Fortunately, these deferral arrangements have not been material and represent a cumulative impact of less than $0.01 per share through 2021.
The impact of local job losses for office using sectors in the Washington Metro region has been limited with no office using sector losing more than 4% of the total workforce year-over-year, according to BLS data.
45% of our multifamily residents and 56% of our office tenants are employed in professional and business services, government or information sector jobs.
Over 95% of the multifamily units that have been constructed over the past seven years are unaffordable for renters who earn $75,000 per year or less.
A segment, which comprises 57% of the Washington Metro rental base.
Over 75% of WashREIT's units are affordable to those renters with a sustainable rent to income ratio of 30% or lower.
Also driving our long-term demand fundamentals is that 80% of our multifamily portfolio is located in Northern Virginia, where job growth is the strongest and job losses have been the lowest.
CBRE released its annual Tech-30 market report earlier this month, which ranks the nation's top tech markets in terms of resilience and potential for growth.
Tech sector leasing activity in Northern Virginia is expected to increase in the coming quarters with more than 1.5 million square feet of active requirements in the pipeline according to CBRE.
We have experienced minimal credit loss to date, largely due to the sale of 75% of our retail NOI last year, including our riskiest big box retail assets.
For the small amount of retail we retained, we collected 95% of contractual retail rents during the third quarter including retail tenants in our office properties.
Our office portfolio is also well positioned with a weighted average lease to maturity of 5.2 years, no exposure to co-working, no single tenant risk, strong and stable collection rates and limited near term lease expirations.
Many of our speculative leasing opportunities which had excellent momentum, pre-pandemic, are in our best assets including Watergate 600, Arlington Tower and Silverline Center.
We collected 99% of cash in contractual rents during the third quarter, and our rent collections through the first three weeks of October are in line with our quarterly trends.
We have offered deferred payment programs to residents who have been financially impacted by the pandemic, and only $58,000 of deferred multifamily rent remains outstanding year-to-date.
The impact of COVID-19 on the Washington Metro market has been contained primarily through the leisure and hospitality, education and health and retail sectors, which represent over 75% of Washington Metro job losses, but only 55% of total job losses nationally through August.
These three sectors comprise approximately 20% of our resident exposure, and only 8% of our office tenant exposure.
We collected 97% of cash rents from office tenants during the third quarter and over 99% of contractual rents, which excludes rent that has been deferred.
Year-to-date, we've agreed to defer a net $1.4 million of rent for office tenants, and we expect to collect 80% of that deferred rent by year-end 2021, with the balance thereafter.
Retail comprised 6% of NOI year-to-date, and while retail tenants have struggled the most, we collected 88% of cash rents in the third quarter.
Excluding deferred rent, our collection rate was approximately 95% during the third quarter.
Year-to-date, we've agreed to defer a net $1 million of rent for retail tenants, and we expect to collect 50% of that rent by year-end 2021.
Overall, we've only deferred a small portion of rent and the expected cumulative cash NOI impact is less than a $0.01 per share through year-end 2021.
During the third quarter, we incurred approximately $0.01 per share of bad debt expense, and it was primarily attributable to COVID-19.
Turning to the balance sheet, we are pleased to report that we've addressed upcoming debt maturity needs and further strengthened our already strong liquidity position by executing a $350 million 10-year Green Bond.
As of September 30, we have approximately $520 million of liquidity.
We reported core FFO of $0.36 per diluted share.
Compared to the prior year, overall same-store NOI declined 4.9% and 3.6% for the third quarter and year-to-date periods on a GAAP basis, and 4.1% and 2.9% respectively on a cash basis.
Our multifamily same-store NOI decreased by 3.8% year-over-year on a GAAP and cash basis.
Gross lease rates for suburban properties increased 1.1% during the third quarter on a blended basis and effective lease rates increased 0.2% on a blended basis.
Gross lease rates for urban properties declined by 2.9% on a blended basis, and effective lease rates for our urban properties declined by 4.6% on a blended basis.
