Some 43 per cent of people live in homes that do not reach acceptable standards in cleanliness, safety and space, housing charity Shelter has said.
Its new Living Home Standard considers affordability, neighbourhood, stability and living conditions - and the charity asked 1,691 adults about their homes.
Of 39 criteria, one "tradable attribute" is that "the home has access to outdoor space, for example a private or shared garden, or balcony".
Shelter said: "Outdoor space was a topic that came up frequently in discussions, however, there was considerable variation in the level of importance that people attached to this. Some felt quite strongly that access to outdoor space such as a garden was essential and important for wellbeing.
"Outdoor space was more likely to be considered essential for families with children, as participants highlighted the importance of children being able to play outside and get fresh air – both for mental and physical wellbeing. Some felt that the need for a garden could be partly dependent on whether there were local parks where children could play instead. On the other hand, some participants felt quite strongly that outside space was too much to expect from the Standard. The combination of strong views means that it was felt most appropriate that this was a tradable part of the Standard."
Shelter and Ipsos MORI developed the Living Home Standard through a series of workshops and surveys with the public, with support from British Gas.
The measurement of homes meeting the standard was calculated based on results from a survey of 1,961 adults across the UK.
The HTA's latest Garden Market Analysis Report said: "Over the last twenty years gardens have become smaller. The proportion of GB adults with a garden has also fallen slightly but significantly from just over 80 per cent in 2000 to around 77 per cemt in 2016 (albeit this is a lower percentage of a bigger population). This is due to a range of factors including the paving over of front gardens to make way for cars through to home extensions, the partitioning of larger housing into flats and falling garden space in new build housing.
"This presents opportunities and threats for the garden industry. Declining areas available for planting present a threat to the size of the potential available market, as well as reducing the visibility of gardens in neighbourhoods and the ‘peer pressure’ that goes with this and encourages householders to garden."However it also presents opportunities for garden products adapted to this changing environment. Forinstance local authorities are recognising the impact on urban flash flooding declining vegetation has and the Greater London Assembly has recently recommended that the Mayor act to reverse the trend for paving over front gardens."