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  • Writer's pictureZack Jurkowski

Do I Need To Replace My Subfloor?

Over time, wood-structure floors can sag. If you're looking to put new flooring in during a bathroom or kitchen renovation, having a crooked or sagging floor can be an issue. Most flooring has specific requirements for flatness. The tolerances range from nearly flat to almost perfectly flat. Flooring like tiles also imposes a limit of deflection, or how much the floor can move or bounce.

For a new flat or level floor, you'll need to rebuild your subfloor. This can be quite the undertaking, but in my experience, it's usually the only option.

How Are Subfloors Rebuilt?

When it comes to redoing a subfloor, there are typically two methods that are commonly used by contractors, each with its advantages and disadvantages. The first method is to laminate plywood over the original subfloor, while the second method involves removing the entire subfloor and reinforcing the underlying joists.

Laminating The Existing Subfloor: A traditional option for flexible flooring

Laminating plywood over the original subfloor is a popular method because it is relatively quick and less expensive compared to removing and replacing the entire subfloor. This method involves screwing down the original subfloor planks, ensuring they are tight, and then gluing and screwing down new plywood on top of the old subfloor.

This approach is ideal when the existing subfloor is in good condition, and the primary objective is to create a level surface for the new flooring. However, it doesn't address structural deficiencies or sagging, which can compromise the structural integrity of the flooring system.

It works well when supple flooring is used, like carpeting or linoleum, though it's worth noting that in my 20 years of working in renovations, I have never installed either; I've only ripped them out.

Replacing The Subfloor: The best option for wood or tile flooring

On the other hand, removing the entire subfloor and reinforcing the underlying joists is the recommended method when structural deficiencies or sagging are present. This process involves removing the old subfloor and reinforcing the joists to ensure that they can adequately support the new subfloor and flooring.

This method is more time-consuming and expensive compared to laminating plywood over the existing subfloor, but it ensures that the subfloor and the overall structure of the floor are sound and able to support the weight of the new flooring.

Which One Should I Choose?

In conclusion, both methods have their advantages and disadvantages, and the method used will depend on the specific needs of the project. While laminating plywood over the existing subfloor is a faster and less expensive option, it may not be suitable when structural issues are present. On the other hand, removing the entire subfloor and reinforcing the joists is the recommended option, but it can be more expensive and time-consuming.

Therefore, it's important to consult with a licensed contractor to determine the most appropriate method for your subfloor renovation project. If you have any questions about which option may be best for your renovation, reach out to us and we would love to help guide you in the right direction.


Montreal Contractors is a qualified company, holding an active bonded license as a General Contractor and Specialized Contractor with the Régie du Bâtiment du Québec (RBQ License: 5767-5480-01), ASP Health & Safety Certification and a $2M liability policy. Our employees have all passed background checks, are registered with CNESST and have their ASP Health and Safety certification.

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