ENCLOSURE: 10 High-Impact Ways to Reduce Embodied Carbon

CECC 12/4/2024

1. Minimize window/opaque-wall ratio. Glazing construction is remarkably high in embodied carbon, typically equivalent to about six inches of concrete. Glazing also has a low R value so a reduced window wall ratio will also conserve on heating and cooling.

2. Avoid using concrete or masonry for exterior wall backup structure, and if you must use them, note that concrete walls have about twice the embodied carbon of CMU walls. Metal or wood stud construction have much lower embodied carbon, and they can be insulated in the stud cavities.

3. Use plain or Type X gypsum board at interior surfaces and minimize the use of fiberglass mat gypsum board for this application.

4. For insulation inside the exterior structural wall, use bio-based insulation such as cellulose, hemp, or timber. Fiberglass batts are a viable low embodied carbon choice for non-bio-based insulation.

5. For exterior sheathing use in the following order of increasing embodied carbon: ½” plywood; 5/8” plywood; ½” OSB; fiberglass mat gypsum board (embodied carbon = 2x ½” plywood).

6. For exterior rigid insulation use in the following order of increasing embodied carbon: TimberBoard; EPS rigid board; GPS rigid board; XPS rigid board with HFO foaming agent; polyiso rigid board.

7. Minimize wall-to-floor ratio: floor-to-floor heights, floor plan aspect ratios, floor plan offsets, and exterior wall offsets, all impact this. Here is a diagram showing the impact of floor plan aspect ratios and floor-to-floor heights.

8. For exterior cladding, avoid concrete, full thickness brick, terra cotta, porcelain tiles, CMU veneer, and thicker natural stones.

9. For exterior cladding, pay attention to the backup system requirements as the embodied carbon can be as high as the cladding material. Avoid using mortar and aluminum channels as part of your cladding support system – both materials are high in embodied carbon.

10. Windows can play a significant role in the amount of embodied carbon in an exterior wall. Smaller windows, e.g., 42” x 42”, can be glazed with annealed (float glass) which has lower embodied carbon than tempered glass. Window frame materials represent a sizable portion of the embodied carbon in a window, and one should use wood for smaller windows and structural composite lumber backers for curtain wall mullions. Laminated glass has a higher embodied carbon content than tempered glass and should be avoided.

This is available as a downloadable pdf on the Documents page.