Chicago Window Expert

Mark Meshulam is an expert witness and consultant for windows, glass and building exteriors.
Mike Marsiglio writes…

I was hoping you can help me with this as the Chicago Conservation code book is very confusing to me.
I am in process of purchasing a new condo that was built in 2008. During the home inspection, it was found that the sliding glass doors contain Low E coating but the bedroom windows do not (all of the unit faces East).
My inspector thought that the Chicago Energy Conservation Code mandates all new construction to have Low E coating on the windows. Do you know what the ruling is on this by chance?

Mark Meshulam responds…
Since I am the Chicago Window Expert and I know everything about windows, I shrewdly decided to defer this tricky question to Patrick Loughran FAIA, PE, LEED AP and Randy Chapple AIA, SE, CSI (former President), CCS, LEED AP, both Associate Principals at Goettsch Partners. If you did not already figure out from the number of initials following their names that these Architects are highly educated professionals, then take my word for it. They and their firm, Goettsch Partners are among the very best Chicago has to offer, and Chicago is world-renowned for our architects. See their website here.

Patrick and Randy respond…

We agree that Chicago’s Energy Conservation Code is difficult to understand; however we will make an attempt at answering Mike’s question. There are two ways for a new glass façade to pass the “Chicago Energy Conservation Code” :

1) Acceptable Practice Method:

For Commercial Design, if your façade is less than 40% glass, the glass properties used on the building facade must meet a minimal performance level. This is the “prescriptive” method. Based on your glass percentage, in most cases where clear glass is used, you will need to use a low-e coating in order to meet the minimum Solar Heat Gain Coefficient (SHGC) requirements described in the code; however if you have between 10-25% glass on the building, it is possible to use a tinted glass that has no low-e coating and still meets the minimum SHGC required by code.

For Residential Design using the “prescriptive” method, only the Glazing U-factor weighs in on the selection of the glass. In this case the SHGC, which is related to the use of low-e coatings, is not considered.

The second method is:

2) Total Building Performance Method:

For commercial as well as residential design, designers can use a computer analysis method, for example “COMcheck“, to verify the enclosure (roof and all exterior walls) as a whole passes the minimum energy performance required by code.

In this method, glass without a low-e coating could be used in some areas of the building, and the overall façade/enclosure could pass the Chicago’s Energy Conservation Code. The best example of this can be seen in high rise building construction in the city. The typical high rise curtain wall glass has a low-e coating; however the lobby level glass is typically monolithic with no low-e coating.

In summary: There is nothing requiring a project to have low-e coating with either method. It all depends on how much glass you have on the building, what type of glass is applied and which method you use. To the best of our knowledge the only place that Low E coatings are required by the Chicago Energy Conservation Code only applies to buildings that rely on renewable energy. Otherwise the requirements are based on the performance standards listed above.

We hope that helps. Good luck.

Patrick Loughran
and
Randy Chapple

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For building envelope enthusiasts,
I recommend two excellent books
written by Patrick Loughran:
 

Falling Glass: Problems and Solutions in Contemporary Architecture
 

Failed Stone: Problems and Solutions with Concrete and Masonry

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