Britain must build more homes – that much is certain. But a relentless focus on how many means we have lost all focus on the types of homes we must be building. This means we risk repeating the mistakes of previous decades, building homes entirely unfit for future generations.

This is the stark conclusion of a new report from Demos, Future Homes. Analysing the trends we expect to be shaping Britain in the future, we find our current approach to housebuilding has not kept pace with these changes. Indeed, we found that one third of the public don’t think new homes will be fit for purpose in thirty years’ time. Putting this right demands a revolution in our approach to housebuilding.

First, new homes must be fit for multigenerational living. This living arrangement is already on the rise: after decades of decline, average household size is rising, in part due to an increase in the number of multigenerational households. But housing design has not kept pace with these changes: our research found that two thirds of the public do not think new homes are not fit for multigenerational living.

We do not bemoan the rise in multigenerational households – quite the opposite. In a time of social isolation, multigenerational living may help to reduce loneliness amongst the elderly, helping them to stay integrated in society and play an active role in family life. More social contact between the young and old could also reduce the scope for intergenerational conflict, fostering mutual understanding between different generations.

Multigenerational housing may also help ease care burdens at both ends of life, making it simpler to look after the elderly, while allowing relatives to more easily help with childcare. It could also reduce the under-occupation of housing by the elderly, freeing homes at the top of the housing ladder. It is no exaggeration to say that in a time of increasing social and political division, building more multigenerational housing could help bring Britain back together – a first step on the path to a more connected society.

That’s why we call on the government to enshrine a commitment to multigenerational housing in its new Future Homes standard. Multigenerational households should also be entitled to council tax discounts and permitted development rights introduced for “granny annexes”, ensuring current housing stock can be made fit for multigenerational living.

We also need to build much more environmentally friendly homes whilst improving the state of our dilapidated housing stock. With the government aiming for net zero carbon emissions by 2050, this will require a radical change to housebuilding – especially when home energy efficiency has not improved since 2015.

To address this we call on the government to reintroduce the zero carbon homes standard and to launch a Green Homes Fund backed by a new, state-backed Green Development Bank. This would allow the government to make ultra-low interest rate loans to fund energy efficiency home improvements, as is widely and successfully done in Germany.

We must also begin to prioritise the creation of green space and gardens when building homes. This isn’t just what the public wants – we found gardens are the most important feature when choosing a home after location – but is good for our health too. Studies show that those living close to green space are more likely to exercise regularly – vital if we are to tackle today’s obesity crisis. That’s why our report calls for the government to introduce a new “green space standard” for all new homes, eventually giving all residents the right to a garden.

We recognise our proposals could increase the cost of housebuilding, potentially raising property prices – a great concern given the state of Britain’s overheated housing market. However, we believe our proposals can be justified for two reasons.

First, much of the recent explosion in property prices derives from land price increases, not construction costs. Therefore, if our changes were introduced alongside sensible policies to bring down land prices, such as a land value tax, their impact on cost would be limited. Second, even if there are additional costs today, the cost of pulling down new homes in just a few decades would be enormous. This has to be avoided.

Homes can be so much more than a roof over our heads, helping us respond to the great challenges of our time – loneliness, climate change, the crisis of care. But this can only happen if Britain ditches its relentless numbers game on housing and begins to care about the types of home we build, not just the number.

Ben Glover is a senior researcher at Demos.