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A four-story, 36-unit affordable multifamily development in Portland’s Mississippi neighborhood has introduced a replicable mass timber housing model that its builders say could reshape how affordable housing is delivered on urban infill sites.

Shortstack Mississippi, completed in March 2025 at 3325 N. Michigan Ave., was developed by Shortstack Housing, a women-owned affordable housing development team based in Portland. The project totals approximately 34,000 square feet and reserves all units for households earning 60 to 80 percent of Area Median Income, with 20 of its 36 units de-signed as three-bedroom family housing – a unit type the development team said is critically underrepresented in walkable urban neighborhoods.

The building employs a hybrid structural system combining panelized wood-framed bearing walls with 139mm, five-ply cross-laminated timber floor and roof panels. Pressure-treated glulam columns were tilted into place to eliminate horizontal seams, and the planning module was developed around standard CLT panel sizes before site assignment, al-lowing the system to adapt across varied infill parcels while minimizing material waste. The CLT structure was erected approximately 20 percent faster than conventional framing methods, with each floor completed in roughly one week, at cost-neutral pricing compared to standard construction.

The tight urban site presented significant challenges, including a steep grade transition be-tween multifamily zoning to the east and single-family homes to the west, causing the building to read as five stories from the commercial corridor and four stories from the adjacent residential side. Many subcontractors were working with CLT for the first time, and a successful code appeal allowed fire-treated plywood to substitute for Type X gypsum sheathing behind balcony ledgers, preserving both fire integrity and design intent.

Safety measures were embedded in the construction approach. Prefabricated CLT panels reduced on-site framing duration and worker exposure to jobsite risks, while crane-assisted installation minimized prolonged elevated work. Intensive preconstruction coordination reduced rework and unsafe field modifications.

The building organized its program around a central courtyard in place of a conventional double-loaded corridor, creating a shared outdoor gathering space for residents. Wood was sourced within 500 miles of Portland from responsibly managed Pacific Northwest forests, and the mass timber structure sequesters carbon relative to conventional construction methods.

Funded in part through the Oregon Housing and Community Services LIFT program, the project was required to achieve 30 percent participation by minority, women, and emerging small businesses. The team exceeded that threshold, reaching 40 percent MWESB participation, and collaborated with Constructing Hope and the Oregon chapter of the National Association of Minority Contractors to support workforce development.

The project was designed by WORKS Architecture and built by Owen Gabbert LLC.