Changing shopping habits, driven by rapid expansion of internet-driven procurement, have led to increased financial problems for many retailers, which has had a negative impact on the retail real estate sector. We continue to monitor the effects of these trends, including the impact of retail customer spending over the long-term. We believe the desirability of our physical locations, the significant diversification of our portfolio, both geographically and by tenant base, and the quality of our portfolio, along with its leading retailers and service providers that sell primarily grocery and basic necessity-type goods and services, position us well to mitigate the impact of these changes. Additionally, most retailers have implemented omni-channel networks that integrate on-line shopping with in-store experiences that has further reinforced the need for bricks and mortar locations. Despite recent market disruption and tenant bankruptcies, we continue to believe there is long-term retailer demand for quality space within strong, strategically located centers.
In 2020, we are experiencing fluctuations due to announced bankruptcies and the repositioning of those spaces. Currently, the impact to occupancy is unknown due to the uncertainty and duration of the pandemic. Previously, a reduction in the availability of quality retail space, as well as continued retailer demand, contributed to the increase in overall rental rates on a same-space basis as we completed new leases and renewed existing leases; however, the magnitude of these increases declined in comparison to previous years due to, among other factors, a continued shift in negotiating leverage to the tenant. Given the uncertainty surrounding the impact of the pandemic, we are unclear of its impact to rental rates and the funding of tenant improvements and allowances. The variability in the mix of leasing transactions as to size of space, market, use and other factors may impact the magnitude of these changes, both positively and negatively. Leasing volume is anticipated to fluctuate due to occupancy and the uncertainty in tenant fallouts related to bankruptcies and tenant non-renewals. Our expectation is that SPNOI growth will continue to decline in 2020.
New Development/Redevelopment
At September 30, 2020, we have two mixed-use projects in the Washington D. C. market and a 30-story, high-rise residential tower at our River Oaks Shopping Center in Houston that were in various stages of development and are partially or wholly owned. We have funded $436.5 million through September 30, 2020 on these projects, and we estimate our aggregate net investment upon completion to be $485.0 million. Due to the impact of COVID-19, we are currently unable to project a stabilization return for these projects.
We have eight redevelopment projects in which we plan to invest approximately $49.2 million. As of September 30, 2020, completed redevelopment projects added approximately 155,000 square feet to the portfolio with an incremental investment totaling $29.0 million. Realization of a stabilized return may take longer than originally planned due to the impact of COVID-19.
We had approximately $39.9 million in land held for development at September 30, 2020 that may either be developed or sold. While we were experiencing some interest from retailers and other market participants in our land held for development, opportunities for economically viable developments remain limited. We intend to continue to pursue additional development and redevelopment opportunities in multiple markets; however, finding the right opportunities remains challenging.
Acquisitions
Acquisitions are a key component of our long-term growth strategy. The availability of quality acquisition opportunities in the market remains sporadic in our targeted markets. Market pricing of retail real estate assets is highly uncertain under current economic conditions. We intend to remain disciplined in approaching these opportunities, pursuing only those that provide appropriate risk-adjusted returns.
Dispositions
Dispositions are also a key component of our ongoing management process where we selectively prune properties from our portfolio that no longer meet our geographic or growth targets. Dispositions provide capital, which may be recycled into properties that are high barrier-to-entry locations within high growth metropolitan markets, and thus have higher long-term growth potential. Additionally, proceeds from dispositions may be used to reduce outstanding debt, further deleveraging our consolidated balance sheet, to repurchase our common shares and/or debt, dependent upon market prices, or to fund acquisitions and both new development and redevelopment projects.