A balcony is a room that people treat as a shelf

This is written to be used rather than admired. Each section below is a decision about the balcony as an outdoor room, and each one has a default.

Depth decides the use

A balcony shallower than the depth of a chair can only ever be leant on, which is a real use but a limited one. Once it is deep enough for a seat with a person in it, plus room to walk past, it becomes somewhere to sit rather than somewhere to look from.

Deeper again, it takes a small table and two chairs, at which point it starts absorbing meals and functions as an extra room. Because depth matters more than length, a long shallow balcony often disappoints while a short deep one gets used constantly. Measuring against actual furniture depth, rather than against the plan, is what predicts whether it will be used.

Wind is the dominant condition

Air accelerates around and over buildings, so a balcony several floors up experiences wind speeds far higher than the street below. Wind dries containers rapidly, breaks soft-stemmed plants and makes sitting outside uncomfortable well before it feels strong indoors. A partial screen or a planted barrier at one end changes the microclimate more effectively than enclosing the whole space.

In practice, anything light must be secured, since furniture cushions and umbrellas falling from height are a serious danger below. Rules about screens, awnings and alterations to a balcony are usually set by the building lease or by local regulations and differ considerably.

Water has to go somewhere

Balcony floors are laid to a fall so water runs to a drain or drips clear, and adding decking or tiles can interrupt that fall. Blocked outlets cause ponding, and standing water on a balcony finds its way into the structure and into the flat below. Watering plants creates the same problem in miniature, so pots need trays or a position where run-off reaches the drain.

Waterproofing on a balcony is a maintenance item, and damage to it is a building matter rather than a decorating one. Anything that involves fixing into the structure or altering the waterproof layer needs the building owner and a qualified professional involved.

Weight and what it can carry

A balcony is a cantilevered structure with a design load, and heavy planters, water containers and stone slabs add substantial permanent weight. Soil is heavy when saturated, and a row of large planters can weigh far more than the furniture and people they surround. Lightweight growing media, fibre containers and raised planting on the supported edge all reduce the load.

Where there is any doubt about capacity, particularly in an older building, the question belongs to a structural engineer.

This is one of the few decorating decisions in a flat with genuine safety consequences, which is why it is worth asking about.

Planting that survives

Containers dry out fast in wind and sun, and a balcony frequently kills plants through drought rather than cold. Larger pots hold more moisture and swing less in temperature, so fewer big containers outperform many small ones.

Plants adapted to exposure, with small tough leaves or grassy forms, tolerate balcony conditions far better than soft-leaved ones. Aspect matters as much as it does indoors: a north-facing balcony in shade all day suits a different palette entirely. Watering is the whole job, and a balcony without a convenient source of water tends to become a store rather than a garden.

Budgets and buildings differ, and old buildings differ most.

Connecting it to the room behind

A balcony gets used in proportion to how easy it is to step onto, so a door that sticks or a high threshold suppresses use. Using the same or a similar floor finish inside and out extends the room visually, even when the door is closed.

Room to room, keeping the sightline from the seating inside through the door means the balcony is part of the room rather than a view of a railing. Light on the balcony in the evening makes the glass read as a view rather than as a black mirror. Storage out there should be deliberate and enclosed, because a balcony full of visible objects shrinks the room it adjoins.

The takeaway

Measure the depth against a real chair, plan for wind and drainage, and keep the load light unless someone has checked it.

A room that is used will always beat a room that is finished.