Stopping Impact Noise Between Floors

What the Frame Is Already Doing on Its Own

Before any resilient product is priced, find out what the existing floor does when thirty people land on it together. A resilient layer interrupts the high-rate, high-frequency part of an impact very effectively and does almost nothing to the low-frequency structural response, so a long-span composite floor whose fundamental frequency lands on one of the first few harmonics of a class instructor's cueing tempo will still hand the offices below a rhythmic pulse through a perfect mat. This is a structural finding, not an acoustic one, and it changes the brief rather than the material list.

AISC Design Guide 11, Vibrations of Steel-Framed Structural Systems Due to Human Activity, is the document that treats rhythmic occupancy as its own load case rather than a variant of walking, and it is the reference to put in front of the structural engineer when the tenant fit-out plan first shows a studio. Outside North America the equivalent conversations run through SCI Publication P354, Design of Floors for Vibration: A New Approach, and through CCIP-016, A Design Guide for Footfall Induced Vibration of Structures, for concrete framing. Human response is assessed against ISO 10137, Bases for Design of Structures — Serviceability of Buildings and Walkways Against Vibrations, and in the United Kingdom against BS 6472-1, with ISO 2631-2 covering exposure to building vibration in the one to eighty hertz band that all of this sits in.

The loading question runs alongside it and gets forgotten more often. IBC Table 1607.1, Minimum Uniformly Distributed Live Loads and Minimum Concentrated Live Loads, lists gymnasium and assembly floors separately from office areas, and EN 1991-1-1 puts areas with possible physical activities in their own imposed-load category for the same reason. A floor plate designed and built as offices has not automatically been designed for what you are about to put on it, and a stack of bumper plates in one corner is a concentrated load nobody drew. Get the existing design assumptions out of the building file before the equipment layout is frozen; the answer sometimes moves the heavy zone to a different bay, which is by an order of magnitude the cheapest acoustic measure available on the job.

Damping matters here in a way it does not in an empty warehouse. The offices below, with their partitions, their ceilings and their contents, contribute damping to the same floor plate the gym sits on, and an open-plan refit of those offices during your defects period can genuinely make the gym above audible where it was not before. Note the assumption you relied on, and say so in writing.

The Resilient Layer Is Not the One the Athletes Are Buying

Sports floor specifications and acoustic specifications both talk about resilience and they mean different things by it. EN 14904, Surfaces for Sports Areas — Indoor Surfaces for Multi-Sports Use, and ASTM F2772, Standard Specification for Athletic Performance Properties of Indoor Sports Floor Systems, grade a floor on shock absorption, vertical deformation and ball behaviour, all of which describe what happens to a person landing on the surface. None of them describes what reaches the floor below. A system can hit a high force-reduction class and still be an ordinary performer as an impact-sound layer, because the two properties are set by different parts of the same product.

The number that belongs in the acoustic specification is the improvement in impact sound insulation, measured to ISO 10140-3 and rated as a single figure through ISO 717-2, or in the North American framework the reduction achieved by a covering over a concrete floor measured to ASTM E2179 and the classification work in ASTM E989. Ask the pad supplier for the test report, ask which base floor it was measured over, and read the base floor description before reading the result: an improvement figure obtained over a heavy concrete slab does not transfer to a lightweight composite deck, and the difference is not a rounding error. Where the supplier can only offer the athletic classification, you have a sports pad with unknown acoustic performance, and saying so is more useful than assuming.

Order the pad against the finished court plus the aprons, run-offs and any zone that continues under fixed equipment, and add trim waste for the perimeter and for every cut-out around an anchor sleeve. Pad arrives in rolls or sheets that do not divide neatly into an irregular plan, and a floor that runs short in the last bay gets finished with whatever is on the van, which is precisely how a continuous resilient plane acquires a hard patch.

The Drop Zone Gets Built Twice

A dumbbell released from shoulder height is a single high-energy event with most of its content low in the spectrum, delivered to an area of a few hundred square millimetres. Nothing in the standard test suite reproduces it — the tapping machine is too light and too fast, and the rubber ball is closer but is still a defined source rather than sixty kilos of rubber-coated steel. That means the free-weight and platform areas are designed by construction rather than by a rating, and they are designed to spread the impact before it reaches the resilient layer instead of asking the resilient layer to absorb a point load.

The trade answer is a platform: a deck of two crossed plywood layers over the resilient pad, with the heavy top rubber laid on it, either recessed so it finishes flush with the surrounding floor or trimmed with a ramped edge. The plywood is what turns a point strike into a distributed load; a heavy rubber tile laid straight onto a thin pad transmits the strike almost as if the pad were not there, and crushes the pad locally until it stops working at all. Competition rules for the sport fix the platform dimensions where competition is actually held, but in a commercial fit-out the platform size comes off the rack layout and the safe working zone around it, so take it off the equipment drawing rather than a standard sheet layout.

Detail the edge before the joiner improvises one. The platform floats, so its trim cannot be screwed to both the platform and the surrounding floor, and the recess has to be formed in the build-up rather than cut into it afterwards. Bar ends land on the edge of platforms constantly, so the trim takes an impact load as well as a foot, and a trim fixed through to the deck is a rigid connection sitting exactly where the heaviest impacts happen.

1. Set the platform positions off the rig and rack layout, not off a sheet grid.
2. Form the recess in the build-up so the platform finishes flush; do not cut one later.
3. Cross the plywood layers and stagger their joints so no joint runs through the full deck thickness.
4. Keep the platform, its trim and the surrounding floor mechanically separate from each other and from the deck.
5. Leave one platform accessible for a drop test before the whole floor is finished over.

Below the Slab: A Ceiling Hung on Clips, Not on Wire

The exposed grid ceiling in the offices below is not an acoustic ceiling in this sense, whatever its tile is rated at. A lay-in grid on plain hanger wire is rigidly connected to the soffit, and impact energy in the deck travels down every one of those wires and radiates off the tile. The intervention that changes the outcome is a boarded ceiling carried on resilient sound-isolation clips with furring channel snapped into them, deep enough below the soffit to leave an air space, with mineral wool laid in the void and the board taken to a continuous seal at the perimeter.

This is night work over an occupied tenancy, which drives the sequence more than the acoustics do. The existing ceiling has to come down and the new one has to be closed in shifts short enough that the office is usable in the morning, so the void has to be surveyed properly first — the sprinkler main, the ductwork runs, the lighting and the containment all have to be resolved against the new ceiling line before the first tile is lifted. Every one of those services that penetrates the new ceiling is a rigid crossing unless it is detailed as an isolated one, and a sprinkler drop with a solid escutcheon plate fixed to both the pipe and the board is a connection straight back to the deck.

Clip layout is a load calculation before it is an acoustic one. Each clip has a manufacturer-published static load range, and both ends of that range matter: overload a clip and its resilient element bottoms out and stops isolating, underload it and it does not settle into its working range either. Two layers of board weigh roughly twice what the estimator assumed when the ceiling was a single-layer allowance, so fix the layer schedule before the clip spacing is set, then work the layout out as rows across the run and fixing points along each channel. That gives the clip count, and the clip count gives the fasteners.

Fastener discipline decides whether any of it works. The screws that fix the clips to the framing or the deck are one item, the screws that fix board to the furring channel are a second, and they are not the same length — a board screw long enough to reach past the channel and bite the structure behind it grounds the ceiling out at that point and quietly undoes several metres of isolation. Keep the two boxes physically apart on site, and count them separately so nobody borrows from the wrong one at the end of a shift.