Replace Subfloor on 2nd Floor: Avoid Costly Mistakes!

Replacing a subfloor on a second story presents unique challenges, but understanding the process is key to avoiding costly mistakes. Incorrect subfloor installation can lead to structural issues, impacting the integrity of your home. Therefore, knowing how to replace subfloor on second floor properly is essential. Lowe's offers a variety of materials suitable for this task, and consulting with a qualified structural engineer is highly recommended before beginning any work. Furthermore, you'll need specialized tools, such as a reciprocating saw, to efficiently remove the old subfloor and ensure a clean surface for the new installation.

Image taken from the YouTube channel Fix This House , from the video titled How To Remove And Replace Rotten Subfloors! DIY For Beginners! .
How to Replace Subfloor on the Second Floor: Avoiding Costly Mistakes
Replacing a subfloor on the second floor of a house can be a significant undertaking, but with careful planning and execution, you can successfully complete the project while avoiding common pitfalls that lead to increased costs and frustration. This guide will walk you through the necessary steps.
1. Assessing the Damage and Planning the Project
Before you even consider picking up a tool, thoroughly assess the damage to your subfloor. This will inform your material selection and project scope.
1.1 Identifying the Problem Areas
- Visually Inspect: Carefully examine the existing flooring and look for signs of water damage (stains, mold), sagging, soft spots, or visible rot.
- Physical Check: Walk across the floor, paying attention to any areas that feel uneven or spongy. A small screwdriver or awl can be used to probe suspicious areas to test for softness.
- Check from Below: If accessible, inspect the subfloor from the ceiling below. Water stains or visible damage are easier to spot from this vantage point.
1.2 Determining the Cause of the Damage
Understanding the source of the problem is crucial. Replacing the subfloor without addressing the underlying cause (e.g., a leaky pipe, roof leak, or condensation) will only lead to recurring issues.
- Water Damage: Identify and repair any leaks promptly. Common culprits include leaky plumbing, faulty roofing, or inadequate ventilation.
- Insect Infestation: Check for signs of termites, carpenter ants, or other wood-destroying insects. If found, consult with a pest control professional.
- Structural Issues: Sagging or uneven floors may indicate a more serious structural problem that requires professional assessment.
1.3 Planning the Scope of the Replacement
Based on your assessment, determine how much of the subfloor needs to be replaced.
- Partial Replacement: If the damage is localized, you may only need to replace a section of the subfloor.
- Full Replacement: Extensive damage may necessitate replacing the entire subfloor.
- Consider Accessibility: Evaluate how you will get materials to the second floor. Will you need to use stairs, a ramp, or a hoist?
2. Preparing for the Replacement
Proper preparation is essential for a smooth and safe project.
2.1 Gathering Tools and Materials
Here's a list of essential tools and materials:
- Tools:
- Safety Glasses
- Dust Mask / Respirator
- Gloves
- Circular Saw
- Reciprocating Saw (for tight spaces)
- Pry Bar
- Hammer or Nail Gun
- Drill/Driver
- Measuring Tape
- Level
- Square
- Pencil
- Stud Finder
- Materials:
- Subfloor Sheathing (typically plywood or OSB; check local building codes for requirements)
- Construction Adhesive
- Fasteners (nails or screws, appropriate for the thickness of the subfloor)
- Shims (for leveling)
- Caulk (for sealing gaps)
- Construction Lumber (for replacing damaged joists, if needed)
2.2 Safety Precautions
- Wear appropriate personal protective equipment (PPE): Safety glasses, dust mask/respirator, and gloves are essential.
- Turn off power: Disconnect electricity to the area to avoid electrical hazards.
- Ventilation: Ensure adequate ventilation to minimize exposure to dust and fumes.
- Structural Support: Before removing large sections of the subfloor, ensure that the area is adequately supported to prevent collapse. Temporary supports may be necessary.
2.3 Removing Existing Flooring and Subfloor
- Remove existing flooring: Carefully remove any flooring materials (carpet, tile, hardwood) to expose the subfloor.
- Cut the subfloor: Using a circular saw, cut the subfloor along the joists. Be careful not to cut into the joists themselves.
- Pry up sections: Use a pry bar to carefully remove the cut sections of the subfloor.
- Clean up debris: Thoroughly clean up any debris, including nails, screws, and dust.
3. Installing the New Subfloor
With the old subfloor removed, you can now install the new subfloor.
3.1 Inspecting and Preparing the Joists
- Inspect joists: Check the joists for any signs of damage (rot, insect infestation, or cracks).
- Repair or replace damaged joists: If necessary, repair or replace damaged joists before installing the new subfloor. Consult with a structural engineer if you suspect significant structural issues.
- Leveling: Use shims to level the joists, ensuring a flat and even surface for the new subfloor.
3.2 Cutting and Installing the Subfloor Sheathing
- Measure and cut: Carefully measure and cut the subfloor sheathing to fit the space.
- Apply adhesive: Apply construction adhesive to the tops of the joists.
- Position and fasten: Position the subfloor sheathing onto the joists and fasten it securely with nails or screws. Follow the manufacturer's recommendations for fastener spacing.
- Stagger seams: Stagger the seams between sheets of subfloor to increase strength and prevent cracking.
- Leave a small gap: Leave a small gap (approximately 1/8 inch) between sheets of subfloor to allow for expansion and contraction.
3.3 Securing and Finishing
- Countersink fasteners: Ensure that all nails and screws are countersunk to avoid interfering with the installation of the finished flooring.
- Fill gaps: Fill any gaps or cracks with caulk or wood filler.
- Sand rough edges: Sand any rough edges to create a smooth surface.
4. Avoiding Common Mistakes
Here's a table of common mistakes and how to avoid them:

