LEED Fenestration Modeling Question

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I am a bit confused when modeling unrated vertical fenestration for the proposed
model. 90.1 states that we need to use the values determined in accordance with
NFRC 100 or we can use the data in Table A8.2 for vertical fenestration per
Exception b, Section

If so, the values in Table A8.2 exceed the maximum allowed fenestration u-values
listed in Table 5.5-5 (my zone), so will this not disqualify the proposed
building model?

I have often found it impossible to get the architect to supply the NFRC
assembly ratings of the glazing and field erected curtain-wall systems.

I have used the LBNL Window 6.3 program to calculate the vertical fenestration
ratings, but 90.1 Section states that the fenestration product shall
have a permanently installed nameplate or the manufacturer shall provide a
signed and dated certification for the installed fenestration.

I don't see any wiggle-room where 90.1 allows the modeler to calculate the NFRC
rating of vertical fenestration.

Saying that, I have submitted projects where I calculated the fenestration
assembly u-values without any kick-back from the GBCI.

I am concerned that the reviewers will push this issue since it is now clearly
defined on the new Section 1.4 Table and if I submit my own ratings I will end
up remodeling the project and/or the proposed building envelope will be rejected
since it doesn't meet the mandatory requirements of Section 5.4.

Any thoughts?

Thank you,

Paul Diglio, CEM, CBCP

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Joined: 2011-09-30
Reputation: 400


I recently received the following comment in a LEED review for a LEED-NC v2009 project:
[cid:image001.png at 01CE39E7.4EDD07E0]
This implies that Window v6.3 calculations are acceptable in lieu of NFRC ratings. The comment does not exclude the modeler from performing the calculation.
Of course, I have no idea if this is boilerplate language or if LEED reviewers have discretion here. It is also possible that requirements will become stricter for newer projects.


William Bishop, PE, BEMP, LEED AP

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Thanks Bill, the comment you received is encouraging.

Paul Diglio, CEM, CBCP

Paul Diglio's picture
Joined: 2011-09-30
Reputation: 400

The NFRC CMAST database includes ratings for a growing number storefront
and curtainwall products, where ratings are generated using the NFRC
Component Modeling Approach (CMA). These are project-specific ratings
based on specific combinations of frame, glazing unit, and spacer, but
if they match your proposed design, I would guess that LEED would accept
these ratings as an acceptable substitute for your own WINDOW/THERM



David Reddy3's picture
Joined: 2011-09-30
Reputation: 0

Good morning, Paul,

It appears you are confusing the prescriptive envelope requirements with the mandatory provisions. The envelope minimum performance can be violated when using an energy model to show overall building performance. Hope this helps!

Cam Fitzgerald

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Joined: 2011-09-30
Reputation: 0

FYI, another practical way to account for the effects of the framing is to use the charts provided by the curtain wall framing manufacturers.

For example, here is the detailed catalog for the Kawneer system 1600 type 1:


The charts and data (from pages 32) on allow us to estimate overall u-value and SHGC based on center of glass values and the ratio of Vision Area to Total Area (%).

It?s fairly straightforward to document the Vision Area, but a very good rule of thumb is 90%.

For example, if we had glass with a COG U-value of 0.28 and 90% Vision Area (i.e. 10% framing), the overall/System/Assembly U-value would be ~ 0.44

My experience is that this is completely acceptable for LEED/GBCI. These charts were created by application engineers working for the framing companies, which I?m assuming they know this stuff way better than I do. If you look at page 35, it says the U-factors, SHGC, and VT values are determined in accordance with NFRC 100 and 200.

Other framing vendors, like EFCO, have similar charts that we can use.

In my view, this is good enough to document assembly performance. I would use the charts and move on. If the new Table 1.4 includes space for a comment, I would reference the charts, and submit the charts if asked.

There really is no other way to do this except try to calculate ourselves, which why bother when we have these charts. If we ask the architects, often times, they will not understand what we are asking for. They will probably only be familiar with the glass properties, not the combination of glass + framing. The glass vendor will only give you performance data for the glass, not the combination of glass and framing. I?m not sure why section exists, except for packaged windows. I haven?t found anybody that will give you a permanently installed nameplate or official certification for the entire fenestration system, at least for custom systems often encountered in commercial construction (i.e. curtain wall versus packaged windows). Maybe the requirement are met in other parts of country by somebody, but for now, I?ve found these charts from the curtain wall vendors to be very effective from a cost and time standpoint.

I would welcome any additional feedback on this.

Hope this is helpful.

Thanks! ?



James A. Hess, PE, CEM, BEMP

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Joined: 2011-09-30
Reputation: 401

Just as an aside, in Seattle we've been dealing with NFRC requirements for
at least the last six years. Our local energy code requires NFRC
certification for all glazing products, otherwise you must use similar
default values to ASHRAE 90.1 Appendix A which obviously costs the project
money making up for the terrible default values.

The way to get proper NFRC values is to inform the architects about the
requirements for a LEED project and make sure the project specifications
require the curtainwall manufacturer to provide an NFRC certified product.
This usually comes in the form of an NFRC Simulation Report which is a
preliminary simulation that is certified prior to installation on the site.

For more information on how the City of Seattle enforces these requirements
you can read the following:

[image: Inline image 1]

Robby Oylear's picture
Joined: 2011-09-30
Reputation: 202


I appreciate the excellent feedback. The document you referenced is excellent info.

