Seattle-based developer Touchstone announced Tuesday it had found an equity partner in Texas-based USAA Real Estate, moving it closer to redeveloping the former Troy Laundry block in South Lake Union into a new 820,000-square-foot complex.

Touchstone’s proposal for two L-shaped office towers was approved last month by the Seattle Department of Planning and Development, a necessary step before a building permit can be issued.

The first phase is a 12-story tower of 380,000 square feet at the corner of Boren Avenue and Thomas Street, and the second phase is a 13-story tower. Touchstone acquired the property from The Seattle Times in June 2011 for $18.4 million, records show.

The site sits across the street from’s headquarters, a proximity that could be attractive to future office tenants. Colliers International is marketing the office space, targeting it at technology firms, Touchstone said.

Unlimited Digital Access. $1 for 4 weeks.

The project will demolish most of two landmarked buildings — the Troy Laundry building and the Boren Investment Co. warehouse — but will retain their facades.

The Troy building, which faces Fairview Avenue, is a relic of the early 20th century when the Cascade neighborhood was a hub for commercial laundries. The developer will have to remove tons of soil contaminated by laundry operations for nearly 60 years.

While Touchstone declined to comment on its timeline for the project, documents filed in November show the developer planned to demolish and excavate the site from fall 2013 through summer 2014 and to complete construction on at least one tower in early 2016.

USAA Real Estate is the real-estate investment arm of United Services Automobile Association, a company that provides financial services to military families.

Officials said it was USAA Real Estate’s first joint venture with Touchstone, which is also developing Hill7, a hotel-and-office complex along Boren Avenue between Stewart and Howell streets.

Terms of the partnership weren’t disclosed.

Sanjay Bhatt: 206-464-3103 or On Twitter @sbhatt