6 Easy Steps to Replace Subfloor

Replace Subfloor

Subfloor replacement can be a daunting task, but it’s one of the most important steps in ensuring the longevity of your flooring. If you’re experiencing squeaky or uneven floors, it may be time to consider replacing the subfloor. While this may seem like a major undertaking, it’s actually a relatively straightforward process that can be completed in a weekend with the right tools and materials. In this guide, we’ll walk you through the steps involved in replacing your subfloor, from removing the old subfloor to installing the new one.

Before you begin, it’s important to gather the necessary tools and materials. You’ll need a pry bar, a hammer, a circular saw, a jigsaw, a drill, a level, screws, nails, and of course, the new subfloor material. Once you have everything you need, you can begin the process of removing the old subfloor. Start by prying up the old subfloor with a pry bar. Be careful not to damage the joists or the flooring above. Once the old subfloor is removed, you can clean the joists and inspect them for any damage. If there are any damaged joists, they will need to be replaced before you install the new subfloor.

Now that the joists are clean and inspected, you can begin installing the new subfloor. Start by cutting the subfloor material to size using a circular saw or a jigsaw. Then, nail or screw the subfloor to the joists. Be sure to use screws or nails that are long enough to penetrate the joists by at least 1 inch. Once the subfloor is installed, you can level it using a level and a shim. Finally, you can install the new flooring over the subfloor.

Assess the Damage

Before embarking on a subfloor replacement project, a thorough assessment of the damage is crucial. This meticulous inspection provides essential insights into the extent of the deterioration and helps determine the appropriate repair strategy. Here’s a step-by-step guide to help you evaluate the damage effectively:

Visual Inspection

Begin by meticulously examining the affected area for visible signs of damage. Look for sagging, buckling, or unevenness in the flooring. These irregularities may indicate that the subfloor has weakened or rotted. Check for cracks, splits, or holes, which could signify structural issues or moisture penetration. Pay close attention to areas where water may have accumulated, such as around pipes or appliances, as they are prone to moisture damage.

Probing and Testing

To further assess the subfloor’s condition, carefully probe it with a blunt object, such as a flathead screwdriver. Soft or spongy areas indicate rot or excessive moisture. Use a moisture meter to measure the moisture content of the subfloor. Readings above 15% may suggest moisture-related damage requiring immediate attention. Tapping on the subfloor can also provide valuable information. A hollow sound may indicate delamination or loose boards, while a solid sound usually signifies a secure subfloor.

Identifying the Cause

Determining the underlying cause of the subfloor damage is essential for preventing future issues. Look for leaks or plumbing problems that may have caused water damage. Inspect the roof and gutters for potential moisture sources. Check the crawl space or basement for signs of excessive humidity or standing water. Identifying the root cause will help you develop targeted solutions to prevent further damage.

Gather the Necessary Materials

Replacing subflooring requires various materials to ensure a sturdy and efficient repair. Before beginning the project, gather the following essential items:

Subflooring

Determine the type and thickness of subflooring suitable for your project. Common choices include plywood, OSB (oriented strand board), or underlayment-grade plywood. Ensure the subflooring matches the structural requirements of your floor system.

Underlayment

Underlayment provides a moisture barrier and reduces noise. Choose an underlayment compatible with your flooring type, such as felt paper, foam, or vapor barrier.

Adhesive

Select an appropriate adhesive for bonding the subflooring to the joists or existing subfloor. Common options include construction adhesive, liquid nails, or screws.

Fasteners

Use screws or nails to secure the subflooring to the joists or existing subfloor. Choose fasteners with sufficient length and thickness to provide a solid hold.

Tools

Gather the necessary tools, including a circular saw or reciprocating saw, drill, hammer, utility knife, and safety glasses. Additionally, a level, chalk line, and measuring tape are essential for accurate measurements and installation.

