Wood Floor Underlays, Insulation & Sound Proofing

Underlay plays a crucial role in the successful installation and long-term performance of wooden floors, offering a range of benefits that protect the flooring and enhance comfort within a space. While not always strictly necessary depending on the type of wooden floor and subfloor, it is highly recommended for any floating engineered flooring installations or for laminate flooring.  

Purpose & Benefits of the Underlays

• One of the primary functions of underlay is to provide a moisture barrier. Wooden floors are susceptible to moisture fluctuations, which can lead to warping, cupping, or gapping. Underlay, particularly types with integrated moisture protection, helps to prevent moisture from the subfloor (especially concrete) from reaching the wooden planks, thus protecting the investment in the flooring.  

• Sound reduction is another significant advantage of using underlay. Wooden floors can be noisy underfoot, generating impact sound that travels to rooms below. Underlay absorbs and dampens this sound, creating a quieter environment within the room and reducing noise transmission to lower levels, which is particularly beneficial in multi-story buildings.  

• Underlay also contributes to thermal insulation. It adds an extra layer that helps to retain heat within the room, making the floor feel warmer underfoot and potentially improving energy efficiency by reducing heat loss through the floor.  

• Furthermore, underlay can help to level minor imperfections in the subfloor, providing a smoother and more stable base for the wooden flooring. This helps to prevent excessive movement and stress on the wooden planks, contributing to the overall stability and longevity of the floor.  

• Beyond protection and stability, underlay also adds a layer of cushioning, which enhances the comfort of walking on the wooden floor. This can make a noticeable difference, especially with harder wood species.

What Types of Underlays are Available?

Underlay for wooden floors comes in various types, primarily differentiated by their material composition and the specific benefits they offer, which in turn relate to their quality. Here are some of the common types of underlays available on the market:  

Common Underlay Materials:

• Foam & Compact Foam Underlays: Typically made from polyethylene or polyurethane foam. This is often the most budget-friendly option.

• Rubber Underlay: Made from natural or recycled rubber. It is denser and heavier than foam.

• Cork Underlay: An eco-friendly option made from the bark of cork oak trees.  

• Fibreboard Underlay: Composed of compressed wood fibers.  

• Felt Underlay: Often made from recycled textile fibers or wool, though less commonly used under wood floors compared to carpet.

• Combination Underlay: These underlays combine different materials, such as foam with a foil backing, to offer multiple benefits.  

• XPS Foam: Extruded polystyrene foam, known for being resilient and moisture-resistant.

Glue-down Rubber Insulation for Sound-Proofing

A very effective material for soundproofing is the rubber insulation. It often involves recycled materials, such as recycled rubber granules and sometimes cork granules, bound together and is effective for reducing impact noise and adding mass to block sound transmission and universally one of the "best" soundproofing solution for all situations. However, the most effective soundproofing often involves using a combination of different materials and techniques tailored to the specific type of noise and the area being treated (floors, walls, ceilings).  

Rubber is excellent for:

• Impact Sound Reduction: Its density and elasticity make it highly effective at absorbing the energy from impacts, such as footsteps, making it an ideal underlay for floors.  

• Adding Mass: Rubber, including products like Mass Loaded Vinyl (MLV), is dense and adds mass to structures, which helps to block airborne sound transmission.

Sound Proofing & Thermal Insulation with Floorboards & Between Joists

When considering the best type of material for insulation between joists, it's important to clarify whether the primary goal is thermal insulation or acoustic insulation, as different materials excel in these areas.

Acoustic Insulation (Soundproofing):

The most commonly recommended material for acoustic insulation between joists is mineral wool, such as Rockwool (stone wool) or fiberglass. These materials are effective because of their fibrous and dense nature, which helps to:

• Absorb Airborne Sound: Mineral wool traps sound waves within its structure, reducing the amplification that can occur in empty cavities between joists (the "drum effect"). This is particularly effective for reducing the transmission of airborne noises like voices and music.  

• Improve the Performance of a Soundproofing System: While mineral wool on its own is not a complete soundproofing solution (it primarily absorbs rather than blocks sound), it is a crucial component in multi-layered soundproofing systems that also incorporate mass and decoupling elements to address both airborne and impact noise.

Higher density acoustic mineral wool is generally preferred over lower density thermal-grade insulation for soundproofing applications between joists.  

How to Choose the Right Insulation & Underlay?

The type of flooring you are installing (solid wood, engineered wood, laminate, vinyl) will influence the type of underlay and insulation that is compatible and recommended by the manufacturer.  

• Engineered Wood Flooring: Often benefit from underlay for moisture protection, sound reduction, and comfort. Thinner engineered flooring products will go best with underlays of up to 3 mm and any type of rubber glue-down products.

• Solid Wood Flooring: Apart of Junckers solid wood flooring, which offers the option for floating installation, all other solid wood flooring products require glue-down or nail-down installation. Therefore, the only option for sound-proofing here comes with Regupol and dB FFR glue-down rubber underlays.

• Laminate Flooring: Typically requires an underlay for stability and sound reduction - thickness of the underlay should not exceed 3 mm, however a 5 mm fibreboard underlay is a good solution for subfloors with floorboards, due to their generally imperfect level.

• Herringbone & Chevron Parquet Flooring: All parquet flooring products require glue-down installation and therefore, the only option for sound-proofing here comes with Regupol and dB FFR glue-down rubber underlays.

• Mosaic Fingers Flooring: This flooring products is quite thin and due to size of the pieces comprising the product, it requires smooth and solid subfloor. It is not compatible with underlays or any insulation materials.

• LVT / SPC Flooring: Due to its thickness and the fragile click - the floating LVT / SPC type of this flooring product comes with 1 mm built-in underlay and additional underlay is not required.

The table below provides a comparison of some of the most common types of insulation products available on the market today.