Everything Subfloor: What You Need To Know Before DIY

The subfloor is the foundation of a floor and provides support to the materials that are installed on top. It should be prepared with care, made out of durable material, and properly installed before any other flooring is added. If this isn’t done correctly, the homeowner will have issues like squeaky floors or rooms where water pools after it rains. This blog post will discuss everything you need to know about your subfloor!

The proper preparation and installation of your subfloors will ensure the longevity and functionality of your new flooring.

In most cases, homeowners do not realize how important a good subfloor is and the extensive preparation required to determine its integrity.

To ensure the overall performance of your new floors, it is crucial to ensure the subfloor is properly prepared.

Subfloor preparation is critical to the success of any home improvement project. The following are some factors that are important to prepare a subfloor. But first, let’s define what exactly a subfloor is.

 What Is A Subfloor?

In a building, a subfloor is the foundation floor. 

Concrete and plywood are both common types of subflooring. The subfloor of basements is typically made of cement, while the subfloor of aboveground construction is typically made of plywood or structural grade particleboard.

In above-ground level floors, a subfloor is generally plywood or structural particleboard (in Australia & New Zealand). It provides an even, stable surface for your new flooring to be installed on top of. It also creates a space for insulation between the joists or rafters below which can help keep any air from getting trapped in there.

If someone is installing new flooring directly on top of old flooring, without ripping up the old flooring, the old flooring can also be referred to as a subfloor.  

If you’re getting new flooring, you will want to know what type of subfloor is under your existing floor. If it’s plywood or particleboard, they’ll need that information so they can plan how much material and time are needed for installation.

There are a variety of factors to consider before installing new floors directly over old ones though. Putting a new floor over an old one can cause a variety of problems, including the appearance of the flooring, appliances that may not fit, and doors that cannot swing freely.

Also, if someone has old hardwood floors on an uneven subfloor, it may be a good idea to rip up the old flooring and install new plywood or particleboard subflooring.

Subflooring: Why Is It Important?

How important is subflooring? Answer: Because a floor can only be as good as its subfloor, it is very important. In direct relation to the flooring, the subfloor is a critical component, so if the subfloor is defective, the flooring will become underperforming or failing.

Not having a properly flat and dry subfloor, not being properly cleaned, not being structurally sound or otherwise faulty in any way will lead to a host of unwanted consequences, ranging from:

  • High spots are excessively worn out
  • Spots that are uneven
  • Lifespan is reduced
  • Surface irregularities that are unsightly
  • There is squeaking within the flooring system
  • There is sagging in some areas of the flooring system
  • Excessive shifting and movement
  • A decrease in comfort when walking on the floor
  • Damage to the flooring system
  • The separation between the subfloor and top flooring material

If left unattended, these issues can worsen over time and, at worst, lead to the need for flooring repair or replacement.

There are a number of ways to avoid these problems, but the most effective way is through comprehensive subfloor preparation. It should be noted that this can take up to two days and will require some tools such as: chisels, crowbars or hammers (to remove old flooring), drills (for preparing holes for new screws), and a saw (for cutting the subfloor).

Subfloor Preparation Requirements

The subfloor will need some degree of preparation, regardless of the type of flooring you select. Depending on the installation, there will be specific preparations to make.

Before a subfloor can be used as a base, several considerations must be addressed:

  • Thorough cleaning and removal of all dust and debris is performed
  • Flat (level within 5 millimeters for every 3 meters)
  • Good structural integrity
  • In order to maintain an even surface, grout lines must be filled in if tile is used as the subfloor
  • It is imperative to sand or repair plywood subfloors with cement compound in order to ensure a level surface
  • Minor irregularities can be covered with underlayment, but it is not a fix for major problems
  • Make sure that no nails or screws are loose
  • The subfloor is completely dry

Questions To Ask Before Installing New Floors

Several questions need to be addressed before installation:

  • What kind of flooring will be installed?
  • Is it a remodel or a new construction?
  • Has the pH and moisture of the subfloor been tested?
  • Are you working on a commercial project or a residential one?
  • Do you have a level, dry, smooth, and clean subfloor?
  • Which subfloor does the current floor rest on?
  • How was the compound or sealer applied?
  • Has there been a crawl space built?

The following is merely a general overview of some of the most important aspects of subfloor preparation.

Other Considerations

It is also important to take into account “grade levels” when evaluating the integrity of a subfloor. A home is divided into several levels:

  • Floors above ground level, such as floors two and three
  • Ground floor – ground level of the building
  • A basement is a floor beneath the ground level (below grade).

Different aspects have different effects on each of these levels. An on-grade installation, for example, should take into account the ventilation in the basement or crawlspace.

For a ground-level subfloor, the ground floor is the surface on which the subfloor will rest. A concrete slab or wood flooring should be considered for this area, but it must be level and solid before installing a new piece of plywood or carpet.

If you are building a crawl space beneath your home, you need to consider adding ventilation in order to prevent any problems with humidity.

The same is true for a basement, but you must also consider drainage and how to prevent water from pooling in the area where your subfloor will be installed.

Below-grade installations are plagued by moisture problems.

Ground-level floors are less prone to moisture damage, so an on-grade installation should work well for this type of surface.

For above-ground installations, the subfloor must be able to bear the weight of the flooring before an installation can be done.

 Can An Owner Handle Subfloor Prep?

Can I do subfloor prep myself? The answer depends on the specific project, the type of flooring, how much experience an owner has, and many other factors. For example, for some simple kind of subfloor installations, an owner might be able to prepare a subfloor by laying down a vapor barrier and adding insulation etc. But for many installations, an owner will need to hire someone who has the proper tools and experience to do it correctly.

If you have any questions about subfloor preparation, you should consult a professional. A growing trend is for homeowners to install their own flooring, but it is important to get expert assistance and knowledge before embarking on the DIY method.

What are the benefits of hiring a professional? Hiring a qualified subfloor installer can help to ensure that your floors will last longer. For example, an experienced contractor may be able to treat wood with chemicals or sealants in order to protect it from moisture and pests. They might also install underlayment for carpeting installation, which provides a barrier between the carpet and wood that prevents stains.

Removing Old Subflooring

If you are going to DIY, or at least do some of it yourself, you are going to need to start by removing all of the old flooring.

This can be done by prying up any nails with a crowbar or hammer, using an electric screwdriver for screws, and pulling out staples with pliers or other tools. When this has been completed, it’s time to get to work on the subfloor.

 First, you will need a good pry bar and heavy hammer for wood floors or a crowbar for vinyl flooring that needs to be removed. Make sure your method is appropriate before proceeding! Next, break up any boards with nails in them by using the screwdriver and pry bar. Then, use the crowbar to remove any nails in solid flooring or pull up boards with staples by first using a flathead screwdriver to get under it.

 Finally, sweep up all of the debris from your workspace and vacuum thoroughly before applying new subflooring.

The cost for this process varies depending on the type of flooring you are preparing for, but getting rid of the old subflooring yourself is at least something in reach of the average do-it-yourself person, before calling in the professionals to proceed with putting in the new subfloor.


Skipping subfloor preparation can lead to costly and frustrating problems in the future if you don’t pay attention to it.

When prepping your subfloor, there are many factors to take into consideration, and that’s where professional experience comes in. It takes years of experience, industry-specific knowledge, and a thorough understanding of subflooring to prepare a subfloor correctly, so proceed with caution if you want to do it yourself.

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