Focusing on the fourth quarter of 2021, our FFO per share was $0.51, in line with market consensus.
Portfolio operating metrics were solid with same-store NOI on a cash basis increasing 5.8%.
We leased approximately 400,000 square feet, generated a 3% increase in second-generation cash rents and executed an average lease term of six and a half years, illustrating the longer-term view taken by most of our customers.
Overall, leasing activity remained robust and well dispersed across the portfolio with over 40 leases and amendments executed during the fourth quarter.
Today, our leasing pipeline stands at over 500,000 square feet of negotiations.
And we're trading LOIs on an additional 1 million square feet, which positions Piedmont for space absorption in 2022 and with only about 1 million square feet of existing leases expiring or about 6% of the portfolio.
For example, during the past year in our Burlington submarket, three competitive Class A buildings comprising over 400,000 square feet have been repurposed to labs, helping to push net effective rents for office space to pre-pandemic levels.
As an example, during the fourth quarter, we signed a 55,000 square foot lease at our Connection Drive property in Dallas to serve as the new corporate headquarters of an undisclosed Fortune 500 company.
And in that same market during the second quarter, we signed a 44,000 square foot lease to serve as the corporate headquarters for a large national beverage distributor.
However, net effective rents are approximately 2% to 5% lower.
For example, JLL Research noted that 84% of Atlanta leasing activity in the fourth quarter was in Class A or trophy product.
In Orlando, net effective rents are still trailing pre-pandemic levels by about 5% as a result of increased concessions.
I would add, we are fortunate to have limited vacancy and near-term lease expirations at our 60 Broad Street property in Lower Manhattan and virtually no expirations at our Washington, D.C. properties for more than two years.
Piedmont leased almost 2.3 million square feet, which was in line with our average pre-COVID annual leasing levels.
In addition, the increase in second-generation cash rents was seven and a half percent, which helped increase same-store cash NOI for the year by almost 7%.
And finally, our tenant retention ratio was in line with prior years at approximately 70%.
Looking ahead, approximately 750,000 square feet of tenant leasing has yet to commence as of this year-end or is in some form of abatement.
This backlog creates organic growth opportunities going into 2022 associated with approximately $26 million in future annualized cash rents.
In addition, approximately 60% of the portfolio's vacancy and 85% of 2022's lease expirations resided in our Sunbelt properties, where we are experiencing the greatest level of leasing velocity.
We are currently in discussions on a pipeline of over $1 billion of high-quality assets primarily for properties in our Sunbelt markets.
In addition, new construction costs have escalated by 15% to 20% versus pre-pandemic pricing driven by an increase in both raw materials and labor.
In 2021, we completed over $50 million of incremental investment in our properties, upgrading assets to remain best-in-class within their respective submarkets.
During the quarter, we expanded our Atlanta market footprint with the acquisition of 999 Peachtree Street.
As you all know, the 999 acquisition marks our entry into Midtown Atlanta submarket.
The iconic Class A LEED-Platinum 28-story building, a 622,000 square feet with 77% leased at acquisition.
We purchased it for $360 a square foot, which we estimate is over 40% below replacement cost.
We're working with Gensler, a tenant at the building to complete the redesign of 999s arrival experience in public spaces, including a modernized and expanded lobby, energized outdoor space and other enhanced amenities, which will complete over the next 12 to 18 months, and we'll revitalize this asset in a fraction of the time and cost of new construction.
With a 10-foot glass window line across 70% of the facade this asset will effectively compete against new construction at a fraction of the cost with an expected all-in basis in the low $400 per square foot versus new product costing in excess of $650 per square foot, creating substantial pricing leverage for our building when compared to that new development.
The $224 million acquisition of 999 is being funded through multiple dispositions.
Immediately after quarter end, the disposition of 225 and 235 presidential Way in Boston closed in a reverse 1031 exchange for $129 million or a mid-5s cap rate.
The acquisition of 999 Peachtree Street during the fourth quarter as well as the completion of two non-core dispositions just after the quarter end, now makes Atlanta our largest market based on annualized lease revenue.
