Precision, Protection & Progress: Sealing Seattle’s New World-Class Medical Tower

Providence Swedish, a leading healthcare campus in Seattle, is expanding with the North Tower development. This 12-story acute care facility will include 24 advanced operating suites, a 31-room emergency department, 72 acuity-adaptable ICU beds, centralized imaging, and shell space for future clinical expansion.
The project spans approximately 60,000 square feet of vertical waterproofing surface and focuses solely on wall assemblies. To ensure long-term watertight performance in a medical facility, the structure required full continuity of waterproofing from below-grade to above-grade, including a new below-grade tunnel connecting to a future medical outpatient tower.

Providence Swedish selected Mortenson as general contractor, with Inland Waterproofing as the installing subcontractor. Perkins & Will is the project architect, and RDH Building Science serves as the waterproofing consultant. Stantec is providing third-party inspection services required for warranty compliance. GCP was selected as a specialty building materials provider.

Construction began in Q1 2024. Below-grade waterproofing was completed in Q4 2024, and air barrier installation is underway as of 2025. The North Tower is scheduled to open in Fall 2027.

Importantly, this project stands out not only for its complexity and clinical importance, but also for its leadership. Women held key roles across every major stakeholder group, including Mortenson, Inland Waterproofing, RDH, and GCP. Their guidance and collaboration were instrumental in driving progress and precision at every stage of this high-performance, high-profile build.

The Challenges:

Delivering high-performance waterproofing for a hospital expansion project in the heart of Seattle requires more than technical knowledge; it demands coordination, clarity, and consistency across trades and timelines. At the Providence Swedish expansion, several complex factors had to be overcome to ensure a fully sealed, high-performance building envelope.

Integrating Systems Without Gaps
The below-grade waterproofing had to tie into a hot rubber waterproofing system and the air barriers, presenting design collaboration and compatibility issues.

Zero Tolerance for Failure
As a critical healthcare facility, the structure can not risk any water ingress. This required continuous, unambiguous waterproofing coverage.

High-Pressure Site Conditions
The project environment was demanding, both in schedule and performance expectations. Applicator Inland Waterproofing faced strict quality control standards and exposure time limits, with no margin for error.

Specification and Product Compatibility Barriers
The original design specified multiple manufacturers for different components of the envelope system. This fragmented approach posed risks: compatibility issues at transitions, potential conflicts over warranty accountability, and greater installation complexity.

The Solution:

In the face of these multifaceted challenges, it became clear that success would require more than just high-performance products — it would take hands-on technical support, adaptability on site, and unwavering collaboration across teams. 

Although GCP was originally brought on to supply their PREPRUFE® below-grade waterproofing system, its products were not specified for the above-grade air barrier. A competitor was the basis-of-design, and GCP was listed only as an alternate. While the air barrier applicator initially bid the basis-of-design product, the general contractor recognized the value of a single-source manufacturer and requested the installation of GCP’s PERM-A-BARRIER® Air Barrier System to prevent the compatibility issues previously encountered at the tie-in between the below-grade waterproofing and hot rubberized asphalt. GCP’s technical team demonstrated how a unified system could eliminate these issues, reduce risk, and simplify installation. This decision ensured a fully compatible, high-performing envelope system and simplified warranty coverage.

The team leveraged GCP’s 6Sides+ system, an integrated, single-manufacturer waterproofing and air barrier portfolio that provides continuous protection from below-grade foundations through vertical walls, all under one warranty.

GCP supported the installation process with custom tie-in details and technical guidance, proactive site visits, and rapid response to field conditions, allowing the project team to move forward with confidence at every stage of installation.

Key components of the 6Sides+ system included:

• PREPRUFE® Waterproofing System
  Built with Advanced Bond™ Technology, PREPRUFE® forms a fully bonded, high-performance waterproofing layer that resists water ingress, lateral migration, and settlement damage, ideal for below-grade foundation walls.
• PREPRUFE® Liquid Flashing
  A cold-applied, two-part detailing compound used to seal penetrations and membrane transitions. It accelerates installation, reduces labor, and delivers a durable, fully bonded seal even in low-temperature conditions

• PERM-A-BARRIER® Air Barrier System
  GCP’s above-grade solution provided a seamless tie-in to the below-grade membrane, completing the envelope with a continuous, compatible barrier. The following products were selected for their performance and application-specific benefits:

  • PERM-A-BARRIER® Ultra Wall Membranes and Flashing
    A high-temperature-stable, impermeable membrane ideal for use under metal coping, behind metal cladding, and at parapet tie-ins. With a 30-mil aluminum-faced film, this solution withstands in-service temperatures up to 300°F, offers UV stability up to 12 months, and meets NFPA 285 fire performance as part of various assemblies. Its 100% butyl adhesive prevents adhesive drip, making it ideal for demanding wall and roof transitions.
  • PERM-A-BARRIER® VPL 50RS UV Stable Wall Membrane
    A liquid-applied air barrier that rapidly resists wash-off, allowing work to continue during rainy conditions. This breathable membrane permits water vapor to escape while remaining impermeable to liquid water. It can be applied at temperatures as low as 10°F, exposed for up to 12 months behind open joints, and contributes to energy efficiency by minimizing air leakage and condensation risk.

  Together, these materials formed a fully integrated system, enabling single-source accountability, eliminating transition conflicts, and ensuring long-term durability. GCP’s in-field presence and real-time support helped streamline installation and mitigate delays, reinforcing trust across the project team.

Results:

With a mission-critical healthcare facility at stake, success required more than meeting specs, it demanded precision, collaboration, and real-time problem solving. The Providence Swedish North Tower project achieved all three, with GCP’s 6Sides+ system playing a central role in delivering performance, efficiency, and long-term value.

Watertight Performance with Seamless Warranty Coverage
GCP’s 6Sides+ solution delivered a fully integrated waterproofing and air barrier system, with continuity from below-grade to above-grade, and no ambiguity at tie-ins or transitions. The result: one manufacturer, one coordinated system, one warranty.

Simplified Execution Under Pressure
Despite tight schedules, high scrutiny, and technical complexity, the project stayed on track. Inland Waterproofing’s expert application, combined with GCP’s responsive field support and clear detailing, enabled the team to meet deadlines without compromising quality.

Empowered Female Leadership Across the Project
This project marked a standout example of inclusive leadership in commercial construction. Women held key roles at every major stakeholder organization - Mortenson, Inland Waterproofing, RDH Building Science, and GCP - demonstrating that technical excellence and collaborative leadership go hand in hand. Their presence helped drive coordination, solve problems efficiently, and maintain accountability across disciplines.

Long-Term Protection for Critical Infrastructure
With the medical tower’s structure now sealed by a continuous, high-performance barrier system, Providence Swedish is prepared to offer uninterrupted care in a resilient, energy-efficient environment for decades to come.

This project not only delivered water and air-tight results, it set a benchmark for technical collaboration, inclusive leadership, and envelope continuity in complex healthcare construction.