Aluminum Storefront SHGC & U Value

[QuestionThat]

2009 IECC & Table 502.3
Trying to understand SHGC & U-value requirements for aluminum storefront.

Climate zone 3 requires
.60 U factor for "metal framing with or without thermal break".
.25 SHGC for "all frame types"
Think this is referring to storefront framing components only (no glass).
So don't understand where the glazing U-values & SHGC comes into play.
Is there some type of formula for combining the framing and the glass to figure out overall u-factors & shgc's?
Or is the manufacturer of the glass? storefront? responsible for providing me with this information?

Shop drawings as currently submitted indicate the following:
Glazing- .29 Winter & .27 Summer U-Value
.27 SHGC
Storefront- .37 U-Value
.254 SHGC

Combining framing & glazing SHGC's and U-Values:
U-Value .37 (Storefront) & .29 Winter w/ .27 Summer (Glazing)
SHGC .254 (Storefront) & .27 SHGC (Glazing)

Not sure what to do next to determine if the glazing assembly meets code.

Note also that this glazing assembly is also incorporated into a tube steel frame and I'm trying to make sure the entire assembly meets code as a unit with or without insulating the tube steel.

 

[RLGA]

The values in Table 502.3 are for the entire glazed assembly. Section 502.3 states "Fenestration shall comply with Table 502.3." Fenestration, in Chapter 2, is defined to be assemblies "with glass and nonglass glazing materials"; therefore, glass is part of the fenestration. Thus, since the section and table reference "fenestration," then the values in the table include the glazing.

All the table is doing is segregating the fenestration performance based on the type of frame it has.

 

[QuestionThat]

The values in Table 502.3 are for the entire glazed assembly. Section 502.3 states "Fenestration shall comply with Table 502.3." Fenestration, in Chapter 2, is defined to be assemblies "with glass and nonglass glazing materials"; therefore, glass is part of the fenestration. Thus, since the section and table reference "fenestration," then the values in the table include the glazing.

All the table is doing is segregating the fenestration performance based on the type of frame it has.

OK. Understood and thanks!
So when we're talking storefront and I have U values for both the framing and the glazing, which value do I choose?
Also, regarding the fact that the storefront will be installed in a steel frame used to support the storefront, would you say that this could be considered a fenestration assembly and then the table values would then be assigned to the assembly? Especially since "Metal framing with or without thermal break" is the category?

 

[RLGA]

OK. Understood and thanks!
So when we're talking storefront and I have U values for both the framing and the glazing, which value do I choose?
Also, regarding the fact that the storefront will be installed in a steel frame used to support the storefront, would you say that this could be considered a fenestration assembly and then the table values would then be assigned to the assembly? Especially since "Metal framing with or without thermal break" is the category?

Is the steel behind the storefront (i.e., interior side only) or is it exposed to the exterior with the aluminum framing on each side? Also, is the steel part of the building structure (i.e., not required just to support the storefront)?

As for determining the overall assembly rating, you'll need to find someone (probably the storefront manufacturer) to provide labels that establish the requirements based on NFRC 705 Component Modeling Approach for determining the values based on ratios of individual component values to the areas within the fenestration assembly. I don't know if this method takes into consideration steel framing.

 

[QuestionThat]

Steel is used to support structure above but it was chosen as a function to integrate with the storefront..... could have been framed with wood. The vast majority of the building is wood frame construction. ALL of the steel frame is infilled with storefront. Storefront rests on steel tube beams and is framed between tube steel columns.
So, yes tubes are "exposed" to the exterior.
That being said, for the original design I had drawn/ specified 2" rigid insulation at the face of the tubes & everything is to be covered with aluminum brake metal. After thinking this through more and more my preference is to leave out the rigid.... but can default back to that IF required. Just want to understand why I'm doing what.....

 

[RLGA]

Since the steel members are part of the building structure, it should be treated just as if they were a wall supporting the storefront. Thus, they should conform to the requirements for walls.

The current IECC and some editions before that have a "component performance alternative" where if you have areas that have a higher performance than required, then they can make up for those areas that have performance that is below what is required. The 2009 IECC does not have that alternative, but you could look to the referenced edition of ASHRAE Standard 90.1 to see if that has something similar since the ASHRAE standard is an acceptable alternative (IECC Section 501.2). If it doesn't, then I suggest requesting a code modification to use the component performance alternative of a later IECC edition.

 

[QuestionThat]

As always. Thanks for your insight. Sounds like I have a lot of work to do.

 

[Mech]

Disregarding the steel structure, the overall U-value / SHGC will be a function of the individual values you have, and the size of the fenestration. The frame manufacturer that I spec provides graphs with glass % compared to overall fenestration size, glass U value, and glass SHGC and overall U and SHGC values. After some easy computations, the overall values can be selected off the graph.

 

[QuestionThat]

OK. Thanks!

 

[ADAguy]

Disregarding the steel structure, the overall U-value / SHGC will be a function of the individual values you have, and the size of the fenestration. The frame manufacturer that I spec provides graphs with glass % compared to overall fenestration size, glass U value, and glass SHGC and overall U and SHGC values. After some easy computations, the overall values can be selected off the graph.

Read my mind before I could ask the question, thanks.

 

[QuestionThat]

Reached out to storefront sub and manufacturer yesterday to try and get assembly values. Will see how that progresses.