Two developers ask the same question — "which floor hits IIC 50?" — and get the same product answer. One building passes acoustical inspection. The other doesn't. The difference usually isn't the floor. It's what's underneath it. Your building's structure type determines how much engineering work your flooring specification has to carry.
Why Structure Type Changes Everything
Acoustic ratings describe an assembly, not a plank. The same acoustical LVT can post very different numbers depending on the deck it sits on, because wood and concrete manage sound by opposite mechanisms.
Open-Web Wood Truss
A wood-framed floor is light and hollow. It has little mass to block airborne sound (STC), and its cavity can amplify low-frequency impact noise unless the assembly is carefully layered with gypsum, resilient channels, insulation, and a ceiling below. On wood, the floor finish and its acoustic layer do a large share of the work — which is exactly why wood-framed multi-family is where acoustical flooring earns its keep.
Concrete Flat-Plate
A concrete slab is heavy and dense. That mass blocks airborne sound almost for free, so STC is rarely the problem. Impact noise (IIC) is — concrete transmits footfall efficiently, and a bare slab with no ceiling below can feel loud even though it's "solid." Here the floor finish's job is impact control, and a drop ceiling below can add several points.
What AFC's Certified Data Shows
The clearest way to see the structure effect is to hold the floor constant and change the assembly. Soundstop Glue Down — our BA-cored acoustical LVT with the backing attached directly under the wear layer — was tested on both:
| Assembly | STC | IIC | HIIC |
|---|---|---|---|
| Wood floor assembly — no separate sound mat | 61 | 56 | 68 |
| 6" concrete with drop ceiling | 62 | 64 | — |
Same floor, two structures. On wood, the assembly clears the STC 50 / IIC 50 code minimum comfortably without a separate sound mat — deleting a material and a trade. On 6" concrete with a drop ceiling, the added mass pushes IIC substantially higher. The takeaway isn't "concrete is better" — it's that the number you can promise depends on the deck, and you should never carry a wood-assembly rating onto a concrete job (or vice versa) without checking.
Three Questions Before You Spec
- What am I building on — wood truss or concrete? It changes which rating is at risk.
- Does my floor's test report match my assembly? A number from a different deck may not apply.
- Can I delete the separate sound mat? On wood, an attached-backing floor often makes it unnecessary — with the certified data to prove it.
Send us your structural section and we'll match the right Soundstop format and the certified report for your assembly.