Surfacing depth by fall height

The CPSC table, as published

The Public Playground Safety Handbook publishes one compact table of minimum compressed loose-fill depths¹. Read it as a statement about compressed depth, which is the depth remaining after the material has settled, not the depth on the day it was delivered.

Two things about this table catch people out. First, it is not a grid. It gives one depth per material and the height that depth covers, so it tells you whether a material is viable at your fall height rather than how much to add if it is not. Second, "wood mulch" and engineered wood fiber are related but not identical products, and a manufactured engineered wood fiber sold to ASTM F2075³ will have its own test report that may rate it differently.

Working depths, fall height by fall height

Turning the table above into the grid people actually want gives the following. Every cell is the minimum compressed depth supported by the CPSC figures. Where a cell says no CPSC figure, the material is not covered by that data at that height and you need product specific test data or a different material.

The pattern is worth absorbing before you compare quotes. Sand and pea gravel are cheap and they cap out low. Wood products cover the normal range of public playground heights. Shredded rubber does the most work per inch of depth. That ranking is the real reason material choice and equipment height get decided together, not one after the other. Sand and pea gravel covers where the low cap is still acceptable.

Uncompressed depth versus compressed depth

Loose fill arrives fluffy and ends up dense. Uncompressed depth is what you measure the afternoon it is spread. Compressed depth is what remains after weeks of traffic, rain and settlement, and it is what the safety rating refers to.

For engineered wood fiber, the gap is large. The material is designed to knit together, and knitting together means losing volume. Industry practice is to install roughly 25 percent more depth than the compressed figure you need, so a 9 inch compressed specification is installed at about 12 inches. Sand and gravel settle less. Shredded rubber settles least of all, which is part of why its depth requirement is lower and more stable.

How much material to actually order

Volume is the thing that goes wrong on the purchase order. A cubic yard covers 27 square feet at 12 inches deep, 36 square feet at 9 inches, and 54 square feet at 6 inches. Apply the compaction allowance before you divide.

Then add the first top-up to the budget, not to next year's wish list. Wood fiber typically needs its first significant replenishment within the first 12 to 24 months as settlement and displacement take effect. The surfacing depth calculator does this arithmetic against a real use zone area, and budget breakdown shows where surfacing sits against equipment and site work.

Why unitary surfaces are not on this chart

Poured-in-place rubber, rubber tiles and bonded systems are not specified by depth from a general table at all. They are specified by tested thickness for a stated fall height, from the manufacturer's own ASTM F1292 report, because the performance depends on the binder, the granule size, the density of the cushion layer and the base underneath. Two poured systems at the same nominal thickness can carry different ratings.

That has three consequences when you write a spec:

1. Quote the fall height, not the thickness. Let the manufacturer size the system and put their F1292 report behind it. If you specify 2.5 inches and it underperforms, the thickness was your decision.
2. The base is part of the rating. A poured system tested over a specified base and installed over a different one is no longer the tested assembly. Drainage and base layers covers what these systems need underneath.
3. Thickness varies across the site. A unitary surface is usually thicker under the tall structure and thinner on the connecting routes. Do not let a single average thickness appear on the drawing.

Poured-in-place rubber and rubber tiles go through the thickness question in detail, including the case where a pad beneath the wear layer carries the entire rating.

Where depth disappears first

A chart describes a uniform surface. Playgrounds are not uniform. Depth is lost in predictable places: under swing seats, at slide exits, at the foot of climbers and firefighter poles, along the edges of the containment, and at the bottom of any slope. Those are also the places where the fall is most likely, which is an unhappy coincidence built into how children play.

Practical consequence: inspect by depth probe in the high wear spots rather than by eye across the middle. The middle almost always looks fine. The inspection checklist and surfacing upkeep put this on a schedule that survives staff turnover.

What to do next

Work in this order. Measure the fall height using fall height and use zones, pick the material against the caps in the tables above, apply the compaction allowance, then ask the supplier for the ASTM F1292 report for that exact product at that exact depth.

If the answer comes back expensive, the cheapest fix is almost never a different material. It is a lower deck. If the answer comes back complicated, read how surfacing works for what the rating is actually promising, and compare whole life costs in the surfacing cost comparison.