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How Do I Know if I Need Underlayment?

Installing a new flooring system in your home is one of the best ways to increase your property value and change the visual aesthetic of the rooms. Most homeowners don’t understand the structure of a flooring system. Its layers of components are essential for the floor’s durability and functionality. The underlayment is out of sight, but it’s a crucial component of any flooring system. Underlayment adds comfort, stability, and soundproofing to the flooring system. But how do I know if I need underlayment?

How Do I Know if I Need Underlayment?

Flooring Underlayment Explained

Depending on the application, the flooring underlayment can consist of hard or soft materials. It fits under the floor covering and between the top and subfloor materials. Installing underlayment removes minor imperfections in the subfloor, and softens the feeling of the floor surface, making it comfortable to walk across.

The underlayment also acts as a vapor barrier, protecting your floors against moisture accumulation, which spurs mold growth. The underlayment also provides deadening, resulting in a sound-reduction effect. Cork, foam, and rubber are examples of common soft underlayment materials used in flooring systems. Hardboard and plywood are examples of hard underlayment materials.

Where Underlayment Fits in a Floor Structure

Most residential flooring systems consist of four layers. Let’s unpack these components from the top down.

The Subfloor

This layer utilizes materials like plywood or OSB, and it’s part of the home’s initial construction. It’s pre-installed by the construction team and ready for layering into the flooring system.

Plywood and OSB panels are essential for strengthening the floor and form part of the home’s structural integrity. The subfloor supports the joists and features materials ranging from 19/32″ to 1 1/8″ thick.


The underlayment lays on top of the subfloor, preparing the surface for the floorboards. Typically, underlayment materials range between ¼” and ½” thick, providing a flat, smooth surface in preparation for the floor cover.

The choice of underlayment materials depends on the needs of the floor cover. Hardboard, plywood, and cement boards are popular choices. However, in many cases, the type of underlayment is just a foam-padded layer, offering more spring in the flooring system after installation.

Floor Covering

The floor covering is the final layer. It’s part of the flooring you step on and can feature design with various materials. Carpets, hardwood boards, and vinyl floorboards are all popular choices.


The joists are lateral framing members featuring wood materials. The members rest on the foundation beams and walls, providing structural support for the framing system. Joists feature construction with 2×10 or 2×12 engineered microlam or wooden members.

What are the Benefits of Installing Underlayment?

The underlayment is a thin material resting between the subfloor and the flooring cover. The choice of underlayment depends on the floor covering you intend to install. The subfloor is a part of the home’s structural framework, but the underlayment features softer materials in most installations.

The underlayment smooths out all the bumps and dips in the subfloor, providing a smooth surface for installing the floor covering. Correct underlayment installation offers a firm surface, with some give to be kinder on the feet when walking across the floor covering.

For instance, it’s common to use foam underlayment in hardwood or vinyl board installations. The foam underlayment provides some give under your feet and prevents cracking and creaking of the floor covering.

Improve Structural Stability

A firm underlayment offers additional stability across the entire flooring system. It’s a good choice for older properties where the subfloor features construction with boards instead of plywood or OSB sheets.

Improves Tile Adhesion

Homeowners can fit cement board as the underlayment If they’re installing tiles. The cement boards provide the optimal surface for bonding ceramic tiles. The tile doesn’t properly adhere when applied directly to the subfloor.
The expansion and contraction of the subfloor lead to cracks forming in the tiles. The underlayment provides a layer between the subfloor and tiles, preventing expansion and contraction of the floor covering in different seasons.

Smooth the Surface

The underlayment offers a predictable, smooth surface compared to the subfloor. The subfloor provides structural support and isn’t a smooth, seamless surface. The underlayment fills in the gaps, dips, and divots in the subfloor, allowing for a clean installation of the floor covering.

When Is Underlayment Not Necessary?

Flooring underlayment isn’t always necessary in a flooring system in the following applications.

  • When tiling over vinyl boards.
  • When fitting a pre-attached laminate underlayment.
  • In new construction projects.

It’s important to keep the underlayment as thin as possible. Thick underlayment may cause offset issues between rooms utilizing different flooring covers.

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