Savers who don't own their home could be hurtling towards a pensions crisis as the bill for renting in retirement reaches almost £420,000, This is Money can reveal.A quarter of those aged 60 to 65 are already living in financial poverty, but this is set to get worse in the coming years if increasing numbers need to fork out for rising rental costs, experts warn.Retirees still renting in their golden years now need a staggering £419,000 extra in their pension pots to meet their housing costs compared to those who own their own homes, fresh analysis from Standard Life reveals.This is based on projected rental prices over a 20-year retirement, which were calculated using Office for National Statistics rental data. It assumes rental growth of 3.8 per cent a year.The cost has risen from £398,000 last year, meaning today’s retirees need to find an extra £21,000 for their housing costs.In one part of the country, almost £860,000 is needed for renting in later life. Retirees in London will need to fork out some £859,000 for rent over a 20-year retirementIt means swathes of people are set to plunge into financial difficulty in retirement if they don’t already own a property.Monthly rents could more than double from £1,160 today to £2,350 by 2046, the research shows.If a worker was to retire this year, they would need to pay £13,910 for their annual rent. But by the 20th year of their retirement, they will need to find £28,250, the study forecasts.But retire in five or ten years' time, and the total cost will be higher still as rental prices continue to soar.Plus, rental costs could climb by more than 3.8 per cent a year if the market is particularly strong.The majority of current retirees – some 82 per cent – are homeowners, according to a Standard Life survey, but this number is only expected to dwindle in the coming years as property price tags climb even further out of reach.Renting in retirement is set to become far more common, says Catherine Foot, of the Standard Life Centre for the Future of Retirement.The proportion of households that rent privately has doubled in the past two decades. And one in three retired households could be renting by 2044, according to the Association of British Insurers.Foot adds: ‘It exposes a fundamental flaw in our current pension system, which is built on the assumption that housing costs fall in later life.’Single retirees need £13,900 a year to meet a basic standard of living in later life, according to Pensions UK figures, which are widely used by the industry as the benchmark for costs in retirement.It's enough to spend £57 a week on groceries, a week-long holiday in the UK and up to £460 for clothing and shoes, among other expenses.But this assumes you own your home and have paid off the mortgage. Add in rental costs and the amount needed this year alone will double to £27,810, the Standard life calculations reveal.For moderate and comfortable lifestyles, £32,700 and £45,400 are needed, but these also assume you own your own home.Pete Cowell, also of Standard Life says: ‘For a growing number of people, housing costs could be the single biggest expense they face in later life, adding many thousands of pounds a year to the income needed to maintain a minimum standard of living.’Retirement postcode lotteryPensioners in some parts of the country will need to fork out more than double the £419,000 headline figure for rental costs in retirement.In London, where rents are currently a staggering £28,520 a year, costs will rise to £57,940 by 2046.It means savers need to cough up some £859,000 in total for housing costs.