Prepare the Subfloor Area

1. Remove Obstacles and Old Flooring

Remove any furniture, appliances, and fixtures from the room to make the installation area accessible. If you’re replacing old flooring, carefully remove it using any necessary tools, such as a pry bar or circular saw. Ensure that all nails or screws are removed to avoid damaging the new subfloor.

2. Inspect the Joists and Beams

Examine the joists and beams supporting the subfloor for any signs of damage, decay, or rot. If you find any issues, address them before installing the new subfloor to prevent further damage. You may need to replace damaged joists or reinforce weak areas with additional supports.

3. Level the Subfloor Frame

Using a level, check if the subfloor frame is level. If there are any uneven areas, use shims or self-leveling compound to adjust the level until it’s even. This is crucial for ensuring a stable and flat surface for the new subfloor.

4. Install Subfloor Blocking and Bracing

a. Subfloor Blocking

Install blocking between the joists at least 16 inches on center and perpendicular to them. This helps distribute the load and prevent the subfloor from sagging. Use lumber that is the same thickness as the joists and screws to secure them.

b. Cross-Bracing

To provide additional stability, consider installing cross-bracing between the joists. Cut diagonal braces from 2×4 lumber and secure them to the joists with screws. This creates a truss system that prevents joists from twisting and buckling.

c. Perimeter Blocking

Install blocking around the perimeter of the subfloor, parallel to the joists. This provides support for the edges of the subfloor and helps prevent warping.

Check for Levelness

Ensuring a level subfloor is crucial before laying new flooring. Use a 6-foot level to check for any irregularities.

Levelness Tolerance Table:

Span (feet)	Acceptable Variation (inches)
6	1/16
8	1/8
10	3/16

Hold the level horizontally on the subfloor, spanning the longest distance possible. If the level shows any deviation from the level surface beyond the acceptable variation noted in the table, the subfloor requires leveling.

To level the subfloor, use self-leveling compounds or shims. Self-leveling compounds are poured onto the subfloor and spread evenly, creating a flat surface. Shims are thin pieces of wood or plastic inserted between the subfloor and joists to adjust the height.

Troubleshooting Common Issues

Replacing subfloor can be a challenging task, and you may encounter various issues along the way. Here’s how to troubleshoot and resolve some common problems:

1. Squeaky or Bouncy Subfloor

This indicates loose or damaged joists. Tighten any loose nails or screws, or replace the damaged joists if necessary.

2. Sagging Subfloor

This can be caused by excessive weight, improper support, or moisture damage. Reinforce the joists with additional support or replace the affected area.

3. Uneven Subfloor

This can occur due to uneven joist spacing or improper installation. Level the subfloor by adding shims or planing down high spots.

4. Damp or Rotted Subfloor

Fix any leaks or moisture sources, remove the affected area, and replace it with moisture-resistant material.

5. Holes or Cracks in Subfloor

Repair holes and cracks by patching them with scrap plywood or wood filler.

6. Loose or Broken Nails

Replace loose nails with longer ones or add screws for better hold.

7. Incorrect Joist Spacing

Adjust the joist spacing to meet building codes and support the floor load.

8. Lack of Ventilation Under Subfloor

Install vents or create openings to allow airflow and prevent moisture buildup.

9. Improper Insulation Below Subfloor

Ensure proper insulation to prevent thermal loss and moisture problems.

10. Choosing the Wrong Subfloor Material

Select the appropriate subfloor material based on the type of flooring to be installed, the subfloor’s intended use, and the climate conditions.

How To Replace Subfloor

Replacing a subfloor is a major home repair project, but it’s one that can be completed by do-it-yourselfers with the right tools and materials. The first step is to remove the old subfloor. This can be done by prying up the boards with a pry bar or by using a reciprocating saw to cut through the nails. Once the old subfloor is removed, you can install the new subfloor. The new subfloor should be made of plywood or OSB (oriented strand board). It should be at least 3/4-inch thick and it should be installed with screws or nails. Once the new subfloor is installed, you can install the new flooring.