- IIC = impact sound (footsteps, dropped things). STC = airborne sound (voices, TV). Higher is quieter.
- Stratas usually care most about IIC. Hard floors are louder below than carpet.
- A rating belongs to the whole assembly: slab plus underlay plus floor (plus the ceiling below). Not the plank alone.
- Get the bylaw's number and the approval process before you buy anything.
What the numbers mean
Both are lab-tested ratings for a floor-ceiling assembly. Building codes set a baseline for new construction, and many strata bylaws set their own minimum for owners replacing carpet with hard floors. Some ask for a field test after install.
Why the box number can mislead you
- Manufacturers test on a specific slab thickness, sometimes with a suspended ceiling below. Your building may differ.
- A plank might list a great IIC "with underlay X." Use a different underlay and the number doesn't apply.
- Ask for the actual test report and compare its assembly to your building.
How to pass
- Get the bylaw: the minimum rating, approved products (if any), and whether a test is required.
- Pick a floor whose maker publishes tested assemblies with an approved acoustic underlay.
- Submit the specs to strata and get approval in writing.
- Install with isolation at the walls (no hard contact between floor and walls) as the system specifies.
Which floors are quietest
- Quietest hard options: glue-down vinyl or engineered over an approved acoustic underlay, and cork-backed vinyl.
- Tricky: thin click laminate on basic foam. It sounds hollow and can fail IIC.
- Carpet is still the quietest overall, which is why bylaws compare to it.
More on condos: condo and strata flooring · underlay explained.
Common questions
What is IIC rating for flooring?
Impact Insulation Class measures how well a floor-ceiling assembly reduces impact noise like footsteps to the unit below. Higher numbers are quieter.
What is the difference between IIC and STC?
IIC measures impact sound (footsteps, dropped objects). STC measures airborne sound (voices, music). Condo flooring bylaws usually focus on IIC.
What IIC rating do condos require?
It varies by strata. Check your bylaws for the exact minimum and whether a field test is required. Building codes set a baseline, and many stratas set higher requirements for hard floors.
Does underlay affect IIC rating?
Yes, a lot. The rating applies to the whole assembly, so the acoustic underlay is often what makes a hard floor pass.
Who's writing this: Rose and Thorn Flooring is a flooring company in Surrey, BC. We install floors for a living, so yes, we'd love to do yours. But nobody pays us to say nice things about a product, and we don't earn commission from any brand. If something here is wrong or out of date, text us at 604-716-4160 and we'll fix it.