OK I don't know and these figures are from the USA where the world is different. Except I don't think that it is:
Of course, we’re not so resistant to reality that we still believe traditional family life in America implies a single-working spouse and a couple of rug rats. But not many of us grasp how little that resembles the current American household — or the current American homebuyers.
The presentation goes on to point out that these traditional - and even non-traditional - families are a minority of house purchaser (and by implication a minority of housing demand). Indeed just shy of 60% of all US households consist of just one or two people. And I suspect the same is true for the UK.
Yet we're still building a mix of housing that is overwhelmingly focused towards families - to that traditional mom, dad and two-point-four kids. In the USA nearly two-thirds of the housing market consists of family housing (over there this is the 'single family detached house'). By comparison, 55% of UK owner-occupied housing stock is either detached or semi-detached.
In the UK, the ONS estimates that two-thirds of new households formed will not have dependent children (i.e. they will be either single adults or couples without children) yet, when we look at housing completions by housing type, 60% of new build are houses nearly all of which are three or more bedroom 'family' homes.
There does seem to be something of an imbalance in the system. Partly this is because assessed need and actual demand for homes differ - you may only 'need' a one-bed flat but you'll buy a three-bed semi because it gives you things (a garden, a spare room, space for an office/games room, a garage and so forth) that the pokey little flat won't provide. But there's also a continuing presumption in the minds of planners that housing demand - driven as it is by new household formation - is about families rather than other sorts of people.
At the moment we are, for example, spending a great deal of money (both individually and via the paying of taxes) to adapt homes for people who are ageing. On top of this we are spending comparable amounts of money shuttling between the homes of these ageing people providing support and related social care services. This is because the current provision of housing - whether sale or for rent - for older people does not meet the expectations of those older people merely the 'needs' as identified by planners. As a result older people choose not to move into the current provision - there's no spare room, no garden, no office come games room, no garage.
We need to think much harder about how we match what we know about needs (and especially predictable future needs) with public expectations about what a home should contain. This needs a reconsideration of housing in local centres - indeed in city and town centres - and about whether the needs of older people can be met in a better way than at present. In concluding, I'll give you one observation - a real one that came from a real person who said she wasn't selling her (unsuitable) house and moving to a brand new specialist housing complex for the simple reason that it was not only in town but also in the middle of a council estate.