Consider the following image (img_1)

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I guess the whole thing is called a floor framing system and subfloor is a part of the system. So subfloor is a part of floor. is my understanding right?


2 Answers 2


Subfloor is a part of the floor but has a different purpose. Without a solid sheet that spans the joints and the ends are supported, how can you install tile or wood flooring? In the oldest residential constructions I’ve seen, they used either two layers of thick wood planks (bottom acting as a subfloor) or boards run diagonally as the subfloor. Today, we almost exclusively see OSB, but the purpose is the same. It provides even support for the floor.

  • Do you know what the correct term for the space between the joists the foundations is? I've been calling it a subfloor or crawl space.
    – abdnChap
    Jan 30, 2020 at 11:47
  • 1
    @abdnChap crawl space is the term used where I live Jan 30, 2020 at 12:09
  • 1
    @abdnChap The unfinished space under the joists and inside the perimeter of the foundation walls is considered or called the crawlspace.If it is tall enough to include a living space, then it is called a basement
    – Jack
    Jan 30, 2020 at 15:01
  • solid timber flooring can be applied directly to joists, and usually is.
    – Jasen
    Feb 1, 2020 at 4:21

The subfloor is the support used so the final floor covering (the "pretty one - tiles or polished wood etc) is properly supported.

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