318 Lofts Passive House Apartments

This 6-story, 20-unit Passive House apartment building located in Seattle’s Capitol Hill neighborhood replaces an aging and inefficient 2-story, 6-unit building from the 1950s. The project aims to create a modern building that ensures long-term sustainability, durability, and affordability for both the owners and the building’s residents.

The narrow site is 40ft wide with powerlines located at the street. Our challenge was to create a modern building, with traditional materials, meeting the constraints of the site. The site’s limitations worked to our advantage with a design stepping the building back from the street, breaking up the tall massing, and creating a ground-level experience that relates more directly to the neighboring buildings. The visual and physical break provides options for a roof deck and reduces the experience of a looming building overhead while at street level.

The compact floor plate allows for a maximum of only four units per floor, meaning each unit is a desirable corner unit with two sides of windows. Along the west side of the building, the units enjoy city views. While the large windows along the west and east façades can contribute to overheating due to solar gains, a combination of solar shades, balconies, and triple-paned windows mitigate this risk by lowering the heat gain factor in these areas.

The cladding materials are modern and attractive, chosen to age slowly. A muted palette offers a timeless appearance to fit into the neighborhood aesthetic. Inside, the design was inspired by the Pacific Northwest, with cozy, comforting materials and colors that reflect the building’s location and enhance the city views from the rooftop deck. The central stair tower stands out with an ombré pattern that accents the otherwise neutral material palette. Though recessed and not immediately evident, a brief glimpse of this stand-out element is visible from the street.

As a Passive House building, efficiency and interior comfort were key to the design. The high levels of insulation, triple pane windows, and efficient heating and cooling systems make it significantly more efficient than a standard apartment building of the same size. Mechanical systems are grouped together per floor to keep them simple for lower maintenance cost and increased reliability. The interior environment is serviced by a Heat Recovery Ventilator (HRV) system, which provides continuous filtered and conditioned air. Along with the air-sealed and well-insulated envelope, this makes for stable internal temperatures year-round. Grouping the systems on each floor also reduces the impact of maintenance on residents where services will affect only one floor rather than the whole building.

As Board & Vellum is performing the energy modeling, design, passive house detailing, and PHIUS Certification in-house, this fostered a design efficiency where impacts of design decisions could be analyzed for their impact on energy performance in real-time. Through close collaboration with the contractor and the team of consultants, we were able to identify opportunities for cost savings and reduced construction complexity without compromising the project’s integrity as a Passive House building.

A long-term investment, the owners opted to include Passive House design principles to buffer their tenants against increasing energy costs. By including the super-efficient systems dictated by Passive House design, they are able to keep rental costs competitive while providing a high level of comfort and lower street noise to increase tenant retention and reduce the cost to the owner.

Notes & Credits
This project will be constructed by Cascade Built.
Structural Engineering by Yu & Trochalakis.
Civil Engineering by Bush, Roed and Hitchings, Inc.
Landscape Architecture by KKLA.
MEP by Staengl Engineering.
Envelope and PHIUS Rating by RDH Building Science.
Energy Modeling and PHIUS Certification by Board & Vellum.