Economic Conditions
The economy in the United States has been adversely impacted as a result of the COVID-19 pandemic. Economic conditions directly affect the demand for office space, our primary income producing asset. The broad 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
As of March 31, 2021, our real estate portfolio was comprised of 33 operating properties, which we refer to as our operating properties, and one redevelopment property, which we refer to as our redevelopment property, that is in the process of being redeveloped. We collectively refer to our operating and our redevelopment properties as our owned portfolio. Our 33 operating properties were approximately 81.9% leased as of March 31, 2021, a decrease from 85.0% leased as of December 31, 2020. The 3.1% decrease in leased space was a result of the impact of lease expirations and terminations, which exceeded leasing completed during the three months ended March 31, 2021. As of March 31, 2021, we had approximately 1,725,000 square feet of vacancy in our operating properties compared to approximately 1,397,000 square feet of vacancy at December 31, 2020. During the three months ended March 31, 2021, we leased approximately 377,000 square feet of office space, of which approximately 370,000 square feet were with existing tenants, at a weighted average term of 9.3 years. On average, tenant improvements for such leases were $18.67 per square foot, lease commissions were $10.23 per square foot and rent concessions were approximately nine months of free rent. Average GAAP base rents under such leases were $28.46 per square foot, or 1.7% lower than average rents in the respective properties as applicable compared to the year ended December 31, 2020.
We reclassify redevelopment properties as operating properties when the property redevelopment is complete and leasing has stabilitized. Given the length of the redevelopment and lease-up process, the reclassification of a property may take a significant amount of time.
As of March 31, 2021, our sole redevelopment property was an approximately 111,000 square foot property known as Stonecroft in Chantilly, Virginia. 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 March 31, 2021, we had incurred approximately $2.3 million in redevelopment costs. We anticipate completing the redevelopment by July 31, 2021.
Our property known as Blue Lagoon in Miami, Florida, was substantially completed during the first quarter of 2021, and had previously been classified as a redevelopment property. As of March 31, 2021, the property had leases signed and a tenant occupying approximately 73.1% of the rentable square feet 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.
As of March 31, 2021, leases for approximately 4.9% and 8.8% of the square footage in our owned portfolio are scheduled to expire during 2021 and 2022, respectively. As the second quarter of 2021 begins, we believe that our operating properties are well stabilized, with a balanced lease expiration schedule, and that existing vacancy is being actively marketed to numerous potential tenants. While leasing activity at our properties has continued, we believe that the COVID-19 pandemic and related containment and mitigation measures may limit or delay new tenant leasing during at least the second quarter of 2021 and potentially in future periods.
While we cannot generally predict when an existing vacancy in our owned portfolio will be leased or if existing tenants with expiring leases will renew their leases or what the terms and conditions of the lease renewals will be, we expect to renew or sign new leases at then-current market rates for locations in which the buildings are located, which could be above or below the expiring rates. Also, we believe the potential exists for any of our tenants to default on its lease or to seek the protection