In total gross lease rates declined approximately 1.7% on a blended basis during the third quarter and effective lease rates declined 3.1% on a blended basis.
During the quarter, average same store occupancy dipped slightly but increased back to 94% at quarter end.
Operating portfolio occupancy which excludes Trove, our recently delivered property that is in initial lease up was 94.6% at September 30, up from 94.3% for the end of the second quarter.
Same-store office NOI declined 4.9% on a GAAP basis and 3.7% on a cash basis, driven by an expected decline in parking income, a couple of known and expected move-outs and credit losses related to COVID-19.
While parking income increased by about 24% compared to the second quarter, as transient parking increased, we have experienced monthly parking contract cancellations as full reentry has been delayed.
Same-store NOI decreased at our residual retail centers, which we report as other by approximately $300,000 on a GAAP basis and $270,000 on a cash basis driven primarily by higher credit loss, which included receivables due from retail tenants impacted back COVID-19 deemed uncollectible.
The combined write-off for all office and retail tenants was less than $0.01 per share and was primarily related to COVID-19.
Turning to leasing activity, while velocity and touring was hit by the economic shut down, we signed approximately 40,000 square feet of office renewals, approximately 8,000 square feet of retail renewals, and 19,000 square feet of new office leases and 6000 square feet of new retail leases during the quarter.
We achieved rental rate increases of 17.6% on a GAAP basis and 3.4% on a cash basis for office renewals and 10% on a GAAP basis and negative 3.9% on a cash basis for new office leases.
Rental rates increased 16.4% on a GAAP basis and 3.3% on a cash basis for retail renewals and remained relatively flat on a GAAP and cash basis for new retail leases.
The impact of operational cost saving initiatives at our commercial properties reduced operating cost by approximately $680,000 net of tenant recoveries during the third quarter.
This step down in cost savings compared to the $850,000 of cost savings recognized in the second quarter was primarily related to higher cleaning expenses due to an increase in the number of spaces being utilized at our office properties.
Today, approximately 50% of our office spaces are being utilized by some of the tenants personnel.
We are reinstating full-year 2020 guidance with the core FFO per share range of $1.44 per share to $1.46 per share.
We expect our multifamily NOI to range from $59.25 million to $59.75 million.
Non-same-store NOI, which includes Trove to range from $26.75 million to $27.25 million.
Office NOI to range from $81.5 million to $82 million and other NOI to range from $11.5 million to $12 million.
Multifamily occupancy increased 30 basis points during the quarter supported by strong demand for our suburban properties, which allowed us to maintain occupancy for growing rents and preserving our seasonal rent roll.
Our suburban retention was very strong at 63% during the third quarter, compared to the Washington Metro suburban average of 58%.
Our urban retention was 55% during the third quarter, well above the Washington Metro urban average of 46%.
Total portfolio retention was 58% during the third quarter compared to the Washington Metro overall average of 54% according to RealPage.
Urban application volumes rebounded from March lows and trended 40% above prior year levels during the third quarter and remained above prior year levels through October.
We now expect to incur a loss between $400,000 to $500,000 in 2020, and continue to expect to reach breakeven occupancy near year-end.
We still have approximately 39,000 square feet of signed leases that have not yet rent commenced, and expect 16,000 square feet of those signed leases to commence by year-end.
Currently, we expect to achieve additional operating cost savings of approximately $525,000 during the fourth quarter.
We expect G&A including lease expenses to range from $23.5 to $24 million and interest expense to range from $37.5 million to $37.75 million.
We now expect development expenditures to range from $30 million to $35 million.
At our current stock price, we believe that we offer a compelling value proposition for investors, with a 7% dividend yield on a dividend that we are covering, a strong liquidity position, our development and renovation pipeline that can and will be reactivated once conditions improve, and a solid long-term growth story.

Summary:
We reported core FFO of $0.36 per diluted share.
We are reinstating full-year 2020 guidance with the core FFO per share range of $1.44 per share to $1.46 per share.