Guards and railings

How far apart can spindles be, and what is the no climb rule?

Q: How far apart can spindles be, and what is the no climb rule?

No opening through a deck guard may allow a 100 mm (3 15/16 in) sphere to pass. That is the whole rule, and it applies to the gaps between pickets, on the stair as well as the deck, the gap under the bottom rail, and the triangle beside a stair stringer.On a guard more than 4.2 m (13 ft 9 5/16 in) above the ground there is a second rule: nothing in it may be climbable. A horizontal rail that reads as a ladder rung is the usual failure.On a deck 600 mm (23 9/16 in) or less off the ground, where no guard is required at all, a guard you build anyway must have openings either 100 mm (3 15/16 in) or less, or more than 200 mm (7 13/16 in).

There is no rule that says pickets go 4 in apart. There is a rule that says nothing a 100 mm (3 15/16 in) ball can pass through may exist in the guard, and a gap just under 4 in is what falls out of it. Change the gap below and watch the test run.

The short answer

No opening through a deck guard may allow a 100 mm (3 15/16 in) sphere to pass. That is the whole rule, and it applies to the gaps between pickets, on the stair as well as the deck, the gap under the bottom rail, and the triangle beside a stair stringer.

On a guard more than 4.2 m (13 ft 9 5/16 in) above the ground there is a second rule: nothing in it may be climbable. A horizontal rail that reads as a ladder rung is the usual failure.

On a deck 600 mm (23 9/16 in) or less off the ground, where no guard is required at all, a guard you build anyway must have openings either 100 mm (3 15/16 in) or less, or more than 200 mm (7 13/16 in).

Why a sphere and not a measurement

The code does not measure gaps. It tests them with a shape, because a gap can be narrow in one direction and wide in another. A cable rail that is 90 mm (3 1/2 in) between cables still fails if the cables can be pushed apart. A slot in a decorative panel that measures 80 mm (3 3/16 in) by 200 mm (7 13/16 in) passes a tape measure and fails a ball.

The sphere is 100 mm (3 15/16 in) across. A gap of exactly 4 in is just wider than the sphere and fails, so the usual working number for wood is 3 7/8 in clear, which also leaves room for treated lumber to shrink as it dries.

The four places it is missed

Under the bottom rail. The gap between the bottom rail and the deck surface is an opening in the guard like any other. Builders leave it generous so the deck can be swept, and it fails.
The triangle beside a stair stringer. Where the raked guard meets the treads, the opening between the bottom rail, the tread and the riser is a triangle, and on a stair guard it is judged by the same sphere. A closed stringer, with the treads housed inside it, closes that triangle.
The gaps between the stair pickets. They follow the same rule as the deck's, measured square to the pickets, and a stair guard laid out from one post leaves whatever is left at the bottom.
A cable rail that has gone slack. Cable passes on the day it is tensioned and fails two winters later. This is a real maintenance item, not a theoretical one.

The no climb rule

Above 4.2 m (13 ft 9 5/16 in) the guard may have no member, attachment or opening between 140 mm (5 9/16 in) and 900 mm (35 7/16 in) above the walking surface that facilitates climbing. In plain terms: nothing a child can get a foot on. Horizontal rails, wide bottom rails and decorative lattice are all out at that height.

Below 4.2 m (13 ft 9 5/16 in) the rule does not apply, which is why horizontal cable and slat guards are legal on an ordinary back deck and not on a fourth floor balcony. It is worth saying out loud that legal and wise are not the same word here.

Counting the pickets

Picket count is one of the few deck quantities that falls straight out of the geometry, which is why the demonstration above works it out for you. The arithmetic is: pitch equals the clear gap plus the picket thickness, and the count is the run divided by the pitch, rounded up, plus the one at the end.

That number is a checking number, not an order. Corners, gate posts and a run that does not divide evenly all move it. It is enough to tell you whether a quote is in the right country.

Where this comes from

National Building Code of Canada, Part 9, Section 9.8.8, Guards. The 100 mm (3 15/16 in) sphere, the 140 mm (5 9/16 in) to 900 mm (35 7/16 in) no climb zone and the 4.2 m (13 ft 9 5/16 in) threshold are from this section.
City of Edmonton, Uncovered Deck Design Guide, Section 4, Guards, including the 100 mm (3 15/16 in) or less, or more than 200 mm (7 13/16 in) rule for a voluntary guard on a low deck.

Nothing on this page is an approval or a design. Code editions change and every authority having jurisdiction has the final word. Check your numbers with yours before you build.