Mr Tiernan, a freelance journalist in his late 60s, had been warned that they were coming to the property in Shankill - three notices from the Dublin County Sheriff's Office that a court order for possession was imminent had come through his door in the last five weeks.
He told the Sunday Independent: "When I went downstairs the guys were already in the hall. They'd cut the lock. There were eight or 10 guys and several gardai.
"They just shouted 'we are from the Sheriff's Office in Dublin and we are coming to take possession of your house'."
He added: "I suppose you could say I physically tried to prevent them.
"It was unbelievably embarrassing. I wasn't allowed back into my house at all. A row of men stood in front of my gate."
His wife and son were allowed to get dressed and "pick up a few things, but only a few."
Mr Tierney added: "Eventually, my wife and son came out, with their few things, and we got into our car and drove away.
"It's an awful shock, after 27 years."
The family are now staying with relatives while they look for a home to rent.
Mr Tierney's financial problems began after he got a €315,000 loan from KBC Bank in 2005.
He bought two properties in Co Kildare and had planned on turning one of them into the family's "dream home" - but the financial crash happened shortly after.
He ran into trouble with mortgage repayments in 2010 and by 2016, KBC had moved against him. The courts granted the bank a possession order on the property last year.
Mr Tierney revealed that he regrets not cooperating with the Sheriff's Office in the last five weeks and is speaking out to encourage others facing eviction to do the dame. He hopes to stars a "movement."
Mr Tierney explained: "I know this sounds like a big-headed thing to say, but I would like to become the new Michael Davitt.
"I am not for a moment saying that banks should not be repaid their debts. But breaking someone's door at 6am is not the way to go about it.
"Another way should be found to allow people to stay in their homes.
"The approach by banks has been way, way too aggressive over the past number of years and people have been worn down with stress and fear.
"The problem is everyone is afraid, because they are trying to do a deal with their own bank and they don't want to go public.
"There is no doubt that the people who have been evicted and who are facing eviction were prepared to come together, this business would be stopped, the Government would have to do something."
A statement from KBC Ireland said repossession of a family home is "always the very last resort" for the bank.