Heartwood is the first building in the United States completed as-of-right under the new Type-IV codes. Representing a significant development in tall timber construction, Heartwood provides not only “missing middle” housing for Seattle, but a replicable model for future tall timber buildings across the country. &nbsp;Heartwood is a 67,000 SF apartment building, providing missing middle housing for families making 60-100% of Seattle’s Area Median Income (AMI). Heartwood shares its site with the three-story affordable Helen V Apartments, owned and managed by the same local nonprofit, Community Roots Housing. Together, the Heartwood amenity spaces create a shared, unifying courtyard for both projects and communities.

alongside an outdoor courtyard, bike parking, retail, and laundry.

– missing middle housing targeting 60-100% of Area Medium Income (AMI).&nbsp;

far in excess of a comparable light-wood frame building. Over the building’s long life, market conditions and owner’s goals may change.&nbsp;

to adjust to changing market conditions.

An end-of-life analysis by the University of Washington projects that 80% of the Mass Timber in Heartwood will be reused in other, new Mass Timber buildings. Unusable portions of the superstructure will be reconstituted as OSB or Particle Board, which can themselves been recycled up to 3 times. These process involve only a small amount of C0₂ loss at each stage, meaning that most of the carbon sequestered in the wood will remain so for centuries.&nbsp;

extends the biophilic nature of the project to all units inhabitants of the building.

this all-timber assembly is the first of its kind to meet a 2hr fire resistance rating without introducing any steel connections. This joint is ready for use in type IV-C and IV-B construction, and provides the basis for a construction system that can be adapted in practically endless variety.

and a neighboring apartment building that needed to remain accessible, site disturbance during construction had to be kept to an absolute minimum.

minimizing site disturbance through prefabrication and just-in-time delivery, facilitating a lean, clean, and quiet construction site. &nbsp;

and recently it has become the primary center in the rise of engineered mass timber products. Relying on regional supply chains limits carbon expenditure and promotes local and rural infrastructure and labor markets. The wood products used in Heartwood were all sourced within a 500-mile radius, using sustainably harvested methods. Specific Environmental Product Declarations from each regional mass timber source are being tracked as part of the Life-Cycle Analysis work currently underway for Heartwood at the University of Washington.

is its proprietary, two-hour rated column and beam connection, developed by Timberlab in collaboration with atelierjones and DCI Engineers.

such as concrete and steel wherever possible. Using strategic materials-based decisions led to a lower-carbon footprint as well as lower costs.&nbsp;

in part due to the high lateral requirements of the seismic zone.

minimizing the volume of concrete required.

reduced an estimated 11% off the structural budget.

In 2024, the University of Washington is publishing a full Life Cycle Analysis (LCA) of Heartwood’s superstructure, tracking its Global Warming Potential and comparing it to a conventional concrete building of the same size.The Global Warming Potential (GWP) for Heartwood’s superstructure was 38% lower compared to an equivalent concrete building. When offsetting the CO₂ sequestered in the timber, the net result is a 108% reduction.

Through early energy modeling, Heartwood also minimized its operational carbon, a benefit to its residents and the long-term management of the building by a long-standing Seattle affordable housing focused non-profit. The building is projected to perform approximately 25% better than the 2015 Washington State Energy Code requirements and has a projected EUI of 23.9.

provided schedule and constructability advantages over conventional options and further added to the overall biogenic carbon benefit of the project.