# ComCheck and large fenestration areas IECC 2012



## leothebuilder (Nov 26, 2013)

I have a building that was designed under the 2006 codes. The building was never constructed because of the economy. The owners now want to proceed and the plans need to be updated to current 2012 codes. The building has fenestration on all four walls in excess of the allowed 30% under the 2012 IECC. The option is to use comcheck that uses the ASRAE 90.1

The comcheck ASHRAE 90.1 program allows me to use the large fenestration areas in excess of 40%.

I thought ASHRAE 90.1 (2010) doesn't allow windows in excess of 40% of wall area, or is that just when using the prescriptive method.

The ComCheck ASHRAE 90.1 software does allow me to enter values in excess of 40% and provided I use the correct materials the envelope passes.

Using the ComCheck 2012 IECC , the software issues a warning that you exceed the allowable window area.

I just want to make sure I am on the correct path before I go much further with updating plans.

Any input or advise would be appreciated.


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## Codegeek (Nov 26, 2013)

A similar question was in another thread - try this - http://www.thebuildingcodeforum.com/forum/commercial-energy-codes/10288-glazed-curtain-wall-allowed.html


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## leothebuilder (Nov 26, 2013)

Thanks Codegeek.

I did read that thread previously but it did not give me any definitive answer.

As I mentioned, using ComCheck with 2012 IECC the program will warn you that the windows exceed the allowable limit and the envelope will fail.

It does not allow any further trade offs such as increasing roof insulation.

Using ComCheck with ASHRAE 90.1 the program does allow windows in excess 40%, it does not warn you, it does not fail the envelope.

The question is if ComCheck with ASHRAE 90.1 allows trade offs so you can exceed the 40% glazing.


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## Codegeek (Nov 26, 2013)

I just spoke with someone in our office who has more experience with ComCheck than myself.  He said that yes, under the 90.1 provisions in ComCheck, you can exceed the 40% provided you meet the other requirements and the building as a whole will still pass.  If you use ComCheck under the IECC provisions, it will limit you to 40% glazing.  So, it sounds like you're ok.

One way we were able to get a building with more glazing to pass using the IECC provisions was to put spandrel glass in with an insulated wall behind it.  We still got the glazing effect, but the envelop was then compliant and we did not exceed 40% of the glazing limitation.

I hope this helps.


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## leothebuilder (Nov 26, 2013)

Yes thanks...that helps.

Just needed to know that I was on the right track !!


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