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LCA for LEED: Impact categories in Tally vs EPDs

Kristian Kicinski

Associate Principal / Director of Sustainability

Bassetti Architects

LEEDuser Premium Member

7 thumbs up

August 19, 2022

We are trying to figure out how we are going to meet the LEED Credit for Building Life Cycle Impact Reduction for the first time.

One approach we're trying out: We're taking the results of our Tally model and looking at potential reductions from low-carbon concrete. However, the problem I am encountering is that when I take some of our mix designs and compare the EPDs with the results of our Tally model, I'm seeing the following (this is an example from a specific mix design):

EPD results:

GWP: 55% compared to Tally

Acidification: 84% compared to Tally

Eutrophication: 300% compared to Tally

Ozone Depletion: 1,580% compared to Tally

Smog Formation: 109% compared to Tally

Other similar mix designs from other projects and other concrete suppliers have similar results. So while we're hitting, often exceeding, our GWP reduction targets with these mixes, we're way off in the other impact categories which means we can't demonstrate LEED compliance. Has anyone else seen this happen with Tally? Does anyone know where Tally is pulling its impact data from? CLF does not appear to publish baselines for the impact categories other than GWP. Is there another baseline we could use for comparison?

I'm open to any advice on demonstrating compliance with the LEED credit.

Thanks!

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MJ Wojewodzki

Senior Associate

Quinn Evans

LEEDuser Basic Member

0 thumbs up

Sun, 08/21/2022 - 15:03

I've been using the Athena Sustainability Institute's Impact Estimator with the NRMCA Life Cycle report regional averages as a baseline. So far the mixes I've used on projects turn out fairly similar to the baselines, or better when we allow the concrete mix supplier more leeway. One problem I've run into is the fly ash/slag combo seems to perform better than just slag at the same total percentage in the mix. Some structural engineers won't allow the fly ash slag mix and some put limits on slag so there are challenges even matching the regional average if your structural engineer's parameters are too limiting. Lesson learned to test out some mix designs on a material estimator (like the ASI Impact Estimator) based on what the engineer will allow prior to finalizing CDs. I personally have not used Tally for this so I can't address your questions about where they get their baselines.

Efrie Escott

Kieran Timberlake

LEEDuser Basic Member

0 thumbs up

Mon, 08/22/2022 - 17:13

Hello all, The intent behind the way Tally calculates concrete is that you can use the pre-packaged "regional" mix as your baseline and then use a custom concrete mix to match the mix used in your building. There are specific techniques to account for things like Carbon Cure, if you need them, but generally Tally is not meant to be an EPD-based tool, as background data has HUGE influence on the final results, and Tally intentionally uses standardized background data (GaBi tool, data from the 2017 technology, North American geography).

Kristian Kicinski

Associate Principal / Director of Sustainability

Bassetti Architects

LEEDuser Premium Member

7 thumbs up

Mon, 08/22/2022 - 19:23

Thanks Efrie! We tried entering the mix designs as custom mixes in Tally since I posted this, and that seems much more promising. I could tell using the EPD’s to compare to Tally was an apples to oranges thing, so we’re continuing to look at other options. It’s been hard to get my head around that LEED credit- there doesn’t seem to be much guidance on defining the baseline. I feel like we’re just “making stuff up” as we go along. Kristian From: Efrie E

Justin Schwartzhoff

Architect & Embodied Carbon Specialist

LMN Architects

LEEDuser Basic Member

0 thumbs up

Mon, 08/29/2022 - 17:25

Hi Kristian, I’m catching up on a back log of SD Leaders posts, so someone may have answered this already. If not, here’s our take: Tally gets its numbers from the NRMCA industry wide EPD, which you can see mentioned at the end of the report. We had a similar issue when we first started applying plant specific EPD numbers to our data, especially when we were using the industry averages (any of the preset items for x% SCMs). Using the regional mix averages got us closer, but on most of our project now, we use the regional average from this report (page ~50 is when they start) and use the volume reported by tally to compute both the regional average impacts and the procured mix impacts. This has largely fixed the issue with other impact areas, but has also meant that some of our GWP reductions aren’t as good in areas where SCM use is already high. I need to double check, but I believe the latest versions of Tally include the regional area averages. Unfortunately, however, using the preset mix designs for SCM content does not work with the regional baselines, as the mix percentages are based off of modifications to the national average mix. You end up with a similar issue where the baseline numbers vary widely from the “reduced” numbers. Hope that helps! Justin Schwartzhoff LMN Architects – Explore our new site lmnarchitects.com<%20lmnarchitects.com%20> – M 206 812 6488 O 206 682 3460 Linkedin | Twitter | Instagram From: Kristia