Wooden or Steel Playground Posts? How to Choose the Structure Material

Timber does not rot because it is timber. It rots because it stays wet, and the place it stays wet is the 100 mm just above and just below ground level, where soil moisture, rainwater running down the post and the absence of air movement combine into the worst possible conditions for a wood-destroying fungus. Ground-line rot is the single most common reason a timber playground is condemned early, and it is a design detail rather than a material property.

Three details change the outcome. First, keep the timber out of the ground: a galvanised steel shoe or post base that lifts the timber clear of soil and lets the base of the post dry. Second, shed water away from the post rather than into it — a chamfered or capped top, and no upward-facing end grain. Third, drain the footing: a concrete collar that traps standing water around the post is worse than no collar at all. A timber structure built with these three details will outlast a superficially similar one built without them by a decade or more.

This is also the question to put to a supplier. "What is your post base detail?" is a far more informative question than "how long does the wood last?", because the answer to the second one is a guess and the answer to the first one is a drawing.

A hot-dip galvanised post does not fail by rusting through. It fails where the coating is absent or damaged: at cut edges and drilled holes made after galvanising, at welds with porosity or spatter that the zinc could not cover properly, and at the site of a mechanical impact that took the coating off and was never touched up. Paint over a steel structure is a coating schedule, and like any coating schedule it is only as good as its preparation.

So the questions that matter for a steel structure are: was it galvanised after fabrication, or were holes drilled and edges cut afterwards? What coating thickness was specified and what does the inspection certificate say? Were the internal surfaces of hollow sections protected, and are there drainage holes so that water cannot sit inside a closed section? A tube that fills with condensate and cannot drain will corrode from the inside out, and nothing about the outside appearance will tell you it is happening.

On the coast, the same logic as for slides applies to the whole structure — see the stainless steel grading discussion in the 304 vs 316 comparison. Galvanising performs well in marine atmospheres for a long time, but the fixings, brackets and moving parts are where chloride attack shows first, and specifying stainless fixings is a cheap way to avoid it.

The honest whole-life comparison is not purchase price against purchase price. A timber structure needs an annual visit that includes re-tightening fixings, sanding and treating exposed surfaces, and replacing any section that has started to soften. A steel structure needs annual inspection and occasional local repair where the coating has been damaged. If the timber maintenance never happens, the structure does not degrade gracefully — it fails at the ground line, and it fails in a way that closes the play area.

This is why timber tends to be the right answer for clients who already run a grounds maintenance regime and have the budget line for it, and the wrong answer for a client buying a structure to be forgotten about. It is worth saying plainly to a client considering timber on price alone: the initial saving is real, and it is normally spent back within the first decade on maintenance and section replacement unless the design details and the maintenance regime are both right.

Timber wins on surface temperature, and in a hot climate that is not a small thing. A bare metal post in full sun can be painful to touch; a timber post in the same conditions stays warm but usable. On equipment where children grip the structure — climbing frames, nets, balancing trails — that difference shows up in how the equipment is actually used through the middle of the day.

Timber also wins on character, and that has real procurement weight. Natural play schemes, parkland settings, heritage sites and landscape architect-led designs frequently specify robinia or oak because steel reads as municipal furniture in a place where the design intent is the opposite. In those projects the material choice is made before the engineering discussion starts, and the useful contribution is not to argue with it but to make sure the durability class, the preservative treatment and the base detail are all specified properly.

For timber: the species, the durability class to EN 350, the use class to EN 335, the preservative type and retention level, and whether the timber is FSC or PEFC certified if the client has a timber policy. Note that several traditional preservatives are restricted or banned in the EU and other markets, so a supplier still offering them is a supplier to check carefully. Ask for the post base drawing, not a description of it.

For steel: the steel grade, the galvanising standard and minimum coating thickness, whether powder coating is applied over the galvanising or instead of it, the treatment of cut edges and drilled holes made after galvanising, and the drainage provision inside hollow sections. Both lists are short, and a supplier who can answer them without going away to check is a supplier who builds to a specification rather than to a price.