The senator, who owns a house in Cavendish, P.E.I., is coming under increasing pressure to prove he lives primarily in the province he is appointed to represent.
Under the Constitution, senators must be resident in the province from which they are appointed.
The 2012 property tax assessment obtained by CBC News shows Duffy wasn't given a provincial tax credit, which the province says on a government website goes to properties where "50 per cent or more of the owners reside in P.E.I. for 183 consecutive days or more each taxation year defined as Jan. 1 to Dec. 31."
There is a tax credit listed for Duffy's P.E.I. home being owner-occupied.
Duffy has also claimed $42,802.43 in living expenses in Ottawa since Sept. 1, 2010, the earliest date for which expenses are published.
Senators who mainly live more than 100 kilometres outside of the National Capital Region can claim up to $21,000 a year in housing allowance to help them maintain a home in the Ottawa area, as well as in the region they represent.
Audit report expected by end of month
Duffy declined to comment when asked for reaction by CBC News.
On Monday, he said in an email that he has responded to the Senate's request for information.
"That's in the hands of Senator David Tkachuk and his [board of] internal economy committee and they will deal with this. I have no further comment," Duffy wrote.
The Senate has asked senators to prove where they live, requiring them to provide copies of driving licences, health cards, tax information and other documents that could prove their primary residence. They had until Jan. 31 to submit the information.
In an interview with CBC News, Tkachuk said the committee has responses from almost all senators.
"I expect that by the time the auditor starts looking at it, and we have a report, about two, three weeks, we should have it all done. End of February, I hope," Tkachuk said.
'Acted in P.E.I.'s best interests'
Government Senate Leader Marjory LeBreton said she's waiting for the board of internal economy to complete its work before discussing the matter.
"It's very clear that [Duffy] is a senator for Prince Edward Island. He has always acted in Prince Edward Island's best interests," she said.
Before he was appointed to the Senate on Jan. 2, 2009, Duffy had worked as a journalist in Ottawa since the 1970s.
The senator has also claimed $147,274.61 in travel to P.E.I. in the 28 months since Sept. 1, 2010.
P.E.I. Health Minister Doug Currie confirmed yesterday that Duffy applied in December for a new health card from the province, that the card is not a renewal, and that somebody had contacted his office about the application.
'This is absurd'
In question period Tuesday, NDP ethics critic Charlie Angus compared Duffy's living expenses with someone trying to receive Employment Insurance for which they weren't eligible.
"This government would come down on them like a ton of bricks," Angus said.
"What happened to those Reform Party zealots who promised that they would clean up Ottawa? They sit obediently behind the Conservative [government] House leader who's been doing back flips ... trying to pass off Mike Duffy as a constituency rep. I mean, this is absurd."
Government House Leader Peter Van Loan pointed to the Senate audit.
"We do have a clear standard on this. I think all people on both sides of the House recognize that all parliamentarians are expected to maintain residences in their home region and in the National Capital Region. We know that the Senate is reviewing those rules and making sure that they are applied properly and that they are appropriate," Van Loan said.
"The Senate is responsible for those rules. They have their own committee that is reviewing that and all the senators that are subject to it to ensure that they are indeed applied properly, as we all expect they will be."
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