I should say I'm talking here about recently-built flats rather than older stock or council blocks. Any flats built in the last ten years - of which there are many - always seem to have something external bolted on.
The reason is because in 2010, when Boris was Mayor, the London Housing Design Guide was published. This established a common set of housing design standards across all tenures in London and provided a heavy nudge towards certain minimum criteria.
Section 4 is titled Dwelling Space Standards and covers such things as minimum floor area, hallway width and storage capacity. Specifically in section 4.10 (Private Open Space) it addresses outdoor provision.
"Private open space is desirable in all circumstances and, in general, the more private open space provided per home, the better. This guide requires that all dwellings should be provided with adequate private open space in the form of a garden, terrace, balcony or glazed wintergarden."
In other words every new home needs outdoor space. It doesn't matter whether you're on the ground floor or the 17th - an outdoor area should be provided.
"A minimum of 5 sq m of private outdoor space is required for all 2 person dwellings and an extra 1 sq m should be provided for each additional occupant."
This rule set 5m² as the minimum outdoor space required for a new one bedroom flat. Add another bedroom and another square metre would be needed. London doesn't have many five bedroom flats, but where they exist they'd need at least 9m² of outdoor space.
There are many ways to design a balcony with an area of five square metres, for example a 1m×5m rectangle or a 2.23m square. But the former would be impractically narrow which is why there's an additional rule regarding minimum dimensions.
"The required minimum width and minimum depth for all balconies and other private external spaces is 1500mm. These minimum areas and dimensions provide sufficient space for either a meal around a small table, clothes drying, or for a family to sit outside with visitors."
It's nice that someone thought about the practicalities of this. If you can't sit outside with a table and chairs, it isn't good enough.
This rule forces every balcony to be at least 1.5m wide and 1.5m deep (which outlaws the 1m×5m rectangle I mentioned earlier). A balcony with the minimum depth of 1½m must therefore have a width of at least 3.33m. Additional residents bump up the width further, so for three people we're talking at least 1½m×4m.
The guidance may prescribe a minimum area and minimum dimensions but it doesn't dictate the balcony's shape. A 2½×2m rectangle also works. So does 3.125m×1.6m. A 2.23m square is perfectly alright.
Even a triangle is acceptable, or something weirdly curved, so long as the overall floor area is sufficient.
And balconies don't have to stick out. It's also OK to have external space set back within the shell of the building (which some with vertigo may prefer).
These new flats on the Olympic Park demonstrate an indented trapezium and a protruding triangle.
The rules certainly give architects a lot of leeway to play with, which is one reason why no one set of flats looks precisely like another.
The guidance allows for glazed wintergardens where exposure to wind, noise or excess height might be a problem, and in very exceptional cases permits "additional internal living space equivalent to the private open space requirement". But the practical default is a proper balcony, which is why you now see so many of them.
I think it's a striking example of how a simple piece of guidance can have a huge impact on the built environment. Many thousands of Londoners have reason to thank Boris's Mayoralty for making their lockdown just a little more bearable.
