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Height limits and clear zones
The deck can go as high as the guardrail you are willing to build: rails become mandatory at 30 in (760 mm), at least 38 in (965 mm) tall for under-fives and 48 in (1.22 m) for ages five to twelve. Around whatever you build, the ground stays clear for at least 6 ft (1.8 m) in every direction, with nothing hard or fixed inside the zone. This guide turns those dimensions into a build sequence.
Six stages, each with a named failure that shows up when the stage is skipped.
A play tower fails in a predictable order when it is built out of order. Layout comes first because every later measurement — footing position, beam length, slide runout — hangs off the use zone. Builders who start with the posts and think about clearance later are the ones who end up moving a fence.
The slow stage is the concrete. Footings go in at 900 mm (36 in) deep and at least 300 mm (12 in) across, below the local frost line, and they need curing time before they carry anything: posts can stand on them after about 48 hours, but swing loads should wait roughly a week while the concrete gains strength. Loading green concrete is the failure that cracks a footing below grade, where nobody sees it until the post leans.
Framing, rails and hanging come last, in that order, because each stage hides the previous stage's bolts. The full sequence, with the failure each skipped stage produces, is below.
As high as the rail you build and the surface you lay under it — the timber is not the limit.
The first threshold is 30 in (760 mm). Below it, a platform can stand open; at or above it, guardrails become mandatory on every open edge. That single number is what most backyard builds are really deciding when they pick a height.
The rail itself is sized to the child. For children under five the rail must be at least 38 in (965 mm) tall; for ages five to twelve it rises to 48 in (1.22 m). A tower built for a four-year-old and a nine-year-old takes the taller rail.
Every opening in that rail — between balusters, under the top rail, around ladder entries — has to dodge the head-trap band. Openings between 3 in (76 mm) and 5 in (127 mm) can wedge a child's head, so build every gap either smaller than 76 mm or larger than 127 mm. There is no safe measurement in between.
At least 6 ft (1.8 m) of clear, surfaced ground in every direction — and the slide adds more.
The use zone is the ground a child can reach by falling, and the rule is simple: 6 ft (1.8 m) in every direction from the equipment, with nothing hard or fixed inside it. Measure from the furthest reach of the equipment — the end of a swung swing, the lip of a platform — not from the posts.
Slides get their own allowance. The exit needs an additional 6 ft (1.8 m) of clear landing beyond the end of the slide, on top of the basic zone, because children leave a slide moving forward. A slide aimed at a fence two metres away fails twice: the fence sits inside the zone and inside the runout.
What fills the zone matters as much as its size. Hard or fixed objects are exactly what the zone exists to exclude, so the landing surface under the tower has to be something a child can fall onto — and the higher the deck, the more that surface has to absorb.
The tape measure decides the safety of a play tower long before the first post is set.
A 2x6 carries a deck. A 2x8 carries a deck with a swing on it.
| Build decision | Dimension | Why it is the rule |
|---|---|---|
| Clear use zone around equipment | 6 ft (1.8 m) in every direction | Falls travel outward; nothing hard or fixed may sit inside |
| Slide exit landing | Extra 6 ft (1.8 m) beyond the slide end | Children leave a slide moving forward; added on top of the zone |
| Guardrail trigger | Deck at 30 in (760 mm) or higher | Open platforms are only allowed below this line |
| Rail height, children under 5 | At least 38 in (965 mm) | Sized so a small child cannot topple over |
| Rail height, ages 5 to 12 | At least 48 in (1.22 m) | The taller rail governs when ages mix |
| Safe openings | Under 3 in (76 mm) or over 5 in (127 mm) | The band between them can trap a child's head |
| Gap between decking boards | 6 mm (1/4 in) | Drains rain and absorbs seasonal swelling |
| Post footings | 900 mm (36 in) deep, 300 mm (12 in) across | Below the frost line so winter cannot lift the tower |
A 2x6 carries the deck; the day you add a swing, the beam grows to a 2x8.
At a standard 40 psf deck load, a 2x6 (38 x 140 mm) beam at 16 in (406 mm) centres spans about 2.9 m (9 ft 6 in). That covers most platform frames without intermediate posts. Swing loads change the calculation — a swung swing pulls sideways and down at once — and any beam carrying hangers needs to be a 2x8 (38 x 184 mm).
Decking boards run 19-25 mm thick and 90-140 mm wide, laid with a 6 mm (1/4 in) gap between them. The gap is not cosmetic: it drains rain and lets the boards swell and shrink with the seasons without buckling against each other.
Outdoors, the metal decides the lifespan. Fixings should be 304 stainless or hot-dip galvanised; standard zinc-plated screws in coastal air corrode through in 1-2 years, staining first and shearing later. Posts bolt to their footings with 5/8 in (16 mm) galvanised anchor bolts — screws are not anchors.
Five repeat offenders account for most backyard tower failures.
None of these are exotic. Every one is a dimension from this guide that somebody rounded down, and each announces itself within a season or two — a lean after the first winter, a rust streak by the second summer, a bounce in the deck the first time two children swing together.
The figures reflect widely published home-playground safety guidance and standard residential deck construction practice.