You can't put a price on fresh air - unless it's in London, that is, in which case the price of fresh air is about 12 per cent of your property's value, according to research from Marsh & Parsons.
The estate agent reckons a bit of outdoor space - ie. a roof terrace or balcony - typically adds 12 per cent to the price of a house in London, although that's as much as 25 per cent in Chelsea.
Access to a communal garden is almost as good, increasing your property's value by an average of 11 per cent (or as much as 20 per cent in the likes of Little Venice or Holland Park).
On average, outdoor space in the capital tends to cost £897 per sq ft - which rises to £1,925 in South Kensington.
Apparently, a third of London homes have access to some outdoor space. According to the estate agent, they tend to attract more interest and sell faster than equivalent homes with no outdoor space.
Worth noting, if you're about to sell.