Driven by strong operating income and continued improvement in portfolio valuations, our GAAP earnings were $0.72 per diluted share for the first quarter as compared to $0.42 per diluted share in the fourth quarter.
Our GAAP book value per share increased almost 9% to $10.76 at March 31st as compared to $9.91 at December 31st.
GAAP earnings finished well in excess of our $0.16 per share first quarter dividend.
Leading third-party data shows new single-family home sales in the first quarter were up approximately 37% year-over-year, with existing home sales up approximately 15% in the same period.
The median home sales price rose 11% year-over-year and homes that require a nonconforming mortgage are showing similar trends, particularly in growing secondary metro areas.
Occupancy rates also continue to be at record highs with a weighted average of 93% in the top 20 metros.
Our team's crisp execution resulted in a combined after-tax net operating contribution of $51 million for residential and BPL mortgage banking.
This was driven by record residential loan purchase commitments, continued momentum in business purpose lending and execution of three securitizations exceeding $1 billion in issuance across Redwood Residential and CoreVest.
Lock volumes in the first quarter rose 22% to $4.6 billion as mortgage rates rose during the quarter, but much less precipitously than benchmark interest rates.
This led to a sustained uptick in refinance volumes, which represented 62% of our total locks for the quarter.
We were able to place one of our two securitizations during the quarter via reverse inquiry and settled $1.4 billion of whole loan sales.
As an example, the loans underlying our most recent securitization had an average age of approximately 45 days.
This went back by $361 million in jumbo loans.
During the first quarter, we achieved several milestones on our technology road map, including the onboarding of the majority of our Sequoia securitizations on to DVO 1, a third-party solution for accessing, reporting and analyzing standardized loan-level data for our Sequoia securitizations.
This was an important enhancement to our original Rapid funding program rolled out last year, which was successful in facilitating $274 million of purchases from an initial group of participating sellers.
Overall, we originated $386 million of business purpose loans during the quarter, comprised of $253 million of single-family rental loans and $133 million of bridge loans.
While SFR loan production was down from a seasonally strong fourth quarter, and bridge fundings rose 33%, driven by increased usage in lines of credit and initial fundings on several recently completed build-for-rent financings.
In all, 71% of originations in the first quarter were from repeat customers.
We deployed $73 million net of financing into new investments during the quarter, primarily new issue CoreVest SFR securities and newly originated Bridgeland.
Combined 90-plus delinquencies across our Sequoia and CoreVest securitization platforms now stand below 2%, and 90-plus day bridge delinquencies are below 3.5%, significant outperformance versus the marketplace.
Since January, we have completed calls on three Sequoia transactions totaling $75 million in loans and plan to call several others throughout the remainder of the year.
Contributing to GAAP earnings of $0.72 per share for the quarter and generating a 10% economic return on book value for the quarter.
After the payment of our $0.16 dividend, which we increased by 14% in the first quarter, our book value increased 9% during the quarter to $10.76 per share.
Moving forward, we generally expect margins to normalize back toward levels that still achieve a 20%-plus return on capital.
At CoreVest, mortgage banking income normalized during the quarter while continuing to generate very strong operating returns on capital of nearly 30%, driven in part by marginal tightening on securitization execution.
In relation to the three Sequoia deals we've called through April, we acquired $75 million of jumbo loans on to our balance sheet.
Related to these calls, we expect to record GAAP realized gains of $7 million associated with the underlying securities, the majority of which will not flow through book value, and a net book value benefit of approximately $2 million versus our December 31st fair values, which is inclusive of estimated loan premium.
Inclusive of these recent calls, we estimate over $600 million in loans underlying our securities could be callable in 2021.
Shifting to the tax side, we had REIT taxable income of $0.09 per share in the first quarter and $0.47 per share of taxable income at our TRS, again driven by income from our mortgage banking operations.
We ended the first quarter with unrestricted cash of $426 million.
After allocating additional working capital to our mortgage banking operations during the first quarter to support growing loan volumes, and net of other corporate and risk capital, we estimate we had approximately $225 million of capital available for investment at March 31st.
Our non-recourse leverage ratio increased to 1.9 times at March 31st from 1.3 times at the end of 2020, and total leverage in our investment portfolio remained consistent from the prior quarter at around 0.9 times.
While returns from our operating businesses well exceeded 20% in the first quarter, we expect these returns to normalize during the remainder of the year, particularly for residential mortgage banking as our capital allocation now reflects a more steady state pipeline and levels of loan inventory on balance sheet.
Cash flow expectations generally improved across the portfolio, and inclusive of our previously reported 5% fair value increase in our securities portfolio during the quarter, we now estimate go forward returns relative to our March 31st GAAP basis to be between 10% and 11%, inclusive of potential upside from potential borrowing costs in the second half of the year.

Summary:
Driven by strong operating income and continued improvement in portfolio valuations, our GAAP earnings were $0.72 per diluted share for the first quarter as compared to $0.42 per diluted share in the fourth quarter.
Contributing to GAAP earnings of $0.72 per share for the quarter and generating a 10% economic return on book value for the quarter.