“He’s from Hawaii, okay?” said Obama’s senior advisor David Axelrod. “He likes it warm. You could grow orchids in there.”

Thus did a rule of the George W Bush administration — coat and tie in the Oval Office at all time — fall by the wayside. Obama promised to bring change to Washington and he has — not just in substance, but in presidential style.

Although his presidency is barely a week old, some of Obama’s work habits are already becoming clear. He shows up at the Oval Office shortly before 9 am, roughly two hours later than his predecessor. Obama likes to have his workout first thing in the morning, at 6:45.

He reads several papers, eats breakfast with his family and helps pack his daughters, Malia and Sasha, off to school before making the 30-second commute downstairs. He eats dinner with his family, then often returns to work; aides have seen him in the Oval Office as late as 10 pm, reading briefing papers for the next day.

“The chance to be under the same roof with his kids, essentially to live over the store, to be able to see them whenever he wants, to wake up with them, have breakfast and dinner with them. That has made him a very happy man,” Axelrod said.

In the West Wing, Obama is a bit of a wanderer. When Bush wanted to see a member of his staff, the aide was summoned to the Oval Office. But Obama tends to roam the halls. One day last week, he turned up in the office of his press secretary Robert Gibbs, who was in the unfortunate position of having his feet up on the desk when the boss walked in.

Under Bush, meetings started early. He once locked Secretary of State Colin L Powell out of the Cabinet Room when Powell showed up a few minutes late. In the Obama White House, meetings start on time and often finish late.

Over the weekend, Obama’s aides did not quite know how to dress. Some showed up in jeans, some in coats and ties. So the President issued an informal edict for “business casual” on weekends - and set his own example. He showed up on Saturday for a briefing with chief economic advisor Lawrence H Summers, dressed in slacks and a gray sweater over a white buttoned-down shirt. Veterans of the Bush White House are shocked.

“I had on khakis and a buttoned-down shirt, and I had to stand by the door and get chewed out for about 15 minutes,” Dan Bartlett, who was counselor to Bush.

For Obama, lunch generally means a cheeseburger, chicken or fish in his dining room off the Oval Office.