Rising housing costs mean the number of homes containing three generations of a family will treble in the next 20 years, a building society claims.
More children could be living with their grandparents
According to a report for the Skipton Building Society the number will rise from 75,000 to 200,000.
It cites increased costs of residential care and financial pressures on first time buyers as causes of the change.
Pension under-funding coupled with increased life expectancy may also be a contributory factor.
The extended family in one house was a regular feature of life in the UK for many years, until rising prosperity meant more people could afford to buy property to the point where home owning is the norm.
Jennifer Holloway of the Skipton Building Society said that this is changing due to rising levels of debt and the high cost of property.
"These issues are likely to get worse and so combining incomes and sharing mortgage repayments may well be the only alternative for some families," she said.
The survey was carried by the worldtocom.com futures network.
A spokesman for the organization has said although the number is small compared to the 25m UK households, it is a sector that is being completely ignored by urban planners.
Most house building is based on the nuclear family of two parents and two point four children who leave home after finishing their education.
"The nuclear family is not dead. It is the future. But a small proportion of households will revert to being extended financial families. It is significant with debt burdens, healthcare and education costs," the spokesman said.
The report has also said that rising costs of childcare constituted for many young families one of their main monthly outgoings.
One conclusion is that live-in childminders in the shape of grandparents will be a powerful incentive to staying in the parental home.
Another finding is that the crisis in pensions will give future retired couples far less to live on and an incentive to either invite the children back home to help out, or sell up the family home, realise their capital and move in with their children.
"The decision is driven from both ends. In some cases it will be a lifestyle choice, in others a necessity
"Either way it is a phenomenon that is not yet factored into people's thinking," the spokesman for worldtocom.com futures network said.
I lived at home with my parents until my son was 18 months old. Whilst I appreciated the financial and practical support, I never felt like we had our own space. You still feel like a child. Now that we live as a "normal" family, the childcare costs are crippling. Maybe I'll have to move back home.
The issues pinpointed by this report have been obvious to me for some time as a single parent supporting a pre-teen and teenage child. Having a partner with children of similar age, when we buy a house together I anticipate that we will have to buy a very large house. Our children will be living with us until possibly well into their 30s presumably until they have paid off their student debts and accumulated enough for a significant deposit. I also anticipate working well after the age of 65 to supplement my probable pension shortfall and possibly my grandchildren. Happy Retirement, not a chance!
Caroline Wallis, Fleet Hants UK
I converted outbuildings to make a "granny" annexe in 1991. Currently this is not required for my parents, however it is deemed a separate dwelling for council tax purposes whether occupied or not. There is now a maximum of 10% discount if unoccupied. This certainly does not encourage making provisions to help extended family.
Rick, Northallerton N Yorks
I have been looking for a home suitable to serve an extended family for the last year with very little success. The space required for each generation of the family is different as is their needs; very few homes meet the requirements. It may be time for planners and developers to realise the market is there for the taking and provide some suitable housing in the future.
I share a house with my parents and my son (three generations). I moved back home when my relationship failed and have been there ever since as house prices were just too high for a single mother to afford along with childcare. I have always worked full time in a job which I love and there was no way I was going to give up a job just so I could get free housing. I did put my name down on a council list 7 years ago, but am still waiting to be offered a property. It does frustrate me when I see people who do not work in their own homes which are paid for by the state, but that is not for me. Five years on and I am hoping to buy my first property with my fiancée within the next 12 months.
Jo Berrill, Coventry
I am married with 2 kids and we share my in-laws house. They have a small annexe. The idea is that we can look after them easily in old age and we get to live in a house that we could never dream of. The house is owned by my in-laws. There are 2 major pit-falls: inheritance tax and the possibility that our in-laws may be forced to sell up if we can no longer look after them and they need to go into a care home.
Eifion Morris, Hope, Flintshire