The current energy code in Arkansas is ASHRAE 90.1-2007, so we have similar requirements regarding fenestration requirements; we just don't have the enforcement part, and we don't address this area in anywhere near as much detail as other parts of the country, like Seattle.

The rest of my commentary is more from the viewpoint of energy modeling for LEED.

I would have thought that when Kawneer provides performance values that they say are in accordance with NFRC 100 and 200, it would be acceptable to use those for energy modeling purposes.

The document you reference basically says no. It basically says that an approved 3rd party must develop the NFRC label certificate specifically for each and every project, and that this certificate would be the basis for determining energy code compliance. We can infer that the values from the certificate should also be the values used for energy modeling for LEED.

It should be noted that per the document you submitted, we can also infer that using energy simulation programs to calculate the assembly values, or using the Window program to calculate the assembly values ourselves, is not allowed either, per strict reading of NFRC requirements and ASHRAE 90.1

This sure is a can of worms we have opened here. The USGBC/GBCI reviewers have not to date enforced these very strict fenestration requirements of the energy code. I've worked on and submitted ~ 30 LEED projects and I've never been asked once to provide an official NFRC Label Certificate for the entire project by an NFRC licensed independent Certification and Inspection Agency (IA).

All the LEED reviewers have asked (which is quite reasonable in my opinion) thus far is that we adequately factor in the effects of the framing on the overall fenestration performance. The methods allowed in the past have included using the Window program to estimate performance, using the energy modeling program itself to account for framing, using the charts provided by curtain wall mfg's, etc.

I'm going to continue using these methods until the USGBC/GBCI puts its foot down and says all projects have to include a copy of the NFRC Label certificate.

However, I will research this with our local framing vendors to see what all is required to get this certificate and if it's something they can help with.

If this is simply a matter of requiring the framing vendor to provide a report that certifies that the combination of their product + glazing is NFRC certified, this doesn't seem like a big deal.

However, if the framing vendor is not allowed to do that, but instead a 3rd party has to certify NFRC compliance and issue the NFRC Label Certificate, that may be a bigger deal, or may not be. I have no experience with this. It seems like it would add to project costs, which building owners and developers may frown on.

We can ask the architects to add these requirements to the project and see what happens. All we can do is ask, but if we don't get that information, then we will fall back on the methods we have already been using successfully, unless/until told to change by GBCI/USGBC. :)

Sorry for the long email response.

Thanks! :)



James A. Hess, PE, CEM, BEMP

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Joined: 2011-09-30
Reputation: 401


We've run into similar issues on projects outside of Seattle (enforcement
isn't equal across the State and in the case of Federal buildings they
don't have to comply at all). From what I've seen out of reviewer's
comments they are specifically allowing an exception for the use of the
LBNL Window program. It is not something that technically complies with
ASHRAE 90.1-2010, but from what I understand USGBC can choose to enforce
the code differently than one might for code compliance.

As far as project costs, I've heard estimates of around $5k-$10k for
simulation testing for a third party lab. For a large high-rise building
this may not be much, but I can see it causing heartburn for smaller
projects. As Mr. Reddy pointed out above, there exists a library
of certified values on the NFRC CMAST and CPD websites. Though NFRC
Certified values are project specific for site-built products, if you can
find a similar glazing/framing combination for the curtain wall system your
project is using I'm sure that would be an acceptable pathway to showing
compliance with ASHRAE.


Robby Oylear's picture
Joined: 2011-09-30
Reputation: 202

James and Robby:

Some good points and information.

I always ask the architect to provide the NFRC rating. Usually they contact the
vendors for that information. I actually get acceptable data about 20% of the

I have taken to informing the design team during the DD phase of the project (I
provide Enhanced Commissioning Services also, so am involved early) that I need
the NFRC ratings, so they should verify the vendors can provide this before they
commit to a specific product.

Paul Diglio, CEM, CBCP

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Joined: 2011-09-30
Reputation: 400

For what it is worth, the window manufacturers all grumble that "only
Seattle" enforces the NFRC requirements, even though it is state code

Also worth noting that even though Kawneer is an international brand, they
seem reluctant to get their product NFRC certified, and you can't directly
look up their common storefront products directly in the NFRC Directory:

Some of the local glazing suppliers have evidently had to spring for the
testing themselves to get Kawneer products accepted in Seattle. So, for
example you can find a few combinations of Kawneer 1600 or Trifab 451T
listed under the manufacturer "Goldfinch Brothers, Inc." I'm sure there
must be some other "hidden" examples as well of common glazing products
certified under local glazing company listings.

Nathan Miller - PE, LEEDRAP BD+C, CEM

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Joined: 2011-09-30
Reputation: 200

Robby, Paul, and Nathan

This is all excellent info you have followed up with. I appreciate your follow up responses.

I definitely need to do some more research in this area.

The cost mentioned below by Robby doesn't seem unreasonable, especially for larger projects, and especially given the architects preference for more glass on buildings. With regards to the total project budget, $5K to $10K is rounding error! :)

In addition, I probably will start informing the architects we work with that they are responsible for ensuring the NFRC Label information is provided, in accordance with LEED and ASHRAE requirements, and that gets the monkey off our back. The architects in turn will ask us what to ask for, and after reading that document, I can tell them.

Thanks! :)



James A. Hess, PE, CEM, BEMP

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Joined: 2011-09-30
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Thank you for posting this article. I really enjoyed reading it.

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