Real Estate Operations
Leasing
As of September 30, 2020, our real estate portfolio was comprised of 32 operating properties, which we refer to as our operating properties, and 3 redevelopment properties, which we refer to as our redevelopment properties, that are in the process of being redeveloped, or are completed but not yet stabilized. We collectively refer to our operating and our redevelopment properties as our owned portfolio. Our 32 operating properties were approximately 85.6% leased as of September 30, 2020, a decrease from 87.6% leased as of December 31, 2019. The 2.0% decrease in leased space was a result of the impact of lease expirations and terminations, which exceeded leasing completed during the nine months ended September 30, 2020. As of September 30, 2020, we had approximately 1,376,000 square feet of vacancy in our operating properties compared to approximately 1,175,000 square feet of vacancy at December 31, 2019. During the nine months ended September 30, 2020, we leased approximately 606,000 square feet of office space, of which approximately 259,000 square feet were with existing tenants, at a weighted average term of 7.8 years. On average, tenant improvements for such leases were $33.80 per square foot, lease commissions were $10.71 per square foot and rent concessions were approximately six months of free rent. Average GAAP base rents under such leases were $29.61 per square foot, or 11.8% higher than average rents in the respective properties as applicable compared to the year ended December 31, 2019.
As of September 30, 2020, our three redevelopment properties included an approximately 111,000 square foot property known as Stonecroft in Chantilly, Virginia, an approximately 213,000 square foot property known as Blue Lagoon in Miami, Florida and an approximately 62,000 square foot property known as Forest Park in Charlotte, North Carolina. Given the length of the redevelopment and lease-up process, these properties are not classified as an operating property until, in some cases, years after we commence the project.
Our property known as 801 Marquette in Minneapolis, Minnesota, which was substantially completed at the end of the second quarter of 2017, had been previously classified as a redevelopment property. As of June 30, 2020, the property had leases signed and tenants occupying approximately 37% of the rentable square feet of the property. On September 14, 2020, we entered into a lease agreement with a new tenant with an initial term of 16 years for approximately 71,000 square feet, or 54.8% of the property’s rentable square feet. As a result, as of September 30, 2020, 801 Marquette was approximately 91.8% leased, which we consider stabilized, and has been reclassified as an operating property.
The redevelopment of Stonecroft commenced in August 2020. We expect to incur total redevelopment and lease-up costs of $18.5 million, which includes significant interior work to make the space suitable for multiple tenants, or to accommodate a tenant with accredited security requirements. As of September 30, 2020, we had incurred approximately $1.4 million in redevelopment costs. We anticipate completing the redevelopment by June 30, 2021.
The redevelopment of Blue Lagoon commenced in December 2018 following the maturity of a lease with a major tenant that had occupied 100% of the property. On September 13, 2019, we entered into a lease agreement with a new tenant with an initial term of 16 years for approximately 156,000 square feet, or 73.1% of the property’s rentable square feet. We expect to incur total restoration, redevelopment and lease-up costs of $39.9 million, which include work on the roof of the building, costs to make the space suitable for multiple tenants and to increase parking at the property. As of September 30, 2020, we had incurred approximately $16.5 million in total redevelopment costs. We anticipate completing the redevelopment by the end of 2020.
The redevelopment of Forest Park commenced in January 2019 following the maturity of a lease with a tenant that had occupied 100% of the property through December 31, 2018. We completed the redevelopment during the three months ended June 30, 2020. On July 20, 2020, a tenant lease commenced and occupies approximately 22,000 square feet, or approximately 34.5% of the total rentable square feet, with an initial term of 11 years. On September 24, 2020, we entered into a lease agreement with a new tenant for approximately 28,200 square feet, or 43.9% of the rentable square feet at the property, with an initial term of 7 years. As a result, as of September 30, 2020, Forest Park was approximately 78.4% leased.
As of September 30, 2020, leases for approximately 0.8% and 8.2% of the square footage in our owned portfolio are scheduled to expire during 2020 and 2021, respectively. As the fourth quarter of 2020 begins, we believe that our operating properties are well stabilized, with a balanced lease expiration schedule, and that existing vacancy is being actively marketed