The Specifier's Guide to Acoustical Flooring

Noise is one of the most expensive problems in multi-family and hospitality construction, and one of the most preventable. It rarely shows up as a line item. It shows up later — in move-outs, in one-star reviews, and in the single most expensive repair in the building: tearing up finished floors in occupied units.

This guide covers how acoustical performance actually works between floors, the three ratings that matter, what the building code requires, and how to verify a supplier's numbers before you write them into a spec. Specifiers who get this decision right protect their projects from callbacks, complaints, and a problem that can't be renovated away.

What Actually Determines a Floor's Acoustical Performance?

Here is the single most misunderstood fact in acoustical flooring: the rating belongs to the assembly, not to the floor covering.

A floor-ceiling assembly is a system of four layers, working downward:

• Acoustical floor covering with attached backing — controls impact at the source
• Gypsum underlayment — the mass layer
• Structure — wood truss with cavity insulation, or concrete
• Ceiling treatment — a resilient channel decouples the ceiling and drives STC

Change any one of those layers and the rating changes. This is why a number pulled off a product spec sheet is close to meaningless on its own: the same floor covering can produce wildly different results depending on what's above and below it.

The Three Ratings You Need to Know

There are three ratings in play, and most specifications name only one or two.

Rating	Test Standard	What It Measures	Why It Matters	Code Status
STC	ASTM E90	Airborne sound — voices, television, music	Conversations and TV bleeding between units	Minimum required (typically 50)
IIC	ASTM E492	Impact sound — footsteps, dropped objects	The classic "upstairs neighbor" complaint	Minimum required (typically 50)
HIIC	ASTM E3222	The same impact energy, re-weighted toward high frequencies	Heel clicks, hard soles, dragged furniture — what a hard floor transmits most sharply, and what the floor covering most controls	Not required by code

The nuance worth understanding: standard IIC under-credits the high-frequency energy that hard-surface floors transmit most. HIIC captures it. It isn't in the code — it's specified because it reflects what residents actually hear.

Step-by-Step: How to Specify Acoustical Flooring

1. Start with the assembly, not the product

Identify your structure first — wood-frame or concrete — then the underlayment and the ceiling treatment. Only then choose the floor covering. On wood-frame construction, the resilient-channel decision at the ceiling often does more for STC than anything you do at the floor.

2. Know what the code actually requires

The International Building Code sets sound-transmission provisions for dwelling-unit separation in Section 1206 (it was Section 1207 through the 2015 edition), commonly at STC 50 and IIC 50. Some state housing finance agencies impose stricter requirements on funded projects — check those before you assume the IBC minimum is the target.

3. Decide: separate sound mat, or attached acoustical backing

For two decades the default answer was a separate sound mat between the subfloor and the gypsum underlayment. That assumption is now worth re-testing.

Third-party laboratory testing shows that an acoustically-backed glue-down LVT — with the acoustical layer bonded directly to the back of the plank — can match or outperform a conventional thin-mat assembly, while eliminating an entire construction step. The principle is simple physics: dampening works best when it sits closest to the source of the impact.

Fewer layers means fewer trades, fewer schedule dependencies, and one less thing to install incorrectly.

4. Verify every number against a third-party report

Before a rating goes into your spec, check four things on the actual test report:

• The lab and report number — is it a named, independent laboratory, and can you verify the report?
• The test standard — ASTM E90 for STC, E492 for IIC. Is it the right test for the rating being claimed?
• The assembly tested — the full floor-ceiling build, not just the floor covering
• The numbers — STC, IIC, and whether HIIC was measured at all

If a supplier can't produce the report, you don't have a rating. You have a marketing claim.

5. Document it for the submittal

Assemble the spec sheet, the third-party test reports, the warranty, and the installation and maintenance instructions into one submittal package before the project needs it. Division 09 reviews go faster when the documentation is complete the first time.

What Noise Actually Costs

Acoustics is usually treated as a comfort feature. It's also a financial one.

Turning an apartment unit costs roughly $3,900 when you account for marketing, vacancy days, repairs, and prep (Zego, 2023), with National Apartment Association survey data placing most turns between $1,500 and $3,500 and about one in five above $3,500. On a 200-unit property running near industry-average turnover, even a modest change in renewal rates moves NOI by six figures.

Here's the trap: noise rarely appears in complaint logs. J Turner Research's analysis of 10,000 multi-family satisfaction surveys found noise didn't crack the top ten stated complaints — but it turns up in online reviews and in renewal decisions. Residents don't complain. They quietly leave.

In hospitality, it's louder. Noise has ranked as the most commonly experienced problem reported by hotel guests in J.D. Power's North American studies — and guest reviews price rooms.

How Soundstop Simplifies the Assembly

Advanced Flooring Concepts developed Soundstop to remove a step from this equation: a BA-cored acoustical LVT with the acoustical backing bonded directly to the plank, in both glue-down and SPC click formats.

• Engineered to meet common code targets for airborne (STC) and impact (IIC) sound
• No separate underlayment to source, schedule, or install
• Third-party test reports available for specification packages — every published figure traces to a named, certified Intertek report

Our performance data comes from a library of twelve certified third-party acoustical assemblies, verifiable by report number. We'd rather hand you the report than ask you to trust the number.

Acoustics Is a One-Shot Decision

Paint, counters, and amenities can all be upgraded later. Impact sound can't. It's decided by the assembly, and the assembly is framed and covered during construction. Get it wrong and the only real remedy is tearing up finished floors in occupied units.

That makes the flooring spec one of the highest-leverage, least-reversible decisions on the project — and it's often the one made fastest, off a spec sheet nobody verified. Slow that decision down, ask for the report, and specify the assembly rather than the plank.