The underlay package has an impressive number. Your building has a concrete slab, a particular ceiling below and its own requirements. The number becomes useful only when you know how it was produced.

Ask for the criterion before shopping

Obtain the corporation's current written flooring requirements and application process. Ask what test method, rating and documentation it accepts, whether field testing is required, and whether the rule differs by room or floor finish. There is no single underlay rating that guarantees approval in every Ontario condominium.

The condo renovation guide helps establish the governing documents and approval route. Keep that decision separate from a retailer's statement that a product is 'condo approved'. Approved by which corporation, for which construction?

Read the rating with its assembly

  • IIC

    Impact sound performance of the tested floor-ceiling structure.

  • STC

    Airborne sound performance; it is a different measure.

  • Component improvement

    A change measured under stated test conditions, not a whole-floor promise.

  • Your proposed floor

    Match materials, substrate and ceiling conditions to the accepted evidence.

Read the tested assembly

Schluter: sound control explains that IIC evaluates the whole floor-ceiling structure. Check the substrate, slab or wood construction, finish, underlay and ceiling beneath in the test report. A result achieved with a suspended ceiling should not be presented as a promise for a unit with no comparable ceiling below.

STC concerns airborne sound; IIC concerns impact sound. Do not substitute one for the other. A component's improvement figure and a whole-assembly rating also answer different questions, so keep their labels and test methods intact.

Check installation compatibility too

A sound product must still be suitable beneath the chosen flooring. Confirm approved thickness, compressibility, fastening or adhesive method and perimeter detail with the flooring manufacturer. More cushioning is not automatically better for a floating floor's joints.

Do not double layers to chase a bigger number without an approved assembly. Ask the supplier and installer to provide the actual proposed build-up, including transitions and finished height. The substitution guide is useful when one specified layer becomes unavailable.

Keep the approval tied to the installation

Save product labels, test reports, approved drawings and installation photographs. If the crew proposes another underlay on delivery day, pause for review rather than treating the change as invisible. A different layer can affect both the flooring warranty and the basis of approval.

Keep pre-close photographs and an installation record, but remember that photographs do not establish acoustic performance. The aim is an approved, correctly installed assembly, not a collection of high numbers from unrelated brochures.