Let me move on now to the development pipeline and start with the good work being done at Assembly Row in Somerville, Massachusetts. First, the planning and documentation with Partners HealthCare on the 12-acre former IKEA site is going extremely well, and we hope to have fully-executed documents completed over the summer to allow for a planned construction start by Partners this fall. In a piece of very good news, the deal now contemplates development rights for 900,000 square feet of office space, up from 700,000, making room for Partners' 4,700 plus employees moving in over several years beginning as early as 2016. We continue to work through the accompanying retail plan on that site, which we would own. That investment is expected to include a service retail destination including a drug store, a health club and additional food and service alternatives. We're estimating something in the range of a $35 million investment and about 110,000 square feet, but we'll report with more specificity on this piece and the entire Partners transaction once all the documentation is done.
On the other end of the Assembly site, we're proud to report that 97% of the retail space in our Phase 1 development is committed. That's 46 out of 51 outlet, restaurant and entertainment tenants that will open beginning now with the AMC Theater and then throughout the summer in anticipation of a full lineup in the fall. Leases executed in this first quarter included J.Crew, PUMA, Orbis, Motherhood Maternity, Aveda Salon and Sugar Heaven; while real estate committee approved-deals included Kenneth Cole, Express, Carter's, Oshkosh and Francesca's.
The first residential move-ins have begun in AvalonBay's apartments, and external construction on the block 2 office building is nearing completion. We're getting close on some office leasing in that building and as I noted, are virtually done with the retail lease in its base. The future looks very bright for Assembly Row and I hope that we'll be talking about another phase in the not-too-distant future.