Stairwell void

What is a stairwell void?

A stairwell void (zrkadlo schodiska) is the open space that a staircase leaves between its flights and landings. Looking down through it, you see from one floor to the floor below. The edges of the upper floor form the rim of the opening. The stair layout defines the void, so changing the flights or the landings changes the void.

Decree 532/2002 Z. z. uses the term in § 28 ods. 5, which speaks of a stair or inclined ramp with a well (schodište so zrkadlom). The decree does not define the term. This page uses the common meaning from building practice.

In Slovak family houses the void is usually a rectangle or a U-shaped opening around a straight or quarter-turn stair. Its size is the space left once the flights, the landing widths and the handrail clearances are fixed. That is why the void is decided on the stair drawing and not on the floor plan alone.

What types of stairwell void are there?

Designers work with four common forms. They differ mainly in whether the void is walled and how much light it carries down.

Form	What it is	Light down to lower floors	Typical use
Open well	Unwalled void between flights and landings, edged by a railing	High when a roof light sits above it	Family houses with a central stair
Partly walled void	Open on one side, closed by a wall or glazed screen on the others	Medium	Stairs set against an exterior wall
Enclosed stair shaft	Stair closed by walls and doors at each floor	Low, unless the stair has its own window	Multi-storey buildings with a protected stair
Double-height void	Open space over two storeys, often with the stair running through it	High at the top, lower at the bottom	Living rooms and entrance halls

Where does a stairwell void need a railing, and how high?

The open edges of a void are a fall hazard at every landing and along the edge of the upper floor. Decree 532/2002 Z. z. requires a railing at every walkable surface of a building with a fall hazard that people can reach (§ 28 ods. 1). The railing must resist loads in the horizontal and the vertical direction. A handrail goes on the sloping railing of the stair itself, at 900 to 1,200 mm (§ 28 ods. 8).

For a stair or ramp with a well, § 28 ods. 5 gives no railing height. It says the minimum height must match the Slovak technical standards. The footnote names STN 74 3305 on guard railings and STN 73 8106. Both are paid documents, so this page quotes no value from them. For other free edges, the basic minimum height in § 28 ods. 4 is 1,000 mm, and that height includes the handrail. A lower value of 900 mm is allowed only if the free depth is at most 3 m.

How wide may the gaps in a railing be for child safety?

The decree allows a railing to be solid, to have panel infill, vertical bars or a lattice. Gaps may be at most 120 mm wide in an apartment building and 80 mm in premises for children (§ 28 ods. 6). A family house is not named. A designer who knows that small children will live there should choose the narrower value and avoid horizontal bars that a child can climb. Where a foot could slip under the railing, the decree also requires a toe board at least 100 mm high (§ 28 ods. 7).

Does the width of the void matter?

The decrees read for this page give no minimum width of the void. The clear width of the flight, the landing dimensions and the step width come from STN 73 4130, the standard that § 27 ods. 2 names. That standard is paid, so this page quotes no value from it. The void is the space left after those dimensions are set. A wider void lets more light pass down, and a narrow one leaves less clearance beside the handrail.

How does a stairwell void affect daylight?

Decree 532/2002 Z. z. requires the stair space to be lit and ventilated (§ 27 ods. 9). Decree 259/2008 Z. z. requires adequate daylight in interiors where people stay for long periods (§ 4 ods. 3). The same decree names corridors and stairs as examples of spaces with short-stay use. It gives them their own temperature and air change values (§ 2 ods. 10). The rooms that open onto the void therefore need a check on their own windows.

Light from above reaches the lower floors only through the void, so depth matters. A deep, narrow void with a small roof light gives a dim stair and dark rooms below it. The usual check for the rooms around the void is the daylight factor, which measures how much daylight reaches a point inside a room.

How does a stairwell void affect fire safety?

Decree 94/2004 Z. z. covers stairs in § 46 ods. 1. Where a fire compartment has several stairs, only one must meet the fire-resistance requirements. That is the stair on an escape route for more than ten people. Under § 46 ods. 2, the load-bearing structure of a stair inside a fire compartment must reach at least criterion R. A protected escape route is the exception. Section 64 ods. 2 caps the distance between the stairs of a building at 60 m.

An open void can carry smoke and hot air from one floor to the next. A designer who opens a void in a multi-storey house should bring the fire-safety requirements in early, before the floor plan is fixed.

How warm does the stair around a void need to be?

The void adds air volume to heat. Annex 2, Table 4 of decree 259/2008 Z. z. gives corridors and stairs an operative temperature of 15 to 18 °C. It also gives 2 to 3 air changes per hour. Plan the heating of the stair to those values and not to living-room targets.

How is a stairwell void different from an atrium or a light well?

All three are open vertical spaces, but they serve different purposes. A stairwell void exists to hold a stair, and the open area is what the stair leaves behind. An atrium house organises the whole house around a deliberately large central court. A light well is a narrow opening, usually on one side, that brings daylight to a basement or a dark room.

Feature	Stairwell void	Atrium	Light well
Main purpose	Passage for a stair	Central court that organises the house	Daylight to a dark room
Size is set by	The flights and landings	The plan of the whole house	The room it lights
Floors it crosses	Usually two adjoining floors	Often all floors	Often one or two

What should you check when you plan a stairwell void?

1. Fix the stair type and its flights first, since the void is the opening the stair leaves.
2. Check the daylight in the stair and in the rooms that open onto the void, using the daylight factor.
3. Set a railing along every open edge and at each landing, and check its height against the current standard.
4. Choose a baluster gap of 80 mm or less where small children will live.
5. In a multi-storey house, ask the fire-safety designer to check the stair and escape-route rules under decree 94/2004 Z. z.
6. Plan the heating of the stair to the values in decree 259/2008 Z. z.: 15 to 18 °C and 2 to 3 air changes per hour.

What are the common misconceptions about stairwell voids?

• A void always makes a house brighter. It carries light down only when light comes in above it, and a deep void can leave the lower floors dimmer than before.
• Any open stair is a stairwell void. A stair with a closed side and no opening in the floor has no void.
• A void is only a design feature. The same safety rules apply to it as to any other opening in a floor.