is limited to 40 percent.
 
I can't get the "reply with quote" to work. The way I read the IECC, you have three options for code compliance - ASHRAE or IECC Prescriptive or IECC Performance. If the IECC Performance option is chosen and ComCheck is the tool that is used and still requires the glazing to be no more than 40 percent, then I don't see how it works.

I don't see how a glazed curtain wall can be allowed as ASHRAE also limits fenestrations to 40 percent, at least that's what I'm reading in 5.5.4.2 of the 2010 ASHRAE 90.1.

Am I missing something or are glazed curtain walls going to be a thing of the past?
 
I pulled this from a comparison performed by Pacific Northwest Labratories and glazng is certainly being restricted;

Vertical fenestration area is now limited to 30% of above-grade wall area. The previous maximum of 40% is still allowed in Climate Zones 1-6, provided half of the conditioned floor is in a daylight zone, controls are installed, and the VT/SHGC ratio is at least 1.1.

http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-21435.pdf

There must be a solution, we all have to dig a bit more
 
curtain walls can be built. >40% fenestration is allowed. However, you cannot demonstrate compliance thru comcheck, you have to use energy modeling software like DOE2 that can do trade offs between major systems. Comcheck only trade within major systems..ex. Within bldg envelope like windows vs. roofs. Energy modeling calculates whole building performance and shows compliance through projected energy usage for the bldg. of course this is assuming you can offset the energy loss of installing curtain glass with another strategy ..like solar panels, sunscreen device..etc.
 
40% - exemptions

So this is how you could be exempt from the 40% glazing, if you pass the DOE2 system and have an energy model that basically states your building isn't an energy hog....?

Does anyone have any visual examples (screen shots) of how this was done? I imagine this is how they get away with skyscrapers in New York City. Those are 100% glazing...but people in the midwest have to be under 40%? That doesn't make any sense. There has to be a way to make a building all curtain wall and still meet IECC2009 or 2012.
 
IECC section 407 Total Building Performance specifically permits fenestration over 40% in the actual design, but your standard reference design must limit fenestration to 40%. Table C407.5.1 glazing component block. You have to use a more sophisticated model than Comcheck, DOE-2 or BLAST are mentioned in the ASHRAE, IECC says the program must meet ASHRAE 140.
 
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