How high does a deck railing have to be, and when do I need one?

The 600 mm (23 9/16 in) threshold, and what counts as the ground

The trigger is not the height of the deck above the lawn you are standing on. It is the height above the surface beside the deck, and the code looks 1.2 m (47 3/16 in) out from the edge to find it.

So a deck sitting 500 mm (19 11/16 in) above the back yard needs no guard, and the same deck sitting 500 mm (19 11/16 in) above a patio that drops another 400 mm (15 11/16 in) over a retaining wall 900 mm (35 7/16 in) away does need one, because the total drop within 1.2 m (47 3/16 in) is more than 600 mm (23 9/16 in). The same applies where the ground slopes away steeper than 1 in 2, roughly 30 degrees. Edmonton spells this out and adds that a building permit comes with it.

A guard is also not required along a side that is built against a wall at least as high as the guard would have been.

900 mm (35 7/16 in) or 1.07 m (42 in)

The general requirement is 1.07 m (42 in). Houses and individual dwelling units get a narrower allowance: 900 mm (35 7/16 in), but only while the walking surface being protected is less than 1.8 m (5 ft 10 13/16 in) above the ground.

The part people get wrong is what happens on a sloping yard. Once any part of that walking surface reaches 1.8 m (5 ft 10 13/16 in) above the ground below it, the allowance is gone for the whole platform. You do not build the lower guard along the shallow end and the higher one along the deep end. The guard goes up all the way round.

The stair is measured differently

Where the deck needs a guard, any side of the stair that is not against a wall needs one too, at least 900 mm (35 7/16 in) high measured vertically from the nosing of the step, not from the deck. The openings in a stair guard follow the same limits as the deck guard.

A guard is not a handrail. They are two different things doing two different jobs, and a stair can need both. The handrail answer covers when.

A low deck with a voluntary guard

If the deck is 600 mm (23 9/16 in) or less off the ground you do not need a guard, and you may still want one. If you build it, the openings have to be either 100 mm (3 15/16 in) or less, or more than 200 mm (7 13/16 in). That looks like a strange rule until you picture a toddler putting a head through a 150 mm (6 in) gap in a rail that was never required in the first place.

Holding the guard up

The height is the easy part. The load is what fails. A guard has to resist a person falling against it, and that load goes through the post connection into the framing.

• Fasten wood guard posts with lag screws or through bolts. Not nails, and not a notched post trusting the notch.
• Add rim blocking behind a side mounted post so the load has somewhere to go.
• Use joists and rim boards of at least nominal 2x8 where wood guards are side mounted, so there is enough depth to bolt to. That recommendation appears in both the deck span guide and the Edmonton guide.
• A manufactured guard of metal, vinyl or glass has to show compliance through a CCMC evaluation report, a testing report, or Alberta engineer stamped drawings, and then be installed exactly the way that document says.
• Glass has to be factory marked tempered or laminated safety glass conforming to the named Canadian standard.

What to check on a deck you already own

1. Measure from the deck surface to the top of the guard. Under 900 mm (35 7/16 in) is a problem on any deck more than 600 mm (23 9/16 in) high.
2. Measure the deck height at its worst corner, not its best one.
3. Push hard on the guard at the middle of a run. Movement means the post connection, not the picket spacing, is what needs work.
4. Look at the bottom of every guard post for the dark stain that says water has been sitting there.