economic market conditions in the United States are typically affected by numerous factors, including but not limited to, inflation and employment levels, energy prices, the pace of economic growth and/or recessionary concerns, uncertainty about government fiscal, monetary, trade and tax policies, changes in currency exchange rates, geopolitical events, the regulatory environment, the availability of credit, and interest rates. As of the date of this report, the impact of the COVID-19 pandemic and related fallout from containment and mitigation measures, such as work from home arrangements and the closing of various businesses, is adversely affecting current economic conditions in the United States.
Real Estate Operations
Leasing
As of December 31, 2020, our real estate portfolio was comprised of 32 operating properties, which we refer to as our operating properties, and 2 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 85.0% leased as of December 31, 2020, a decrease from 87.6% leased as of December 31, 2019. The 2.6% decrease in leased space was a result of the impact of lease expirations and terminations, which exceeded leasing completed during the year ended December 31, 2020. As of December 31, 2020, we had approximately 1,397,000 square feet of vacancy in our operating properties compared to approximately 1,175,000 square feet of vacancy at December 31, 2019. During the year ended December 31, 2020, we leased approximately 1,130,000 square feet of office space, of which approximately 762,000 square feet were with existing tenants, at a weighted average term of 8.3 years. On average, tenant improvements for such leases were $34.07 per square foot, lease commissions were $11.36 per square foot and rent concessions were approximately five months of free rent. Average GAAP base rents under such leases were $28.47 per square foot, or 7.7% higher than average rents in the respective properties as applicable compared to the year ended December 31, 2019.
As of December 31, 2020, our two redevelopment properties included an approximately 111,000 square foot property known as Stonecroft in Chantilly, Virginia and an approximately 213,000 square foot property known as Blue Lagoon in Miami, Florida. 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, 801 Marquette was approximately 91.8% leased, which we consider stabilized, and has been reclassified as an operating property.
Our property known as Forest Park in Charlotte, North Carolina, which was substantially completed at the end of the second quarter of 2020, had previously been classified as a redevelopment property. 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 December 31, 2020, Forest Park was approximately 78.4% 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 December 31, 2020, we had incurred approximately $1.8 million in redevelopment costs. We anticipate completing the redevelopment by July 31, 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