How we cut embodied carbon by 41% on a library renovation

When the owner of a 1970s municipal library asked us to renovate instead of rebuild, we agreed to track embodied carbon from the first sketch. The final number came in 41% below the baseline we set at the start. This is how that happened, and what we would carry into the next project.

Start with a baseline

Before drawing anything, we modeled a typical renovation of the same size using standard assemblies and common suppliers. That gave us a number to beat. Without it, every later decision would have been a guess about whether we were improving things.

We repeated the model at the end of each design phase, so the team could see how every choice moved the total. When a decision pushed the number up, we talked about it the same day instead of finding out at the end.

Keep what already works

The biggest saving came from the structure. The concrete frame was sound, so we kept all of it and cut only the openings we needed for a new stair and a light well. Reusing the frame avoided most of the carbon a new building would have used.

We also kept the original masonry facade and repaired it, rather than replacing it with a new envelope. The old brick suited the neighborhood, and the repair work was quicker and cheaper than demolition and rebuilding.

Choose new materials carefully

Where we did add material, we asked suppliers for product-specific data and picked the lower option when performance was equal. Timber floors, recycled steel and low-cement concrete patches made up most of the new work.

Some choices were close calls. A thicker insulation layer would save energy for decades but added carbon on day one, so we modeled both and kept the version that paid back within eight years.

What we would do again

Set the baseline early, report the number at every review, and give the whole team a reason to care about it. The 41% reduction did not come from one clever idea. It came from many small decisions made with the number in front of us.

We would also bring the contractor in earlier. Several of the best savings came from conversations on site, and we found them late.