Maximum
England
Maximum gap in guarding
No opening should allow a 100 mm sphere to pass
Guarding to a stair, landing, balcony or floor edge in a dwelling
Largest sphere that may pass through any opening in guarding to a stair, landing, balcony or floor edge.
Basis in regulation
How to check it on site
Test with a 100 mm gauge at the widest point of every bay, including the triangular gap at the bottom of a flight and between the string and the first baluster.
Common failure
Balusters spaced evenly across a bay without allowing for the tapered gap at the foot of the flight.
Last updated 23 August 2026. This is our editorial summary of publicly available regulation, not building control approval or a warranty determination.