Do I need to put an underlay down before installing SPC?

Core conclusion: Yes, in the vast majority of cases, SPC flooring requires and strongly recommends the installation of an Underlayment.

Although SPC (Stone Plastic Composite) flooring itself is renowned for its hardness, stability and durability, the base layer is not superfluous. It plays the role of a "multi-functional enhancer", capable of elevating the already outstanding performance of SPC flooring to a new level of greater comfort, quietness and durability.

Ⅰ.First of all, let's briefly understand the structure of SPC flooring

SPC flooring is typically composed of four layers:

Wear Layer: The most transparent layer on the surface, resistant to scratches.

Decor Layer: A pattern layer printed with wood grain or stone grain.

SPC Core Layer (Core Layer) : This is the "backbone" of the floor. It is formed by extruding limestone powder (stone powder), polyvinyl chloride (plastic), and stabilizers under high temperature and high pressure after being mixed. It is extremely hard and stable, and hardly expands or contracts due to changes in temperature and humidity. This is also the reason why it is called "unbreakable".

Backing Layer: Some SPC flooring is pre-attached with a layer of cork, IXPE (radiation cross-linked polyethylene) or EVA (ethylene-vinyl acetate copolymer) material backing layer by the manufacturer when leaving the factory. This pre-attached base layer is what we often refer to as "Attached Underlayment".

The key point is here: If your SPC flooring is of the "with included padding" style, then you don't need to purchase additional padding. However, if your SPC flooring is a bare board without a base layer included, you definitely need to purchase and lay the base layer yourself.

Ⅱ. Why does a "hard" SPC still require a "soft" bedding layer? The five core functions of the cushion layer

The reason why foreign professional installers and floor manufacturers strongly recommend the use of underlayers is based on the following crucial reasons:

1. Enhance the Comfort & Underfoot Feel

Although SPC flooring is thinner than traditional vinyl or laminate (reinforced composite flooring), its core layer remains hard. If it is directly laid on a hard cement floor or tile, the feeling when stepping on it will be very stiff, cold and lack "elasticity". The cushion layer provides a soft cushioning layer, just like adding a comfortable insole to the shoes, which can significantly improve the feeling of walking and reduce leg fatigue. This is particularly important for families with elderly people and children.

2. Excellent Sound Absorption & Noise Reduction performance

This is one of the most important functions of the cushion layer and is also a point that foreign building codes (especially for apartment buildings) highly value.

Impact Insulation Class (IIC) : The cushion layer can effectively absorb impact sounds such as footsteps and falling objects, preventing them from being transmitted through the floor to the rooms downstairs. Without a cushion layer, the neighbors downstairs might clearly hear every step you make upstairs.

Air Sound insulation (STC - Sound Transmission Class) : It can also reduce airborne noises such as conversation sounds and TV sounds in the room.

In foreign countries, the property management terms (HOA Rules) of many apartments and townhouses explicitly require that floor installation must meet specific IIC and STC ratings to ensure quietness in the neighborhood, and choosing the appropriate bedding is the only way to achieve this goal.

3. Subfloor perfection Correction

No ground is absolutely flat. No matter how well the self-leveling of cement is done, there may still be tiny depressions, cracks or unevenness. Although SPC flooring is connected by interlocking and has a certain degree of flexibility, if it is laid on an uneven ground, long-term uneven force distribution can cause the interlocking parts to loosen and make Squeaking sounds. In the most severe cases, it may even lead to the interlocking parts breaking. Professional base layers have a certain thickness and elasticity, which can make up for minor ground defects (it is generally recommended that the height difference within 2 meters does not exceed 3 millimeters), providing a uniform and flat load-bearing foundation for SPC flooring and greatly extending its service life.

4. Moisture Barrier

Although the SPC core layer itself is 100% waterproof, the moisture on the ground (especially the cement floor on the first floor) remains a potential threat. Moisture can erode the clamps of floor locks (if they are metal locks, they may rust) and may breed mold, affecting indoor air quality. Many base layers are equipped with an attached plastic film (usually 6mil polyethylene), which can act as an additional moisture-proof layer, preventing underground moisture from rising and providing double protection for the entire floor system.

5. Increase Thermal Insulation

SPC material conducts heat relatively quickly. In cold seasons, SPC flooring without a cushion layer will feel extremely cold. As an insulating layer, the cushion layer can effectively prevent the cold air from beneath the ground from conducting up, keeping the floor surface relatively warm, enhancing the overall comfort of the room, and indirectly saving a little heating cost.

Ⅲ. How to Choose the Right Underlay for SPC Flooring?

Not all underlays are suitable for SPC flooring. Choosing the wrong type of cushion layer will instead undermine the stability of the floor.

1. Choose a thin and dense cushion layer

SPC stands for rigid locking floor. Overly thick and soft bedding layers (such as some very thick foam bedding layers) can cause the floor to have an "elastic" or "sunken" feeling when walking, which can exert continuous stress on the locking system. Over time, this may lead to damage to the locking system. The thickness of the cushion layer professionally recommended for SPC flooring is usually between 1mm and 2mm. The material is dense and can provide support rather than being overly soft and elastic.

2. Recommended mainstream cushion layer materials

IXPE (Radiation Cross-linked polyethylene) : This is currently the high-end choice on the market. With a closed-cell structure, it has excellent moisture-proof performance, is antibacterial and mold-proof, and has good resilience and durability. It is an ideal companion for SPC flooring.

EVA (ethylene-vinyl acetate copolymer) : A common foam material with an economical price. However, high-density EVA should be chosen. Low-quality EVA is prone to being flattened and losing its elasticity under heavy pressure.

Cork: A natural sound and heat insulation material, environmentally friendly and comfortable to walk on. However, it is necessary to pay attention to its moisture resistance. It is best to choose a composite cork cushion layer with a moisture-proof film.

Combination Underlayment: Usually composed of IXPE or EVA combined with a layer of plastic moisture-proof film, it offers a "one-stop" solution and is the most convenient and common choice.

3. Be sure to abide by the Manufacturer's Warranty.

This is of vital importance! Before purchasing the base layer, be sure to check your SPC floor warranty terms. Some floor manufacturers (especially those that offer floor layers with padding) will explicitly state that if third-party additional padding is used, the product warranty will be invalidated. Because they have already matched the floor with the optimal bedding layer, additional bedding layers may change the mechanical properties of the floor. Always take the installation guide of the floor manufacturer as the highest standard.

Summary

From the perspective of a professional flooring industry, laying a base layer for SPC flooring is by no means superfluous; rather, it is a standard, professional and wise practice.

For SPC boards without the included cushion layer: The cushion layer is a necessity. It protects your investment by providing functions such as sound insulation, buffering, leveling and moisture-proofing, greatly enhancing the quality of life and the lifespan of the floor.

For SPC boards with "built-in padding" : The padding is a contraindicated item. Do not add any extra ones, otherwise the lock may be damaged and the warranty may become invalid.

Therefore, the answer is "Does SPC need a cushion layer?" The correct process for this question is:

Make sure that the SPC flooring you purchased comes with a base layer.

If it comes with it, just install it directly and there's no need to buy it again.

If you don't bring your own, you must purchase a thin and dense professional cushion layer.

Ultimately, be sure to follow the official installation instructions provided by the flooring brand you purchase.

Using the cushion layer correctly can make your SPC flooring not only strong and durable, but also quiet, warm and comfortable, truly achieving the experience of a quality home.