Many modern homes and commercial areas nowadays are insulating their installed subfloors underneath their flooring at home because of its many benefits, including thermal efficiency and the highest R-Value insulation. 

It also helps reduce energy expenditure and energy costs, not to mention the use of artificial air. Insulating the subfloors is a great way to keep your home comfortable year-round, especially during winter or other harsh weather conditions.

It also adds more comfort and luxury to the living experience of homeowners. 

If you’re planning on insulating your subfloors, we’re here to provide you with the fundamental information to better understand them. This article includes the flooring layers, subfloor thickness, and its benefits.

What is a Subfloor?

Flooring is comprised of four layers— each one has its crucial functions. The four layers are joists, subfloor, underlayment, and flooring covering. These layers make up a durable and steady flooring surface. Below are the parts and their functions:

1. Joists

Joist, also referred to as band sill, is a wooden frame that rests horizontally within the foundation walls and the two beams and is commonly constructed from engineered wood, laminated wood, or dimensional lumber measuring 2-by-10 or 2-by-12 dimensions.

Joists are the pillars of the entire framing system, which provide structural support to all other parts of the floor and help enhance the firmness of the subfloor sheathing. They are also built to give support to carry the load or weight on which the floor holds.

Today’s Homeowner Tips

To know the presence of the joist in your subfloor, you can tap the floor with a hammer from one corner or edge and listen for a hollow/thud sound. The thud or hollow sound you will hear will determine the area on which the joist is installed. 

2. Underlayment

Underlayment is the floor layer installed above the sub-floor and below the floor covering, which is normally about 1/4- or 1/2-inch thick. It is made of foam-like or soft materials, such as sponge rubber, felt, cork, recycled plastic, or foam.  

The underlayment rectifies and smoothens the subfloor’s blemishes and provides a level surface for the floor covering, which enhances the comfort below one’s feet. It also helps dampen the sound of footsteps and the wear on the floor covering.

Moreover, the underlayment preserves the warmth while acting as a moisture barrier. 

3. Floor Covering

Flooring covering, also known as the flooring or the finish floor, is the visible surface covering all fundamental layers of the flooring system. 

The floor covering is the surface you walk on and see. It provides a decorative, durable, and sturdy base where you place the furniture or other furnishings at home and helps make the floor easy to maintain and clean. 

4. Subfloor

A subfloor is the floor structure that holds up all other layers, which is located between the underlayment and joists. 

It rests above the joists and acts as a foundation of the floor covering and underlayment, which helps increase the durability and rigidity of the flooring system.

The subfloor also helps distribute the sustained weight of everything in your house, including furniture, appliances, weight, and the traffic generated by pets and people, and smoothens the surface, making the floor more comfortable to walk on. It also makes the upper floor covering easier to install and enhances the overall look of the floor. 

Here are the most common materials used for subfloor. 

One of the most commonly used materials for subfloor is plywood, which is made of pressed wood veneer sheets glued together using an adhesive. Plywood is durable and sturdy, which provides stable support for the subfloor.

Another popular material for subfloor is Oriented Strand Board (OSB). It is an engineered wood board manufactured by joining wood strands with resin, which creates a strong and durable panel able to resist warping, deflection, cracking, delamination, and shape distortion. OSB boards/panels are also lightweight and easy to install.

The only drawback of OSB panels is it holds moisture, which can result in damages to the floorboards.

Particleboard is another commonly used subfloor material. It is a floor panel made of wood particles (small chips, strands, fines, shavings) glued together. The source of particles is from the residues of wood-using industries or sawmills.

Related: How to Remove and Replace Rotten Particleboard Subflooring

Concrete is a common subfloor material for both residential and commercial applications. It uses slabs, which creates a sturdy and durable subfloor ideal for basements, patios, garages, or other utility areas. 

Wood planks are the traditional materials used for subfloors inside the homes, especially during the mid-twentieth century. They are usually made of fir, bamboo, timber, pine, or softwood. Though nowadays, wood planks are now seldomly used because they are being replaced by other types of subflooring, such as plywood. 

What are the Benefits of a Subfloor?

Subfloor is an important part of the flooring system because it provides a stable and durable foundation for the flooring and helps distribute the loads generated by elements occupying the building or the inside your home. 

The subfloor also acts as the additional support to hold and control the movement of joists and helps protect the flooring from mold and moisture, which can cause damage to the surface floor. It also regulates and controls the temperature of the floor, especially when it gets cold during winter or hot during summer.

Another benefit of a subfloor is it enhances the performance and longevity of the flooring. It also helps reduce the installation time and expenses for installation.

What Is the Optimal Subfloor Thickness for Insulation?

The optimal subfloor thickness for insulation may vary, depending on the spacing of the joists and the materials used. For the spacing of the joists, the farther apart the spacing, the greater the required thickness for the subflooring.

For a plywood subfloor with joists spaced 16 inches apart or less, the optimal thickness should be 15/32-inches. If the joists are spaced farther apart—16 inches to 19.2 inches, it’s best to use 3/4-inch plywood.

For Oriented Strand Board (OSB) subfloors, the standard thickness should be 23/32-inch if the spacing of the joists is up to 16 inches apart. If the joists are spaced apart about 24 inches or higher, the required thickness should be 1-inch.

Final Thoughts

Having good flooring for your home is essential because it serves as the foundation of the structure of your house. Four layers make up the floor—joists, subfloor, underlayment, and flooring covering, on which these parts form a stable and durable floor system. It also adds up to the beauty and comfort of the atmosphere.

Today’s Homeowner Tips

If you plan on enhancing your house’s thermal performance, the best way to do this is to insulate your subfloors—the floor layer in-between the underlayment and joists. For optimal insulation, make sure to follow the appropriate thickness of the subfloor mentioned above.

Think you might need professional help with your flooring installation? Use the form below to connect with local flooring pros:

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avatar for Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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