Steel extrusions EPD?

I would like to compare aluminum extrusions (mullions) to steel extrusions (mullions) but I don’t seem to find an EPD for steel mullions.
Please advise.

Hi Victoria. In my experience steel mullions are really just structural steel shapes used to support window walls. So you could use a standard structural steel EPDs. In some cases steel plates are added within aluminum extrusions as steel is stiffer and stronger than aluminum. To compare you’d have to be able to define functionally equivalent window wall systems.

Hi Victoria, Thanks for reaching out. It is unlikely that you will find a specific EPD for mullions, but it is possible to compare finished steel with finished aluminium at a generic level which, depending upon how detailed you want to be in your analysis, can be helpful. Also with steel, much depends upon the production route (BOF/BF or EAF) etc. which can affect the calculations. Also, do be aware that EPDs are good as LCA tool and are only as good as the input data. More authentic the input data to the EPD process, the more robust the numbers. EPDs that use the same data sources simply generate the same outcome (e.g. EcoInvent etc). Regards, Guy Mercer (M: +44 7583054430 E:

Thank you @ksimonen and @guy.mercer.
I am working in several airport projects. A few years ago I was using curtain wall EPD for the calculations like I did for all my other projects too.

I found several issues with curtain wall EPDs: some available ones in database were already expired, some didn’t pass the software check, and also there are discrepancies in (A1-A3) results: from ~60 kgCO2/m2 to ~360 kgCO2/m2 depending on manufacturer.
The most updated Kawneer EPDs have GWP total and als reported separately, frame vs glass. However, still not accurate for my calculations.

It seemed like the most accurate option given that each airport has different mullion configuration and also different glass was to do mullions and glass separately. To my surprise, the difference in results was significantly higher than total curtain wall GWP (for other project types I have not found the difference to be that big since the window to wall ratio is not as high as for airport concourse).

I found this research a few months ago: (PDF) A Comparative Study on Environmental Life Cycle Impacts of Curtain Walls (
Which shows that other materials (steel or timber) have lower GWP than aluminum mullions, however, I have not been able to run the calculations myself yet and prove it for any of my projects.

I also found other steel framed curtain wall EPDs which had even higher GWP than aluminum framed, which confirms Guy’s point of BOF vs EAF.

The problem with the mullions is that I have other materials within the mullion itself (for aluminum mullion I will still have PVC and stainless steel for example) so what I have been doing is adding 15% of my total volume of material to the calculations of my GWP (maybe this is too high). For aluminum, I have calculated the area of the profile (with an average wall thickness of 1/8") and then multiplying by total lenght. With this cf total, I obtain total weight (using the material density (typical) specified in the EPD). EPD: Thermally improved aluminium extrusion, anodized, 2660 - 2840 kg/m3 (Aluminum Extruders Council (AEC))

What you are both sugesting is that I do the same for steel mullion and use the same EPD as for Fabricated hollow structural steel sections, North American industry average, 7800 kg/m3 (American Institute of Steel Construction (AISC) & Steel Tube Institute)?

If I calculate the weight same as I do for the aluminum mullion, would that be good enough for comparison or will I be missing something?


Not sure I understand your question, but can’t just trade out material using the same area. The mullions must be sized based on loads, spans, material and cross section to be designed as functionally equivalent.

Thanks Kate.
I see what you are saying now, that makes total sense, my brain is not functioning properly. I will discuss with structural, architectural, and curtain wall manufacturer.

I found this article with some good information.


1 Like