What is guarding, and what do the 900mm and 100mm figures mean?
The barrier at the edge of a stair, a landing, a balcony or a change of level. The height it has to reach, the gap nothing may exceed, why horizontal rails are a problem, and what makes one fail.
- Difficulty
- intermediate
- Time
- 8 min
- Read
- 5 min
- Safety
- warning
Short answer
Guarding stops people falling from an edge. Approved Document K's guidance for a dwelling is at least 900mm high on a flight of stairs and on landings and balconies within a dwelling, with no gap anywhere in it that a 100mm sphere can pass through. It has to resist a sideways load, which means the fixings and the newels matter more than the infill.
This is one of the small number of building requirements that exists purely because of what happens to children, and the two numbers are worth knowing for that reason alone. It is also the requirement most often quietly broken by a well-intentioned home improvement.
Safety
Step by step
- Identify where guarding is required.Any edge with a drop that people can reach: the open side of a stair flight, a landing, a balcony, a mezzanine, a raised deck, and the edge of any floor above a change of level. It is not only about stairs.
- Learn the height.Approved Document K gives at least 900mm for a stair flight and for landings and balconies within a dwelling, measured from the pitch line on a flight and from the floor on a landing. Other buildings and external situations have different figures.
- Learn the gap.No opening anywhere in the guarding may allow a 100mm sphere to pass. It applies to the gaps between spindles, the gap under a bottom rail, the gap at a newel, and the triangular gap between a tread, a riser and the bottom of the balustrade.
- Understand why horizontal rails are a problem.Guarding in a dwelling that children can use should not be readily climbable. A ladder of horizontal rails is exactly that, which is why vertical infill, glass or mesh is the normal approach in a house.
- Remember that guarding takes a sideways load.It is designed to be shoved into, not leant on gently. That load goes into the newels and their joints, and into whatever the newel is fixed to. This is why the fixings are the part that matters and why a beautifully made balustrade on a poor base is not safe.
- Check the whole run, not the obvious bit.The failure is almost always at a junction — where the handrail meets a newel, where a newel is fixed to the floor, or where a run of spindles meets a wall. Push gently at each junction rather than in the middle of a span.
- Treat a change of infill as a real alteration.Replacing spindles with glass panels or a horizontal system changes the loads and the gaps. It is worth checking against the requirements and, if the guarding itself is being rebuilt, with building control.
Tips
- Test the 100mm gap with something 100mm across rather than by eye. A cricket ball is close enough to be a useful check and the result is usually surprising near the bottom of a flight.
- The triangular gap formed by the tread, the riser and the bottom of the balustrade is the one everyone forgets, and on an open-string stair it is often the biggest opening in the whole run.
- Temporary stair gates protect a toddler from the flight. They do not close a gap in the guarding, and a child who can no longer use the stairs still explores the landing.
Common mistakes
- Removing spindles to open up a hallway — It removes the guarding. Whatever replaces it has to meet the same height and gap requirements, and an open edge in a house with children is a serious hazard rather than a design choice.
- Fitting a horizontal rope, cable or rail balustrade in a family home — It is climbable, and cable systems also tend to spread under load so the gap grows exactly when it matters. Vertical infill or a solid panel is the appropriate approach in a dwelling.
- Fixing a newel post to a floating floor or to floorboards alone — The newel has to transmit a sideways load into the structure. Fixed into a floating layer, it has nothing to push against, and the whole balustrade is as strong as that fixing.
If it doesn't work
The balustrade moves noticeably when leaned on
Cause: A newel joint or a newel base fixing that has failed — Fix: Stop using that side of the stair and get it repaired. The correct repair fixes the newel into the structure; tightening the handrail to the spindles does nothing about the load path.
The gaps between spindles look wide
Cause: Spindles removed or spaced out during earlier work, or a stair built before the current guidance — Fix: Measure with a 100mm object. Adding intermediate spindles is a straightforward and worthwhile job, particularly with young children in the house.
A gap under the bottom rail on a landing
Cause: The rail set clear of the floor for cleaning, or a floor build-up that has changed the geometry — Fix: Close it. It is guarding, and a gap at floor level is exactly the one a small child finds.
Questions people ask
Does old guarding have to be brought up to standard?
There is no general obligation to upgrade existing guarding. The requirement applies when it is built or altered. With small children in the house it is worth doing regardless of obligation.
What height is required for a landing or balcony?
Approved Document K gives at least 900mm within a dwelling for stairs, landings and balconies, with higher figures in other building types and situations. External guarding and buildings other than dwellings have their own values, so check the situation rather than applying one number everywhere.
Can I use glass?
Yes, and it is common. It has to be an appropriate safety glass and it has to be able to take the loads, which is a design matter — a glass balustrade is engineered rather than chosen from a catalogue by appearance.
What about a deck or a raised patio?
The same principle applies at an external change of level, and GuideHQ has a guide on deck balustrade height and spacing. The figures for external guarding are not identical to the internal ones.