Adjusting our lease percentage for the disposition transactions our pro forma lease percentage as of December 31 would have been 87%.
Additionally, approximately 63% of our annualized lease revenue is now generated from our Sunbelt properties and our goal is to have 70% to 75% of our ARR generated by our Sunbelt markets before the end of 2023.
Looking back on 2021, core FFO for the year was $1.97 per diluted share, a 4% increase over 2020 and in excess of the upper end of our original guidance range for the year.
This growth in core FFO overcame an approximately 1% reduction in our overall lease percentage on a year-over-year basis.
The decrease in occupancy was driven by several factors: Reduced leasing activity during 2020 in the first half of 2021 as a result of the pandemic, a number of sizable lease expirations at recently acquired properties in Atlanta and Dallas that were underwritten as part of their respective acquisitions and the purchase of the 77% leased 999 Peachtree Street property.
After incorporating the just completed disposition activity in January of 2022, our pro forma lease percentage as of December 31 would have been 87%.
We reported $0.51 per diluted share of core FFO for the quarter.
That's an 11% increase over the fourth quarter of 2020.
Our core FFO achievement during the fourth quarter also reflects the repurchase of approximately 1 million shares of our common stock at an average price of $17.76 per share during the quarter, leaving approximately $150 million in board authorized capacity under our share repurchase program.
As is often the case, gap typically just dictates early recognition of potential losses and the decision to shorten the hold period for this asset did result in the recognition of a $41 million impairment charge that is included in our fourth quarter results of operations.
On the flip side, the sale of 225, 235 presidential Way will result in the recognition of an estimated $50 million gain during the first quarter of 2022 when the sell closed.
AFFO generated during the fourth quarter was approximately $39 million, which is well above our current $26 million quarterly dividend level.
Our board has indicated that given our cash NOI growth over the last few years, the fact that we're approaching the conclusion of the large construction restacking project for the State of New York at 60 Broad, and the time since our last dividend increase, they will be reviewing our dividend payout amount during 2022.
Our annual debt -- net debt to core EBITDA ratio as of the end of the fourth quarter of 2021 was 5.7 times and we reported $210 million of unused capacity on our line of credit.
Taking into consideration the completed disposition activity occurring right after year-end, with the net sales proceeds received in January, our current available capacity on our $500 million line of credit is approximately $320 million, with an approximate $120 million more expected later this quarter from the payoff of a note receivable.
Adjusting for the application of proceeds from the two closed January sales, our pro forma debt to gross asset ratio at year-end would have been approximately 35%.
Finally, we're introducing 2022 annual financial guidance for core FFO in the range of $1.97 to $2.07 per diluted share.
It also assumes a neutral amount of asset recycling during the year with about $350 million to $450 million each of acquisitions and additional dispositions.
This net neutral activity excludes the recently completed sales of the presidential Way assets and Two Pierce Place property that were used to fund the 999 Peachtree Street acquisition.
The guidance assumes general and administrative expenses in the range of $29 million to $31 million for the year.
Our same-store cash NOI growth is expected to be flat for the year with a number of abatements occurring during 2022 due to the lease renewals and newly commencing leases such as 160,000 square foot renewal at 1155 Perimeter Center West in Atlanta, and a 56,000 square foot lease at 400 Virginia in Washington, D.C. As well as downtimes between leases associated with new tenant build-outs, such as a 67,000 square-foot lease at 5 and 15 Wayside in Boston and a 44,000 square foot lease at One Lincoln in Dallas.
Accrual-based store NOI is expected to grow from 1% to 3% during the year.
Likewise, our lease percentage is expected to grow to approximately 88%.
But again, this estimate is subject to the lease percentages of the properties involved was $350 million to $450 million of potential recycling transactions completed during the year.

Summary:
Focusing on the fourth quarter of 2021, our FFO per share was $0.51, in line with market consensus.
We reported $0.51 per diluted share of core FFO for the quarter.
Finally, we're introducing 2022 annual financial guidance for core FFO in the range of $1.97 to $2.07 per diluted share.