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…
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
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
Need a referral to an Architect or Engineer?
To whom it may concern,
Very poor quality answer. Not to explain the benefit of low e glass
for both SHGC and U values is not providing appropriate information.
Warm Regards
Marc LaFrance
US DOE Window R&D Manager
Hi Marc,
Would you like to contribute the additional ideas.
Your contribution would be very welcome.
Best regards,
Mark Meshulam
Executive VP
Builders Architectural
We have a low e success story fact sheet that you can reference. I was
just shocked that an article about low e in Chicago did not address U
value improvement.
Here is the fact sheet:
U.S. Department of Energy Low-E Success Story
Marc
When the members of AAMA and I developed the table that was eventually approved and adopted as Table 502.3 of the 2006 IECC, which the 2009 Chicago Energy Conservation Code is based upon, our intent was to require low-e coating on all fenestration WHEN prescriptive based design was used. We basically said “Let’s figure out what the U-factor would be if you took the glass package needed to achieve the residential value (0.35 – which is basically double pane low-e with inert gas fill) and put in into different framing systems.
Charlie Curcija, who has been a tremendous resource for our industry, did the modeling work for us. The result was that U-values of 0.45 could be achieved with some thermally broken curtainwall systems, while placing that same package in a operable commercial window framing system resulted in 0.55, and entrance doors, which are sometimes required to have a 10 or 12 inch high bottom plate due to ADA, would only go to 0.80.
Other parties felt low-e should always be required for residential – hence the 0.40 performance cap on residential fenestration when performance based design is used.
There is no such cap for commercial fenestration when performance based design is used. Theoretically uncoated glazing could be used in commercial buildings under the Chicago Energy Conservation Code if performance based design is used, but if that is done, the increased heat loss and gain would have to be made up in some other aspect of the building design.
I hope I have not put you to sleep with this explanation.
Julie Ruth, P.E.
JRuth Code Consulting
Hi Julie,
Thanks for that explanation. It is good to dialog with someone actually involved in the creation of codes.
I don’t see a disagreement between your comments and those of Randy and Patrick in this article. Did I miss something?
It appears that the numbers your team has derived are in synch with current industry capabilities. What about the future? Are there plans to tighten the requirements along the lines of what the Federal Government is targeting: .30U and .30 SHGC?
Further, it seems that air infiltration, despite being a major contributor to heat loss, is the poor ignored cousin in all of these conversations. When is the code-producing industry going to take this on?
And finally, I am wide awake when discussing this subject. It’s the readers that concern me. Wake up guys, We’re done now!
Thanks again,
Mark