A survey for the charity found that 44% of working families with children, equating to 3.8 million households across the country, could not pay their rent or mortgage for more than one month if they became unemployed and could not immediately find work.
Researchers also found that more than one quarter (29%) of families would face immediately being unable to afford their home if they lost their income amid low levels of savings, which would be around 2.4 million households if the figures were projected across the UK.
Despite signs that the economy is recovering, Shelter warned that millions of ordinary families, whose budgets are already at "breaking point", are at serious risk of losing their home if they face any sudden cut in income.
Liz Clare, who is a helpline advisor at Shelter, said: "Every day we see the proof that just one piece of bad luck, like a sudden job loss or illness, could tip any of us into a spiral that puts the family home at risk. Sky-high housing costs and stagnating wages mean that saving is becoming a thing of the past for many people."
Campbell Robb, chief executive of Shelter, said: "The Government must make sure the safety net is strong enough to stop families falling through the gaps."
Shelter's findings were projected from research among more than 7,000 adults, of which over 4,500 pay a rent or mortgage. The charity urged anyone who is worried about losing their home to get in contact.