Mistake | Solution |
---|---|
Ignoring the cause of damage | Identify and fix the underlying cause of the damage before replacing the subfloor. |
Using the wrong materials | Use subfloor sheathing that meets local building codes and is appropriate for the intended use. |
Incorrect fastener spacing | Follow the manufacturer's recommendations for fastener spacing to ensure a secure installation. |
Uneven joists | Level the joists with shims before installing the new subfloor to create a flat and even surface. |
Not staggering seams | Stagger the seams between sheets of subfloor to increase strength and prevent cracking. |
Neglecting safety | Always wear appropriate PPE and follow safety precautions to avoid injuries. |
Not accounting for expansion | Leave a small gap between sheets of subfloor to allow for expansion and contraction. |
Cutting joists | Be extremely careful when cutting existing subfloor to not damage the joists. Use appropriate tools (reciprocating saw) in confined spaces. |
Video: Replace Subfloor on 2nd Floor: Avoid Costly Mistakes!
FAQs: Replacing Subfloor on 2nd Floor
Here are some frequently asked questions about replacing subfloor on the second floor to help you avoid costly mistakes.
Can I replace a section of subfloor instead of the entire thing?
Yes, you often can. If only a portion of your second-floor subfloor is damaged, like from water leaks, you can cut out and replace just that section. This saves time and money. However, ensure the surrounding subfloor is solid and not compromised. When you replace the section, consider how to replace subfloor on second floor and its potential impact on structural integrity.
What type of subfloor material is best for a second floor?
Plywood or OSB (Oriented Strand Board) are common choices. Plywood offers better resistance to moisture. However, OSB is often more cost-effective. Consider the existing subfloor material and the environmental conditions. The goal when you consider how to replace subfloor on second floor is to find the right balance between cost, durability and your current existing subfloor.
Do I need a permit to replace subfloor on a second floor?
It depends on your local building codes. Replacing subfloor is considered structural work in some areas, especially if it involves a large area or load-bearing components. Check with your local building department to determine if a permit is required before you start. Also, remember how to replace subfloor on second floor has special requirements since it is on the second floor, and not on the ground.
How can I minimize dust and mess when removing the old subfloor?
Seal off the work area with plastic sheeting to contain the dust. Use a shop vacuum with a HEPA filter to clean up debris as you go. Cutting the subfloor into smaller, manageable pieces also helps minimize dust and makes disposal easier. Think about how to replace subfloor on second floor in smaller sections to minimize mess.